Early 2013 non-detection of sub-GHz emission from the passage of cloud G2 near Sgr A*

ATel #4922; N. E. Kassim (NRL), S. D. Hyman (SBC), H. Intema (NRAO), T. E. Clarke (NRL), R. Subrahmanyan (NRAO, RRI)
on 27 Mar 2013; 20:47 UT
Credential Certification: Scott Hyman (shyman@sbc.edu)

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We observed Sgr A* with the GMRT in late January and early February 2013 in search of enhanced meter-wavelength emission resulting from the interaction of the cloud G2 with the accretion disk of Sgr A* (Gillessen et al. 2012, Nature, 481, 51; Narayan et al. 2012, ApJ, 757, L20). Recent models suggest that the bow shock of G2 has already crossed pericenter and that peak radio synchrotron emission should occur in February or March 2013 (Sadowski et al. 2013, arXiv:1303.3893), about a half year sooner than predicted by earlier models. Detection at sub-GHz is favored but depends on the location and extent of the turnover due to synchrotron self-absorption. We detect Sgr A* on January 30 and February 8, 2013 with flux densities of 0.3 +- 0.1 Jy and 0.5 +- 0.2 Jy at 330 and 610 MHz, respectively. These values are consistent with the previously reported quiescent values (0.3 +- 0.1 at 330 MHz by Nord et al. 2004, AJ, 601, L51; 0.5 +- 0.1 Jy at 610 MHz by Roy & Rao 2004, MNRAS, 349, L25; and 0.22 +- 0.06 Jy at 330 MHz, 0.45 +- 0.10 Jy at 610 MHz by An et al. 2005, ApJ, 634, L49). While a small increase is possible, an enhancement of several Janskys or more as suggested by most models is not detected. We note that a few of the models presented in Sadowski et al. (2013) predict the peak radio emission to occur about the time of our observations (e.g., the co-rotating orbit model N0C and the zero ambient magnetic field model N0B) and therefore could be less favored than the ones predicting a peak in March 2013.