Chandra/HETGS observations of the brightest flare seen from SgrA*

Abstract

Starting in 2012, we began an unprecedented observational program focused on the supermassive black hole in the center of our Galaxy, SgrA*, utilizing the High Energy Transmission Grating Spectrometer (HETGS) instrument on the Chandra X-Ray Observatory. These observations will allow us to measure the quiescent X-ray spectra of SgrA* for the first time at both high spatial and spectral resolution. The X-ray emission of SgrA*, however, is known to flare roughly daily by factors of a few to ten times over quiescent emission levels, with rarer flares extending to factors of greater than 100times quiescence. Here we report an observation performed on 2012 February 9 wherein we detected what are the highest peak flux and fluence flare ever observed from SgrA*. The flare, which lasted for 5.6ks and had a decidedly asymmetric profile with a faster decline than rise, achieved a mean absorbed 2-8keV flux of (8.5 ± 0.9) × 10-12 erg cm-2 s-1. The peak flux was 2.5times higher, and the total 2-10keV emission of the event was approximately 1039erg. Only one other flare of comparable magnitude, but shorter duration, has been observed in SgrA* by XMM-Newton in 2002 October. We perform spectral fits of this Chandra-observed flare and compare our results to the two brightest flares ever observed with XMM-Newton. We find good agreement among the fitted spectral slopes (Γ ∼ 2) and X-ray absorbing columns (N H ∼ 15 × 1022cm -2) for all three of these events, resolving prior differences (which are most likely due to the combined effects of pileup and spectral modeling) among Chandra and XMM-Newton observations of SgrA* flares. We also discuss fits to the quiescent spectra of SgrA*. © 2012. The American Astronomical Society. All rights reserved.