Making cosmic movies with the Murchison Widefield Array
While telescopes have been capable of capturing a single “picture” of the sky for quite some time, the high demand for the use of world-class facilities and historically limited fields of view on offer meant that repeat observations of the same areas of sky were sparse. Next-generation widefield instruments, such as the Murchison Widefield Array (MWA), break down this paradigm and achieve many repeat observations of the same piece of sky with less competition. By taking multiple images of the sky, they can effectively make cosmic movies of the Universe. Each single image (equivalent to the frames of a movie) captures time-domain information about that region of the sky and allows for the detection of new types of objects that might only be observable for a short time, for example explosions.
In a new study by CAASTRO researchers and colleagues of the international MWA consortium, observations were obtained from the (by now decommissioned) MWA 32-tile prototype telescope (MWA-32T) at 154 MHz. Operating at such low radio frequencies (80 to 300 MHz), the Southern hemisphere sky is poorly explored in the image domain, and therefore offers discovery of sources and subsequent physical processes potentially unique in this regime.
The researchers’ recent publication (Monthly Notices of the Royal Astronomical Society) explored the variability of a sample of 105 low frequency radio sources within the MWA-32T’s field of view. Fifty-one images were obtained in 2010 and 2011 that covered a field of view of 1430 deg2 centred on the bright radio galaxy Hydra A (click to watch the movie). They identified four bright candidate variable radio sources that displayed low levels of short timescale variability (26 minutes), likely caused by simplifications in the calibration strategy or ionospheric effects. On the timescale of one year though, two sources showed significant variability, attributed to either refractive scintillation or intrinsic variability. No radio transients were found, but the team could place upper limits on the occurrence of such sources. Surveys are currently underway with the 128-tile MWA system to probe this dynamic parameter space further.
by M. Bell
M. E. Bell, T. Murphy, D. L. Kaplan, P. Hancock, B. M. Gaensler, J. Banyer, K. Bannister, C. Trott, N. Hurley-Walker, R. B. Wayth, J. -P. Macquart, W. Arcus, D. Barnes, G. Bernardi, J. D. Bowman, F. Briggs, J. D. Bunton, R. J. Cappallo, B. E. Corey, A. Deshpande, L. deSouza, D. Emrich, R. Goeke, L. J. Greenhill, B. J. Hazelton, D. Herne, J. N. Hewitt, M. Johnston-Hollitt, J. C. Kasper, B. B. Kincaid, R. Koenig, E. Kratzenberg, C. J. Lonsdale, M. J. Lynch, S. R. McWhirter, D. A. Mitchell, M. F. Morales, E. Morgan, D. Oberoi, S. M. Ord, J. Pathikulangara, T. Prabu, R. A. Remillard, A. E. E. Rogers, A. Roshi, J. E. Salah, R. J. Sault, N. Udaya Shankar, K. S. Srivani, J. Stevens, R. Subrahmanyan, S. J. Tingay, M. Waterson, R. L. Webster, A. R. Whitney, A. Williams, C. L. Williams, J. S. B. Wyithe in MNRAS (2013) “A survey for transients and variables with the Murchison Widefield Array 32-tile prototype at 154 MHz”