Chandra-HETGS Observations of the Brightest Flare Seen from Sgr A*. (arXiv:1209.6354v1 [astro-ph.HE])

Chandra-HETGS Observations of the Brightest Flare Seen from Sgr A*. (arXiv:1209.6354v1 [astro-ph.HE]):
Starting in 2012, we began an unprecedented observational program focused on
the supermassive black hole in the center of our Galaxy, Sgr A*, utilizing the
High Energy Transmission Gratings Spectrometer (HETGS) instrument on the
Chandra X-ray Observatory. These observations will allow us to measure the
quiescent X-ray spectra of Sgr A* for the first time at both high spatial and
spectral resolution. The X-ray emission of Sgr A*, 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 100 times quiescence.
Here were report an observation performed on 2012 February 9 wherein we
detected what is the highest peak flux and fluence flare ever observed from Sgr
A*. The flare, which lasted for 5.6 ks and had a decidedly asymmetric profile
with a faster decline than rise, achieved a mean absorbed 2-8 keV flux of
(8.5+/-0.9)X10^{-12} erg cm^{-2} s^{-1}. The peak flux was 2.5 times higher,
and the total 2-10 keV emission of the event was approximately 10^{39} erg.
Only one other flare of comparable magnitude, but shorter duration, has been
observed in Sgr A* 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 (Gamma~2) and X-ray absorbing columns (N_H~15X10^{22} cm^{-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 Sgr A* flares. We also discuss fits to
the quiescent spectra of Sgr A*.