NuSTAR Observation of Galactic Center Molecular Clouds: Reconstructing Sgr A* X-ray Outburst History
Abstract
The Galactic Center (GC) supermassive black hole Sgr A* radiates at a level about 9 orders of magnitude lower than its Eddington luminosity. But indication of its glorious past has come from X-ray observations of surrounding molecular clouds. Their varying neutral iron lines and continuum emission could be due to reflection of Sgr A* X-ray outbursts in the past few centuries. However, such observational facts can also be explained by low energy cosmic ray electron (LECRe) bombardment. In this talk, I present the NuSTAR observations of the GC molecular clouds. Their substructures at energies greater than 10 keV are revealed for the first time. We applied physical models of X-ray reflection and LECRe to the broadband X-ray spectra. Results show that the X-ray reflection model is preferred over the LECRe model for all the clouds. The X-ray emission from cloud Sgr B2 points to a faraway illuminating source with photon index of 2 and a luminosity of ~1039 erg s-1, most likely due to a past giant X-ray outburst from Sgr A*. The Sgr A clouds requires a fainter and more recent X-ray outburst, revealing different stages of the Sgr A* X-ray outbursts.
- Publication:
-
IAU General Assembly
- Pub Date:
- August 2015
- Bibcode:
- 2015IAUGA..2255913Z