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8 results on '"Lynch, M. J."'

1. An analysis of the halo and relic radio emission from Abell 3376 from Murchison Widefield Array observations

Author

George, Lijo T., Dwarakanath, K. S., Johnston-Hollitt, M., Hurley-Walker, N., Hindson, L., Kapińska, A. D., Tingay, S. J., Bell, M., Callingham, J. R., For, Bi-Qing, Hancock, P. J., Lenc, E., McKinley, B., Morgan, J., Offringa, A., Procopio, P., Staveley-Smith, L., Wayth, R. B., Wu, Chen, Zheng, Q., Bernardi, G., Bowman, J. D., Briggs, F., Cappallo, R. J., Corey, B. E., Deshpande, A. A., Emrich, D., Goeke, R., Greenhill, L. J., Hazelton, B. J., Kaplan, D. L., Kasper, J. C., Kratzenberg, E., Lonsdale, C. J., Lynch, M. J., McWhirter, S. R., Mitchell, D. A., Morales, M. F., Morgan, E., Oberoi, D., Ord, S. M., Prabu, T., Rogers, A. E. E., Roshi, A., Shankar, N. Udaya, Srivani, K. S., Subrahmanyan, R., Waterson, M., Whitney, R. L. Webster A. R., Williams, A., and Williams, C. L.

Subjects
Astrophysics::High Energy Astrophysical Phenomena, Astrophysics of Galaxies (astro-ph.GA), FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics - Astrophysics of Galaxies, Astrophysics::Galaxy Astrophysics
Abstract

We have carried out multiwavelength observations of the near-by ($z=0.046$) rich, merging galaxy cluster Abell 3376 with the Murchison Widefield Array (MWA). As a part of the GaLactic and Extragalactic All-sky MWA survey (GLEAM), this cluster was observed at 88, 118, 154, 188 and 215 MHz. The known radio relics, towards the eastern and western peripheries of the cluster, were detected at all the frequencies. The relics, with a linear extent of $\sim$ 1 Mpc each, are separated by $\sim$ 2 Mpc. Combining the current observations with those in the literature, we have obtained the spectra of these relics over the frequency range 80 -- 1400 MHz. The spectra follow power laws, with $\alpha$ = $-1.17\pm0.06$ and $-1.37\pm0.08$ for the west and east relics, respectively ($S \propto \nu^{\alpha}$). Assuming the break frequency to be near the lower end of the spectrum we estimate the age of the relics to be $\sim$ 0.4 Gyr. No diffuse radio emission from the central regions of the cluster (halo) was detected. The upper limit on the radio power of any possible halo that might be present in the cluster is a factor of 35 lower than that expected from the radio power and X-ray luminosity correlation for cluster halos. From this we conclude that the cluster halo is very extended ($>$ 500 kpc) and/or most of the radio emission from the halo has decayed. The current limit on the halo radio power is a factor of ten lower than the existing upper limits with possible implications for models of halo formation., Comment: 10 pages, 6 figures

Published
2015
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2. A new layout optimization technique for interferometric arrays, applied to the Murchison Widefield Array

Author

Beardsley, A. P., Hazelton, B. J., Morales, M. F., Capallo, R.J., Goeke, Robert F, Emrich, D., Lonsdale, Colin John, Arcus, W., Barnes, D., Bernardi, G., Bowman, J. D., Bunton, J. D., Corey, Brian E, Deshpande, A., deSouza, L., Gaensler, B. M., Greenhill, L. J., Herne, D., Hewitt, Jacqueline N, Kaplan, D. L., Kasper, J. C., Kincaid, Barton B., Koenig, R., Kratzenberg, Eric W, Lynch, M. J., McWhirter, S. R., Mitchell, D. A., Morgan, Edward H, Oberoi, Divya, Ord, S. M., Pathikulangara, J., Prabu, T., Rogers, Alan E E, Roshi, A., Salah, Joseph E., Sault, R. J., Shankar, N. Udaya, Srivani, K. S., Stevens, J., Subrahmanyan, R., Tingay, S. J., Wayth, R. B., Waterson, M., Webster, R. L., Whitney, Alan R, Williams, A., Williams, C. L., Wyithe, J. S. B., Remillard, Ronald A, Haystack Observatory, and MIT Kavli Institute for Astrophysics and Space Research

Abstract

Antenna layout is an important design consideration for radio interferometers because it determines the quality of the snapshot point spread function (PSF, or array beam). This is particularly true for experiments targeting the 21-cm Epoch of Reionization signal as the quality of the foreground subtraction depends directly on the spatial dynamic range and thus the smoothness of the baseline distribution. Nearly all sites have constraints on where antennas can be placed - even at the remote Australian location of the Murchison Widefield Array (MWA) there are rock outcrops, flood zones, heritages areas, emergency runways and trees. These exclusion areas can introduce spatial structure into the baseline distribution that enhances the PSF sidelobes and reduces the angular dynamic range. In this paper we present a new method of constrained antenna placement that reduces the spatial structure in the baseline distribution. This method not only outperforms random placement algorithms that avoid exclusion zones, but surprisingly outperforms random placement algorithms without constraints to provide what we believe are the smoothest constrained baseline distributions developed to date. We use our new algorithm to determine antenna placements for the originally planned MWA, and present the antenna locations, baseline distribution and snapshot PSF for this array choice., U.S. National Science Foundation (grants AST CAREER-0847753, AST-0457585, AST-0908884 and PHY-0835713), Australian Research Council (grants LE0775621 and LE0882938), U.S. Air Force Office of Scientific Research (grant FA9550-0510247)

Published
2012

3. WSClean: Widefield interferometric imager

Author

Offringa, A. R., Mckinley, B., Hurley-Walker, N., Briggs, F. H., Wayth, R. B., Kaplan, D. L., Bell, M. E., Feng, L., Neben, A. R., Hughes, J. D., Rhee, J., Murphy, T., Bhat, N. D. R., Bernardi, G., Bowman, J. D., Cappallo, R. J., Corey, B. E., Deshpande, A. A., Emrich, D., Ewall-Wice, A., Gaensler, B. M., Goeke, R., Greenhill, L. J., Hazelton, B. J., Hindson, L., Johnston-Hollitt, M., Jacobs, D. C., Justin Kasper, Kratzenberg, E., Lenc, E., Lonsdale, C. J., Lynch, M. J., Mcwhirter, S. R., Mitchell, D. A., Morales, M. F., Morgan, E., Kudryavtseva, N., Oberoi, D., Ord, S. M., Pindor, B., Procopio, P., Prabu, T., Riding, J., Roshi, D. A., Shankar, N. Udaya, Srivani, K. S., Subrahmanyan, R., Tingay, S. J., Waterson, M., Webster, R. L., Whitney, A. R., Williams, A., and Williams, C. L.

5. The murchison widefield array

Author

Mitchell, D. A., Greenhill, L. J., Ord, S. M., Bernardi, G., Wayth, R. B., Edgar, R. G., Clark, M. A., Dale, K., Hanspeter Pfister, Gleadow, S. J., Arcus, W., Briggs, F. H., Benkevitch, L., Bowman, J. D., Bunton, J. D., Burns, S., Cappallo, R. J., Corey, B. E., Oliveira-Costa, A., Desouza, L., Doeleman, S. S., Derome, M. F., Emrich, D., Glossop, M., Goeke, R., Krishna, M. R. G., Hazelton, B., Herne, D. E., Hewitt, J. N., Kamini, P. A., Kaplan, D. L., Kasper, J. C., Kincaid, B. B., Kocz, J., Kowald, E., Kratzenberg, E., Kumar, D., Lonsdale, C. J., Lynch, M. J., Madhavi, S., Matejek, M., Mcwhirter, S. R., Morales, M. F., Morgan, E., Oberoi, D., Pathikulangara, J., Prabu, T., Rogers, A., Salah, J. E., Sault, R. J., Shankar, N. U., Srivani, K. S., Stevens, J., Tingay, S. J., Vaccarella, A., Waterson, M., Webster, R. L., Whitney, A. R., Williams, A., and Williams, C.

Subjects
Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics - Instrumentation and Methods for Astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM)
Abstract

It is shown that the excellent Murchison Radio-astronomy Observatory site allows the Murchison Widefield Array to employ a simple RFI blanking scheme and still calibrate visibilities and form images in the FM radio band. The techniques described are running autonomously in our calibration and imaging software, which is currently being used to process an FM-band survey of the entire southern sky., Accepted for publication in Proceedings of Science [PoS(RFI2010)016]. 6 pages and 3 figures. Presented at RFI2010, the Third Workshop on RFI Mitigation in Radio Astronomy, 29-31 March 2010, Groningen, The Netherlands

8. Observing the Sun with the Murchison Widefield Array

Author

Oberoi, D., Sharma, R., Bhatnagar, S., Lonsdale, C. J., Matthews, L. D., Cairns, I. H., Tingay, S. J., Benkevitch, L., Donea, A., White, S. M., Bernardi, G., Bowman, J. D., Briggs, F., Cappallo, R. J., Corey, B. E., Deshpande, A., David Emrich, Gaensler, B. M., Goeke, R., Greenhill, L. J., Hazelton, B. J., Johnston-Hollitt, M., Kaplan, D. L., Kasper, J. C., Kratzenberg, E., Lynch, M. J., Mcwhirter, S. R., Mitchell, D. A., Morales, M. F., Morgan, E., Offringa, A. R., Ord, S. M., Prabu, T., Rogers, A. E. E., Roshi, A., Salah, J. E., Shankar, N. Udaya, Srivani, K. S., Subrahmanyan, R., Waterson, M., Wayth, R. B., Webster, R. L., Whitney, A. R., William, A., Williams, C. L., and IEEE

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