A Study Of The X-ray Emission From The Galactic Center

X-ray observations of the Galactic Center(GC),in particular those afforded by the Chandra X-ray Observatory,provide a unique way to trace stellar populations and study high-energy activities in the GC.The investigation of the GC X-ray emission is com-posed of two parts:i)We present an updated catalog of X-ray point sources in the inner 500."(～20 pc)of the GC,where the nuclear star cluster(NSC)stands,based on a total of 4.5 Ms of Chandra observations taken from 1999 September to 2013 April.A total of 3619 sources are detected in the 2-8 keV band,among which～3500 are probable GC sources and～1300 are new identifications.We explore their global source proper-ties,including long-term variability,cumulative spectra,luminosity function,and spa-tial distribution.Based on the equivalent width and relative strength of the iron lines,we suggest that in addition to the arguably predominant population of magnetic cat-aclysmic variables(CVs),non-magnetic CVs contribute substantially to the detected sources,especially in the lower-luminosity group.ii)We have investigated the linear X-ray filament,G359.944-0.052,previously identified as a likely X-ray counterpart of a parsec-scale jet from the Galactic Center super-massive black hole(SMBH),Sagittar-ius A*(Sgr A*),using a total of～5.6 Ms ultra-deep Chandra observations taken from September 1999 to July 2017.We find no flux or spectral variation in G359.944-0.052 after the G2 periapsis passage around early 2014,however,a moderate flux increase of～2σ significance might be associated with the periapsis passage of G1 in early 2001.The filament exhibits an unusually hard spectrum(photon-index ≤1)in its portion clos-est to Sgr A*(i.e.,n ear-side)and a significant spectral softening in the more distant portion,which can be interpreted as synchrotron cooling of the relativistic electrons moving along the jet path.In particular,the hard spectrum of the near-side suggests a piling up of quasi-monoenergetic electrons caused by rapid radiative cooling.The spectral and temporal properties of G359.944-0.052 strengthen the case of it being the X-ray counterpart of a jet launched by Sgr A*.