The Nature of the 10 kilosecond X-ray flare in Sgr A*

Abstract

The X-ray mission Chandra has observed a dramatic X-ray flare -- a brightening by a factor of 50 for only three hours -- from Sgr A*, the Galactic Center supermassive black hole. Sgr A* has never shown variability of this amplitude in the radio and we therefore argue that a jump of this order in the accretion rate does not seem the likely cause. Based on our model for jet-dominated emission in the quiescent state of Sgr A*, we suggest that the flare is a consequence of extra electron heating near the black hole. This can either lead to direct heating of thermal electrons to T_e~6*10^11 K and significantly increased synchrotron-self Compton emission, or result from non-thermal particle acceleration with increased synchrotron radiation and electron Lorentz factors up to gamma_e>10^5. While the former scenario is currently favored by the data, simultaneous VLBI, submm, mid-infrared and X-ray observations should ultimately be able to distinguish between the two cases.Comment: Astronomy & Astrophysics Letters, in press, 4 pages, 3 figures, also available at http://www.mpifr-bonn.mpg.de/staff/hfalcke/publications.html#sgrxvar, final version with minor modifications, clearer figur