Brightening of Sgr A* at 32 GHz from VLA observations

ATel #5014; A. Brunthaler (MPIfR), H. Falcke (Nijmegen/ASTRON), G. C. Bower (UC Berkley), J. Ott (NRAO), M. J. Reid (CfA)
on 26 Apr 2013; 16:53 UT
Credential Certification: Andreas Brunthaler (brunthal@mpifr-bonn.mpg.de)

Tweet

We report Jansky Very Large Array observations that were taken on April 26, 2013 between 10:15:24 and 12:14:53 UT. The observations were part of the NRAO monitoring of the Galactic Center/G2 Cloud Encounter service observation. Recently an extended X-ray flare has been reported (ATel #5006, #5008, #5011). Here we report on the VLA Ka-Band (31-33 GHz) observations. After a preliminary data reduction, using the NRAO CASA pipeline, we find a peak flux density at the position of Sgr A* of 1.5 +/- 0.1 Jy. The resolution of the observations was 5" x 2" at a position angle of -172 deg. Apart from Sgr A West and Sgr A* no obvious other bright source >50 mJy (5 sigma) is seen in a field of 3 arcmin diameter centered on Sgr A*. However, the diffuse flux in the extended structure of Sgr A West can be up to 0.32 Jy. The last flux measurement in the series of service observing was on March 23, 2013, where Sgr A* had a flux of 1.179 +/- 0.002 Jy (plus an additional 10% absolute flux density uncertainty). During the 3.3 year weekly monitoring of Sgr A* (2001-2003, Herrnstein et al. 2004, AJ 127, 3399) the average flux of Sgr A* was 0.926 +/- 0.16 Jy and 1.001 +/- 0.21 at 22 and 43 GHz respectively, where the error is the one sigma variation of the lightcurve around the mean. The maximum fluxes were 1.64 +/- 0.1 and 1.87 +/- 0.16 Jy at these frequencies. For an average spectral index of 0.2 this would correspond to an average flux of 0.99 Jy and a maximum of 1.75 Jy at 32 GHz. Hence we conclude that Sgr A* is presently in an unusual high state close to but not yet exceeding its all-time high level as also indicated in ATel #5013. More information about the NRAO service observations can be found here: https://science.nrao.edu/science/service-observing