Sgr A* at 22 GHz around the G2 peri-center passing with Japanese VLBI Network
M. Tsuboi, Y. Asaki (ISAS/JAXA), Y. Yonekura, Y. Miyamoto (Ibaraki Univ.), H. Kaneko, M. Seta, N. Nakai (Univ. of Tsukuba), O. Kameya, M. Miyoshi (NAOJ), H. Takaba, K. Wakamatsu (Gifu Univ.), Y. Fukuzaki (GSI), K. Uehara (Univ. of Tokyo), and M. Sekido (NICT)
We have been monitoring Sgr A* at 22 GHz since Feb. 2013 with a sub-array of Japanese VLBI Network (JVN) (ATEL#4923, #5013) in order to explore the flux density variability with the G2 cloud approaching (Gillessen et al. 2012). The data before 2014/76 had been reported in ATEL #5184 and #6004. Here, we present the (preliminary) result during the period from 2014/77 to 2014/108. The sub-array consists of Mizusawa 10-m RT, Takahagi /Hitachi 32-m RT, and Gifu 11-m RT. Tsukuba 32-m RT and Kashima 34-m RT have joined it sometimes. Because the sub-array has projected baselines of 90- 140 km, we can observe the flux density of Sgr A* itself avoiding the contamination from extended structure surrounding Sgr A* and the flux density decrease by partially resolved-out. The average flux density in DOY= 2014/77-2014/108(11) is S\nu= 1.23+/- 0.28 Jy. The number in the parenthesis is number of observation epochs in the observation period. The error shows the scattering range (r.m.s.) of the observed flux densities. The average and scattering range are consistent with the previously observed values. We have observed no strong flare of Sgr A* although it is around the expected peri-center passing (Gillessen et al. 2013, Phifer et al. 2013).
radio,agn,black hole,transient