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Hard X-ray Morphological and Spectral Studies of The Galactic Center Molecular Cloud Sgr B2: Constraining Past Sgr A* Flaring Activity

Zhang, Shuo and Hailey, Charles J. and Mori, Kaya and Clavel, Maïca and Terrier, Régis and Ponti, Gabriele and Goldwurm, Andrea and Bauer, Franz E. and Boggs, Steven E. and Craig, William W. and Christensen, Finn E. and Harrison, Fiona A. and Hong, Jaesub and Nynka, Melania and Stern, Daniel and Soldi, Simona and Tomsick, John A. and Zhang, William W. (2015) Hard X-ray Morphological and Spectral Studies of The Galactic Center Molecular Cloud Sgr B2: Constraining Past Sgr A* Flaring Activity. Astrophysical Journal, 815 (2). Art. No. 132. ISSN 0004-637X. doi:10.1088/0004-637X/815/2/132.

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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^*. 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^* outburst is constrained to L_(3-79keV) ~ 5 x 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^* 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) x 10^(39) erg s^(-1) and a CR ionization rate of ζ_H =(6-10) x 10^(-15) H^(-1) s^(-1. These measurements can become powerful tools to constrain the GC CR population.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Zhang, Shuo0000-0002-2967-790X
Mori, Kaya0000-0002-9709-5389
Clavel, Maïca0000-0003-0724-2742
Ponti, Gabriele0000-0003-0293-3608
Bauer, Franz E.0000-0002-8686-8737
Boggs, Steven E.0000-0001-9567-4224
Christensen, Finn E.0000-0001-5679-1946
Harrison, Fiona A.0000-0003-2992-8024
Nynka, Melania0000-0002-3310-1946
Stern, Daniel0000-0003-2686-9241
Tomsick, John A.0000-0001-5506-9855
Zhang, William W.0000-0002-1426-9698
Additional Information:© 2015. The American Astronomical Society. Received 2015 July 24; accepted 2015 November 7; published 2015 December 21. 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.
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
NASA Earth and Space Science FellowshipNNX13AM31
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)UNSPECIFIED
Marie Curie FellowshipFP-PEOPLE-2012- IEF-331095
Bundesministerium für Wirtschaft und Technologie (BMWi)BMWI/DLR, FKZ 50 OR 1408
Deutsches Zentrum für Luft- und Raumfahrt (DLR)UNSPECIFIED
Max Planck SocietyUNSPECIFIED
Centre National d'Études Spatiales (CNES)UNSPECIFIED
Subject Keywords:Galaxy: center; ISM: clouds; X-rays: individual (Sgr B2) ; X-rays: ISM
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2015-14
Issue or Number:2
Record Number:CaltechAUTHORS:20150818-085908117
Persistent URL:
Official Citation:Shuo Zhang et al 2015 ApJ 815 132
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59675
Deposited By: Joy Painter
Deposited On:19 Aug 2015 17:32
Last Modified:10 Nov 2021 22:23

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