Search

Your search keyword '"R. Ojha"' showing total 7 results
Start Over Author "R. Ojha" Database NASA Technical Reports
7 results on '"R. Ojha"'

1. The Fourth Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope

Author

M. Ajello, R. Angioni, M. Axelsson, J. Ballet, G. Barbiellini, D. Bastieri, J. Becerra Gonzalez, R. Bellazzini, E. Bissaldi, E. D. Bloom, R. Bonino, E. Bottacini, P. Bruel, S. Buson, F. Cafardo, R. A. Cameron, E. Cavazzuti, S. Chen, C. C. Cheung, S. Ciprini, D. Costantin, S. Cutini, F. D’Ammando, P. de la Torre Luque, R. de Menezes, F. de Palma, A. Desai, N. Di Lalla, L. Di Venere, A. Domínguez, F. Fana Dirirsa, E. C. Ferrara, J. Finke, A. Franckowiak, Y. Fukazawa, S. Funk, P. Fusco, F. Gargano, S. Garrappa, D. Gasparrini, N. Giglietto, F. Giordano, M. Giroletti, D. Green, I. A. Grenier, S. Guiriec, S. Harita, E. Haywood, D. Horan, R. Itoh, G. Jóhannesson, M. Kovac’evic’, F. Krauss, M. Kreter, M. Kuss, S. Larsson, C. Leto, J. Li, I. Liodakis, F. Longo, F. Loparco, B. Lott, M. N. Lovellette, P. Lubrano, G. M. Madejski, S. Maldera, A. Manfreda, G. Martí-Devesa, F. Massaro, M. N. Mazziotta, I. Mereu, M. Meyer, G. Migliori, N. Barrios, T. Mizuno, M. E. Monzani, A. Morselli, I. V. Moskalenko, M. Negro, R. Nemmen, E. Nuss, L. S. Ojha, R. Ojha, N. Omodei, M. Orienti, E. Orlando, J. F. Ormes, V. S. Paliya, Z. Pei, H. Peña-Herazo, M. Persic, M. Pesce-Rollins, L. Petrov, F. Piron, H. Poon, G. Principe, S. Rainò, R. Rando, B. Rani, M. Razzano, S. Razzaque, A. Reimer, O. Reimer, F. K. Schinzel, D. Serini, C. Sgrò, E. J. Siskind, G. Spandre, P. Spinelli, D. J. Suson, Y. Tachibana, D. J. Thompson, D. F. Torres, E. Torresi, E. Troja, J. Valverde, P. van Zyl, and M. Yassine

Subjects
Astrophysics, Astronomy
Abstract

The fourth catalog of active galactic nuclei (AGNs) detected by the Fermi Gamma-ray Space Telescope Large Area Telescope (4LAC) between 2008 August 4 and 2016 August 2 contains $2863$ objects located at high Galactic latitudes (| b| > 10^9). It includes 85% more sources than the previous 3LAC catalog based on 4 yr of data. AGNs represent at least 79% of the high-latitude sources in the fourth Fermi-Large Area Telescope Source Catalog (4FGL), which covers the energy range from 50 MeV to 1 TeV. In addition, 344 gamma-ray AGNs are found at low Galactic latitudes. Most of the 4LAC AGNs are blazars (98%), while the remainder are other types of AGNs. The blazar population consists of 24% Flat Spectrum Radio Quasars (FSRQs), 38% BL Lac-type objects, and 38% blazar candidates of unknown types (BCUs). On average, FSRQs display softer spectra and stronger variability in the gamma-ray band than BL Lacs do, confirming previous findings. All AGNs detected by ground-based atmospheric Cerenkov telescopes are also found in the 4LAC.

Published
2020
Full Text
View/download PDF

2. The Fourth Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope

Author

M. Ajello, R. Angioni, M. Axelsson, J. Ballet, G. Barbiellini, D. Bastieri, J. Becerra Gonzalez, R. Bellazzini, E. Bissaldi, E. D. Bloom, R. Bonino, E. Bottacini, P. Bruel, S. Buson, F. Cafardo, R. A. Cameron, E. Cavazzuti, S. Chen, C. C. Cheung, S. Ciprini, D. Costantin, S. Cutini, F. D'Ammando, P. de la Torre Luque, R. de Menezes, F. de Palma, A. Desai, N. Di Lalla, L. Di Venere, A. Dominguez, F. Fana Dirirsa, E. C. Ferrara, J. Finke, A. Franckowiak, Y. Fukazawa, S. Funk, P. Fusco, F. Gargano, S. Garrappa, D. Gasparrini, N. Giglietto, F. Giordano, M. Giroletti, D. Green, I. A. Grenier, S. Guiriec, S. Harita, E. Hays, D. Horan, R. Itoh, G. Jóhannesson, M. Kovac’evic’, F. Krauss, M. Kreter, M. Kuss, S. Larsson, C. Leto, J. Li, I. Liodakis, F. Longo, F. Loparco, B. Lott, M. N. Lovellette, P. Lubrano, G. M. Madejski, S. Maldera, A. Manfreda, G. Martí-Devesa, F. Massaro, M. N. Mazziotta, I. Mereu, M. Meyer, G. Migliori, N. Mirabal, T. Mizuno, M. E. Monzani, A. Morselli, I. V. Moskalenko, M. Negro, R. Nemmen, E. Nuss, L. S. Ojha, R. Ojha, N. Omodei, M. Orienti, E. Orlando, J. F. Ormes, V. S. Paliya, Z. Pei, H. Peña-Herazo, M. Persic, M. Pesce-Rollins, L. Petrov, F. Piron, H. Poon, G. Principe, S. Raino', R. Rando, B. Rani, M. Razzano, S. Razzaque, A. Reimer, O. Reimer, F. K. Schinzel, D. Serini, C. Sgro', E. J. Siskind, G. Spandre, P. Spinelli, D. J. Suson, Y. Tachibana, D. J. Thompson, D. F. Torres, E. Torresi, E. Troja, J. Valverde, P. van Zyl, and M. Yassine

Subjects
Astrophysics
Abstract

The fourth catalog of active galactic nuclei (AGNs) detected by the Fermi Gamma-ray Space Telescope Large Area Telescope (4LAC) between 2008 August 4 and 2016 August 2 contains $2863$ objects located at high Galactic latitudes (|b|>10°). It includes 85% more sources than the previous 3LAC catalog based on 4 yr of data. AGNs represent at least 79% of the high-latitude sources in the fourth Fermi-Large Area Telescope Source Catalog (4FGL), which covers the energy range from 50 MeV to 1 TeV. In addition, 344 gamma-ray AGNs are found at low Galactic latitudes. Most of the 4LAC AGNs are blazars (98%), while the remainder are other types of AGNs. The blazar population consists of 24% Flat Spectrum Radio Quasars (FSRQs), 38% BL Lac-type objects, and 38% blazar candidates of unknown types (BCUs). On average, FSRQs display softer spectra and stronger variability in the gamma-ray band than BL Lacs do, confirming previous findings. All AGNs detected by ground-based atmospheric Cerenkov telescopes are also found in the 4LAC.

Published
2020
Full Text
View/download PDF

3. Fermi Large Area Telescope Fourth Source Catalog

Author

S. Abdollahi, F. Acero, M. Ackermann, M. Ajello, W. B. Atwood, M. Axelsson, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, J. Becerra Gonzalez, R. Bellazzini, A. Berretta, E. Bissaldi, R. D. Blandford, E. D. Bloom, R. Bonino, E. Bottacini, T. J. Brandt, J. Bregeon, P. Bruel, R. Buehler, T. H. Burnett, S. Buson, R. A. Cameron, R. Caputo, P. A. Caraveo, J. M. Casandjian, D. Castro, E. Cavazzuti, E. Charles, S. Chaty, S. Chen, C. C. Cheung, G. Chiaro, S. Ciprini, J. Cohen-Tanugi, L. R. Cominsky, J. Coronado-Blázquez, D. Costantin, A. Cuoco, S. Cutini, F. D'Ammando, M. DeKlotz, P. de la Torre Luque, F. de Palma, A. Desai, S. W. Digel, N. Di Lalla, M. Di Mauro, L. Di Venere, A. Dominguez, D. Dumora, F. Fana Dirirsa, S. J. Fegan, E. C. Ferrara, A. Franckowiak, Y. Fukazawa, S. Funk, P. Fusco, F. Gargano, D. Gasparrini, N. Giglietto, P. Giommi, F. Giordano, M. Giroletti, T. Glanzman, D. Green, I. A. Grenier, S. Griffin, M.-H. Grondin, J. E. Grove, S. Guiriec, A. K. Harding, K. Hayashi, E. Hays, J. W. Hewitt, D. Horan, G. Jóhannesson, T. J. Johnson, T. Kamae, M. Kerr, D. Kocevski, M. Kovac’evic’, M. Kuss, D. Landriu, S. Larsson, L. Latronico, M. Lemoine-Goumard, J. Li, I. Liodakis, F. Longo, F. Loparco, B. Lott, M. N. Lovellette, P. Lubrano, G. M. Madejski, S. Maldera, D. Malyshev, A. Manfreda, E. J. Marchesini, L. Marcotulli, G. Martí-Devesa, P. Martin, F. Massaro, M. N. Mazziotta, J. E. McEnery, I. Mereu, M. Meyer, P. F. Michelson, N. Mirabal, T. Mizuno, M. E. Monzani, A. Morselli, I. V. Moskalenko, M. Negro, E. Nuss, R. Ojha, N. Omodei, M. Orienti, E. Orlando, J. F. Ormes, M. Palatiello, V. S. Paliya, D. Paneque, Z. Pei, H. Peña-Herazo, J. S. Perkins, M. Persic, M. Pesce-Rollins, V. Petrosian, L. Petrov, F. Piron, H. Poon, T. A. Porter, G. Principe, S. Raino', R. Rando, M. Razzano, S. Razzaque, A. Reimer, O. Reimer, Q. Remy, T. Reposeur, R. W. Romani, P. M. Saz Parkinson, F. K. Schinzel, D. Serini, C. Sgro', E. J. Siskind, D. A. Smith, G. Spandre, P. Spinelli, A. W. Strong, D. J. Suson, H. Tajima, M. N. Takahashi, D. Tak, J. B. Thayer, D. J. Thompson, L. Tibaldo, D. F. Torres, E. Torresi, J. Valverde, B. Van Klaveren, P. van Zyl, K. Wood, M. Yassine, and G. Zaharijas

Subjects
Astrophysics
Abstract

We present the fourth Fermi Large Area Telescope catalog (4FGL) of gamma-ray sources. Based on the first eight years of science data from the Fermi Gamma-ray Space Telescope mission in the energy range from 50 MeV to 1 TeV, it is the deepest yet in this energy range. Relative to the 3FGL catalog, the 4FGL catalog has twice as much exposure as well as a number of analysis improvements, including an updated model for the Galactic diffuse gamma-ray emission, and two sets of light curves (one-year and two-month intervals). The 4FGL catalog includes 5064 sources above 4 sigma significance, for which we provide localization and spectral properties. Seventy-five sources are modeled explicitly as spatially extended, and overall, 358 sources are considered as identified based on angular extent, periodicity, or correlated variability observed at other wavelengths. For 1336 sources, we have not found plausible counterparts at other wavelengths. More than 3130 of the identified or associated sources are active galaxies of the blazar class, and 239 are pulsars.

Published
2020
Full Text
View/download PDF

4. A gamma-ray determination of the Universe’s star formation history

Author

S. Abdollahi, M. Ackermann, M. Ajello, W. Atwood, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, J. Becerra González, R. Bellazzini, E. Bissaldi, R. Blandford, E. Bloom, R. Bonino, E. Bottacini, S. Buson, J. Bregeon, P. Bruel, R. Buehler, R. Cameron, R. Caputo, P. A. Caraveo, E. Cavazzuti, E. Charles, S. Chen, T. Cheung, G. Chiaro, S. Ciprini, J. Cohen-Tanugi, L. Cominsky, J. Conrad, D. Costantin, S. Cutini, F. D’Ammando, F. de Palma, A. Desai, S. Digel, N. Di Lalla, M. Di Mauro, L. Di Venere, A. Domínguez, C. Favuzzi, S. Fegan, J. Finke, A. Franckowiak, Y. Fukazawa, S. Funk, P. Fusco, G. Gallardo Romero, F. Gargano, D. Gasparrini, N. Giglietto, F. Giordano, M. Giroletti, D. Green, I. Grenier, L. Guillemot, S. Guiriec, D. H. Hartmann, E. Hays, K. Helgason, D. Horan, G. Jóhannesson, D. Kocevski, M. Kuss, S. Larsson, L. Latronico, J. Li, F. Longo, F. Loparco, B. Lott, M. Lovellette, P. Lubrano, G. Madejski, J. Magill, S. Maldera, A. Manfreda, L. Marcotulli, M. Mazziotta, J. McEnery, M. Meyer, P. Michelson, T. Mizuno, M. E. Monzani, A. Morselli, I. Moskalenko, M. Negro, E. Nuss, R. Ojha, N. Omodei, M. Orienti, E. Orlando, J. Ormes, M. Palatiello, V. Paliya, D. Paneque, J. Perkins, M. Persic, M. Pesce-Rollins, V. Petrosian, F. Piron, T. Porter, J. R. Primack, G. Principe, S. Rainò, R. Rando, M. Razzano, S. Razzaque, A. Reimer, O. Reimer, P. Saz Parkinson, C. Sgrò, E. J. Siskind, G. Spandre, P. Spinelli, D. J. Suson, H. Tajima, M. Takahashi, J. Thayer, L. Tibaldo, D. F. Torres, E. Torresi, G. Tosti, A. Tramacere, E. Troja, J. V. Valverde, G. Vianello, M. Vogel, K. Wood, and G. Zaharijas

Published
2018
Full Text
View/download PDF

6. Tanami Blazars in the IceCube Pev Neutrino Fields

Author

F Krauãÿ, M Kadler, K Mannheim, R Schulz, J Truestedt, J Wilms, R Ojha, E Ros, G Anton, W Baumgartner, T Beuchert, J Blanchard, C Burkel, B Carpenter, T Eberl, P G Edwards, D Eisenacher, D Elsasser, K Fehn, U Fritsch, N Gehrels, C Grafe, C Großberger, H Hase, S Horiuchi, C James, A Kappes, U Katz, A Kreikenbohm, I Kreykenbohm, M Langejahn, K Leiter, E Litzinger, J E J Lovell, C Muller, C Phillips, C Plotz, J Quick, T Steinbring, J Stevens, D J Thompson, and A K Tzioumis

Subjects
Astrophysics
Abstract

The IceCube Collaboration has announced the discovery of a neutrino flux in excess of the atmospheric background. Owing to the steeply falling atmospheric background spectrum, events at PeV energies most likely have an extraterrestrial origin. We present the multiwavelength properties of the six radio-brightest blazars that are positionally coincident with these events using contemporaneous data of the TANAMI blazar sample, including high-resolution images and spectral energy distributions. Assuming the X-ray to γ-ray emission originates in the photoproduction of pions by accelerated protons, the integrated predicted neutrino luminosity of these sources is high enough to explain the two detected PeV events.

Published
2014
Full Text
View/download PDF

7. The Unusual Multiwavelength Properties of the Gamma-Ray Source PMN J1603-4904

Author

Cornelia Muller, M Kadler, R Ojha, M Bock, F Kraub, G B Taylor, J Wilms, J Blanchard, B Carpenter, T Dauser, M Dutka, P G Edwards, N Gehrels, C Grobberger, H Hase, S Horiuchi, A Kreikenbohm, J E J Lovell, W McConville, C Phillips, C Ploetz, T Pursimo, J Quick, E Ros, R Schulz, J Stevens, S J Tingay, J Trustedt, A K Tzioumis, and J A Zensus

Subjects
Astronomy
Abstract

Context. We investigate the nature and classification of PMNJ1603-4904, a bright radio source close to the Galactic plane, which is associated with one of the brightest hard-spectrum gamma-ray sources detected by Fermi/LAT. It has previously been classified as a low peaked BL Lac object based on its broadband emission and the absence of optical emission lines. Optical measurements, however, suffer strongly from extinction and the absence of pronounced short-time gamma-ray variability over years of monitoring is unusual for a blazar. Aims. In this paper, we are combining new and archival multi-wavelength data of PMNJ1603-4904 in order to reconsider the classification and nature of this unusual gamma-ray source. Methods. For the first time, we study the radio morphology of PMNJ1603-4904 at 8.4GHz and 22.3GHz, and its spectral properties on milliarcsecond scales, based on VLBI observations from the TANAMI program. We combine the resulting images with multi-wavelength data in the radio, IR, optical/UV, X-ray, and gamma-ray regimes. Results. PMNJ1603-4904 shows a symmetric brightness distribution at 8.4 GHz on milliarcsecond scales, with the brightest, and most compact component in the center of the emission region. The morphology is reminiscent of a compact symmetric object (CSO). Such objects, thought to be young radio galaxies, have been predicted to produce gamma-ray emission but have not been detected as a class by the Fermi gamma-ray telescope so far. Sparse (u, v)-coverage at 22.3GHz prevents an unambiguous modeling of the source morphology at this higher frequency. Moreover, infrared measurements reveal an excess in the spectral energy distribution (SED), which can be modeled with a blackbody with a temperature of about 1600 K, and which is usually not present in blazar SEDs. Conclusions. The TANAMI VLBI data and the shape of the broadband SED challenge the current blazar classification of one of the brightest gamma-ray sources in the sky. PMNJ1603-4904 seems to be either a highly peculiar BL Lac object or a misaligned jet source. In the latter case, the intriguing VLBI structure opens room for a possible classification of PMNJ1603-4904 as a gamma-ray bright CSO.

Published
2014
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results