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Limits on Radio Frequency Flux Density Changes in Sgr A*

ATel #5025; Geoffrey C. Bower (UC Berkeley), Andreas Brunthaler (MPIfR), Heino Falcke (ASTRON, Nijmegen)
on 27 Apr 2013; 23:10 UT
Credential Certification: Geoffrey C Bower (gbower@astro.berkeley.edu)

Subjects: Radio, AGN, Black Hole, Soft Gamma-ray Repeater, Transient

Referred to by ATel #: 5159

We report new limits on changes low frequency emission for Sgr A* based on Jansky VLA observations obtained on 2013 April 26. Data were obtained through the NRAO Service Observing program (https://science.nrao.edu/science/service-observing/service-observing). The JVLA is currently in the compact D-configuration, providing low resolution observations in which Sgr A* is heavily confused by diffuse structure associated with Sgr A West and East. Resolution at 1 GHz is ~>1 arcminute. We use a visibility differencing technique between recent D-configuration observations that provides improved limits on any point source structures in the field. This uses the subset of visibilities that fall in the same (u,v) cells between observations in two separate epochs. We measure flux density differences relative to the 2013 March 23 observations: 1459.7 GHz -0.05 +/- 0.42 Jy 2979.4 GHz -0.03 +/- 0.32 Jy 5436.0 GHz 0.07 +/- 0.21 Jy 8936.0 GHz 0.02 +/- 0.07 Jy Frequencies are the main for each of the spectral windows associated with L, S, C, and X band observations. A spectrum is available at http://astro.berkeley.edu/~gbower/fluxdifference_130426-130323.png Similar differences are obtained for the comparison with 2013 February 18 observations. These results are consistent with upper limits or small changes in flux density found in higher frequency observations (ATeL #5013, #5014, #5018, #5024). These results indicate no detectable radio emission in Sgr A* associated with an SGR (ATeL #5006, #5020) or with shocked emission driven by the G2 cloud.