Hard X-Ray Morphological and Spectral Studies of the Galactic Center Molecular Cloud Sgr B2: Constraining Past Sgr A* Flaring Activity
Journal
Date Issued
2015
Author(s)
Zhang, Shuo
•
Hailey, Charles J.
•
Mori, Kaya
•
Clavel, Maïca
•
Terrier, Régis
•
•
Goldwurm, Andrea
•
Bauer, Franz E.
•
Boggs, Steven E.
•
Christensen, Finn E.
•
Craig, William W.
•
Harrison, Fiona A.
•
Hong, Jaesub
•
Nynka, Melania
•
Soldi, Simona
•
Stern, Daniel
•
Tomsick, John A.
•
Zhang, William W.
Description
This work was supported under NASA Contract No. NNG08FD60C and made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by NASA. We thank the NuSTAR Operations, Software, and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). This research has also made use of data obtained with XMM-Newton , an ESA science mission with instruments and contribution directly funded by ESA Member States and NASA. S.Z. is supported by NASA Headquarters under the NASA Earth and Space Science Fellowship Program—Grant “NNX13AM31.” F.E.B. acknowledges support from CONICYT-Chile and the Ministry of Economy, Development, and Tourism’s Millennium Science Initiative. G.P. acknowledges support via an EU Marie Curie Intra European fellowship under contract no. FP-PEOPLE-2012-IEF-331095 and Bundesministerium für Wirtschaft und Technologie/Deutsches Zentrum für Luft-und Raumfahrt (BMWI/DLR, FKZ 50 OR 1408) and the Max Planck Society. M.C., A.G., R.T., and S.S. acknowledge support by CNES.
Abstract
In 2013, NuSTAR observed the Sgr B2 region and for the first time resolved its hard X-ray emission on subarcminute scales. Two prominent features are detected above 10 keV: a newly emerging cloud, G0.66-0.13, and the central 90″ radius region containing two compact cores, Sgr B2(M) and Sgr B2(N), surrounded by diffuse emission. It is inconclusive whether the remaining level of Sgr B2 emission is still decreasing or has reached a constant background level. A decreasing X-ray emission can be best explained by the X-ray reflection nebula scenario, where the cloud reprocesses a past giant outburst from Sgr A{}\star . In the X-ray reflection nebula (XRN) scenario, the 3-79 keV Sgr B2 spectrum allows us to self-consistently test the XRN model using both the Fe Kα line and the continuum emission. The peak luminosity of the past Sgr A{}\star outburst is constrained to {L}3-79{keV}̃ 5× {10}38 {erg} {{{s}}}-1. A newly discovered cloud feature, G0.66-0.13, shows different timing variability. We suggest that it could be a molecular clump located in the Sgr B2 envelope reflecting the same Sgr A{}\star outburst. In contrast, if the Sgr B2 X-ray emission has reached a constant background level, it would imply an origin of low-energy cosmic-ray (CR) proton bombardment. In this scenario, from the NuSTAR measurements we infer a CR ion power of {dW}/{dt}=(1-4)× {10}39 {erg} {{{s}}}-1 and a CR ionization rate of {\zeta }{{H}}=(6-10)× {10}-15 {{{H}}}-1\quad {{{s}}}-1. These measurements can become powerful tools to constrain the GC CR population.
Volume
815
Issue
2
Start page
132
Issn Identifier
0004-637X
Ads BibCode
2015ApJ...815..132Z
Rights
open.access
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