Author: "Lam, M. T." / Database: OAIster - Searchworks@Jio Institute Digital Library Search Results

Your search keyword '"Lam, M. T."' showing total 92 results

Start Over Author "Lam, M. T." Database OAIster

92 results on '"Lam, M. T."'

1. Comparing Recent Pulsar Timing Array Results on the Nanohertz Stochastic Gravitational-wave Background

Author: Agazie, G, Antoniadis, J, Anumarlapudi, A, Archibald, A, Arumugam, P, Arumugam, S, Arzoumanian, Z, Askew, J, Babak, S, Bagchi, M, Bailes, M, Nielsen, A, Baker, P, Bassa, C, Bathula, A, Becsy, B, Berthereau, A, Bhat, N, Blecha, L, Bonetti, M, Bortolas, E, Brazier, A, Brook, P, Burgay, M, Burke-Spolaor, S, Burnette, R, Caballero, R, Cameron, A, Case, R, Chalumeau, A, Champion, D, Chanlaridis, S, Charisi, M, Chatterjee, S, Chatziioannou, K, Cheeseboro, B, Chen, S, Chen, Z, Cognard, I, Cohen, T, Coles, W, Cordes, J, Cornish, N, Crawford, F, Cromartie, H, Crowter, K, Curylo, M, Cutler, C, Dai, S, Dandapat, S, Deb, D, Decesar, M, Degan, D, Demorest, P, Deng, H, Desai, S, Desvignes, G, Dey, L, Dhanda-Batra, N, Di Marco, V, Dolch, T, Drachler, B, Dwivedi, C, Ellis, J, Falxa, M, Feng, Y, Ferdman, R, Ferrara, E, Fiore, W, Fonseca, E, Franchini, A, Freedman, G, Gair, J, Garver-Daniels, N, Gentile, P, Gersbach, K, Glaser, J, Good, D, Goncharov, B, Gopakumar, A, Graikou, E, Griessmeier, J, Guillemot, L, Gultekin, K, Guo, Y, Gupta, Y, Grunthal, K, Hazboun, J, Hisano, S, Hobbs, G, Hourihane, S, Hu, H, Iraci, F, Islo, K, Izquierdo-Villalba, D, Jang, J, Jawor, J, Janssen, G, Jennings, R, Jessner, A, Johnson, A, Jones, M, Joshi, B, Kaiser, A, Kaplan, D, Kapur, A, Kareem, F, Karuppusamy, R, Keane, E, Keith, M, Kelley, L, Kerr, M, Key, J, Kharbanda, D, Kikunaga, T, Klein, T, Kolhe, N, Kramer, M, Krishnakumar, M, Kulkarni, A, Laal, N, Lackeos, K, Lam, M, Lamb, W, Larsen, B, Lazio, T, Lee, K, Levin, Y, Lewandowska, N, Littenberg, T, Liu, K, Liu, T, Liu, Y, Lommen, A, Lorimer, D, Lower, M, Luo, J, Luo, R, Lynch, R, Lyne, A, Ma, C, Maan, Y, Madison, D, Main, R, Manchester, R, Mandow, R, Mattson, M, Mcewen, A, Mckee, J, Mclaughlin, M, Mcmann, N, Meyers, B, Meyers, P, Mickaliger, M, Miles, M, Mingarelli, C, Mitridate, A, Natarajan, P, Nathan, R, Ng, C, Nice, D, Nitu, I, Nobleson, K, Ocker, S, Olum, K, Oslowski, S, Paladi, A, Parthasarathy, A, Pennucci, T, Perera, B, Perrodin, D, Petiteau, A, Petrov, P, Pol, N, Porayko, N, Possenti, A, Prabu, T, Leclere, H, Radovan, H, Rana, P, Ransom, S, Ray, P, Reardon, D, Rogers, A, Romano, J, Russell, C, Samajdar, A, Sanidas, S, Sardesai, S, Schmiedekamp, A, Schmiedekamp, C, Schmitz, K, Schult, L, Sesana, A, Shaifullah, G, Shannon, R, Shapiro-Albert, B, Siemens, X, Simon, J, Singha, J, Siwek, M, Speri, L, Spiewak, R, Srivastava, A, Stairs, I, Stappers, B, Stinebring, D, Stovall, K, Sun, J, Surnis, M, Susarla, S, Susobhanan, A, Swiggum, J, Takahashi, K, Tarafdar, P, Taylor, J, Taylor, S, Theureau, G, Thrane, E, Thyagarajan, N, Tiburzi, C, Toomey, L, Turner, J, Unal, C, Vallisneri, M, van der Wateren, E, van Haasteren, R, Vecchio, A, Venkatraman Krishnan, V, Verbiest, J, Vigeland, S, Wahl, H, Wang, S, Wang, Q, Witt, C, Wang, J, Wang, L, Wayt, K, Wu, Z, Young, O, Zhang, L, Zhang, S, Zhu, X, Zic, A, Agazie G., Antoniadis J., Anumarlapudi A., Archibald A. M., Arumugam P., Arumugam S., Arzoumanian Z., Askew J., Babak S., Bagchi M., Bailes M., Nielsen A. B., Baker P. T., Bassa C. G., Bathula A., Becsy B., Berthereau A., Bhat N. D. R., Blecha L., Bonetti M., Bortolas E., Brazier A., Brook P. R., Burgay M., Burke-Spolaor S., Burnette R., Caballero R. N., Cameron A., Case R., Chalumeau A., Champion D. J., Chanlaridis S., Charisi M., Chatterjee S., Chatziioannou K., Cheeseboro B. D., Chen S., Chen Z. -C., Cognard I., Cohen T., Coles W. A., Cordes J. M., Cornish N. J., Crawford F., Cromartie H. T., Crowter K., Curylo M., Cutler C. J., Dai S., Dandapat S., Deb D., DeCesar M. E., DeGan D., Demorest P. B., Deng H., Desai S., Desvignes G., Dey L., Dhanda-Batra N., Di Marco V., Dolch T., Drachler B., Dwivedi C., Ellis J. A., Falxa M., Feng Y., Ferdman R. D., Ferrara E. C., Fiore W., Fonseca E., Franchini A., Freedman G. E., Gair J. R., Garver-Daniels N., Gentile P. A., Gersbach K. A., Glaser J., Good D. C., Goncharov B., Gopakumar A., Graikou E., Griessmeier J. -M., Guillemot L., Gultekin K., Guo Y. J., Gupta Y., Grunthal K., Hazboun J. S., Hisano S., Hobbs G. B., Hourihane S., Hu H., Iraci F., Islo K., Izquierdo-Villalba D., Jang J., Jawor J., Janssen G. H., Jennings R. J., Jessner A., Johnson A. D., Jones M. L., Joshi B. C., Kaiser A. R., Kaplan D. L., Kapur A., Kareem F., Karuppusamy R., Keane E. F., Keith M. J., Kelley L. Z., Kerr M., Key J. S., Kharbanda D., Kikunaga T., Klein T. C., Kolhe N., Kramer M., Krishnakumar M. A., Kulkarni A., Laal N., Lackeos K., Lam M. T., Lamb W. G., Larsen B. B., Lazio T. J. W., Lee K. J., Levin Y., Lewandowska N., Littenberg T. B., Liu K., Liu T., Liu Y., Lommen A., Lorimer D. R., Lower M. E., Luo J., Luo R., Lynch R. S., Lyne A. G., Ma C. -P., Maan Y., Madison D. R., Main R. A., Manchester R. N., Mandow R., Mattson M. A., McEwen A., McKee J. W., McLaughlin M. A., McMann N., Meyers B. W., Meyers P. M., Mickaliger M. B., Miles M., Mingarelli C. M. F., Mitridate A., Natarajan P., Nathan R. S., Ng C., Nice D. J., Nitu I. C., Nobleson K., Ocker S. K., Olum K. D., Oslowski S., Paladi A. K., Parthasarathy A., Pennucci T. T., Perera B. B. P., Perrodin D., Petiteau A., Petrov P., Pol N. S., Porayko N. K., Possenti A., Prabu T., Leclere H. Q., Radovan H. A., Rana P., Ransom S. M., Ray P. S., Reardon D. J., Rogers A. F., Romano J. D., Russell C. J., Samajdar A., Sanidas S. A., Sardesai S. C., Schmiedekamp A., Schmiedekamp C., Schmitz K., Schult L., Sesana A., Shaifullah G., Shannon R. M., Shapiro-Albert B. J., Siemens X., Simon J., Singha J., Siwek M. S., Speri L., Spiewak R., Srivastava A., Stairs I. H., Stappers B. W., Stinebring D. R., Stovall K., Sun J. P., Surnis M., Susarla S. C., Susobhanan A., Swiggum J. K., Takahashi K., Tarafdar P., Taylor J., Taylor S. R., Theureau G., Thrane E., Thyagarajan N., Tiburzi C., Toomey L., Turner J. E., Unal C., Vallisneri M., van der Wateren E., van Haasteren R., Vecchio A., Venkatraman Krishnan V., Verbiest J. P. W., Vigeland S. J., Wahl H. M., Wang S., Wang Q., Witt C. A., Wang J., Wang L., Wayt K. E., Wu Z., Young O., Zhang L., Zhang S., Zhu X. -J., Zic A., Agazie, G, Antoniadis, J, Anumarlapudi, A, Archibald, A, Arumugam, P, Arumugam, S, Arzoumanian, Z, Askew, J, Babak, S, Bagchi, M, Bailes, M, Nielsen, A, Baker, P, Bassa, C, Bathula, A, Becsy, B, Berthereau, A, Bhat, N, Blecha, L, Bonetti, M, Bortolas, E, Brazier, A, Brook, P, Burgay, M, Burke-Spolaor, S, Burnette, R, Caballero, R, Cameron, A, Case, R, Chalumeau, A, Champion, D, Chanlaridis, S, Charisi, M, Chatterjee, S, Chatziioannou, K, Cheeseboro, B, Chen, S, Chen, Z, Cognard, I, Cohen, T, Coles, W, Cordes, J, Cornish, N, Crawford, F, Cromartie, H, Crowter, K, Curylo, M, Cutler, C, Dai, S, Dandapat, S, Deb, D, Decesar, M, Degan, D, Demorest, P, Deng, H, Desai, S, Desvignes, G, Dey, L, Dhanda-Batra, N, Di Marco, V, Dolch, T, Drachler, B, Dwivedi, C, Ellis, J, Falxa, M, Feng, Y, Ferdman, R, Ferrara, E, Fiore, W, Fonseca, E, Franchini, A, Freedman, G, Gair, J, Garver-Daniels, N, Gentile, P, Gersbach, K, Glaser, J, Good, D, Goncharov, B, Gopakumar, A, Graikou, E, Griessmeier, J, Guillemot, L, Gultekin, K, Guo, Y, Gupta, Y, Grunthal, K, Hazboun, J, Hisano, S, Hobbs, G, Hourihane, S, Hu, H, Iraci, F, Islo, K, Izquierdo-Villalba, D, Jang, J, Jawor, J, Janssen, G, Jennings, R, Jessner, A, Johnson, A, Jones, M, Joshi, B, Kaiser, A, Kaplan, D, Kapur, A, Kareem, F, Karuppusamy, R, Keane, E, Keith, M, Kelley, L, Kerr, M, Key, J, Kharbanda, D, Kikunaga, T, Klein, T, Kolhe, N, Kramer, M, Krishnakumar, M, Kulkarni, A, Laal, N, Lackeos, K, Lam, M, Lamb, W, Larsen, B, Lazio, T, Lee, K, Levin, Y, Lewandowska, N, Littenberg, T, Liu, K, Liu, T, Liu, Y, Lommen, A, Lorimer, D, Lower, M, Luo, J, Luo, R, Lynch, R, Lyne, A, Ma, C, Maan, Y, Madison, D, Main, R, Manchester, R, Mandow, R, Mattson, M, Mcewen, A, Mckee, J, Mclaughlin, M, Mcmann, N, Meyers, B, Meyers, P, Mickaliger, M, Miles, M, Mingarelli, C, Mitridate, A, Natarajan, P, Nathan, R, Ng, C, Nice, D, Nitu, I, Nobleson, K, Ocker, S, Olum, K, Oslowski, S, Paladi, A, Parthasarathy, A, Pennucci, T, Perera, B, Perrodin, D, Petiteau, A, Petrov, P, Pol, N, Porayko, N, Possenti, A, Prabu, T, Leclere, H, Radovan, H, Rana, P, Ransom, S, Ray, P, Reardon, D, Rogers, A, Romano, J, Russell, C, Samajdar, A, Sanidas, S, Sardesai, S, Schmiedekamp, A, Schmiedekamp, C, Schmitz, K, Schult, L, Sesana, A, Shaifullah, G, Shannon, R, Shapiro-Albert, B, Siemens, X, Simon, J, Singha, J, Siwek, M, Speri, L, Spiewak, R, Srivastava, A, Stairs, I, Stappers, B, Stinebring, D, Stovall, K, Sun, J, Surnis, M, Susarla, S, Susobhanan, A, Swiggum, J, Takahashi, K, Tarafdar, P, Taylor, J, Taylor, S, Theureau, G, Thrane, E, Thyagarajan, N, Tiburzi, C, Toomey, L, Turner, J, Unal, C, Vallisneri, M, van der Wateren, E, van Haasteren, R, Vecchio, A, Venkatraman Krishnan, V, Verbiest, J, Vigeland, S, Wahl, H, Wang, S, Wang, Q, Witt, C, Wang, J, Wang, L, Wayt, K, Wu, Z, Young, O, Zhang, L, Zhang, S, Zhu, X, Zic, A, Agazie G., Antoniadis J., Anumarlapudi A., Archibald A. M., Arumugam P., Arumugam S., Arzoumanian Z., Askew J., Babak S., Bagchi M., Bailes M., Nielsen A. B., Baker P. T., Bassa C. G., Bathula A., Becsy B., Berthereau A., Bhat N. D. R., Blecha L., Bonetti M., Bortolas E., Brazier A., Brook P. R., Burgay M., Burke-Spolaor S., Burnette R., Caballero R. N., Cameron A., Case R., Chalumeau A., Champion D. J., Chanlaridis S., Charisi M., Chatterjee S., Chatziioannou K., Cheeseboro B. D., Chen S., Chen Z. -C., Cognard I., Cohen T., Coles W. A., Cordes J. M., Cornish N. J., Crawford F., Cromartie H. T., Crowter K., Curylo M., Cutler C. J., Dai S., Dandapat S., Deb D., DeCesar M. E., DeGan D., Demorest P. B., Deng H., Desai S., Desvignes G., Dey L., Dhanda-Batra N., Di Marco V., Dolch T., Drachler B., Dwivedi C., Ellis J. A., Falxa M., Feng Y., Ferdman R. D., Ferrara E. C., Fiore W., Fonseca E., Franchini A., Freedman G. E., Gair J. R., Garver-Daniels N., Gentile P. A., Gersbach K. A., Glaser J., Good D. C., Goncharov B., Gopakumar A., Graikou E., Griessmeier J. -M., Guillemot L., Gultekin K., Guo Y. J., Gupta Y., Grunthal K., Hazboun J. S., Hisano S., Hobbs G. B., Hourihane S., Hu H., Iraci F., Islo K., Izquierdo-Villalba D., Jang J., Jawor J., Janssen G. H., Jennings R. J., Jessner A., Johnson A. D., Jones M. L., Joshi B. C., Kaiser A. R., Kaplan D. L., Kapur A., Kareem F., Karuppusamy R., Keane E. F., Keith M. J., Kelley L. Z., Kerr M., Key J. S., Kharbanda D., Kikunaga T., Klein T. C., Kolhe N., Kramer M., Krishnakumar M. A., Kulkarni A., Laal N., Lackeos K., Lam M. T., Lamb W. G., Larsen B. B., Lazio T. J. W., Lee K. J., Levin Y., Lewandowska N., Littenberg T. B., Liu K., Liu T., Liu Y., Lommen A., Lorimer D. R., Lower M. E., Luo J., Luo R., Lynch R. S., Lyne A. G., Ma C. -P., Maan Y., Madison D. R., Main R. A., Manchester R. N., Mandow R., Mattson M. A., McEwen A., McKee J. W., McLaughlin M. A., McMann N., Meyers B. W., Meyers P. M., Mickaliger M. B., Miles M., Mingarelli C. M. F., Mitridate A., Natarajan P., Nathan R. S., Ng C., Nice D. J., Nitu I. C., Nobleson K., Ocker S. K., Olum K. D., Oslowski S., Paladi A. K., Parthasarathy A., Pennucci T. T., Perera B. B. P., Perrodin D., Petiteau A., Petrov P., Pol N. S., Porayko N. K., Possenti A., Prabu T., Leclere H. Q., Radovan H. A., Rana P., Ransom S. M., Ray P. S., Reardon D. J., Rogers A. F., Romano J. D., Russell C. J., Samajdar A., Sanidas S. A., Sardesai S. C., Schmiedekamp A., Schmiedekamp C., Schmitz K., Schult L., Sesana A., Shaifullah G., Shannon R. M., Shapiro-Albert B. J., Siemens X., Simon J., Singha J., Siwek M. S., Speri L., Spiewak R., Srivastava A., Stairs I. H., Stappers B. W., Stinebring D. R., Stovall K., Sun J. P., Surnis M., Susarla S. C., Susobhanan A., Swiggum J. K., Takahashi K., Tarafdar P., Taylor J., Taylor S. R., Theureau G., Thrane E., Thyagarajan N., Tiburzi C., Toomey L., Turner J. E., Unal C., Vallisneri M., van der Wateren E., van Haasteren R., Vecchio A., Venkatraman Krishnan V., Verbiest J. P. W., Vigeland S. J., Wahl H. M., Wang S., Wang Q., Witt C. A., Wang J., Wang L., Wayt K. E., Wu Z., Young O., Zhang L., Zhang S., Zhu X. -J., and Zic A.
Published: 2024

2. Comparing recent PTA results on the nanohertz stochastic gravitational wave background

Author: The International Pulsar Timing Array Collaboration, Agazie, G., Antoniadis, J., Anumarlapudi, A., Archibald, A. M., Arumugam, P., Arumugam, S., Arzoumanian, Z., Askew, J., Babak, S., Bagchi, M., Bailes, M., Nielsen, A. -S. Bak, Baker, P. T., Bassa, C. G., Bathula, A., Bécsy, B., Berthereau, A., Bhat, N. D. R., Blecha, L., Bonetti, M., Bortolas, E., Brazier, A., Brook, P. R., Burgay, M., Burke-Spolaor, S., Burnette, R., Caballero, R. N., Cameron, A., Case, R., Chalumeau, A., Champion, D. J., Chanlaridis, S., Charisi, M., Chatterjee, S., Chatziioannou, K., Cheeseboro, B. D., Chen, S., Chen, Z. -C., Cognard, I., Cohen, T., Coles, W. A., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., Curyło, M., Cutler, C. J., Dai, S., Dandapat, S., Deb, D., DeCesar, M. E., DeGan, D., Demorest, P. B., Deng, H., Desai, S., Desvignes, G., Dey, L., Dhanda-Batra, N., Di Marco, V., Dolch, T., Drachler, B., Dwivedi, C., Ellis, J. A., Falxa, M., Feng, Y., Ferdman, R. D., Ferrara, E. C., Fiore, W., Fonseca, E., Franchini, A., Freedman, G. E., Gair, J. R., Garver-Daniels, N., Gentile, P. A., Gersbach, K. A., Glaser, J., Good, D. C., Goncharov, B., Gopakumar, A., Graikou, E., Grießmeier, J. -M., Guillemot, L., Gültekin, K., Guo, Y. J., Gupta, Y., Grunthal, K., Hazboun, J. S., Hisano, S., Hobbs, G. B., Hourihane, S., Hu, H., Iraci, F., Islo, K., Izquierdo-Villalba, D., Jang, J., Jawor, J., Janssen, G. H., Jennings, R. J., Jessner, A., Johnson, A. D., Jones, M. L., Joshi, B. C., Kaiser, A. R., Kaplan, D. L., Kapur, A., Kareem, F., Karuppusamy, R., Keane, E. F., Keith, M. J., Kelley, L. Z., Kerr, M., Key, J. S., Kharbanda, D., Kikunaga, T., Klein, T. C., Kolhe, N., Kramer, M., Krishnakumar, M. A., Kulkarni, A., Laal, N., Lackeos, K., Lam, M. T., Lamb, W. G., Larsen, B. B., Lazio, T. J. W., Lee, K. J., Levin, Y., Lewandowska, N., Littenberg, T. B., Liu, K., Liu, T., Liu, Y., Lommen, A., Lorimer, D. R., Lower, M. E., Luo, J., Luo, R., Lynch, R. S., Lyne, A. G., Ma, C. -P., Maan, Y., Madison, D. R., Main, R. A., Manchester, R. N., Mandow, R., Mattson, M. A., McEwen, A., McKee, J. W., McLaughlin, M. A., McMann, N., Meyers, B. W., Meyers, P. M., Mickaliger, M. B., Miles, M., Mingarelli, C. M. F., Mitridate, A., Natarajan, P., Nathan, R. S., Ng, C., Nice, D. J., Niţu, I. C., Nobleson, K., Ocker, S. K., Olum, K. D., Osłowski, S., Paladi, A. K., Parthasarathy, A., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Petiteau, A., Petrov, P., Pol, N. S., Porayko, N. K., Possenti, A., Prabu, T., Leclere, H. Quelquejay, Radovan, H. A., Rana, P., Ransom, S. M., Ray, P. S., Reardon, D. J., Rogers, A. F., Romano, J. D., Russell, C. J., Samajdar, A., Sanidas, S. A., Sardesai, S. C., Schmiedekamp, A., Schmiedekamp, C., Schmitz, K., Schult, L., Sesana, A., Shaifullah, G., Shannon, R. M., Shapiro-Albert, B. J., Siemens, X., Simon, J., Singha, J., Siwek, M. S., Speri, L., Spiewak, R., Srivastava, A., Stairs, I. H., Stappers, B. W., Stinebring, D. R., Stovall, K., Sun, J. P., Surnis, M., Susarla, S. C., Susobhanan, A., Swiggum, J. K., Takahashi, K., Tarafdar, P., Taylor, J., Taylor, S. R., Theureau, G., Thrane, E., Thyagarajan, N., Tiburzi, C., Toomey, L., Turner, J. E., Unal, C., Vallisneri, M., van der Wateren, E., van Haasteren, R., Vecchio, A., Krishnan, V. Venkatraman, Verbiest, J. P. W., Vigeland, S. J., Wahl, H. M., Wang, S., Wang, Q., Witt, C. A., Wang, J., Wang, L., Wayt, K. E., Wu, Z., Young, O., Zhang, L., Zhang, S., Zhu, X. -J., Zic, A., The International Pulsar Timing Array Collaboration, Agazie, G., Antoniadis, J., Anumarlapudi, A., Archibald, A. M., Arumugam, P., Arumugam, S., Arzoumanian, Z., Askew, J., Babak, S., Bagchi, M., Bailes, M., Nielsen, A. -S. Bak, Baker, P. T., Bassa, C. G., Bathula, A., Bécsy, B., Berthereau, A., Bhat, N. D. R., Blecha, L., Bonetti, M., Bortolas, E., Brazier, A., Brook, P. R., Burgay, M., Burke-Spolaor, S., Burnette, R., Caballero, R. N., Cameron, A., Case, R., Chalumeau, A., Champion, D. J., Chanlaridis, S., Charisi, M., Chatterjee, S., Chatziioannou, K., Cheeseboro, B. D., Chen, S., Chen, Z. -C., Cognard, I., Cohen, T., Coles, W. A., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., Curyło, M., Cutler, C. J., Dai, S., Dandapat, S., Deb, D., DeCesar, M. E., DeGan, D., Demorest, P. B., Deng, H., Desai, S., Desvignes, G., Dey, L., Dhanda-Batra, N., Di Marco, V., Dolch, T., Drachler, B., Dwivedi, C., Ellis, J. A., Falxa, M., Feng, Y., Ferdman, R. D., Ferrara, E. C., Fiore, W., Fonseca, E., Franchini, A., Freedman, G. E., Gair, J. R., Garver-Daniels, N., Gentile, P. A., Gersbach, K. A., Glaser, J., Good, D. C., Goncharov, B., Gopakumar, A., Graikou, E., Grießmeier, J. -M., Guillemot, L., Gültekin, K., Guo, Y. J., Gupta, Y., Grunthal, K., Hazboun, J. S., Hisano, S., Hobbs, G. B., Hourihane, S., Hu, H., Iraci, F., Islo, K., Izquierdo-Villalba, D., Jang, J., Jawor, J., Janssen, G. H., Jennings, R. J., Jessner, A., Johnson, A. D., Jones, M. L., Joshi, B. C., Kaiser, A. R., Kaplan, D. L., Kapur, A., Kareem, F., Karuppusamy, R., Keane, E. F., Keith, M. J., Kelley, L. Z., Kerr, M., Key, J. S., Kharbanda, D., Kikunaga, T., Klein, T. C., Kolhe, N., Kramer, M., Krishnakumar, M. A., Kulkarni, A., Laal, N., Lackeos, K., Lam, M. T., Lamb, W. G., Larsen, B. B., Lazio, T. J. W., Lee, K. J., Levin, Y., Lewandowska, N., Littenberg, T. B., Liu, K., Liu, T., Liu, Y., Lommen, A., Lorimer, D. R., Lower, M. E., Luo, J., Luo, R., Lynch, R. S., Lyne, A. G., Ma, C. -P., Maan, Y., Madison, D. R., Main, R. A., Manchester, R. N., Mandow, R., Mattson, M. A., McEwen, A., McKee, J. W., McLaughlin, M. A., McMann, N., Meyers, B. W., Meyers, P. M., Mickaliger, M. B., Miles, M., Mingarelli, C. M. F., Mitridate, A., Natarajan, P., Nathan, R. S., Ng, C., Nice, D. J., Niţu, I. C., Nobleson, K., Ocker, S. K., Olum, K. D., Osłowski, S., Paladi, A. K., Parthasarathy, A., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Petiteau, A., Petrov, P., Pol, N. S., Porayko, N. K., Possenti, A., Prabu, T., Leclere, H. Quelquejay, Radovan, H. A., Rana, P., Ransom, S. M., Ray, P. S., Reardon, D. J., Rogers, A. F., Romano, J. D., Russell, C. J., Samajdar, A., Sanidas, S. A., Sardesai, S. C., Schmiedekamp, A., Schmiedekamp, C., Schmitz, K., Schult, L., Sesana, A., Shaifullah, G., Shannon, R. M., Shapiro-Albert, B. J., Siemens, X., Simon, J., Singha, J., Siwek, M. S., Speri, L., Spiewak, R., Srivastava, A., Stairs, I. H., Stappers, B. W., Stinebring, D. R., Stovall, K., Sun, J. P., Surnis, M., Susarla, S. C., Susobhanan, A., Swiggum, J. K., Takahashi, K., Tarafdar, P., Taylor, J., Taylor, S. R., Theureau, G., Thrane, E., Thyagarajan, N., Tiburzi, C., Toomey, L., Turner, J. E., Unal, C., Vallisneri, M., van der Wateren, E., van Haasteren, R., Vecchio, A., Krishnan, V. Venkatraman, Verbiest, J. P. W., Vigeland, S. J., Wahl, H. M., Wang, S., Wang, Q., Witt, C. A., Wang, J., Wang, L., Wayt, K. E., Wu, Z., Young, O., Zhang, L., Zhang, S., Zhu, X. -J., and Zic, A.
Abstract: The Australian, Chinese, European, Indian, and North American pulsar timing array (PTA) collaborations recently reported, at varying levels, evidence for the presence of a nanohertz gravitational wave background (GWB). Given that each PTA made different choices in modeling their data, we perform a comparison of the GWB and individual pulsar noise parameters across the results reported from the PTAs that constitute the International Pulsar Timing Array (IPTA). We show that despite making different modeling choices, there is no significant difference in the GWB parameters that are measured by the different PTAs, agreeing within $1\sigma$. The pulsar noise parameters are also consistent between different PTAs for the majority of the pulsars included in these analyses. We bridge the differences in modeling choices by adopting a standardized noise model for all pulsars and PTAs, finding that under this model there is a reduction in the tension in the pulsar noise parameters. As part of this reanalysis, we "extended" each PTA's data set by adding extra pulsars that were not timed by that PTA. Under these extensions, we find better constraints on the GWB amplitude and a higher signal-to-noise ratio for the Hellings and Downs correlations. These extensions serve as a prelude to the benefits offered by a full combination of data across all pulsars in the IPTA, i.e., the IPTA's Data Release 3, which will involve not just adding in additional pulsars, but also including data from all three PTAs where any given pulsar is timed by more than as single PTA., Comment: 21 pages, 9 figures, submitted to ApJ
Published: 2023

3. Searching for continuous Gravitational Waves in the second data release of the International Pulsar Timing Array

Author: Falxa, M., Babak, S., Baker, P. T., Bécsy, B., Chalumeau, A., Chen, S., Chen, Z., Cornish, N. J., Guillemot, L., Hazboun, J. S., Mingarelli, C. M. F., Parthasarathy, A., Petiteau, A., Pol, N. S., Sesana, A., Spolaor, S. B., Taylor, S. R., Theureau, G., Vallisneri, M., Vigeland, S. J., Witt, C. A., Zhu, X., Antoniadis, J., Arzoumanian, Z., Bailes, M., Bhat, N. D. R., Blecha, L., Brazier, A., Brook, P. R., Caballero, N., Cameron, A. D., Casey-Clyde, J. A., Champion, D., Charisi, M., Chatterjee, S., Cognard, I., Cordes, J. M., Crawford, F., Cromartie, H. T., Crowter, K., Dai, S., DeCesar, M. E., Demorest, P. B., Desvignes, G., Dolch, T., Drachler, B., Feng, Y., Ferrara, E. C., Fiore, W., Fonseca, E., Garver-Daniels, N., Glaser, J., Goncharov, B., Good, D. C., Griessmeier, J., Guo, Y. J., Gültekin, K., Hobbs, G., Hu, H., Islo, K., Jang, J., Jennings, R. J., Johnson, A. D., Jones, M. L., Kaczmarek, J., Kaiser, A. R., Kaplan, D. L., Keith, M., Kelley, L. Z., Kerr, M., Key, J. S., Laal, N., Lam, M. T., Lamb, W. G., Lazio, T. J. W., Liu, K., Liu, T., Luo, J., Lynch, R. S., Madison, D. R., Main, R., Manchester, R., McEwen, A., McKee, J., McLaughlin, M. A., Ng, C., Nice, D. J., Ocker, S., Olum, K. D., Osłowski, S., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Porayko, N., Possenti, A., Quelquejay-Leclere, H., Ransom, S. M., Ray, P. S., Reardon, D. J., Russell, C. J., Samajdar, A., Sarkissian, J., Schult, L., Shaifullah, G., Shannon, R. M., Shapiro-Albert, B. J., Siemens, X., Simon, J. J., Siwek, M., Smith, T. L., Speri, L., Spiewak, R., Stairs, I. H., Stappers, B., Stinebring, D. R., Swiggum, J. K., Tiburzi, C., Turner, J., Vecchio, A., Verbiest, J. P. W., Wahl, H., Wang, S. Q., Wang, J., Wu, Z., Zhang, L., Zhang, S., Falxa, M., Babak, S., Baker, P. T., Bécsy, B., Chalumeau, A., Chen, S., Chen, Z., Cornish, N. J., Guillemot, L., Hazboun, J. S., Mingarelli, C. M. F., Parthasarathy, A., Petiteau, A., Pol, N. S., Sesana, A., Spolaor, S. B., Taylor, S. R., Theureau, G., Vallisneri, M., Vigeland, S. J., Witt, C. A., Zhu, X., Antoniadis, J., Arzoumanian, Z., Bailes, M., Bhat, N. D. R., Blecha, L., Brazier, A., Brook, P. R., Caballero, N., Cameron, A. D., Casey-Clyde, J. A., Champion, D., Charisi, M., Chatterjee, S., Cognard, I., Cordes, J. M., Crawford, F., Cromartie, H. T., Crowter, K., Dai, S., DeCesar, M. E., Demorest, P. B., Desvignes, G., Dolch, T., Drachler, B., Feng, Y., Ferrara, E. C., Fiore, W., Fonseca, E., Garver-Daniels, N., Glaser, J., Goncharov, B., Good, D. C., Griessmeier, J., Guo, Y. J., Gültekin, K., Hobbs, G., Hu, H., Islo, K., Jang, J., Jennings, R. J., Johnson, A. D., Jones, M. L., Kaczmarek, J., Kaiser, A. R., Kaplan, D. L., Keith, M., Kelley, L. Z., Kerr, M., Key, J. S., Laal, N., Lam, M. T., Lamb, W. G., Lazio, T. J. W., Liu, K., Liu, T., Luo, J., Lynch, R. S., Madison, D. R., Main, R., Manchester, R., McEwen, A., McKee, J., McLaughlin, M. A., Ng, C., Nice, D. J., Ocker, S., Olum, K. D., Osłowski, S., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Porayko, N., Possenti, A., Quelquejay-Leclere, H., Ransom, S. M., Ray, P. S., Reardon, D. J., Russell, C. J., Samajdar, A., Sarkissian, J., Schult, L., Shaifullah, G., Shannon, R. M., Shapiro-Albert, B. J., Siemens, X., Simon, J. J., Siwek, M., Smith, T. L., Speri, L., Spiewak, R., Stairs, I. H., Stappers, B., Stinebring, D. R., Swiggum, J. K., Tiburzi, C., Turner, J., Vecchio, A., Verbiest, J. P. W., Wahl, H., Wang, S. Q., Wang, J., Wu, Z., Zhang, L., and Zhang, S.
Abstract: The International Pulsar Timing Array 2nd data release is the combination of datasets from worldwide collaborations. In this study, we search for continuous waves: gravitational wave signals produced by individual supermassive black hole binaries in the local universe. We consider binaries on circular orbits and neglect the evolution of orbital frequency over the observational span. We find no evidence for such signals and set sky averaged 95% upper limits on their amplitude h 95 . The most sensitive frequency is 10nHz with h 95 = 9.1 10-15 . We achieved the best upper limit to date at low and high frequencies of the PTA band thanks to improved effective cadence of observations. In our analysis, we have taken into account the recently discovered common red noise process, which has an impact at low frequencies. We also find that the peculiar noise features present in some pulsars data must be taken into account to reduce the false alarm. We show that using custom noise models is essential in searching for continuous gravitational wave signals and setting the upper limit.
Published: 2023
Full Text: View/download PDF

4. The International Pulsar Timing Array second data release: Search for an isotropic Gravitational Wave Background

Author: Antoniadis, J., Arzoumanian, Z., Babak, S., Bailes, M., Nielsen, A. -S. Bak, Baker, P. T., Bassa, C. G., Becsy, B., Berthereau, A., Bonetti, M., Brazier, A., Brook, P. R., Burgay, M., Burke-Spolaor, S., Caballero, R. N., Casey-Clyde, J. A., Chalumeau, A., Champion, D. J., Charisi, M., Chatterjee, S., Chen, S., Cognard, I., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., Dai, S., DeCesar, M. E., Demorest, P. B., Desvignes, G., Dolch, T., Drachler, B., Falxa, M., Ferrara, E. C., Fiore, W., Fonseca, E., Gair, J. R., Garver-Daniels, N., Goncharov, B., Good, D. C., Graikou, E., Guillemot, L., Guo, Y. J., Hazboun, J. S., Hobbs, G., Hu, H., Islo, K., Janssen, G. H., Jennings, R. J., Johnson, A. D., Jones, M. L., Kaiser, A. R., Kaplan, D. L., Karuppusamy, R., Keith, M. J., Kelley, L. Z., Kerr, M., Key, J. S., Kramer, M., Lam, M. T., Lamb, W. G., Lazio, T. J. W., Lee, K. J., Lentati, L., Liu, K., Luo, J., Lynch, R. S., Lyne, A. G., Madison, D. R., Main, R. A., Manchester, R. N., McEwen, A., McKee, J. W., McLaughlin, M. A., Mickaliger, M. B., Mingarelli, C. M. F., Ng, C., Nice, D. J., lowski, S. Os, Parthasarathy, A., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Petiteau, A., Pol, N. S., Porayko, N. K., Possenti, A., Ransom, S. M., Ray, P. S., Reardon, D. J., Russell, C. J., Samajdar, A., Sampson, L. M., Sanidas, S., Sarkissian, J. M., Schmitz, K., Schult, L., Sesana, A., Shaifullah, G., Shannon, R. M., Shapiro-Albert, B. J., Siemens, X., Simon, J., Smith, T. L., Speri, L., Spiewak, R., Stairs, I. H., Stappers, B. W., Stinebring, D. R., Swiggum, J. K., Taylor, S. R., Theureau, G., Tiburzi, C., Vallisneri, M., van der Wateren, E., Vecchio, A., Verbiest, J. P. W., Vigeland, S. J., Wahl, H., Wang, J. B., Wang, J., Wang, L., Witt, C. A., Zhang, S., Zhu, X. J., Antoniadis, J., Arzoumanian, Z., Babak, S., Bailes, M., Nielsen, A. -S. Bak, Baker, P. T., Bassa, C. G., Becsy, B., Berthereau, A., Bonetti, M., Brazier, A., Brook, P. R., Burgay, M., Burke-Spolaor, S., Caballero, R. N., Casey-Clyde, J. A., Chalumeau, A., Champion, D. J., Charisi, M., Chatterjee, S., Chen, S., Cognard, I., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., Dai, S., DeCesar, M. E., Demorest, P. B., Desvignes, G., Dolch, T., Drachler, B., Falxa, M., Ferrara, E. C., Fiore, W., Fonseca, E., Gair, J. R., Garver-Daniels, N., Goncharov, B., Good, D. C., Graikou, E., Guillemot, L., Guo, Y. J., Hazboun, J. S., Hobbs, G., Hu, H., Islo, K., Janssen, G. H., Jennings, R. J., Johnson, A. D., Jones, M. L., Kaiser, A. R., Kaplan, D. L., Karuppusamy, R., Keith, M. J., Kelley, L. Z., Kerr, M., Key, J. S., Kramer, M., Lam, M. T., Lamb, W. G., Lazio, T. J. W., Lee, K. J., Lentati, L., Liu, K., Luo, J., Lynch, R. S., Lyne, A. G., Madison, D. R., Main, R. A., Manchester, R. N., McEwen, A., McKee, J. W., McLaughlin, M. A., Mickaliger, M. B., Mingarelli, C. M. F., Ng, C., Nice, D. J., lowski, S. Os, Parthasarathy, A., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Petiteau, A., Pol, N. S., Porayko, N. K., Possenti, A., Ransom, S. M., Ray, P. S., Reardon, D. J., Russell, C. J., Samajdar, A., Sampson, L. M., Sanidas, S., Sarkissian, J. M., Schmitz, K., Schult, L., Sesana, A., Shaifullah, G., Shannon, R. M., Shapiro-Albert, B. J., Siemens, X., Simon, J., Smith, T. L., Speri, L., Spiewak, R., Stairs, I. H., Stappers, B. W., Stinebring, D. R., Swiggum, J. K., Taylor, S. R., Theureau, G., Tiburzi, C., Vallisneri, M., van der Wateren, E., Vecchio, A., Verbiest, J. P. W., Vigeland, S. J., Wahl, H., Wang, J. B., Wang, J., Wang, L., Witt, C. A., Zhang, S., and Zhu, X. J.
Abstract: We searched for an isotropic stochastic gravitational wave background in the second data release of the International Pulsar Timing Array, a global collaboration synthesizing decadal-length pulsar-timing campaigns in North America, Europe, and Australia. In our reference search for a power law strain spectrum of the form $h_c = A(f/1\,\mathrm{yr}^{-1})^{\alpha}$, we found strong evidence for a spectrally-similar low-frequency stochastic process of amplitude $A = 3.8^{+6.3}_{-2.5}\times10^{-15}$ and spectral index $\alpha = -0.5 \pm 0.5$, where the uncertainties represent 95\% credible regions, using information from the auto- and cross-correlation terms between the pulsars in the array. For a spectral index of $\alpha = -2/3$, as expected from a population of inspiralling supermassive black hole binaries, the recovered amplitude is $A = 2.8^{+1.2}_{-0.8}\times10^{-15}$. Nonetheless, no significant evidence of the Hellings-Downs correlations that would indicate a gravitational-wave origin was found. We also analyzed the constituent data from the individual pulsar timing arrays in a consistent way, and clearly demonstrate that the combined international data set is more sensitive. Furthermore, we demonstrate that this combined data set produces comparable constraints to recent single-array data sets which have more data than the constituent parts of the combination. Future international data releases will deliver increased sensitivity to gravitational wave radiation, and significantly increase the detection probability., Comment: 17 pages, 12 figures, accepted in MNRAS
Published: 2022
Full Text: View/download PDF

5. The International Pulsar Timing Array second data release: Search for an isotropic Gravitational Wave Background

Author: Antoniadis, J., Arzoumanian, Z., Babak, S., Bailes, M., Nielsen, A. -S. Bak, Baker, P. T., Bassa, C. G., Becsy, B., Berthereau, A., Bonetti, M., Brazier, A., Brook, P. R., Burgay, M., Burke-Spolaor, S., Caballero, R. N., Casey-Clyde, J. A., Chalumeau, A., Champion, D. J., Charisi, M., Chatterjee, S., Chen, S., Cognard, I., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., Dai, S., DeCesar, M. E., Demorest, P. B., Desvignes, G., Dolch, T., Drachler, B., Falxa, M., Ferrara, E. C., Fiore, W., Fonseca, E., Gair, J. R., Garver-Daniels, N., Goncharov, B., Good, D. C., Graikou, E., Guillemot, L., Guo, Y. J., Hazboun, J. S., Hobbs, G., Hu, H., Islo, K., Janssen, G. H., Jennings, R. J., Johnson, A. D., Jones, M. L., Kaiser, A. R., Kaplan, D. L., Karuppusamy, R., Keith, M. J., Kelley, L. Z., Kerr, M., Key, J. S., Kramer, M., Lam, M. T., Lamb, W. G., Lazio, T. J. W., Lee, K. J., Lentati, L., Liu, K., Luo, J., Lynch, R. S., Lyne, A. G., Madison, D. R., Main, R. A., Manchester, R. N., McEwen, A., McKee, J. W., McLaughlin, M. A., Mickaliger, M. B., Mingarelli, C. M. F., Ng, C., Nice, D. J., lowski, S. Os, Parthasarathy, A., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Petiteau, A., Pol, N. S., Porayko, N. K., Possenti, A., Ransom, S. M., Ray, P. S., Reardon, D. J., Russell, C. J., Samajdar, A., Sampson, L. M., Sanidas, S., Sarkissian, J. M., Schmitz, K., Schult, L., Sesana, A., Shaifullah, G., Shannon, R. M., Shapiro-Albert, B. J., Siemens, X., Simon, J., Smith, T. L., Speri, L., Spiewak, R., Stairs, I. H., Stappers, B. W., Stinebring, D. R., Swiggum, J. K., Taylor, S. R., Theureau, G., Tiburzi, C., Vallisneri, M., van der Wateren, E., Vecchio, A., Verbiest, J. P. W., Vigeland, S. J., Wahl, H., Wang, J. B., Wang, J., Wang, L., Witt, C. A., Zhang, S., Zhu, X. J., Antoniadis, J., Arzoumanian, Z., Babak, S., Bailes, M., Nielsen, A. -S. Bak, Baker, P. T., Bassa, C. G., Becsy, B., Berthereau, A., Bonetti, M., Brazier, A., Brook, P. R., Burgay, M., Burke-Spolaor, S., Caballero, R. N., Casey-Clyde, J. A., Chalumeau, A., Champion, D. J., Charisi, M., Chatterjee, S., Chen, S., Cognard, I., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., Dai, S., DeCesar, M. E., Demorest, P. B., Desvignes, G., Dolch, T., Drachler, B., Falxa, M., Ferrara, E. C., Fiore, W., Fonseca, E., Gair, J. R., Garver-Daniels, N., Goncharov, B., Good, D. C., Graikou, E., Guillemot, L., Guo, Y. J., Hazboun, J. S., Hobbs, G., Hu, H., Islo, K., Janssen, G. H., Jennings, R. J., Johnson, A. D., Jones, M. L., Kaiser, A. R., Kaplan, D. L., Karuppusamy, R., Keith, M. J., Kelley, L. Z., Kerr, M., Key, J. S., Kramer, M., Lam, M. T., Lamb, W. G., Lazio, T. J. W., Lee, K. J., Lentati, L., Liu, K., Luo, J., Lynch, R. S., Lyne, A. G., Madison, D. R., Main, R. A., Manchester, R. N., McEwen, A., McKee, J. W., McLaughlin, M. A., Mickaliger, M. B., Mingarelli, C. M. F., Ng, C., Nice, D. J., lowski, S. Os, Parthasarathy, A., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Petiteau, A., Pol, N. S., Porayko, N. K., Possenti, A., Ransom, S. M., Ray, P. S., Reardon, D. J., Russell, C. J., Samajdar, A., Sampson, L. M., Sanidas, S., Sarkissian, J. M., Schmitz, K., Schult, L., Sesana, A., Shaifullah, G., Shannon, R. M., Shapiro-Albert, B. J., Siemens, X., Simon, J., Smith, T. L., Speri, L., Spiewak, R., Stairs, I. H., Stappers, B. W., Stinebring, D. R., Swiggum, J. K., Taylor, S. R., Theureau, G., Tiburzi, C., Vallisneri, M., van der Wateren, E., Vecchio, A., Verbiest, J. P. W., Vigeland, S. J., Wahl, H., Wang, J. B., Wang, J., Wang, L., Witt, C. A., Zhang, S., and Zhu, X. J.
Abstract: We searched for an isotropic stochastic gravitational wave background in the second data release of the International Pulsar Timing Array, a global collaboration synthesizing decadal-length pulsar-timing campaigns in North America, Europe, and Australia. In our reference search for a power law strain spectrum of the form $h_c = A(f/1\,\mathrm{yr}^{-1})^{\alpha}$, we found strong evidence for a spectrally-similar low-frequency stochastic process of amplitude $A = 3.8^{+6.3}_{-2.5}\times10^{-15}$ and spectral index $\alpha = -0.5 \pm 0.5$, where the uncertainties represent 95\% credible regions, using information from the auto- and cross-correlation terms between the pulsars in the array. For a spectral index of $\alpha = -2/3$, as expected from a population of inspiralling supermassive black hole binaries, the recovered amplitude is $A = 2.8^{+1.2}_{-0.8}\times10^{-15}$. Nonetheless, no significant evidence of the Hellings-Downs correlations that would indicate a gravitational-wave origin was found. We also analyzed the constituent data from the individual pulsar timing arrays in a consistent way, and clearly demonstrate that the combined international data set is more sensitive. Furthermore, we demonstrate that this combined data set produces comparable constraints to recent single-array data sets which have more data than the constituent parts of the combination. Future international data releases will deliver increased sensitivity to gravitational wave radiation, and significantly increase the detection probability., Comment: 17 pages, 12 figures, accepted in MNRAS
Published: 2022
Full Text: View/download PDF

6. Precision Timing of PSR J0437-4715 with the IAR Observatory and Implications for Low-Frequency Gravitational Wave Source Sensitivity

Author: Lam, M. T., Hazboun, J. S., Lam, M. T., and Hazboun, J. S.
Abstract: While observations of many high-precision radio pulsars of order $\lesssim1~\mu$s across the sky are needed for the detection and characterization of a stochastic background of low-frequency gravitational waves (GWs), sensitivity to single sources of GWs requires even higher timing precision. The Argentine Institute of Radio Astronomy (IAR; Instituto Argentino de Radioastronom\'ia) has begun observations of the brightest-known millisecond pulsar, J0437$-$4715. Even though the two antennas are smaller than other single-dish telescopes previously used for pulsar timing array (PTA) science, the IAR's capability to monitor this pulsar daily coupled with the pulsar's brightness allows for high-precision pulse arrival-time measurements. While upgrades of the facility are currently underway, we show that modest improvements beyond current plans will provide IAR with unparalleled sensitivity to this pulsar. The most stringent upper limits on single GW sources come from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). Observations of PSR J0437$-$4715 will provide a significant sensitivity increase in NANOGrav's "blind spot" in the sky where fewer pulsars are currently being observed. With state-of-the-art instrumentation installed, we estimate the array's sensitivity will improve by a factor of $\approx$2-4 over 10 years for 20% of the sky with the inclusion of this pulsar as compared to a static version of the PTA used in NANOGrav's most recent limits. More modest instrumentation result in factors of $\approx$1.4-3. We identify four other candidate pulsars as suitable for inclusion in PTA efforts. International PTA efforts will also benefit from inclusion of these data given the potential achievable sensitivity., Comment: 14 pages, 2 figures, 4 tables, published in ApJ
Published: 2020
Full Text: View/download PDF

7. Modeling the uncertainties of solar-system ephemerides for robust gravitational-wave searches with pulsar timing arrays

Author: Vallisneri, M., Taylor, S. R., Simon, J., Folkner, W. M., Park, R. S., Cutler, C., Ellis, J. A., Lazio, T. J. W., Vigeland, S. J., Aggarwal, K., Arzoumanian, Z., Baker, P. T., Brazier, A., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., DeCesar, M., Demorest, P. B., Dolch, T., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Garver-Daniels, N., Gentile, P., Good, D., Hazboun, J. S., Holgado, A. M., Huerta, E. A., Islo, K., Jennings, R., Jones, G., Jones, M. L., Kaplan, D. L., Kelley, L. Z., Key, J. S., Lam, M. T., Levin, L., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J. K., van Haasteren, R., Witt, C. A., Zhu, W. W., Vallisneri, M., Taylor, S. R., Simon, J., Folkner, W. M., Park, R. S., Cutler, C., Ellis, J. A., Lazio, T. J. W., Vigeland, S. J., Aggarwal, K., Arzoumanian, Z., Baker, P. T., Brazier, A., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., DeCesar, M., Demorest, P. B., Dolch, T., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Garver-Daniels, N., Gentile, P., Good, D., Hazboun, J. S., Holgado, A. M., Huerta, E. A., Islo, K., Jennings, R., Jones, G., Jones, M. L., Kaplan, D. L., Kelley, L. Z., Key, J. S., Lam, M. T., Levin, L., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J. K., van Haasteren, R., Witt, C. A., and Zhu, W. W.
Abstract: The regularity of pulsar emissions becomes apparent once we reference the pulses' times of arrivals to the inertial rest frame of the solar system. It follows that errors in the determination of Earth's position with respect to the solar-system barycenter can appear as a time-correlated bias in pulsar-timing residual time series, affecting the searches for low-frequency gravitational waves performed with pulsar timing arrays. Indeed, recent array datasets yield different gravitational-wave background upper limits and detection statistics when analyzed with different solar-system ephemerides. Crucially, the ephemerides do not generally provide usable error representations. In this article we describe the motivation, construction, and application of a physical model of solar-system ephemeris uncertainties, which focuses on the degrees of freedom (Jupiter's orbital elements) most relevant to gravitational-wave searches with pulsar timing arrays. This model, BayesEphem, was used to derive ephemeris-robust results in NANOGrav's 11-yr stochastic-background search, and it provides a foundation for future searches by NANOGrav and other consortia. The analysis and simulations reported here suggest that ephemeris modeling reduces the gravitational-wave sensitivity of the 11-yr dataset; and that this degeneracy will vanish with improved ephemerides and with the longer pulsar timing datasets that will become available in the near future., Comment: Fixed typo in author list. Code that supports all calculations and figures is available at github.com/nanograv/11yr_stochastic_analysis/tree/master/bayesephem
Published: 2020
Full Text: View/download PDF

8. Precision Timing of PSR J0437-4715 with the IAR Observatory and Implications for Low-Frequency Gravitational Wave Source Sensitivity

Author: Lam, M. T., Hazboun, J. S., Lam, M. T., and Hazboun, J. S.
Abstract: While observations of many high-precision radio pulsars of order $\lesssim1~\mu$s across the sky are needed for the detection and characterization of a stochastic background of low-frequency gravitational waves (GWs), sensitivity to single sources of GWs requires even higher timing precision. The Argentine Institute of Radio Astronomy (IAR; Instituto Argentino de Radioastronom\'ia) has begun observations of the brightest-known millisecond pulsar, J0437$-$4715. Even though the two antennas are smaller than other single-dish telescopes previously used for pulsar timing array (PTA) science, the IAR's capability to monitor this pulsar daily coupled with the pulsar's brightness allows for high-precision pulse arrival-time measurements. While upgrades of the facility are currently underway, we show that modest improvements beyond current plans will provide IAR with unparalleled sensitivity to this pulsar. The most stringent upper limits on single GW sources come from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). Observations of PSR J0437$-$4715 will provide a significant sensitivity increase in NANOGrav's "blind spot" in the sky where fewer pulsars are currently being observed. With state-of-the-art instrumentation installed, we estimate the array's sensitivity will improve by a factor of $\approx$2-4 over 10 years for 20% of the sky with the inclusion of this pulsar as compared to a static version of the PTA used in NANOGrav's most recent limits. More modest instrumentation result in factors of $\approx$1.4-3. We identify four other candidate pulsars as suitable for inclusion in PTA efforts. International PTA efforts will also benefit from inclusion of these data given the potential achievable sensitivity., Comment: 14 pages, 2 figures, 4 tables, published in ApJ
Published: 2020
Full Text: View/download PDF

9. Modeling the uncertainties of solar-system ephemerides for robust gravitational-wave searches with pulsar timing arrays

Author: Vallisneri, M., Taylor, S. R., Simon, J., Folkner, W. M., Park, R. S., Cutler, C., Ellis, J. A., Lazio, T. J. W., Vigeland, S. J., Aggarwal, K., Arzoumanian, Z., Baker, P. T., Brazier, A., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., DeCesar, M., Demorest, P. B., Dolch, T., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Garver-Daniels, N., Gentile, P., Good, D., Hazboun, J. S., Holgado, A. M., Huerta, E. A., Islo, K., Jennings, R., Jones, G., Jones, M. L., Kaplan, D. L., Kelley, L. Z., Key, J. S., Lam, M. T., Levin, L., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J. K., van Haasteren, R., Witt, C. A., Zhu, W. W., Vallisneri, M., Taylor, S. R., Simon, J., Folkner, W. M., Park, R. S., Cutler, C., Ellis, J. A., Lazio, T. J. W., Vigeland, S. J., Aggarwal, K., Arzoumanian, Z., Baker, P. T., Brazier, A., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., DeCesar, M., Demorest, P. B., Dolch, T., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Garver-Daniels, N., Gentile, P., Good, D., Hazboun, J. S., Holgado, A. M., Huerta, E. A., Islo, K., Jennings, R., Jones, G., Jones, M. L., Kaplan, D. L., Kelley, L. Z., Key, J. S., Lam, M. T., Levin, L., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J. K., van Haasteren, R., Witt, C. A., and Zhu, W. W.
Abstract: The regularity of pulsar emissions becomes apparent once we reference the pulses' times of arrivals to the inertial rest frame of the solar system. It follows that errors in the determination of Earth's position with respect to the solar-system barycenter can appear as a time-correlated bias in pulsar-timing residual time series, affecting the searches for low-frequency gravitational waves performed with pulsar timing arrays. Indeed, recent array datasets yield different gravitational-wave background upper limits and detection statistics when analyzed with different solar-system ephemerides. Crucially, the ephemerides do not generally provide usable error representations. In this article we describe the motivation, construction, and application of a physical model of solar-system ephemeris uncertainties, which focuses on the degrees of freedom (Jupiter's orbital elements) most relevant to gravitational-wave searches with pulsar timing arrays. This model, BayesEphem, was used to derive ephemeris-robust results in NANOGrav's 11-yr stochastic-background search, and it provides a foundation for future searches by NANOGrav and other consortia. The analysis and simulations reported here suggest that ephemeris modeling reduces the gravitational-wave sensitivity of the 11-yr dataset; and that this degeneracy will vanish with improved ephemerides and with the longer pulsar timing datasets that will become available in the near future., Comment: Fixed typo in author list. Code that supports all calculations and figures is available at github.com/nanograv/11yr_stochastic_analysis/tree/master/bayesephem
Published: 2020
Full Text: View/download PDF

10. A pulsar-based time-scale from the International Pulsar Timing Array

Author: Hobbs, G, Guo, L, Caballero, R, Coles, W, Lee, K, Manchester, R, Reardon, D, Matsakis, D, Tong, M, Arzoumanian, Z, Bailes, M, Bassa, C, Bhat, N, Brazier, A, Burke-Spolaor, S, Champion, D, Chatterjee, S, Cognard, I, Dai, S, Desvignes, G, Dolch, T, Ferdman, R, Graikou, E, Guillemot, L, Janssen, G, Keith, M, Kerr, M, Kramer, M, Lam, M, Liu, K, Lyne, A, Lazio, T, Lynch, R, Mckee, J, Mclaughlin, M, Mingarelli, C, Nice, D, Osłowski, S, Pennucci, T, Perera, B, Perrodin, D, Possenti, A, Russell, C, Sanidas, S, Sesana, A, Shaifullah, G, Shannon, R, Simon, J, Spiewak, R, Stairs, I, Stappers, B, Swiggum, J, Taylor, S, Theureau, G, Toomey, L, van Haasteren, R, Wang, J, Wang, Y, Zhu, X, Hobbs, G., Guo, L., Caballero, R. N., Coles, W., Lee, K. J., Manchester, R. N., Reardon, D. J., Matsakis, D., Tong, M. L., Arzoumanian, Z., Bailes, M., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burke-Spolaor, S., Champion, D. J., Chatterjee, S., Cognard, I., Dai, S., Desvignes, G., Dolch, T., Ferdman, R. D., Graikou, E., Guillemot, L., Janssen, G. H., Keith, M. J., Kerr, M., Kramer, M., Lam, M. T., Liu, K., Lyne, A., Lazio, T. J. W., Lynch, R., McKee, J. W., McLaughlin, M. A., Mingarelli, C. M. F., Nice, D. J., Osłowski, S., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Possenti, A., Russell, C. J., Sanidas, S., Sesana, A., Shaifullah, G., Shannon, R. M., Simon, J., Spiewak, R., Stairs, I. H., Stappers, B. W., Swiggum, J. K., Taylor, S. R., Theureau, G., Toomey, L., van Haasteren, R., Wang, J. B., Wang, Y., Zhu, X. J., Hobbs, G, Guo, L, Caballero, R, Coles, W, Lee, K, Manchester, R, Reardon, D, Matsakis, D, Tong, M, Arzoumanian, Z, Bailes, M, Bassa, C, Bhat, N, Brazier, A, Burke-Spolaor, S, Champion, D, Chatterjee, S, Cognard, I, Dai, S, Desvignes, G, Dolch, T, Ferdman, R, Graikou, E, Guillemot, L, Janssen, G, Keith, M, Kerr, M, Kramer, M, Lam, M, Liu, K, Lyne, A, Lazio, T, Lynch, R, Mckee, J, Mclaughlin, M, Mingarelli, C, Nice, D, Osłowski, S, Pennucci, T, Perera, B, Perrodin, D, Possenti, A, Russell, C, Sanidas, S, Sesana, A, Shaifullah, G, Shannon, R, Simon, J, Spiewak, R, Stairs, I, Stappers, B, Swiggum, J, Taylor, S, Theureau, G, Toomey, L, van Haasteren, R, Wang, J, Wang, Y, Zhu, X, Hobbs, G., Guo, L., Caballero, R. N., Coles, W., Lee, K. J., Manchester, R. N., Reardon, D. J., Matsakis, D., Tong, M. L., Arzoumanian, Z., Bailes, M., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burke-Spolaor, S., Champion, D. J., Chatterjee, S., Cognard, I., Dai, S., Desvignes, G., Dolch, T., Ferdman, R. D., Graikou, E., Guillemot, L., Janssen, G. H., Keith, M. J., Kerr, M., Kramer, M., Lam, M. T., Liu, K., Lyne, A., Lazio, T. J. W., Lynch, R., McKee, J. W., McLaughlin, M. A., Mingarelli, C. M. F., Nice, D. J., Osłowski, S., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Possenti, A., Russell, C. J., Sanidas, S., Sesana, A., Shaifullah, G., Shannon, R. M., Simon, J., Spiewak, R., Stairs, I. H., Stappers, B. W., Swiggum, J. K., Taylor, S. R., Theureau, G., Toomey, L., van Haasteren, R., Wang, J. B., Wang, Y., and Zhu, X. J.
Abstract: We have constructed a new time-scale, TT(IPTA16), based on observations of radio pulsars presented in the first data release from the International Pulsar Timing Array (IPTA). We used two analysis techniques with independent estimates of the noise models for the pulsar observations and different algorithms for obtaining the pulsar time-scale. The two analyses agree within the estimated uncertainties and both agree with TT(BIPM17), a post-corrected time-scale produced by the Bureau International des Poids et Mesures (BIPM). We show that both methods could detect significant errors in TT(BIPM17) if they were present. We estimate the stability of the atomic clocks from which TT(BIPM17) is derived using observations of four rubidium fountain clocks at the US Naval Observatory. Comparing the power spectrum of TT(IPTA16) with that of these fountain clocks suggests that pulsar-based time-scales are unlikely to contribute to the stability of the best time-scales over the next decade, but they will remain a valuable independent check on atomic time-scales. We also find that the stability of the pulsar-based time-scale is likely to be limited by our knowledge of solar-system dynamics, and that errors in TT(BIPM17) will not be a limiting factor for the primary goal of the IPTA, which is to search for the signatures of nano-Hertz gravitational waves.
Published: 2020

11. Results for the International Pulsar Timing Array Second Mock Data Challenge: New Techniques and Challenges for the Detection of Low-Frequency Gravitational-Wave Signals

Author: Baker, P. T., Brook, P. R., Fiore, W. C., Garver-Daniels, N., Kaiser, A. R., Lam, M. T., Shapiro-Albert, B. J., Witt, C. A., Baker, P. T., Brook, P. R., Fiore, W. C., Garver-Daniels, N., Kaiser, A. R., Lam, M. T., Shapiro-Albert, B. J., and Witt, C. A.
Abstract: We present a detailed analysis of the International Pulsar Timing Array (IPTA) Second Mock Data Challenge. We tested our analysis methods using the open datasets, and then analyzed the closed datasets. In both the open and the closed datasets, we were able to detect some, but not all, of the injected gravitational wave signals. This work presents two search cases that are not well explored in the pulsar timing array (PTA) literature: a simultaneous search for a stochastic GW background and an individual loud super-massive black hole binary (SMBHB) and a simultaneous search for two SMBHB sources. While we have constructed a cohesive framework for performing these GW searches, our analyses required fine-tuning of the sampling method used in order to appropriately converge. Given the nature of real PTA data in which multiple sources will be present in data, improved techniques will be required in the future to accurately detect and characterize these GW signals., Comment: 25 pages, 9 figures
Published: 2019

12. The NANOGrav 11-year Data Set: Constraints on Planetary Masses Around 45 Millisecond Pulsars

Author: Behrens, E. A., Ransom, S. M., Madison, D. R., Arzoumanian, Z., Crowter, K., DeCesar, M. E., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Gentile, P. A., Jones, G., Jones, M. L., Lam, M. T., Levin, L., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., Ng, C., Nice, D. J., Pennucci, T. T., Perera, B. B. P., Ray, P. S., Spiewak, R., Stairs, I. H., Stovall, K., Swiggum, J. K., Zhu, W. W., Behrens, E. A., Ransom, S. M., Madison, D. R., Arzoumanian, Z., Crowter, K., DeCesar, M. E., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Gentile, P. A., Jones, G., Jones, M. L., Lam, M. T., Levin, L., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., Ng, C., Nice, D. J., Pennucci, T. T., Perera, B. B. P., Ray, P. S., Spiewak, R., Stairs, I. H., Stovall, K., Swiggum, J. K., and Zhu, W. W.
Abstract: We search for extrasolar planets around millisecond pulsars using pulsar timing data and seek to determine the minimum detectable planetary masses as a function of orbital period. Using the 11-year data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), we look for variations from our models of pulse arrival times due to the presence of exoplanets. No planets are detected around the millisecond pulsars in the NANOGrav 11-year data set, but taking into consideration the noise levels of each pulsar and the sampling rate of our observations, we develop limits that show we are sensitive to planetary masses as low as that of the moon. We analyzed potential planet periods, P, in the range 7 days < P < 2000 days, with somewhat smaller ranges for some binary pulsars. The planetary mass limit for our median-sensitivity pulsar within this period range is 1 M_moon (P / 100 days)^(-2/3)., Comment: Revised and accepted by ApJ Letters
Published: 2019
Full Text: View/download PDF

13. The NANOGrav 11-Year Data Set: Limits on Gravitational Wave Memory

Author: Aggarwal, K., Arzoumanian, Z., Baker, P. T., Brazier, A., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., Decesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Garver-Daniels, N., Gentile, P., Good, D., Hazboun, J. S., Holgado, A. M., Huerta, E. A., Islo, K., Jennings, R., Jones, G., Jones, M. L., Kaplan, D. L., Kelley, L. Z., Key, J. S., Lam, M. T., Lazio, T. J. W., Levin, L., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J. K., Taylor, S. R., Vallisneri, M., Van Haasterer, R., Vigeland, S. J., Witt, C. A., Zhu, W. W., Aggarwal, K., Arzoumanian, Z., Baker, P. T., Brazier, A., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., Decesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Garver-Daniels, N., Gentile, P., Good, D., Hazboun, J. S., Holgado, A. M., Huerta, E. A., Islo, K., Jennings, R., Jones, G., Jones, M. L., Kaplan, D. L., Kelley, L. Z., Key, J. S., Lam, M. T., Lazio, T. J. W., Levin, L., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J. K., Taylor, S. R., Vallisneri, M., Van Haasterer, R., Vigeland, S. J., Witt, C. A., and Zhu, W. W.
Abstract: The mergers of supermassive black hole binaries (SMBHBs) promise to be incredible sources of gravitational waves (GWs). While the oscillatory part of the merger gravitational waveform will be outside the frequency sensitivity range of pulsar timing arrays (PTAs), the non-oscillatory GW memory effect is detectable. Further, any burst of gravitational waves will produce GW memory, making memory a useful probe of unmodeled exotic sources and new physics. We searched the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 11-year data set for GW memory. This dataset is sensitive to very low frequency GWs of $\sim3$ to $400$ nHz (periods of $\sim11$ yr $-$ $1$ mon). Finding no evidence for GWs, we placed limits on the strain amplitude of GW memory events during the observation period. We then used the strain upper limits to place limits on the rate of GW memory causing events. At a strain of $2.5\times10^{-14}$, corresponding to the median upper limit as a function of source sky position, we set a limit on the rate of GW memory events at $<0.4$ yr$^{-1}$. That strain corresponds to a SMBHB merger with reduced mass of $\eta M \sim 2\times10^{10}M_\odot$ and inclination of $\iota=\pi/3$ at a distance of 1 Gpc. As a test of our analysis, we analyzed the NANOGrav 9-year data set as well. This analysis found an anomolous signal, which does not appear in the 11-year data set. This signal is not a GW, and its origin remains unknown., Comment: 10 pages, 6 figures, submitted to ApJ
Published: 2019
Full Text: View/download PDF

14. A Deep Targeted Search for Fast Radio Bursts from the Sites of Low-Redshift Short Gamma-Ray Bursts

Author: Madison, D. R., Agarwal, D., Aggarwal, K., Young, O., Cromartie, H. T., Lam, M. T., Chatterjee, S., Cordes, J. M., Garver-Daniels, N., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., Ransom, S. M., Wharton, R. S., Madison, D. R., Agarwal, D., Aggarwal, K., Young, O., Cromartie, H. T., Lam, M. T., Chatterjee, S., Cordes, J. M., Garver-Daniels, N., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., Ransom, S. M., and Wharton, R. S.
Abstract: Some short gamma-ray bursts (SGRBs) are thought to be caused by the mergers of binary neutron stars which may sometimes produce massive neutron star remnants capable of producing extragalactic fast radio bursts (FRBs). We conducted a deep search for FRBs from the sites of six low-redshift SGRBs. We collected high time- and frequency-resolution data from each of the sites for 10 hours using the 2 GHz receiver of the Green Bank Telescope. Two of the SGRB sites we targeted were visible with the Arecibo Radio Telescope with which we conducted an additional 10 hours of 1.4 GHz observations for each. We searched our data for FRBs using the GPU-optimized dedispersion algorithm $\texttt{heimdall}$ and the machine-learning-based package $\texttt{FETCH}$ (Fast Extragalactic Transient Candidate Hunter). We did not discover any FRBs, but would have detected any with peak flux densities in excess of 87 mJy at the Green Bank Telescope or 21 mJy at Arecibo with a signal-to-noise ratio of at least 10. The isotropic-equivalent energy of any FRBs emitted from these sites in our bands during our observations must not have exceeded a few times $10^{38}$ erg, comparable to some of the lowest energy bursts yet seen from the first known repeating FRB 121102., Comment: 10 pages, 2 figures, submitted to AJ
Published: 2019
Full Text: View/download PDF

15. A pulsar-based timescale from the International Pulsar Timing Array

Author: Hobbs, G., Guo, L., Caballero, R. N., Coles, W., Lee, K. J., Manchester, R. N., Reardon, D. J., Matsakis, D., Tong, M. L., Arzoumanian, Z., Bailes, M., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burke-Spolaor, S., Champion, D. J., Chatterjee, S., Cognard, I., Dai, S., Desvignes, G., Dolch, T., Ferdman, R. D., Graikou, E., Guillemot, L., Janssen, G. H., Keith, M. J., Kerr, M., Kramer, M., Lam, M. T., Liu, K., Lyne, A., Lazio, T. J. W., Lynch, R., McKee, J. W., McLaughlin, M. A., Mingarelli, C. M. F., Nice, D. J., Oslowski, S., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Possenti, A., Russell, C. J., Sanidas, S., Sesana, A., Shaifullah, G., Shannon, R. M., Simon, J., Spiewak, R., Stairs, I. H., Stappers, B. W., Swiggum, J. K., Taylor, S. R., Theureau, G., Toomey, L., van Haasteren, R., Wang, J. B., Wang, Y., Zhu, X. J., Hobbs, G., Guo, L., Caballero, R. N., Coles, W., Lee, K. J., Manchester, R. N., Reardon, D. J., Matsakis, D., Tong, M. L., Arzoumanian, Z., Bailes, M., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burke-Spolaor, S., Champion, D. J., Chatterjee, S., Cognard, I., Dai, S., Desvignes, G., Dolch, T., Ferdman, R. D., Graikou, E., Guillemot, L., Janssen, G. H., Keith, M. J., Kerr, M., Kramer, M., Lam, M. T., Liu, K., Lyne, A., Lazio, T. J. W., Lynch, R., McKee, J. W., McLaughlin, M. A., Mingarelli, C. M. F., Nice, D. J., Oslowski, S., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Possenti, A., Russell, C. J., Sanidas, S., Sesana, A., Shaifullah, G., Shannon, R. M., Simon, J., Spiewak, R., Stairs, I. H., Stappers, B. W., Swiggum, J. K., Taylor, S. R., Theureau, G., Toomey, L., van Haasteren, R., Wang, J. B., Wang, Y., and Zhu, X. J.
Abstract: We have constructed a new timescale, TT(IPTA16), based on observations of radio pulsars presented in the first data release from the International Pulsar Timing Array (IPTA). We used two analysis techniques with independent estimates of the noise models for the pulsar observations and different algorithms for obtaining the pulsar timescale. The two analyses agree within the estimated uncertainties and both agree with TT(BIPM17), a post-corrected timescale produced by the Bureau International des Poids et Mesures (BIPM). We show that both methods could detect significant errors in TT(BIPM17) if they were present. We estimate the stability of the atomic clocks from which TT(BIPM17) is derived using observations of four rubidium fountain clocks at the US Naval Observatory. Comparing the power spectrum of TT(IPTA16) with that of these fountain clocks suggests that pulsar-based timescales are unlikely to contribute to the stability of the best timescales over the next decade, but they will remain a valuable independent check on atomic timescales. We also find that the stability of the pulsar-based timescale is likely to be limited by our knowledge of solar-system dynamics, and that errors in TT(BIPM17) will not be a limiting factor for the primary goal of the IPTA, which is to search for the signatures of nano-Hertz gravitational waves., Comment: accepted by MNRAS
Published: 2019
Full Text: View/download PDF

16. The International Pulsar Timing Array: Second data release

Author: Perera, B. B. P., DeCesar, M. E., Demorest, P. B., Kerr, M., Lentati, L., Nice, D. J., Oslowski, S., Ransom, S. M., Keith, M. J., Arzoumanian, Z., Bailes, M., Baker, P. T., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burgay, M., Burke-Spolaor, S., Caballero, R. N., Champion, D. J., Chatterjee, S., Chen, S., Cognard, I., Cordes, J. M., Crowter, K., Dai, S., Desvignes, G., Dolch, T., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Goldstein, J. M., Graikou, E., Guillemot, L., Hazboun, J. S., Hobbs, G., Hu, H., Islo, K., Janssen, G. H., Karuppusamy, R., Kramer, M., Lam, M. T., Lee, K. J., Liu, K., Luo, J., Lyne, A. G., Manchester, R. N., McKee, J. W., McLaughlin, M. A., Mingarelli, C. M. F., Parthasarathy, A. P., Pennucci, T. T., Perrodin, D., Possenti, A., Reardon, D. J., Russell, C. J., Sanidas, S. A., Sesana, A., Shaifullah, G., Shannon, R. M., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stappers, B. W., Swiggum, J. K., Taylor, S. R., Theureau, G., Tiburzi, C., Vallisneri, M., Vecchio, A., Wang, J. B., Zhang, S. B., Zhang, L., Zhu, W. W., Zhu, X. J., Perera, B. B. P., DeCesar, M. E., Demorest, P. B., Kerr, M., Lentati, L., Nice, D. J., Oslowski, S., Ransom, S. M., Keith, M. J., Arzoumanian, Z., Bailes, M., Baker, P. T., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burgay, M., Burke-Spolaor, S., Caballero, R. N., Champion, D. J., Chatterjee, S., Chen, S., Cognard, I., Cordes, J. M., Crowter, K., Dai, S., Desvignes, G., Dolch, T., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Goldstein, J. M., Graikou, E., Guillemot, L., Hazboun, J. S., Hobbs, G., Hu, H., Islo, K., Janssen, G. H., Karuppusamy, R., Kramer, M., Lam, M. T., Lee, K. J., Liu, K., Luo, J., Lyne, A. G., Manchester, R. N., McKee, J. W., McLaughlin, M. A., Mingarelli, C. M. F., Parthasarathy, A. P., Pennucci, T. T., Perrodin, D., Possenti, A., Reardon, D. J., Russell, C. J., Sanidas, S. A., Sesana, A., Shaifullah, G., Shannon, R. M., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stappers, B. W., Swiggum, J. K., Taylor, S. R., Theureau, G., Tiburzi, C., Vallisneri, M., Vecchio, A., Wang, J. B., Zhang, S. B., Zhang, L., Zhu, W. W., and Zhu, X. J.
Abstract: In this paper, we describe the International Pulsar Timing Array second data release, which includes recent pulsar timing data obtained by three regional consortia: the European Pulsar Timing Array, the North American Nanohertz Observatory for Gravitational Waves, and the Parkes Pulsar Timing Array. We analyse and where possible combine high-precision timing data for 65 millisecond pulsars which are regularly observed by these groups. A basic noise analysis, including the processes which are both correlated and uncorrelated in time, provides noise models and timing ephemerides for the pulsars. We find that the timing precisions of pulsars are generally improved compared to the previous data release, mainly due to the addition of new data in the combination. The main purpose of this work is to create the most up-to-date IPTA data release. These data are publicly available for searches for low-frequency gravitational waves and other pulsar science., Comment: Submitted to MNRAS and in review, 23 pages, 5 figures
Published: 2019
Full Text: View/download PDF

17. The NANOGrav 11-Year Data Set: Evolution of Gravitational Wave Background Statistics

Author: Hazboun, J. S., Simon, J., Taylor, S. R., Lam, M. T., Vigeland, S. J., Islo, K., Key, J. S., Arzoumanian, Z., Baker, P. T., Brazier, A., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Crowter, K., Cromartie, H. T., DeCesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E., Fonseca, E., Garver-Daniels, N., Gentile, P., Good, D., Holgado, A. M., Huerta, E. A., Jennings, R., Jones, G., Jones, M. L., Kaiser, A. R., Kaplan, D. L., Kelley, L. Z., Lazio, T. J. W., Levin, L., Lommen, A. N., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J., Turner, J. E., Vallisneri, M., van Haasteren, R., Witt, C. A., Zhu, W. W., Hazboun, J. S., Simon, J., Taylor, S. R., Lam, M. T., Vigeland, S. J., Islo, K., Key, J. S., Arzoumanian, Z., Baker, P. T., Brazier, A., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Crowter, K., Cromartie, H. T., DeCesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E., Fonseca, E., Garver-Daniels, N., Gentile, P., Good, D., Holgado, A. M., Huerta, E. A., Jennings, R., Jones, G., Jones, M. L., Kaiser, A. R., Kaplan, D. L., Kelley, L. Z., Lazio, T. J. W., Levin, L., Lommen, A. N., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J., Turner, J. E., Vallisneri, M., van Haasteren, R., Witt, C. A., and Zhu, W. W.
Abstract: An ensemble of inspiraling supermassive black hole binaries should produce a stochastic background of very low frequency gravitational waves. This stochastic background is predicted to be a power law, with a spectral index of -2/3, and it should be detectable by a network of precisely timed millisecond pulsars, widely distributed on the sky. This paper reports a new "time slicing" analysis of the 11-year data release from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) using 34 millisecond pulsars. Methods to flag potential "false positive" signatures are developed, including techniques to identify responsible pulsars. Mitigation strategies are then presented. We demonstrate how an incorrect noise model can lead to spurious signals, and show how independently modeling noise across 30 Fourier components, spanning NANOGrav's frequency range, effectively diagnoses and absorbs the excess power in gravitational-wave searches. This results in a nominal, and expected, progression of our gravitational-wave statistics. Additionally we show that the first interstellar medium event in PSR J1713+0747 pollutes the common red noise process with low-spectral index noise, and use a tailored noise model to remove these effects., Comment: 14 pages, 13 figures, fixed typo in abstract of earlier version
Published: 2019
Full Text: View/download PDF

18. NANOGrav Education and Outreach: Growing a Diverse and Inclusive Collaboration for Low-Frequency Gravitational Wave Astronomy

Author: The NANOGrav Collaboration, Baker, P. T., Blumer, H., Brazier, A., Chatterjee, S., Christy, B., Crawford, F., DeCesar, M. E., Dolch, T., Garver-Daniels, N. E., Hazboun, J. S., Holley-Bockelmann, K., Kaplan, D. L., Key, J . S., Klein, T. C., Lam, M. T., Lewandowska, N., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., McMann, N., Page, J., Palliyaguru, N. T., Romano, J. D., Siemens, X., Swiggum, J. K., Taylor, S. R., Williamson, K., The NANOGrav Collaboration, Baker, P. T., Blumer, H., Brazier, A., Chatterjee, S., Christy, B., Crawford, F., DeCesar, M. E., Dolch, T., Garver-Daniels, N. E., Hazboun, J. S., Holley-Bockelmann, K., Kaplan, D. L., Key, J . S., Klein, T. C., Lam, M. T., Lewandowska, N., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., McMann, N., Page, J., Palliyaguru, N. T., Romano, J. D., Siemens, X., Swiggum, J. K., Taylor, S. R., and Williamson, K.
Abstract: The new field of gravitational wave astrophysics requires a growing pool of students and researchers with unique, interdisciplinary skill sets. It also offers an opportunity to build a diverse, inclusive astronomy community from the ground up. We describe the efforts used by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) NSF Physics Frontiers Center to foster such growth by involving students at all levels in low-frequency gravitational wave astrophysics with pulsar timing arrays (PTAs) and establishing collaboration policies that ensure broad participation by diverse groups. We describe and illustrate the impact of these techniques on our collaboration as a case study for other distributed collaborations., Comment: Submitted as a State of the Profession White Paper for the Astro2020 Decadal Survey (10 pages + cover and references, 6 figures)
Published: 2019

19. The NANOGrav Program for Gravitational Waves and Fundamental Physics

Author: Brazier, A., Chatterjee, S., Cohen, T., Cordes, J. M., DeCesar, M. E., Demorest, P. B., Hazboun, J. S., Lam, M. T., Lynch, R. S., McLaughlin, M. A., Ransom, S. M., Siemens, X., Taylor, S. R., Vigeland, S. J., Brazier, A., Chatterjee, S., Cohen, T., Cordes, J. M., DeCesar, M. E., Demorest, P. B., Hazboun, J. S., Lam, M. T., Lynch, R. S., McLaughlin, M. A., Ransom, S. M., Siemens, X., Taylor, S. R., and Vigeland, S. J.
Abstract: We describe the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) and its efforts to directly detect and study gravitational waves and other synergistic physics and astrophysics using radio timing observations of millisecond pulsars., Comment: NANOGrav APC white paper submission for Astro2020. Updated cover image credits
Published: 2019

20. High-Precision X-ray Timing of Three Millisecond Pulsars with NICER: Stability Estimates and Comparison with Radio

Author: Deneva, J. S., Ray, P. S., Lommen, A., Ransom, S. M., Bogdanov, S., Kerr, M., Wood, K. S., Arzoumanian, Z., Black, K., Doty, J., Gendreau, K. C., Guillot, S., Harding, A., Lewandowska, N., Malacaria, C., Markwardt, C. B., Price, S., Winternitz, L., Wolff, M. T., Guillemot, L., Cognard, I., Baker, P. T., Blumer, H., Brook, P. R., Cromartie, H. T., Demorest, P. B., DeCesar, M. E., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Garver-Daniels, N., Gentile, P. A., Jones, M. L., Lam, M. T., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., Ng, C., Nice, D. J., Pennucci, T. T., Spiewak, R., Stairs, I. H., Stovall, K., Swiggum, J. K., Vigeland, S. J., Zhu, W. W., Deneva, J. S., Ray, P. S., Lommen, A., Ransom, S. M., Bogdanov, S., Kerr, M., Wood, K. S., Arzoumanian, Z., Black, K., Doty, J., Gendreau, K. C., Guillot, S., Harding, A., Lewandowska, N., Malacaria, C., Markwardt, C. B., Price, S., Winternitz, L., Wolff, M. T., Guillemot, L., Cognard, I., Baker, P. T., Blumer, H., Brook, P. R., Cromartie, H. T., Demorest, P. B., DeCesar, M. E., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Garver-Daniels, N., Gentile, P. A., Jones, M. L., Lam, M. T., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., Ng, C., Nice, D. J., Pennucci, T. T., Spiewak, R., Stairs, I. H., Stovall, K., Swiggum, J. K., Vigeland, S. J., and Zhu, W. W.
Abstract: The Neutron Star Interior Composition Explorer (NICER) is an X-ray astrophysics payload on the International Space Station. It enables unprecedented high-precision timing of millisecond pulsars without the pulse broadening and delays due to dispersion and scattering within the interstellar medium that plague radio timing. We present initial timing results from a year of data on the millisecond pulsars PSR B1937+21 and PSR J0218+4232, and nine months of data on PSR B1821-24. NICER time-of-arrival uncertainties for the three pulsars are consistent with theoretical lower bounds and simulations based on their pulse shape templates and average source and background photon count rates. To estimate timing stability, we use the $\sigma_z$ measure, which is based on the average of the cubic coefficients of polynomial fits to subsets of timing residuals. So far we are achieving timing stabilities $\sigma_z \approx 3 \times 10^{-14}$ for PSR B1937+21 and on the order of $10^{-12}$ for PSRs B1821$-$24 and J0218+4232. Within the span of our \textit{NICER} data we do not yet see the characteristic break point in the slope of $\sigma_z$; detection of such a break would indicate that further improvement in the cumulative root-mean-square (RMS) timing residual is limited by timing noise. We see this break point in our comparison radio data sets for PSR B1821-24 and PSR B1937+21 on time scales of $> 2$ years., Comment: 30 pages, 15 figures; accepted to ApJ
Published: 2019
Full Text: View/download PDF

21. Estimates of Fast Radio Burst Dispersion Measures from Cosmological Simulations

Author: Pol, N., Lam, M. T., McLaughlin, M. A., Lazio, T. J. W., Cordes, J. M., Pol, N., Lam, M. T., McLaughlin, M. A., Lazio, T. J. W., and Cordes, J. M.
Abstract: We calculate the dispersion measure (DM) contributed by the intergalactic medium (IGM) to the total measured DM for fast radio bursts (FRBs). We use the MareNostrum Instituto de Ciencias del Espacio (MICE) Onion Universe simulation (Fosalba et al. 2008) to track the evolution of the dark matter particle density over a large range of redshifts. We convert this dark matter particle number density to the corresponding free electron density and then integrate it to find the DM as a function of redshift. This approach yields an intergalactic DM of $\rm DM_{\rm IGM}(z = 1) = 800^{+7000}_{-170}$ pc cm$^{-3}$, with the large errors representative of the structure in the IGM. We place limits on the redshifts of the current population of observed FRBs. We also use our results to estimate the host galaxy contribution to the DM for the first repeater, FRB 121102, and show that the most probable host galaxy DM contribution, $\rm DM_{\rm host} \approx 310$ pc cm$^{-3}$, is consistent with the estimate made using the Balmer emission lines in the spectrum of the host galaxy, $\rm DM_{\rm Balmer} = 324$ pc cm$^{-3}$ (Tendulkar et al. 2017). We also compare our predictions for the host galaxy contribution to the DM for the observations of FRB 180924 (Bannister et al. 2019) and FRB 190523 (Ravi et al. 2019), both of which have been localized to a host galaxy., Comment: Resubmitted to ApJ following second round of referee comments. Expanded sub-section comparing our results to those from other works (Sec. 3.3)
Published: 2019
Full Text: View/download PDF

22. On Frequency-Dependent Dispersion Measures and Extreme Scattering Events

Author: Lam, M. T., Lazio, T. J. W., Dolch, T., Jones, M. L., McLaughlin, M. A., Stinebring, D. R., Surnis, M., Lam, M. T., Lazio, T. J. W., Dolch, T., Jones, M. L., McLaughlin, M. A., Stinebring, D. R., and Surnis, M.
Abstract: Radio emission propagating over an Earth-pulsar line of sight provides a unique probe of the intervening ionized interstellar medium (ISM). Variations in the integrated electron column density along this line of sight, or dispersion measure (DM), have been observed since shortly after the discovery of pulsars. As early as 2006, frequency-dependent dispersion measures have been observed and attributed to several possible causes. Ray-path averaging over different effective light-cone volumes through the turbulent ISM contributes to this effect as will DM misestimation due to radio propagation across compact lensing structures such as those caused by "extreme scattering events". We present methods to assess the variations in frequency-dependent dispersion measures due to the turbulent ISM versus these compact lensing structures along the line of sight. We analyze recent Low-Frequency Array (LOFAR) observations of PSR J2219+4754 to test the underlying physical mechanism of the observed frequency-dependent DM. Previous analyses have indicated the presence of strong lensing due to compact overdensities halfway between the Earth and pulsar. Instead we find the frequency dependence of the DM timeseries for PSR J2219+4754 is consistent with being due solely to ISM turbulence and there is no evidence for any extreme scattering event or small-scale lensing structure. The data show possible deviations from a uniform turbulent medium, suggesting that there may be an enhanced scattering screen near one of the two ends of the line of sight. We present this analysis as an example of the power of low-frequency observations to distinguish the underlying mechanisms in frequency-dependent propagation effects., Comment: 16 pages, 7 figures, accepted by ApJ
Published: 2019
Full Text: View/download PDF

23. A novel disorder involving dyshematopoiesis, inflammation, and HLH due to aberrant CDC42 function

Author: Lam, M. T., Coppola, S., Krumbach, O. H. F., Prencipe, G., Insalaco, A., Cifaldi, C., Brigida, I., Zara, E., Scala, S., Di Cesare, S., Martinelli, S., Di Rocco, M., Pascarella, A., Niceta, M., Pantaleoni, F., Ciolfi, A., Netter, P., Carisey, A. F., Diehl, M., Akbarzadeh, M., Cont, F., Merli, P., Pastore, A., Mortera, S. L., Camerini, S., Farina, L., Buchholzer, M., Pannone, L., Cao, T. N., Coban-Akdemir, Z. H., Jhangiani, S. N., Muzny, D. M., Gibbs, R. A., Basso-Ricci, L., Chiriaco, M., Dvorsky, R., Putignani, L., Carsetti, R., Janning, P., Stray-Pedersen, A., Erichsen, H. C., Horne, A. C., Bryceson, Y. T., Torralba-Raga, L., Ramme, K., Rosti, V., Bracaglia, C., Messia, V., Palma, P., Finocchi, A., Locatelli, Franco, Chinn, I. K., Lupski, J. R., Mace, E. M., Cancrini, C., Aiuti, A., Ahmadian, M. R., Orange, J. S., De Benedetti, F., Tartaglia, M., Locatelli F. (ORCID:0000-0002-7976-3654), Lam, M. T., Coppola, S., Krumbach, O. H. F., Prencipe, G., Insalaco, A., Cifaldi, C., Brigida, I., Zara, E., Scala, S., Di Cesare, S., Martinelli, S., Di Rocco, M., Pascarella, A., Niceta, M., Pantaleoni, F., Ciolfi, A., Netter, P., Carisey, A. F., Diehl, M., Akbarzadeh, M., Cont, F., Merli, P., Pastore, A., Mortera, S. L., Camerini, S., Farina, L., Buchholzer, M., Pannone, L., Cao, T. N., Coban-Akdemir, Z. H., Jhangiani, S. N., Muzny, D. M., Gibbs, R. A., Basso-Ricci, L., Chiriaco, M., Dvorsky, R., Putignani, L., Carsetti, R., Janning, P., Stray-Pedersen, A., Erichsen, H. C., Horne, A. C., Bryceson, Y. T., Torralba-Raga, L., Ramme, K., Rosti, V., Bracaglia, C., Messia, V., Palma, P., Finocchi, A., Locatelli, Franco, Chinn, I. K., Lupski, J. R., Mace, E. M., Cancrini, C., Aiuti, A., Ahmadian, M. R., Orange, J. S., De Benedetti, F., Tartaglia, M., and Locatelli F. (ORCID:0000-0002-7976-3654)
Abstract: Hemophagocytic lymphohistiocytosis (HLH) is characterized by immune dysregulation due to inadequate restraint of overactivated immune cells and is associated with a variable clinical spectrum having overlap with more common pathophysiologies. HLH is difficult to diagnose and can be part of inflammatory syndromes. Here, we identify a novel hematological/autoinflammatory condition (NOCARH syndrome) in four unrelated patients with superimposable features, including neonatal-onset cytopenia with dyshematopoiesis, autoinflammation, rash, and HLH. Patients shared the same de novo CDC42 mutation (Chr1:22417990C>T, p.R186C) and altered hematopoietic compartment, immune dysregulation, and inflammation. CDC42 mutations had been associated with syndromic neurodevelopmental disorders. In vitro and in vivo assays documented unique effects of p.R186C on CDC42 localization and function, correlating with the distinctiveness of the trait. Emapalumab was critical to the survival of one patient, who underwent successful bone marrow transplantation. Early recognition of the disorder and establishment of treatment followed by bone marrow transplant are important to survival.
Published: 2019

24. NANOGrav Education and Outreach: Growing a Diverse and Inclusive Collaboration for Low-Frequency Gravitational Wave Astronomy

Author: The NANOGrav Collaboration, Baker, P. T., Blumer, H., Brazier, A., Chatterjee, S., Christy, B., Crawford, F., DeCesar, M. E., Dolch, T., Garver-Daniels, N. E., Hazboun, J. S., Holley-Bockelmann, K., Kaplan, D. L., Key, J . S., Klein, T. C., Lam, M. T., Lewandowska, N., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., McMann, N., Page, J., Palliyaguru, N. T., Romano, J. D., Siemens, X., Swiggum, J. K., Taylor, S. R., Williamson, K., The NANOGrav Collaboration, Baker, P. T., Blumer, H., Brazier, A., Chatterjee, S., Christy, B., Crawford, F., DeCesar, M. E., Dolch, T., Garver-Daniels, N. E., Hazboun, J. S., Holley-Bockelmann, K., Kaplan, D. L., Key, J . S., Klein, T. C., Lam, M. T., Lewandowska, N., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., McMann, N., Page, J., Palliyaguru, N. T., Romano, J. D., Siemens, X., Swiggum, J. K., Taylor, S. R., and Williamson, K.
Abstract: The new field of gravitational wave astrophysics requires a growing pool of students and researchers with unique, interdisciplinary skill sets. It also offers an opportunity to build a diverse, inclusive astronomy community from the ground up. We describe the efforts used by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) NSF Physics Frontiers Center to foster such growth by involving students at all levels in low-frequency gravitational wave astrophysics with pulsar timing arrays (PTAs) and establishing collaboration policies that ensure broad participation by diverse groups. We describe and illustrate the impact of these techniques on our collaboration as a case study for other distributed collaborations., Comment: Submitted as a State of the Profession White Paper for the Astro2020 Decadal Survey (10 pages + cover and references, 6 figures)
Published: 2019

25. Estimates of Fast Radio Burst Dispersion Measures from Cosmological Simulations

Author: Pol, N., Lam, M. T., McLaughlin, M. A., Lazio, T. J. W., Cordes, J. M., Pol, N., Lam, M. T., McLaughlin, M. A., Lazio, T. J. W., and Cordes, J. M.
Abstract: We calculate the dispersion measure (DM) contributed by the intergalactic medium (IGM) to the total measured DM for fast radio bursts (FRBs). We use the MareNostrum Instituto de Ciencias del Espacio (MICE) Onion Universe simulation (Fosalba et al. 2008) to track the evolution of the dark matter particle density over a large range of redshifts. We convert this dark matter particle number density to the corresponding free electron density and then integrate it to find the DM as a function of redshift. This approach yields an intergalactic DM of $\rm DM_{\rm IGM}(z = 1) = 800^{+7000}_{-170}$ pc cm$^{-3}$, with the large errors representative of the structure in the IGM. We place limits on the redshifts of the current population of observed FRBs. We also use our results to estimate the host galaxy contribution to the DM for the first repeater, FRB 121102, and show that the most probable host galaxy DM contribution, $\rm DM_{\rm host} \approx 310$ pc cm$^{-3}$, is consistent with the estimate made using the Balmer emission lines in the spectrum of the host galaxy, $\rm DM_{\rm Balmer} = 324$ pc cm$^{-3}$ (Tendulkar et al. 2017). We also compare our predictions for the host galaxy contribution to the DM for the observations of FRB 180924 (Bannister et al. 2019) and FRB 190523 (Ravi et al. 2019), both of which have been localized to a host galaxy., Comment: Resubmitted to ApJ following second round of referee comments. Expanded sub-section comparing our results to those from other works (Sec. 3.3)
Published: 2019
Full Text: View/download PDF

26. On Frequency-Dependent Dispersion Measures and Extreme Scattering Events

Author: Lam, M. T., Lazio, T. J. W., Dolch, T., Jones, M. L., McLaughlin, M. A., Stinebring, D. R., Surnis, M., Lam, M. T., Lazio, T. J. W., Dolch, T., Jones, M. L., McLaughlin, M. A., Stinebring, D. R., and Surnis, M.
Abstract: Radio emission propagating over an Earth-pulsar line of sight provides a unique probe of the intervening ionized interstellar medium (ISM). Variations in the integrated electron column density along this line of sight, or dispersion measure (DM), have been observed since shortly after the discovery of pulsars. As early as 2006, frequency-dependent dispersion measures have been observed and attributed to several possible causes. Ray-path averaging over different effective light-cone volumes through the turbulent ISM contributes to this effect as will DM misestimation due to radio propagation across compact lensing structures such as those caused by "extreme scattering events". We present methods to assess the variations in frequency-dependent dispersion measures due to the turbulent ISM versus these compact lensing structures along the line of sight. We analyze recent Low-Frequency Array (LOFAR) observations of PSR J2219+4754 to test the underlying physical mechanism of the observed frequency-dependent DM. Previous analyses have indicated the presence of strong lensing due to compact overdensities halfway between the Earth and pulsar. Instead we find the frequency dependence of the DM timeseries for PSR J2219+4754 is consistent with being due solely to ISM turbulence and there is no evidence for any extreme scattering event or small-scale lensing structure. The data show possible deviations from a uniform turbulent medium, suggesting that there may be an enhanced scattering screen near one of the two ends of the line of sight. We present this analysis as an example of the power of low-frequency observations to distinguish the underlying mechanisms in frequency-dependent propagation effects., Comment: 16 pages, 7 figures, accepted by ApJ
Published: 2019
Full Text: View/download PDF

27. High-Precision X-ray Timing of Three Millisecond Pulsars with NICER: Stability Estimates and Comparison with Radio

Author: Deneva, J. S., Ray, P. S., Lommen, A., Ransom, S. M., Bogdanov, S., Kerr, M., Wood, K. S., Arzoumanian, Z., Black, K., Doty, J., Gendreau, K. C., Guillot, S., Harding, A., Lewandowska, N., Malacaria, C., Markwardt, C. B., Price, S., Winternitz, L., Wolff, M. T., Guillemot, L., Cognard, I., Baker, P. T., Blumer, H., Brook, P. R., Cromartie, H. T., Demorest, P. B., DeCesar, M. E., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Garver-Daniels, N., Gentile, P. A., Jones, M. L., Lam, M. T., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., Ng, C., Nice, D. J., Pennucci, T. T., Spiewak, R., Stairs, I. H., Stovall, K., Swiggum, J. K., Vigeland, S. J., Zhu, W. W., Deneva, J. S., Ray, P. S., Lommen, A., Ransom, S. M., Bogdanov, S., Kerr, M., Wood, K. S., Arzoumanian, Z., Black, K., Doty, J., Gendreau, K. C., Guillot, S., Harding, A., Lewandowska, N., Malacaria, C., Markwardt, C. B., Price, S., Winternitz, L., Wolff, M. T., Guillemot, L., Cognard, I., Baker, P. T., Blumer, H., Brook, P. R., Cromartie, H. T., Demorest, P. B., DeCesar, M. E., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Garver-Daniels, N., Gentile, P. A., Jones, M. L., Lam, M. T., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., Ng, C., Nice, D. J., Pennucci, T. T., Spiewak, R., Stairs, I. H., Stovall, K., Swiggum, J. K., Vigeland, S. J., and Zhu, W. W.
Abstract: The Neutron Star Interior Composition Explorer (NICER) is an X-ray astrophysics payload on the International Space Station. It enables unprecedented high-precision timing of millisecond pulsars without the pulse broadening and delays due to dispersion and scattering within the interstellar medium that plague radio timing. We present initial timing results from a year of data on the millisecond pulsars PSR B1937+21 and PSR J0218+4232, and nine months of data on PSR B1821-24. NICER time-of-arrival uncertainties for the three pulsars are consistent with theoretical lower bounds and simulations based on their pulse shape templates and average source and background photon count rates. To estimate timing stability, we use the $\sigma_z$ measure, which is based on the average of the cubic coefficients of polynomial fits to subsets of timing residuals. So far we are achieving timing stabilities $\sigma_z \approx 3 \times 10^{-14}$ for PSR B1937+21 and on the order of $10^{-12}$ for PSRs B1821$-$24 and J0218+4232. Within the span of our \textit{NICER} data we do not yet see the characteristic break point in the slope of $\sigma_z$; detection of such a break would indicate that further improvement in the cumulative root-mean-square (RMS) timing residual is limited by timing noise. We see this break point in our comparison radio data sets for PSR B1821-24 and PSR B1937+21 on time scales of $> 2$ years., Comment: 30 pages, 15 figures; accepted to ApJ
Published: 2019
Full Text: View/download PDF

28. Results for the International Pulsar Timing Array Second Mock Data Challenge: New Techniques and Challenges for the Detection of Low-Frequency Gravitational-Wave Signals

Author: Baker, P. T., Brook, P. R., Fiore, W. C., Garver-Daniels, N., Kaiser, A. R., Lam, M. T., Shapiro-Albert, B. J., Witt, C. A., Baker, P. T., Brook, P. R., Fiore, W. C., Garver-Daniels, N., Kaiser, A. R., Lam, M. T., Shapiro-Albert, B. J., and Witt, C. A.
Abstract: We present a detailed analysis of the International Pulsar Timing Array (IPTA) Second Mock Data Challenge. We tested our analysis methods using the open datasets, and then analyzed the closed datasets. In both the open and the closed datasets, we were able to detect some, but not all, of the injected gravitational wave signals. This work presents two search cases that are not well explored in the pulsar timing array (PTA) literature: a simultaneous search for a stochastic GW background and an individual loud super-massive black hole binary (SMBHB) and a simultaneous search for two SMBHB sources. While we have constructed a cohesive framework for performing these GW searches, our analyses required fine-tuning of the sampling method used in order to appropriately converge. Given the nature of real PTA data in which multiple sources will be present in data, improved techniques will be required in the future to accurately detect and characterize these GW signals., Comment: 25 pages, 9 figures
Published: 2019

29. The NANOGrav 11-year Data Set: Constraints on Planetary Masses Around 45 Millisecond Pulsars

Author: Behrens, E. A., Ransom, S. M., Madison, D. R., Arzoumanian, Z., Crowter, K., DeCesar, M. E., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Gentile, P. A., Jones, G., Jones, M. L., Lam, M. T., Levin, L., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., Ng, C., Nice, D. J., Pennucci, T. T., Perera, B. B. P., Ray, P. S., Spiewak, R., Stairs, I. H., Stovall, K., Swiggum, J. K., Zhu, W. W., Behrens, E. A., Ransom, S. M., Madison, D. R., Arzoumanian, Z., Crowter, K., DeCesar, M. E., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Gentile, P. A., Jones, G., Jones, M. L., Lam, M. T., Levin, L., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., Ng, C., Nice, D. J., Pennucci, T. T., Perera, B. B. P., Ray, P. S., Spiewak, R., Stairs, I. H., Stovall, K., Swiggum, J. K., and Zhu, W. W.
Abstract: We search for extrasolar planets around millisecond pulsars using pulsar timing data and seek to determine the minimum detectable planetary masses as a function of orbital period. Using the 11-year data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), we look for variations from our models of pulse arrival times due to the presence of exoplanets. No planets are detected around the millisecond pulsars in the NANOGrav 11-year data set, but taking into consideration the noise levels of each pulsar and the sampling rate of our observations, we develop limits that show we are sensitive to planetary masses as low as that of the moon. We analyzed potential planet periods, P, in the range 7 days < P < 2000 days, with somewhat smaller ranges for some binary pulsars. The planetary mass limit for our median-sensitivity pulsar within this period range is 1 M_moon (P / 100 days)^(-2/3)., Comment: Revised and accepted by ApJ Letters
Published: 2019
Full Text: View/download PDF

30. The NANOGrav 11-Year Data Set: Limits on Gravitational Wave Memory

Author: Aggarwal, K., Arzoumanian, Z., Baker, P. T., Brazier, A., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., Decesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Garver-Daniels, N., Gentile, P., Good, D., Hazboun, J. S., Holgado, A. M., Huerta, E. A., Islo, K., Jennings, R., Jones, G., Jones, M. L., Kaplan, D. L., Kelley, L. Z., Key, J. S., Lam, M. T., Lazio, T. J. W., Levin, L., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J. K., Taylor, S. R., Vallisneri, M., Van Haasterer, R., Vigeland, S. J., Witt, C. A., Zhu, W. W., Aggarwal, K., Arzoumanian, Z., Baker, P. T., Brazier, A., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., Decesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Garver-Daniels, N., Gentile, P., Good, D., Hazboun, J. S., Holgado, A. M., Huerta, E. A., Islo, K., Jennings, R., Jones, G., Jones, M. L., Kaplan, D. L., Kelley, L. Z., Key, J. S., Lam, M. T., Lazio, T. J. W., Levin, L., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J. K., Taylor, S. R., Vallisneri, M., Van Haasterer, R., Vigeland, S. J., Witt, C. A., and Zhu, W. W.
Abstract: The mergers of supermassive black hole binaries (SMBHBs) promise to be incredible sources of gravitational waves (GWs). While the oscillatory part of the merger gravitational waveform will be outside the frequency sensitivity range of pulsar timing arrays (PTAs), the non-oscillatory GW memory effect is detectable. Further, any burst of gravitational waves will produce GW memory, making memory a useful probe of unmodeled exotic sources and new physics. We searched the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 11-year data set for GW memory. This dataset is sensitive to very low frequency GWs of $\sim3$ to $400$ nHz (periods of $\sim11$ yr $-$ $1$ mon). Finding no evidence for GWs, we placed limits on the strain amplitude of GW memory events during the observation period. We then used the strain upper limits to place limits on the rate of GW memory causing events. At a strain of $2.5\times10^{-14}$, corresponding to the median upper limit as a function of source sky position, we set a limit on the rate of GW memory events at $<0.4$ yr$^{-1}$. That strain corresponds to a SMBHB merger with reduced mass of $\eta M \sim 2\times10^{10}M_\odot$ and inclination of $\iota=\pi/3$ at a distance of 1 Gpc. As a test of our analysis, we analyzed the NANOGrav 9-year data set as well. This analysis found an anomolous signal, which does not appear in the 11-year data set. This signal is not a GW, and its origin remains unknown., Comment: 10 pages, 6 figures, submitted to ApJ
Published: 2019
Full Text: View/download PDF

31. A pulsar-based timescale from the International Pulsar Timing Array

Author: Hobbs, G., Guo, L., Caballero, R. N., Coles, W., Lee, K. J., Manchester, R. N., Reardon, D. J., Matsakis, D., Tong, M. L., Arzoumanian, Z., Bailes, M., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burke-Spolaor, S., Champion, D. J., Chatterjee, S., Cognard, I., Dai, S., Desvignes, G., Dolch, T., Ferdman, R. D., Graikou, E., Guillemot, L., Janssen, G. H., Keith, M. J., Kerr, M., Kramer, M., Lam, M. T., Liu, K., Lyne, A., Lazio, T. J. W., Lynch, R., McKee, J. W., McLaughlin, M. A., Mingarelli, C. M. F., Nice, D. J., Oslowski, S., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Possenti, A., Russell, C. J., Sanidas, S., Sesana, A., Shaifullah, G., Shannon, R. M., Simon, J., Spiewak, R., Stairs, I. H., Stappers, B. W., Swiggum, J. K., Taylor, S. R., Theureau, G., Toomey, L., van Haasteren, R., Wang, J. B., Wang, Y., Zhu, X. J., Hobbs, G., Guo, L., Caballero, R. N., Coles, W., Lee, K. J., Manchester, R. N., Reardon, D. J., Matsakis, D., Tong, M. L., Arzoumanian, Z., Bailes, M., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burke-Spolaor, S., Champion, D. J., Chatterjee, S., Cognard, I., Dai, S., Desvignes, G., Dolch, T., Ferdman, R. D., Graikou, E., Guillemot, L., Janssen, G. H., Keith, M. J., Kerr, M., Kramer, M., Lam, M. T., Liu, K., Lyne, A., Lazio, T. J. W., Lynch, R., McKee, J. W., McLaughlin, M. A., Mingarelli, C. M. F., Nice, D. J., Oslowski, S., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Possenti, A., Russell, C. J., Sanidas, S., Sesana, A., Shaifullah, G., Shannon, R. M., Simon, J., Spiewak, R., Stairs, I. H., Stappers, B. W., Swiggum, J. K., Taylor, S. R., Theureau, G., Toomey, L., van Haasteren, R., Wang, J. B., Wang, Y., and Zhu, X. J.
Abstract: We have constructed a new timescale, TT(IPTA16), based on observations of radio pulsars presented in the first data release from the International Pulsar Timing Array (IPTA). We used two analysis techniques with independent estimates of the noise models for the pulsar observations and different algorithms for obtaining the pulsar timescale. The two analyses agree within the estimated uncertainties and both agree with TT(BIPM17), a post-corrected timescale produced by the Bureau International des Poids et Mesures (BIPM). We show that both methods could detect significant errors in TT(BIPM17) if they were present. We estimate the stability of the atomic clocks from which TT(BIPM17) is derived using observations of four rubidium fountain clocks at the US Naval Observatory. Comparing the power spectrum of TT(IPTA16) with that of these fountain clocks suggests that pulsar-based timescales are unlikely to contribute to the stability of the best timescales over the next decade, but they will remain a valuable independent check on atomic timescales. We also find that the stability of the pulsar-based timescale is likely to be limited by our knowledge of solar-system dynamics, and that errors in TT(BIPM17) will not be a limiting factor for the primary goal of the IPTA, which is to search for the signatures of nano-Hertz gravitational waves., Comment: accepted by MNRAS
Published: 2019
Full Text: View/download PDF

32. A Deep Targeted Search for Fast Radio Bursts from the Sites of Low-Redshift Short Gamma-Ray Bursts

Author: Madison, D. R., Agarwal, D., Aggarwal, K., Young, O., Cromartie, H. T., Lam, M. T., Chatterjee, S., Cordes, J. M., Garver-Daniels, N., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., Ransom, S. M., Wharton, R. S., Madison, D. R., Agarwal, D., Aggarwal, K., Young, O., Cromartie, H. T., Lam, M. T., Chatterjee, S., Cordes, J. M., Garver-Daniels, N., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., Ransom, S. M., and Wharton, R. S.
Abstract: Some short gamma-ray bursts (SGRBs) are thought to be caused by the mergers of binary neutron stars which may sometimes produce massive neutron star remnants capable of producing extragalactic fast radio bursts (FRBs). We conducted a deep search for FRBs from the sites of six low-redshift SGRBs. We collected high time- and frequency-resolution data from each of the sites for 10 hours using the 2 GHz receiver of the Green Bank Telescope. Two of the SGRB sites we targeted were visible with the Arecibo Radio Telescope with which we conducted an additional 10 hours of 1.4 GHz observations for each. We searched our data for FRBs using the GPU-optimized dedispersion algorithm $\texttt{heimdall}$ and the machine-learning-based package $\texttt{FETCH}$ (Fast Extragalactic Transient Candidate Hunter). We did not discover any FRBs, but would have detected any with peak flux densities in excess of 87 mJy at the Green Bank Telescope or 21 mJy at Arecibo with a signal-to-noise ratio of at least 10. The isotropic-equivalent energy of any FRBs emitted from these sites in our bands during our observations must not have exceeded a few times $10^{38}$ erg, comparable to some of the lowest energy bursts yet seen from the first known repeating FRB 121102., Comment: 10 pages, 2 figures, submitted to AJ
Published: 2019
Full Text: View/download PDF

33. The NANOGrav 11-Year Data Set: Evolution of Gravitational Wave Background Statistics

Author: Hazboun, J. S., Simon, J., Taylor, S. R., Lam, M. T., Vigeland, S. J., Islo, K., Key, J. S., Arzoumanian, Z., Baker, P. T., Brazier, A., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Crowter, K., Cromartie, H. T., DeCesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E., Fonseca, E., Garver-Daniels, N., Gentile, P., Good, D., Holgado, A. M., Huerta, E. A., Jennings, R., Jones, G., Jones, M. L., Kaiser, A. R., Kaplan, D. L., Kelley, L. Z., Lazio, T. J. W., Levin, L., Lommen, A. N., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J., Turner, J. E., Vallisneri, M., van Haasteren, R., Witt, C. A., Zhu, W. W., Hazboun, J. S., Simon, J., Taylor, S. R., Lam, M. T., Vigeland, S. J., Islo, K., Key, J. S., Arzoumanian, Z., Baker, P. T., Brazier, A., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Crowter, K., Cromartie, H. T., DeCesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E., Fonseca, E., Garver-Daniels, N., Gentile, P., Good, D., Holgado, A. M., Huerta, E. A., Jennings, R., Jones, G., Jones, M. L., Kaiser, A. R., Kaplan, D. L., Kelley, L. Z., Lazio, T. J. W., Levin, L., Lommen, A. N., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J., Turner, J. E., Vallisneri, M., van Haasteren, R., Witt, C. A., and Zhu, W. W.
Abstract: An ensemble of inspiraling supermassive black hole binaries should produce a stochastic background of very low frequency gravitational waves. This stochastic background is predicted to be a power law, with a spectral index of -2/3, and it should be detectable by a network of precisely timed millisecond pulsars, widely distributed on the sky. This paper reports a new "time slicing" analysis of the 11-year data release from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) using 34 millisecond pulsars. Methods to flag potential "false positive" signatures are developed, including techniques to identify responsible pulsars. Mitigation strategies are then presented. We demonstrate how an incorrect noise model can lead to spurious signals, and show how independently modeling noise across 30 Fourier components, spanning NANOGrav's frequency range, effectively diagnoses and absorbs the excess power in gravitational-wave searches. This results in a nominal, and expected, progression of our gravitational-wave statistics. Additionally we show that the first interstellar medium event in PSR J1713+0747 pollutes the common red noise process with low-spectral index noise, and use a tailored noise model to remove these effects., Comment: 14 pages, 13 figures, fixed typo in abstract of earlier version
Published: 2019
Full Text: View/download PDF

34. The International Pulsar Timing Array: Second data release

Author: Perera, B. B. P., DeCesar, M. E., Demorest, P. B., Kerr, M., Lentati, L., Nice, D. J., Oslowski, S., Ransom, S. M., Keith, M. J., Arzoumanian, Z., Bailes, M., Baker, P. T., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burgay, M., Burke-Spolaor, S., Caballero, R. N., Champion, D. J., Chatterjee, S., Chen, S., Cognard, I., Cordes, J. M., Crowter, K., Dai, S., Desvignes, G., Dolch, T., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Goldstein, J. M., Graikou, E., Guillemot, L., Hazboun, J. S., Hobbs, G., Hu, H., Islo, K., Janssen, G. H., Karuppusamy, R., Kramer, M., Lam, M. T., Lee, K. J., Liu, K., Luo, J., Lyne, A. G., Manchester, R. N., McKee, J. W., McLaughlin, M. A., Mingarelli, C. M. F., Parthasarathy, A. P., Pennucci, T. T., Perrodin, D., Possenti, A., Reardon, D. J., Russell, C. J., Sanidas, S. A., Sesana, A., Shaifullah, G., Shannon, R. M., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stappers, B. W., Swiggum, J. K., Taylor, S. R., Theureau, G., Tiburzi, C., Vallisneri, M., Vecchio, A., Wang, J. B., Zhang, S. B., Zhang, L., Zhu, W. W., Zhu, X. J., Perera, B. B. P., DeCesar, M. E., Demorest, P. B., Kerr, M., Lentati, L., Nice, D. J., Oslowski, S., Ransom, S. M., Keith, M. J., Arzoumanian, Z., Bailes, M., Baker, P. T., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burgay, M., Burke-Spolaor, S., Caballero, R. N., Champion, D. J., Chatterjee, S., Chen, S., Cognard, I., Cordes, J. M., Crowter, K., Dai, S., Desvignes, G., Dolch, T., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Goldstein, J. M., Graikou, E., Guillemot, L., Hazboun, J. S., Hobbs, G., Hu, H., Islo, K., Janssen, G. H., Karuppusamy, R., Kramer, M., Lam, M. T., Lee, K. J., Liu, K., Luo, J., Lyne, A. G., Manchester, R. N., McKee, J. W., McLaughlin, M. A., Mingarelli, C. M. F., Parthasarathy, A. P., Pennucci, T. T., Perrodin, D., Possenti, A., Reardon, D. J., Russell, C. J., Sanidas, S. A., Sesana, A., Shaifullah, G., Shannon, R. M., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stappers, B. W., Swiggum, J. K., Taylor, S. R., Theureau, G., Tiburzi, C., Vallisneri, M., Vecchio, A., Wang, J. B., Zhang, S. B., Zhang, L., Zhu, W. W., and Zhu, X. J.
Abstract: In this paper, we describe the International Pulsar Timing Array second data release, which includes recent pulsar timing data obtained by three regional consortia: the European Pulsar Timing Array, the North American Nanohertz Observatory for Gravitational Waves, and the Parkes Pulsar Timing Array. We analyse and where possible combine high-precision timing data for 65 millisecond pulsars which are regularly observed by these groups. A basic noise analysis, including the processes which are both correlated and uncorrelated in time, provides noise models and timing ephemerides for the pulsars. We find that the timing precisions of pulsars are generally improved compared to the previous data release, mainly due to the addition of new data in the combination. The main purpose of this work is to create the most up-to-date IPTA data release. These data are publicly available for searches for low-frequency gravitational waves and other pulsar science., Comment: Submitted to MNRAS and in review, 23 pages, 5 figures
Published: 2019
Full Text: View/download PDF

35. The NANOGrav Program for Gravitational Waves and Fundamental Physics

Author: Brazier, A., Chatterjee, S., Cohen, T., Cordes, J. M., DeCesar, M. E., Demorest, P. B., Hazboun, J. S., Lam, M. T., Lynch, R. S., McLaughlin, M. A., Ransom, S. M., Siemens, X., Taylor, S. R., Vigeland, S. J., Brazier, A., Chatterjee, S., Cohen, T., Cordes, J. M., DeCesar, M. E., Demorest, P. B., Hazboun, J. S., Lam, M. T., Lynch, R. S., McLaughlin, M. A., Ransom, S. M., Siemens, X., Taylor, S. R., and Vigeland, S. J.
Abstract: We describe the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) and its efforts to directly detect and study gravitational waves and other synergistic physics and astrophysics using radio timing observations of millisecond pulsars., Comment: NANOGrav APC white paper submission for Astro2020. Updated cover image credits
Published: 2019

36. The International Pulsar Timing Array: second data release

Author: Perera, B, Decesar, M, Demorest, P, Kerr, M, Lentati, L, Nice, D, Osłowski, S, Ransom, S, Keith, M, Arzoumanian, Z, Bailes, M, Baker, P, Bassa, C, Bhat, N, Brazier, A, Burgay, M, Burke-Spolaor, S, Caballero, R, Champion, D, Chatterjee, S, Chen, S, Cognard, I, Cordes, J, Crowter, K, Dai, S, Desvignes, G, Dolch, T, Ferdman, R, Ferrara, E, Fonseca, E, Goldstein, J, Graikou, E, Guillemot, L, Hazboun, J, Hobbs, G, Hu, H, Islo, K, Janssen, G, Karuppusamy, R, Kramer, M, Lam, M, Lee, K, Liu, K, Luo, J, Lyne, A, Manchester, R, Mckee, J, Mclaughlin, M, Mingarelli, C, Parthasarathy, A, Pennucci, T, Perrodin, D, Possenti, A, Reardon, D, Russell, C, Sanidas, S, Sesana, A, Shaifullah, G, Shannon, R, Siemens, X, Simon, J, Spiewak, R, Stairs, I, Stappers, B, Swiggum, J, Taylor, S, Theureau, G, Tiburzi, C, Vallisneri, M, Vecchio, A, Wang, J, Zhang, S, Zhang, L, Zhu, W, Zhu, X, Perera, B. B. P., DeCesar, M. E., Demorest, P. B., Kerr, M., Lentati, L., Nice, D. J., Osłowski, S., Ransom, S. M., Keith, M. J., Arzoumanian, Z., Bailes, M., Baker, P. T., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burgay, M., Burke-Spolaor, S., Caballero, R. N., Champion, D. J., Chatterjee, S., Chen, S., Cognard, I., Cordes, J. M., Crowter, K., Dai, S., Desvignes, G., Dolch, T., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Goldstein, J. M., Graikou, E., Guillemot, L., Hazboun, J. S., Hobbs, G., Hu, H., Islo, K., Janssen, G. H., Karuppusamy, R., Kramer, M., Lam, M. T., Lee, K. J., Liu, K., Luo, J., Lyne, A. G., Manchester, R. N., McKee, J. W., McLaughlin, M. A., Mingarelli, C. M. F., Parthasarathy, A. P., Pennucci, T. T., Perrodin, D., Possenti, A., Reardon, D. J., Russell, C. J., Sanidas, S. A., Sesana, A., Shaifullah, G., Shannon, R. M., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stappers, B. W., Swiggum, J. K., Taylor, S. R., Theureau, G., Tiburzi, C., Vallisneri, M., Vecchio, A., Wang, J. B., Zhang, S. B., Zhang, L., Zhu, W. W., Zhu, X. J., Perera, B, Decesar, M, Demorest, P, Kerr, M, Lentati, L, Nice, D, Osłowski, S, Ransom, S, Keith, M, Arzoumanian, Z, Bailes, M, Baker, P, Bassa, C, Bhat, N, Brazier, A, Burgay, M, Burke-Spolaor, S, Caballero, R, Champion, D, Chatterjee, S, Chen, S, Cognard, I, Cordes, J, Crowter, K, Dai, S, Desvignes, G, Dolch, T, Ferdman, R, Ferrara, E, Fonseca, E, Goldstein, J, Graikou, E, Guillemot, L, Hazboun, J, Hobbs, G, Hu, H, Islo, K, Janssen, G, Karuppusamy, R, Kramer, M, Lam, M, Lee, K, Liu, K, Luo, J, Lyne, A, Manchester, R, Mckee, J, Mclaughlin, M, Mingarelli, C, Parthasarathy, A, Pennucci, T, Perrodin, D, Possenti, A, Reardon, D, Russell, C, Sanidas, S, Sesana, A, Shaifullah, G, Shannon, R, Siemens, X, Simon, J, Spiewak, R, Stairs, I, Stappers, B, Swiggum, J, Taylor, S, Theureau, G, Tiburzi, C, Vallisneri, M, Vecchio, A, Wang, J, Zhang, S, Zhang, L, Zhu, W, Zhu, X, Perera, B. B. P., DeCesar, M. E., Demorest, P. B., Kerr, M., Lentati, L., Nice, D. J., Osłowski, S., Ransom, S. M., Keith, M. J., Arzoumanian, Z., Bailes, M., Baker, P. T., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burgay, M., Burke-Spolaor, S., Caballero, R. N., Champion, D. J., Chatterjee, S., Chen, S., Cognard, I., Cordes, J. M., Crowter, K., Dai, S., Desvignes, G., Dolch, T., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Goldstein, J. M., Graikou, E., Guillemot, L., Hazboun, J. S., Hobbs, G., Hu, H., Islo, K., Janssen, G. H., Karuppusamy, R., Kramer, M., Lam, M. T., Lee, K. J., Liu, K., Luo, J., Lyne, A. G., Manchester, R. N., McKee, J. W., McLaughlin, M. A., Mingarelli, C. M. F., Parthasarathy, A. P., Pennucci, T. T., Perrodin, D., Possenti, A., Reardon, D. J., Russell, C. J., Sanidas, S. A., Sesana, A., Shaifullah, G., Shannon, R. M., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stappers, B. W., Swiggum, J. K., Taylor, S. R., Theureau, G., Tiburzi, C., Vallisneri, M., Vecchio, A., Wang, J. B., Zhang, S. B., Zhang, L., Zhu, W. W., and Zhu, X. J.
Abstract: In this paper, we describe the International Pulsar Timing Array second data release, which includes recent pulsar timing data obtained by three regional consortia: the European Pulsar Timing Array, the North American Nanohertz Observatory for Gravitational Waves, and the Parkes Pulsar Timing Array. We analyse and where possible combine high-precision timing data for 65 millisecond pulsars which are regularly observed by these groups. A basic noise analysis, including the processes which are both correlated and uncorrelated in time, provides noise models and timing ephemerides for the pulsars. We find that the timing precisions of pulsars are generally improved compared to the previous data release, mainly due to the addition of new data in the combination. The main purpose of this work is to create the most up-to-date IPTA data release. These data are publicly available for searches for low-frequency gravitational waves and other pulsar science.
Published: 2019

37. Inzicht in het hoofd van de kijker: Kwalitatief onderzoek naar de betekenisgeving aan de Nederlandse voedseldocumentaire Vleesverlangen door mensen met uiteenlopende voedselpatronen.

Author: Lam, M. 't, Müller, E. (Thesis Advisor), Romondt Vis, P. van, Lam, M. 't, Müller, E. (Thesis Advisor), and Romondt Vis, P. van
Abstract: Dit kwalitatieve onderzoek laat zien welke invloed de normen, waarden, kennis, ervaringen en cultuur van het publiek hebben op de betekenisgeving aan een mediatekst. In dit onderzoek is specifiek geëxploreerd welke betekenissen mensen met uiteenlopende voedselpatronen toekennen aan de Nederlandse voedseldocumentaire Vleesverlangen (Borgdorff, 2015). In Vleesverlangen is te zien hoe hoofdpersoon Marijn Frank worstelt met haar vleesconsumptie. De documentaire focust op de relatie tussen een stuk vlees en het gestorven dier. Twee vleeseters, een flexitariër, een vegetariër en een veganist gaven hun reacties op de documentaire. Door middel van semigestructureerde interviews is vastgesteld welke motivaties de respondenten hebben voor hun voedselpatronen met als doel een link te leggen tussen hun ideeën over vleesconsumptie en hun reacties op de documentaire. Er is gewerkt vanuit de receptietheorie van Ien Ang (1996) en de ideeën over representatie van Stuart Hall (2013). Uitgaande van de receptietheorie en de constructivistische benadering van representatie stonden de openheid van mediateksten en een actief publiek tijdens het onderzoek centraal. De hoofdbevinding is dat Vleesverlangen een verscheidenheid aan reacties oproept en geen reflectie is van de werkelijkheid. Door middel van representatie vormen de respondenten zowel tegenstrijdige als overeenstemmende betekenissen over de voedseldocumentaire. De betekenisgeving aan Vleesverlangen werd beïnvloed door de opvattingen die respondenten hadden over zaken in de realiteit, maar ook door grotere culturele invloeden. Documentairemakers moeten er dan ook rekening mee houden dat hun boodschap niet altijd het gewenste effect bereikt, omdat het publiek actief en creatief betekenis vormt.
Published: 2018

38. Optimizing Pulsar Timing Arrays Observations for Detection and Characterization of Low-Frequency Gravitational Wave Sources

Author: Lam, M. T. and Lam, M. T.
Abstract: Observations of low-frequency gravitational waves will require the highest possible timing precision from an array of the most spin-stable pulsars. We can improve the sensitivity of a pulsar timing array (PTA) to different gravitational-wave sources by observing pulsars with low timing noise over years to decades and distributed across the sky. We discuss observing strategies for a PTA focused on a stochastic gravitational-wave background such as from unresolved supermassive black hole binaries as well as focused on single continuous-wave sources. First we describe the method to calculate a PTA's sensitivity to different gravitational-wave-source classes. We then apply our method to the 45 pulsars presented in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 11-year data set. For expected amplitudes of the stochastic background, we find that all pulsars contribute significantly over the timescale of decades; the exception is for very pessimistic values of the stochastic background amplitude. For individual single sources, we find that a number of pulsars contribute to the sensitivity of a given source but that which pulsars contribute are different depending on the source, or versus an all-sky metric. Our results seem robust to the presence of temporally-correlated red noise in pulsar arrival times. It is critical to obtain more robust pulsar-noise parameters as they heavily affect our results. Our results show that it is also imperative to locate and time as many high-precision pulsars as possible, as quickly as possible, to maximize the sensitivity of next-generation PTA detectors., Comment: 9 pages, 2 figures, submitted to ApJ
Published: 2018
Full Text: View/download PDF

39. The NANOGrav 11-Year Data Set: Limits on Gravitational Waves from Individual Supermassive Black Hole Binaries

Author: Aggarwal, K., Arzoumanian, Z., Baker, P. T., Brazier, A., Brinson, M. R., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Crowter, K., Cromartie, H. T., DeCesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E., Fonseca, E., Garver-Daniels, N., Gentile, P., Hazboun, J. S., Holgado, A. M., Huerta, E. A., Islo, K., Jennings, R., Jones, G., Jones, M. L., Kaiser, A. R., Kaplan, D. L., Kelley, L. Z., Key, J. S., Lam, M. T., Lazio, T. J. W., Levin, L., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J., Taylor, S. R., Turner, J. E., Vallisneri, M., van Haasteren, R., Vigeland, S. J., Witt, C. A., Zhu, W. W., Aggarwal, K., Arzoumanian, Z., Baker, P. T., Brazier, A., Brinson, M. R., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Crowter, K., Cromartie, H. T., DeCesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E., Fonseca, E., Garver-Daniels, N., Gentile, P., Hazboun, J. S., Holgado, A. M., Huerta, E. A., Islo, K., Jennings, R., Jones, G., Jones, M. L., Kaiser, A. R., Kaplan, D. L., Kelley, L. Z., Key, J. S., Lam, M. T., Lazio, T. J. W., Levin, L., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J., Taylor, S. R., Turner, J. E., Vallisneri, M., van Haasteren, R., Vigeland, S. J., Witt, C. A., and Zhu, W. W.
Abstract: Observations indicate that nearly all galaxies contain supermassive black holes (SMBHs) at their centers. When galaxies merge, their component black holes form SMBH binaries (SMBHBs), which emit low-frequency gravitational waves (GWs) that can be detected by pulsar timing arrays (PTAs). We have searched the recently-released North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 11-year data set for GWs from individual SMBHBs in circular orbits. As we did not find strong evidence for GWs in our data, we placed 95\% upper limits on the strength of GWs from such sources as a function of GW frequency and sky location. We placed a sky-averaged upper limit on the GW strain of $h_0 < 7.3(3) \times 10^{-15}$ at $f_\mathrm{gw}= 8$ nHz. We also developed a technique to determine the significance of a particular signal in each pulsar using ``dropout' parameters as a way of identifying spurious signals in measurements from individual pulsars. We used our upper limits on the GW strain to place lower limits on the distances to individual SMBHBs. At the most-sensitive sky location, we ruled out SMBHBs emitting GWs with $f_\mathrm{gw}= 8$ nHz within 120 Mpc for $\mathcal{M} = 10^9 \, M_\odot$, and within 5.5 Gpc for $\mathcal{M} = 10^{10} \, M_\odot$. We also determined that there are no SMBHBs with $\mathcal{M} > 1.6 \times 10^9 \, M_\odot$ emitting GWs in the Virgo Cluster. Finally, we estimated the number of potentially detectable sources given our current strain upper limits based on galaxies in Two Micron All-Sky Survey (2MASS) and merger rates from the Illustris cosmological simulation project. Only 34 out of 75,000 realizations of the local Universe contained a detectable source, from which we concluded it was unsurprising that we did not detect any individual sources given our current sensitivity to GWs., Comment: 10 pages, 11 figures. Accepted by Astrophysical Journal. Please send any comments/questions to S. J. Vigeland (vigeland@uwm.edu)
Published: 2018
Full Text: View/download PDF

40. PSR J2234+0611: A new laboratory for stellar evolution

Author: Stovall, K., Freire, P. C. C., Antoniadis, J., Bagchi, M., Deneva, J. S., Garver-Daniels, N., Martinez, J. G., McLaughlin, M. A., Arzoumanian, Z., Blumer, H., Brook, P. R., Cromartie, H. T., Demorest, P. B., Decesar, M. E., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Gentile, P. A., Jones, M. L., Lam, M. T., Lorimer, D. R., Lynch, R. S., Ng, C., Nice, D. J., Pennucci, T. T., Ransom, S. M., Spiewak, R., Stairs, I. H., Swiggum, J. K., Vigeland, S. J., Zhu, W. W., Stovall, K., Freire, P. C. C., Antoniadis, J., Bagchi, M., Deneva, J. S., Garver-Daniels, N., Martinez, J. G., McLaughlin, M. A., Arzoumanian, Z., Blumer, H., Brook, P. R., Cromartie, H. T., Demorest, P. B., Decesar, M. E., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Gentile, P. A., Jones, M. L., Lam, M. T., Lorimer, D. R., Lynch, R. S., Ng, C., Nice, D. J., Pennucci, T. T., Ransom, S. M., Spiewak, R., Stairs, I. H., Swiggum, J. K., Vigeland, S. J., and Zhu, W. W.
Abstract: We report timing results for PSR J2234+0611, a 3.6-ms pulsar in a 32-day, eccentric (e = 0.13) orbit with a helium white dwarf companion discovered as part of the Arecibo Observatory 327 MHz drift scan survey. The precise timing and the eccentric nature of the orbit allow precise measurements of an unusual number of parameters: a) a precise proper motion of 27.10(3) mas/yr and a parallax of 1.05(4) mas resulting in a pulsar distance of 0.95(4) kpc; this allows a precise estimate of the transverse velocity, 123(5) km/s. Together with previously published spectroscopic measurements of the systemic radial velocity, this allows a full 3-D determination of the system's velocity; b) precise measurements of the rate of advance of periastron, which after subtraction of the contribution of the proper motion yields a total system mass of $1.6518^{+0.0033}_{-0.0035}$ solar masses; c) a Shapiro delay measurement, h_3 = $82 \pm 14$ ns despite the orbital inclination not being near 90 deg; combined with the measurement of the total mass, this yields a pulsar mass of $1.353^{+0.014}_{-0.017}$ solar masses and a companion mass of $0.298^{+0.015}_{-0.012}$ solar masses; d) we measure precisely the secular variation of the projected semi-major axis and detect significant annual orbital parallax; together these allow a determination of the full 3-D orbital geometry, including an unambiguous orbital inclination (i = $138.7^{+2.5}_{-2.2}$ deg) and a position angle for the line of nodes (Omega = $44^{+5}_{-4}$ deg). We discuss the component masses to investigate hypotheses previously advanced to explain the origin of eccentric MSPs. The unprecedented determination of the full 3-D position, motion and orbital orientation of the system, plus the precisely measured pulsar and WD mass and the latter's optical detection make this system an unique test of our understanding of white dwarfs and their atmospheres., Comment: 16 pages, 5 figures, accepted by ApJ
Published: 2018
Full Text: View/download PDF

41. Studying the solar system with the International Pulsar Timing Array

Author: Caballero, R. N., Guo, Y. J., Lee, K. J., Lazarus, P., Champion, D. J., Desvignes, G., Kramer, M., Plant, K., Arzoumanian, Z., Bailes, M., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burgay, M., Burke-Spolaor, S., Chamberlin, S. J., Chatterjee, S., Cognard, I., Cordes, J. M., Dai, S., Demorest, P., Dolch, T., Ferdman, R. D., Fonseca, E., Gair, J. R., Garver-Daniels, N., Gentile, P., Gonzalez, M. E., Graikou, E., Guillemot, L., Hobbs, G., Janssen, G. H., Karuppusamy, R., Keith, M. J., Kerr, M., Lam, M. T., Lasky, P. D., Lazio, T. J. W., Levin, L., Liu, K., Lommen, A. N., Lorimer, D. R., Lynch, R. S., Madison, D. R., Manchester, R. N., McKee, J. W., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Nice, D. J., Osłowski, S., Palliyaguru, N. T., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Possenti, A., Ransom, S. M., Reardon, D. J., Sanidas, S. A., Sesana, A., Shaifullah, G., Shannon, R. M., Siemens, X., Simon, J., Spiewak, R., Stairs, I., Stappers, B., Stinebring, D. R., Stovall, K., Swiggum, J. K., Taylor, S. R., Theureau, G., Tiburzi, C., Toomey, L., van Haasteren, R., van Straten, W., Verbiest, J. P. W., Wang, J. B., Zhu, X. J., Zhu, W. W., Caballero, R. N., Guo, Y. J., Lee, K. J., Lazarus, P., Champion, D. J., Desvignes, G., Kramer, M., Plant, K., Arzoumanian, Z., Bailes, M., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burgay, M., Burke-Spolaor, S., Chamberlin, S. J., Chatterjee, S., Cognard, I., Cordes, J. M., Dai, S., Demorest, P., Dolch, T., Ferdman, R. D., Fonseca, E., Gair, J. R., Garver-Daniels, N., Gentile, P., Gonzalez, M. E., Graikou, E., Guillemot, L., Hobbs, G., Janssen, G. H., Karuppusamy, R., Keith, M. J., Kerr, M., Lam, M. T., Lasky, P. D., Lazio, T. J. W., Levin, L., Liu, K., Lommen, A. N., Lorimer, D. R., Lynch, R. S., Madison, D. R., Manchester, R. N., McKee, J. W., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Nice, D. J., Osłowski, S., Palliyaguru, N. T., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Possenti, A., Ransom, S. M., Reardon, D. J., Sanidas, S. A., Sesana, A., Shaifullah, G., Shannon, R. M., Siemens, X., Simon, J., Spiewak, R., Stairs, I., Stappers, B., Stinebring, D. R., Stovall, K., Swiggum, J. K., Taylor, S. R., Theureau, G., Tiburzi, C., Toomey, L., van Haasteren, R., van Straten, W., Verbiest, J. P. W., Wang, J. B., Zhu, X. J., and Zhu, W. W.
Abstract: Pulsar-timing analyses are sensitive to errors in the solar-system ephemerides (SSEs) that timing models utilise to estimate the location of the solar-system barycentre, the quasi-inertial reference frame to which all recorded pulse times-of-arrival are referred. Any error in the SSE will affect all pulsars, therefore pulsar timing arrays (PTAs) are a suitable tool to search for such errors and impose independent constraints on relevant physical parameters. We employ the first data release of the International Pulsar Timing Array to constrain the masses of the planet-moons systems and to search for possible unmodelled objects (UMOs) in the solar system. We employ ten SSEs from two independent research groups, derive and compare mass constraints of planetary systems, and derive the first PTA mass constraints on asteroid-belt objects. Constraints on planetary-system masses have been improved by factors of up to 20 from the previous relevant study using the same assumptions, with the mass of the Jovian system measured at 9.5479189(3)$\times10^{-4}$ $M_{\odot}$. The mass of the dwarf planet Ceres is measured at 4.7(4)$\times10^{-10}$ $M_{\odot}$. We also present the first sensitivity curves using real data that place generic limits on the masses of UMOs, which can also be used as upper limits on the mass of putative exotic objects. For example, upper limits on dark-matter clumps are comparable to published limits using independent methods. While the constraints on planetary masses derived with all employed SSEs are consistent, we note and discuss differences in the associated timing residuals and UMO sensitivity curves., Comment: Accepted for publication by the Monthly Notices of the Royal Astronomical Society
Published: 2018
Full Text: View/download PDF

42. The NANOGrav 11-year Data Set: Pulse Profile Variability

Author: Brook, P. R., Karastergiou, A., McLaughlin, M. A., Lam, M. T., Arzoumanian, Z., Chatterjee, S., Cordes, J. M., Crowter, K., DeCesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E., Fonseca, E., Gentile, P. A., Jones, G., Jones, M. L., Lazio, T. J. W., Levin, L., Lorimer, D. R., Lynch, R. S., Ng, C., Nice, D. J., Pennucci, T. T., Ransom, S. M., Ray, P. S., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J. K., Zhu, W. W., Brook, P. R., Karastergiou, A., McLaughlin, M. A., Lam, M. T., Arzoumanian, Z., Chatterjee, S., Cordes, J. M., Crowter, K., DeCesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E., Fonseca, E., Gentile, P. A., Jones, G., Jones, M. L., Lazio, T. J. W., Levin, L., Lorimer, D. R., Lynch, R. S., Ng, C., Nice, D. J., Pennucci, T. T., Ransom, S. M., Ray, P. S., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J. K., and Zhu, W. W.
Abstract: Access to 50 years of data has led to the discovery of pulsar emission and rotation variability on timescales of months and years. Most of this long-term variability has been seen in long-period pulsars, with relatively little focus on recycled millisecond pulsars. We have analyzed a 38-pulsar sub-set of the 45 millisecond pulsars in the NANOGrav 11-year data set, in order to review their pulse profile stability. The most variability, on any timescale, is seen in PSRs J1713+0747, B1937+21 and J2145-0750. The strongest evidence for long-timescale pulse profile changes is seen in PSRs B1937+21 and J1643-1224. We have focused our analyses on these four pulsars in an attempt to elucidate the causes of their profile variability. Effects of scintillation seem to be responsible for the profile modifications of PSR J2145-0750. We see evidence that imperfect polarization calibration contributes to the profile variability of PSRs J1713+0747 and B1937+21, along with radio frequency interference around 2 GHz, but find that propagation effects also have an influence. The changes seen in PSR J1643-1224 have been reported previously, yet elude explanation beyond their astrophysical nature. Regardless of cause, unmodeled pulse profile changes are detrimental to the accuracy of pulsar timing and must be incorporated into the timing models where possible., Comment: 38 pages, 25 figures
Published: 2018
Full Text: View/download PDF

43. The NANOGrav 12.5-Year Data Set: The Frequency Dependence of Pulse Jitter in Precision Millisecond Pulsars

Author: Lam, M. T., McLaughlin, M. A., Arzoumanian, Z., Blumer, H., Brook, P. R., Cromartie, H. T., Demorest, P. B., DeCesar, M. E., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Garver-Daniels, N., Gentile, P. A., Jones, M. L., Lorimer, D. R., Lynch, R. S., Ng, C., Nice, D. J., Pennucci, T. T., Ransom, S. M., Spiewak, R., Stairs, I. H., Stovall, K., Swiggum, J. K., Vigeland, S. J., Zhu, W. W., Lam, M. T., McLaughlin, M. A., Arzoumanian, Z., Blumer, H., Brook, P. R., Cromartie, H. T., Demorest, P. B., DeCesar, M. E., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Garver-Daniels, N., Gentile, P. A., Jones, M. L., Lorimer, D. R., Lynch, R. S., Ng, C., Nice, D. J., Pennucci, T. T., Ransom, S. M., Spiewak, R., Stairs, I. H., Stovall, K., Swiggum, J. K., Vigeland, S. J., and Zhu, W. W.
Abstract: Low-frequency gravitational-wave experiments require the highest timing precision from an array of the most stable millisecond pulsars. Several known sources of noise on short timescales in single radio-pulsar observations are well described by a simple model of three components: template-fitting from a finite signal-to-noise ratio, pulse phase/amplitude jitter from single-pulse stochasticity, and scintillation errors from short-timescale interstellar scattering variations. Currently template-fitting errors dominate, but as radio telescopes push towards higher signal-to-noise ratios, jitter becomes the next dominant term for most millisecond pulsars. Understanding the statistics of jitter becomes crucial for properly characterizing arrival-time uncertainties. We characterize the radio-frequency dependence of jitter using data on 48 pulsars in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) timing program. We detect significant jitter in 43 of the pulsars and test several functional forms for its frequency dependence; we find significant frequency dependence for 30 pulsars. We find moderate correlations of rms jitter with pulse width (R = 0.62) and number of profile components (R = 0.40); the single-pulse rms jitter is typically ~1% of pulse phase. The average frequency dependence for all pulsars using a power-law model has index -0.42. We investigate the jitter variations for the interpulse of PSR~B1937+21 and find no significant deviations from the main pulse rms jitter. We also test the time-variation of jitter in two pulsars and find that systematics likely bias the results for high-precision pulsars. Pulsar timing array analyses must properly model jitter as a significant component of the noise within the detector., Comment: 18 pages, 10 figures, submitted to ApJ
Published: 2018
Full Text: View/download PDF

44. The NANOGrav 11-year Data Set: Solar Wind Sounding Through Pulsar Timing

Author: Madison, D. R., Cordes, J. M., Arzoumanian, Z., Chatterjee, S., Crowter, K., DeCesar, M. E., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Gentile, P. A., Jones, G., Jones, M. L., Lam, M. T., Levin, L., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Ransom, S. M., Ray, P. S., Spiewak, R., Stairs, I. H., Stovall, K., Swiggum, J. K., Zhu, W., Madison, D. R., Cordes, J. M., Arzoumanian, Z., Chatterjee, S., Crowter, K., DeCesar, M. E., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E. C., Fonseca, E., Gentile, P. A., Jones, G., Jones, M. L., Lam, M. T., Levin, L., Lorimer, D. R., Lynch, R. S., McLaughlin, M. A., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Ransom, S. M., Ray, P. S., Spiewak, R., Stairs, I. H., Stovall, K., Swiggum, J. K., and Zhu, W.
Abstract: The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has observed dozens of millisecond pulsars for over a decade. We have accrued a large collection of dispersion measure (DM) measurements sensitive to the total electron content between Earth and the pulsars at each observation. All lines of sight cross through the solar wind which produces correlated DM fluctuations in all pulsars. We develop and apply techniques for extracting the imprint of the solar wind from the full collection of DM measurements in the recently released NANOGrav 11-yr data set. We filter out long time scale DM fluctuations attributable to structure in the interstellar medium and carry out a simultaneous analysis of all pulsars in our sample that can differentiate the correlated signature of the wind from signals unique to individual lines of sight. When treating the solar wind as spherically symmetric and constant in time, we find the electron number density at 1 A.U. to be $7.9\pm0.2$ cm$^{-3}$. Our data shows little evidence of long-term variation in the density of the wind. We argue that our techniques paired with a high cadence, low radio frequency observing campaign of near-ecliptic pulsars would be capable of mapping out large-scale latitudinal structure in the wind., Comment: 15 pages, submitted to ApJ
Published: 2018
Full Text: View/download PDF

45. Tests of Gravitational Symmetries with Pulsar Binary J1713+0747

Author: Zhu, W. W., Desvignes, G., Wex, N., Caballero, R. N., Champion, D. J., Demorest, P. B., Ellis, J. A., Janssen, G. H., Kramer, M., Krieger, A., Lentati, L., Nice, D. J., Ransom, S. M., Stairs, I. H., Stappers, B. W., Verbiest, J. P. W., Arzoumanian, Z., Bassa, C. G., Burgay, M., Cognard, I., Crowter, K., Dolch, T., Ferdman, R. D., Fonseca, E., Gonzalez, M. E., Graikou, E., Guillemot, L., Hessels, J. W. T., Jessner, A., Jones, G., Jones, M. L., Jordan, C., Karuppusamy, R., Lam, M. T., Lazaridis, K., Lazarus, P., Lee, K. J., Levin, L., Liu, K., Lyne, A. G., McKee, J. W., McLaughlin, M. A., Osłowski, S., Pennucci, T., Perrodin, D., Possenti, A., Sanidas, S., Shaifullah, G., Smits, R., Stovall, K., Swiggum, J., Theureau, G., Tiburzi, C., Zhu, W. W., Desvignes, G., Wex, N., Caballero, R. N., Champion, D. J., Demorest, P. B., Ellis, J. A., Janssen, G. H., Kramer, M., Krieger, A., Lentati, L., Nice, D. J., Ransom, S. M., Stairs, I. H., Stappers, B. W., Verbiest, J. P. W., Arzoumanian, Z., Bassa, C. G., Burgay, M., Cognard, I., Crowter, K., Dolch, T., Ferdman, R. D., Fonseca, E., Gonzalez, M. E., Graikou, E., Guillemot, L., Hessels, J. W. T., Jessner, A., Jones, G., Jones, M. L., Jordan, C., Karuppusamy, R., Lam, M. T., Lazaridis, K., Lazarus, P., Lee, K. J., Levin, L., Liu, K., Lyne, A. G., McKee, J. W., McLaughlin, M. A., Osłowski, S., Pennucci, T., Perrodin, D., Possenti, A., Sanidas, S., Shaifullah, G., Smits, R., Stovall, K., Swiggum, J., Theureau, G., and Tiburzi, C.
Abstract: Symmetries play an important role in modern theories of gravity. The strong equivalence principle (SEP) constitutes a collection of gravitational symmetries which are all implemented by general relativity. Alternative theories, however, are generally expected to violate some aspects of SEP. We test three aspects of SEP using observed change rates in the orbital period and eccentricity of binary pulsar J1713+0747: 1. the gravitational constant's constancy as part of locational invariance of gravitation; 2. the post-Newtonian parameter $\hat{\alpha}_3$ in gravitational Lorentz invariance; 3. the universality of free fall (UFF) for strongly self-gravitating bodies. Based on the pulsar timing result of the combined dataset from the North American Nanohertz Gravitational Observatory (NANOGrav) and the European Pulsar Timing Array (EPTA), we find $\dot{G}/G = (-0.1 \pm 0.9) \times 10^{-12}\,{\rm yr}^{-1}$, which is weaker than Solar system limits, but applies for strongly self-gravitating objects. Furthermore, we obtain the constraints $|\Delta|< 0.002$ for the UFF test and $-3\times10^{-20} < \hat{\alpha}_3 < 4\times10^{-20}$ at 95% confidence. These are the first direct UFF and $\hat{\alpha}_3$ tests based on pulsar binaries, and they overcome various limitations of previous tests., Comment: 11 pages, 6 figures, and 1 table; submitted to MNRAS
Published: 2018
Full Text: View/download PDF

46. The NANOGrav 11-year Data Set: Pulsar-timing Constraints On The Stochastic Gravitational-wave Background

Author: Arzoumanian, Z., Baker, P. T., Brazier, A., Burke-Spolaor, S., Chamberlin, S. J., Chatterjee, S., Christy, B., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. Thankful, Crowter, K., DeCesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E., Folkner, W. M., Fonseca, E., Garver-Daniels, N., Gentile, P. A., Haas, R., Hazboun, J. S., Huerta, E. A., Islo, K., Jones, G., Jones, M. L., Kaplan, D. L., Kaspi, V. M., Lam, M. T., Lazio, T. J. W., Levin, L., Lommen, A. N., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Park, R. S., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Rasskazov, A., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J., Taylor, S. R., Vallisneri, M., Vigeland, S., Zhu, W. W., Arzoumanian, Z., Baker, P. T., Brazier, A., Burke-Spolaor, S., Chamberlin, S. J., Chatterjee, S., Christy, B., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. Thankful, Crowter, K., DeCesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E., Folkner, W. M., Fonseca, E., Garver-Daniels, N., Gentile, P. A., Haas, R., Hazboun, J. S., Huerta, E. A., Islo, K., Jones, G., Jones, M. L., Kaplan, D. L., Kaspi, V. M., Lam, M. T., Lazio, T. J. W., Levin, L., Lommen, A. N., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Park, R. S., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Rasskazov, A., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J., Taylor, S. R., Vallisneri, M., Vigeland, S., and Zhu, W. W.
Abstract: We search for an isotropic stochastic gravitational-wave background (GWB) in the newly released $11$-year dataset from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). While we find no significant evidence for a GWB, we place constraints on a GWB from a population of supermassive black-hole binaries, cosmic strings, and a primordial GWB. For the first time, we find that the GWB upper limits and detection statistics are sensitive to the Solar System ephemeris (SSE) model used, and that SSE errors can mimic a GWB signal. We developed an approach that bridges systematic SSE differences, producing the first PTA constraints that are robust against SSE uncertainties. We thus place a $95\%$ upper limit on the GW strain amplitude of $A_\mathrm{GWB}<1.45\times 10^{-15}$ at a frequency of $f=1$ yr$^{-1}$ for a fiducial $f^{-2/3}$ power-law spectrum, and with inter-pulsar correlations modeled. This is a factor of $\sim 2$ improvement over the NANOGrav $9$-year limit, calculated using the same procedure. Previous PTA upper limits on the GWB will need revision in light of SSE systematic uncertainties. We use our constraints to characterize the combined influence on the GWB of the stellar mass-density in galactic cores, the eccentricity of SMBH binaries, and SMBH--galactic-bulge scaling relationships. We constrain cosmic-string tension using recent simulations, yielding an SSE-marginalized $95\%$ upper limit on the cosmic string tension of $G\mu < 5.3\times 10^{-11}$---a factor of $\sim 2$ better than the published NANOGrav $9$-year constraints. Our SSE-marginalized $95\%$ upper limit on the energy density of a primordial GWB (for a radiation-dominated post-inflation Universe) is $\Omega_\mathrm{GWB}(f)h^2<3.4\times10^{-10}$., Comment: 21 pages, 12 figures, 9 tables. Published in The Astrophysical Journal. Please send any comments/questions to S. R. Taylor (srtaylor@caltech.edu)
Published: 2018
Full Text: View/download PDF

47. Inzicht in het hoofd van de kijker: Kwalitatief onderzoek naar de betekenisgeving aan de Nederlandse voedseldocumentaire Vleesverlangen door mensen met uiteenlopende voedselpatronen.

Author: Lam, M. 't, Müller, E. (Thesis Advisor), Romondt Vis, P. van, Lam, M. 't, Müller, E. (Thesis Advisor), and Romondt Vis, P. van
Abstract: Dit kwalitatieve onderzoek laat zien welke invloed de normen, waarden, kennis, ervaringen en cultuur van het publiek hebben op de betekenisgeving aan een mediatekst. In dit onderzoek is specifiek geëxploreerd welke betekenissen mensen met uiteenlopende voedselpatronen toekennen aan de Nederlandse voedseldocumentaire Vleesverlangen (Borgdorff, 2015). In Vleesverlangen is te zien hoe hoofdpersoon Marijn Frank worstelt met haar vleesconsumptie. De documentaire focust op de relatie tussen een stuk vlees en het gestorven dier. Twee vleeseters, een flexitariër, een vegetariër en een veganist gaven hun reacties op de documentaire. Door middel van semigestructureerde interviews is vastgesteld welke motivaties de respondenten hebben voor hun voedselpatronen met als doel een link te leggen tussen hun ideeën over vleesconsumptie en hun reacties op de documentaire. Er is gewerkt vanuit de receptietheorie van Ien Ang (1996) en de ideeën over representatie van Stuart Hall (2013). Uitgaande van de receptietheorie en de constructivistische benadering van representatie stonden de openheid van mediateksten en een actief publiek tijdens het onderzoek centraal. De hoofdbevinding is dat Vleesverlangen een verscheidenheid aan reacties oproept en geen reflectie is van de werkelijkheid. Door middel van representatie vormen de respondenten zowel tegenstrijdige als overeenstemmende betekenissen over de voedseldocumentaire. De betekenisgeving aan Vleesverlangen werd beïnvloed door de opvattingen die respondenten hadden over zaken in de realiteit, maar ook door grotere culturele invloeden. Documentairemakers moeten er dan ook rekening mee houden dat hun boodschap niet altijd het gewenste effect bereikt, omdat het publiek actief en creatief betekenis vormt.
Published: 2018

48. The NANOGrav 11-Year Data Set: Limits on Gravitational Waves from Individual Supermassive Black Hole Binaries

Author: Aggarwal, K., Arzoumanian, Z., Baker, P. T., Brazier, A., Brinson, M. R., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Crowter, K., Cromartie, H. T., DeCesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E., Fonseca, E., Garver-Daniels, N., Gentile, P., Hazboun, J. S., Holgado, A. M., Huerta, E. A., Islo, K., Jennings, R., Jones, G., Jones, M. L., Kaiser, A. R., Kaplan, D. L., Kelley, L. Z., Key, J. S., Lam, M. T., Lazio, T. J. W., Levin, L., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J., Taylor, S. R., Turner, J. E., Vallisneri, M., van Haasteren, R., Vigeland, S. J., Witt, C. A., Zhu, W. W., Aggarwal, K., Arzoumanian, Z., Baker, P. T., Brazier, A., Brinson, M. R., Brook, P. R., Burke-Spolaor, S., Chatterjee, S., Cordes, J. M., Cornish, N. J., Crawford, F., Crowter, K., Cromartie, H. T., DeCesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E., Fonseca, E., Garver-Daniels, N., Gentile, P., Hazboun, J. S., Holgado, A. M., Huerta, E. A., Islo, K., Jennings, R., Jones, G., Jones, M. L., Kaiser, A. R., Kaplan, D. L., Kelley, L. Z., Key, J. S., Lam, M. T., Lazio, T. J. W., Levin, L., Lorimer, D. R., Luo, J., Lynch, R. S., Madison, D. R., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Ng, C., Nice, D. J., Pennucci, T. T., Pol, N. S., Ransom, S. M., Ray, P. S., Siemens, X., Simon, J., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J., Taylor, S. R., Turner, J. E., Vallisneri, M., van Haasteren, R., Vigeland, S. J., Witt, C. A., and Zhu, W. W.
Abstract: Observations indicate that nearly all galaxies contain supermassive black holes (SMBHs) at their centers. When galaxies merge, their component black holes form SMBH binaries (SMBHBs), which emit low-frequency gravitational waves (GWs) that can be detected by pulsar timing arrays (PTAs). We have searched the recently-released North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 11-year data set for GWs from individual SMBHBs in circular orbits. As we did not find strong evidence for GWs in our data, we placed 95\% upper limits on the strength of GWs from such sources as a function of GW frequency and sky location. We placed a sky-averaged upper limit on the GW strain of $h_0 < 7.3(3) \times 10^{-15}$ at $f_\mathrm{gw}= 8$ nHz. We also developed a technique to determine the significance of a particular signal in each pulsar using ``dropout' parameters as a way of identifying spurious signals in measurements from individual pulsars. We used our upper limits on the GW strain to place lower limits on the distances to individual SMBHBs. At the most-sensitive sky location, we ruled out SMBHBs emitting GWs with $f_\mathrm{gw}= 8$ nHz within 120 Mpc for $\mathcal{M} = 10^9 \, M_\odot$, and within 5.5 Gpc for $\mathcal{M} = 10^{10} \, M_\odot$. We also determined that there are no SMBHBs with $\mathcal{M} > 1.6 \times 10^9 \, M_\odot$ emitting GWs in the Virgo Cluster. Finally, we estimated the number of potentially detectable sources given our current strain upper limits based on galaxies in Two Micron All-Sky Survey (2MASS) and merger rates from the Illustris cosmological simulation project. Only 34 out of 75,000 realizations of the local Universe contained a detectable source, from which we concluded it was unsurprising that we did not detect any individual sources given our current sensitivity to GWs., Comment: 10 pages, 11 figures. Accepted by Astrophysical Journal. Please send any comments/questions to S. J. Vigeland (vigeland@uwm.edu)
Published: 2018
Full Text: View/download PDF

49. The NANOGrav 11-year Data Set: Pulse Profile Variability

Author: Brook, P. R., Karastergiou, A., McLaughlin, M. A., Lam, M. T., Arzoumanian, Z., Chatterjee, S., Cordes, J. M., Crowter, K., DeCesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E., Fonseca, E., Gentile, P. A., Jones, G., Jones, M. L., Lazio, T. J. W., Levin, L., Lorimer, D. R., Lynch, R. S., Ng, C., Nice, D. J., Pennucci, T. T., Ransom, S. M., Ray, P. S., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J. K., Zhu, W. W., Brook, P. R., Karastergiou, A., McLaughlin, M. A., Lam, M. T., Arzoumanian, Z., Chatterjee, S., Cordes, J. M., Crowter, K., DeCesar, M., Demorest, P. B., Dolch, T., Ellis, J. A., Ferdman, R. D., Ferrara, E., Fonseca, E., Gentile, P. A., Jones, G., Jones, M. L., Lazio, T. J. W., Levin, L., Lorimer, D. R., Lynch, R. S., Ng, C., Nice, D. J., Pennucci, T. T., Ransom, S. M., Ray, P. S., Spiewak, R., Stairs, I. H., Stinebring, D. R., Stovall, K., Swiggum, J. K., and Zhu, W. W.
Abstract: Access to 50 years of data has led to the discovery of pulsar emission and rotation variability on timescales of months and years. Most of this long-term variability has been seen in long-period pulsars, with relatively little focus on recycled millisecond pulsars. We have analyzed a 38-pulsar sub-set of the 45 millisecond pulsars in the NANOGrav 11-year data set, in order to review their pulse profile stability. The most variability, on any timescale, is seen in PSRs J1713+0747, B1937+21 and J2145-0750. The strongest evidence for long-timescale pulse profile changes is seen in PSRs B1937+21 and J1643-1224. We have focused our analyses on these four pulsars in an attempt to elucidate the causes of their profile variability. Effects of scintillation seem to be responsible for the profile modifications of PSR J2145-0750. We see evidence that imperfect polarization calibration contributes to the profile variability of PSRs J1713+0747 and B1937+21, along with radio frequency interference around 2 GHz, but find that propagation effects also have an influence. The changes seen in PSR J1643-1224 have been reported previously, yet elude explanation beyond their astrophysical nature. Regardless of cause, unmodeled pulse profile changes are detrimental to the accuracy of pulsar timing and must be incorporated into the timing models where possible., Comment: 38 pages, 25 figures
Published: 2018
Full Text: View/download PDF

50. Studying the solar system with the International Pulsar Timing Array

Author: Caballero, R. N., Guo, Y. J., Lee, K. J., Lazarus, P., Champion, D. J., Desvignes, G., Kramer, M., Plant, K., Arzoumanian, Z., Bailes, M., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burgay, M., Burke-Spolaor, S., Chamberlin, S. J., Chatterjee, S., Cognard, I., Cordes, J. M., Dai, S., Demorest, P., Dolch, T., Ferdman, R. D., Fonseca, E., Gair, J. R., Garver-Daniels, N., Gentile, P., Gonzalez, M. E., Graikou, E., Guillemot, L., Hobbs, G., Janssen, G. H., Karuppusamy, R., Keith, M. J., Kerr, M., Lam, M. T., Lasky, P. D., Lazio, T. J. W., Levin, L., Liu, K., Lommen, A. N., Lorimer, D. R., Lynch, R. S., Madison, D. R., Manchester, R. N., McKee, J. W., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Nice, D. J., Osłowski, S., Palliyaguru, N. T., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Possenti, A., Ransom, S. M., Reardon, D. J., Sanidas, S. A., Sesana, A., Shaifullah, G., Shannon, R. M., Siemens, X., Simon, J., Spiewak, R., Stairs, I., Stappers, B., Stinebring, D. R., Stovall, K., Swiggum, J. K., Taylor, S. R., Theureau, G., Tiburzi, C., Toomey, L., van Haasteren, R., van Straten, W., Verbiest, J. P. W., Wang, J. B., Zhu, X. J., Zhu, W. W., Caballero, R. N., Guo, Y. J., Lee, K. J., Lazarus, P., Champion, D. J., Desvignes, G., Kramer, M., Plant, K., Arzoumanian, Z., Bailes, M., Bassa, C. G., Bhat, N. D. R., Brazier, A., Burgay, M., Burke-Spolaor, S., Chamberlin, S. J., Chatterjee, S., Cognard, I., Cordes, J. M., Dai, S., Demorest, P., Dolch, T., Ferdman, R. D., Fonseca, E., Gair, J. R., Garver-Daniels, N., Gentile, P., Gonzalez, M. E., Graikou, E., Guillemot, L., Hobbs, G., Janssen, G. H., Karuppusamy, R., Keith, M. J., Kerr, M., Lam, M. T., Lasky, P. D., Lazio, T. J. W., Levin, L., Liu, K., Lommen, A. N., Lorimer, D. R., Lynch, R. S., Madison, D. R., Manchester, R. N., McKee, J. W., McLaughlin, M. A., McWilliams, S. T., Mingarelli, C. M. F., Nice, D. J., Osłowski, S., Palliyaguru, N. T., Pennucci, T. T., Perera, B. B. P., Perrodin, D., Possenti, A., Ransom, S. M., Reardon, D. J., Sanidas, S. A., Sesana, A., Shaifullah, G., Shannon, R. M., Siemens, X., Simon, J., Spiewak, R., Stairs, I., Stappers, B., Stinebring, D. R., Stovall, K., Swiggum, J. K., Taylor, S. R., Theureau, G., Tiburzi, C., Toomey, L., van Haasteren, R., van Straten, W., Verbiest, J. P. W., Wang, J. B., Zhu, X. J., and Zhu, W. W.
Abstract: Pulsar-timing analyses are sensitive to errors in the solar-system ephemerides (SSEs) that timing models utilise to estimate the location of the solar-system barycentre, the quasi-inertial reference frame to which all recorded pulse times-of-arrival are referred. Any error in the SSE will affect all pulsars, therefore pulsar timing arrays (PTAs) are a suitable tool to search for such errors and impose independent constraints on relevant physical parameters. We employ the first data release of the International Pulsar Timing Array to constrain the masses of the planet-moons systems and to search for possible unmodelled objects (UMOs) in the solar system. We employ ten SSEs from two independent research groups, derive and compare mass constraints of planetary systems, and derive the first PTA mass constraints on asteroid-belt objects. Constraints on planetary-system masses have been improved by factors of up to 20 from the previous relevant study using the same assumptions, with the mass of the Jovian system measured at 9.5479189(3)$\times10^{-4}$ $M_{\odot}$. The mass of the dwarf planet Ceres is measured at 4.7(4)$\times10^{-10}$ $M_{\odot}$. We also present the first sensitivity curves using real data that place generic limits on the masses of UMOs, which can also be used as upper limits on the mass of putative exotic objects. For example, upper limits on dark-matter clumps are comparable to published limits using independent methods. While the constraints on planetary masses derived with all employed SSEs are consistent, we note and discuss differences in the associated timing residuals and UMO sensitivity curves., Comment: Accepted for publication by the Monthly Notices of the Royal Astronomical Society
Published: 2018
Full Text: View/download PDF

Catalog

Books, media, physical & digital resources

See catalog results

Searchworks

Select search scope, currently: Articles Catalog books, media & more in Jio Institute collections Articles journal articles & other e-resources

Search

Search Constraints

Refine your results

Search Limiters

Publication Year Range

Publication Type

Database

Publisher

92 results on '"Lam, M. T."'

Search Results

Catalog

Select search scope, currently: Articles

Catalog

books, media & more in Jio Institute collections

Articles

journal articles & other e-resources