Hard X-ray morphological and spectral studies of the galactic center molecular cloud SGR B2: Constraining past SGR A{sup ⋆} flaring activity

Journal Article · Sun Dec 20 04:00:00 EST 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/815/2/132· OSTI ID:22882331

Zhang, Shuo; Hailey, Charles J.; Mori, Kaya; Nynka, Melania ^[1]; Clavel, Maïca; Goldwurm, Andrea ^[2]; Terrier, Régis; Soldi, Simona ^[3]; Ponti, Gabriele ^[4]; Bauer, Franz E. ^[5]; Boggs, Steven E.; Craig, William W.; Tomsick, John A. ^[6]; Christensen, Finn E. ^[7]; Harrison, Fiona A. ^[8]; Hong, Jaesub ^[9]; Stern, Daniel ^[10]

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1. Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States)
2. Service d’Astrophysique/IRFU/DSM, CEA Saclay, F-91191 Gif-sur-Yvette Cedex (France)
3. Unité mixte de recherche Astroparticule et Cosmologie, 10 rue Alice Domon et Léonie Duquet, F-75205 Paris (France)
4. Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, D-85748, Garching bei München (Germany)
5. Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, 306, Santiago 22 (Chile)
6. Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)
7. DTU Space—National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby (Denmark)
8. Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)
9. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
10. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

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{sup ⋆}. 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{sup ⋆} outburst is constrained to L{sub 3−79keV}∼5×10{sup 38} erg s{sup −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{sup ⋆} 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{sup 39} erg s{sup −1} and a CR ionization rate of ζ{sub H}=(6−10)×10{sup −15} H{sup −1} s{sup −1}. These measurements can become powerful tools to constrain the GC CR population.

• OSTI ID: 22882331
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 815; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United Kingdom
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COSMIC GASES
COSMIC RADIATION
EMISSION
GALAXIES
GALAXY NUCLEI
HARD X RADIATION
IONIZATION
LUMINOSITY
NEBULAE
PROTONS
REFLECTION
SPECTRA
STELLAR FLARES
TIME RESOLUTION