The Galactic Bulge Diffuse Emission in Broadband X-Rays with NuSTAR
The diffuse hard X-ray emission that fills the Galactic center, bulge, and ridge is believed to arise from unresolved populations of X-ray binary systems. However, the identity of the dominant class of accreting objects in each region remains unclear. Recent studies of Fe line properties and the low...
| Main Authors: | , , |
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| Other Authors: | |
| Format: | Article |
| Language: | English |
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American Astronomical Society
2020
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| Online Access: | https://hdl.handle.net/1721.1/128869 |
| _version_ | 1811097731895132160 |
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| author | Perez, Kerstin M. Krivonos, Roman Wik, Daniel R |
| author2 | Massachusetts Institute of Technology. Department of Physics |
| author_facet | Massachusetts Institute of Technology. Department of Physics Perez, Kerstin M. Krivonos, Roman Wik, Daniel R |
| author_sort | Perez, Kerstin M. |
| collection | MIT |
| description | The diffuse hard X-ray emission that fills the Galactic center, bulge, and ridge is believed to arise from unresolved populations of X-ray binary systems. However, the identity of the dominant class of accreting objects in each region remains unclear. Recent studies of Fe line properties and the low-energy (<10 keV) X-ray continuum of the bulge indicate a major population fraction of nonmagnetic cataclysmic variables (CVs), in particular quiescent dwarf novae (DNe). This is in contrast to previous high-energy (>10 keV) X-ray measurements of the bulge and ridge, which indicate a dominant population of magnetic CVs, in particular intermediate polars. In addition, NuSTAR broadband measurements have uncovered a much heavier intermediate polar population in the central ∼100 pc than previously assumed, raising the possibility that some fraction of this population extends further from the center. Here we use NuSTAR's large aperture for unfocused photons and its broadband X-ray range to probe the diffuse continuum of the inner ∼1°-3° of the Galactic bulge. This allows us to constrain possible multitemperature components of the spectrum, such as could indicate a mixture of soft and hard populations. Our emissivity is consistent with previous hard X-ray measurements in the bulge and ridge, with the diffuse X-ray luminosity tracing the stellar mass. The spectrum is well described by a singleerature thermal plasma with kT ≈ 8 keV, with no significant emission above 20 keV. This supports that the bulge is dominated by quiescent DNe; we find no evidence of a significant intermediate polar population in the hard X-ray band. ©2019. The American Astronomical Society. All rights reserved.. |
| first_indexed | 2024-09-23T17:04:02Z |
| format | Article |
| id | mit-1721.1/128869 |
| institution | Massachusetts Institute of Technology |
| language | English |
| last_indexed | 2024-09-23T17:04:02Z |
| publishDate | 2020 |
| publisher | American Astronomical Society |
| record_format | dspace |
| spelling | mit-1721.1/1288692022-09-29T23:28:32Z The Galactic Bulge Diffuse Emission in Broadband X-Rays with NuSTAR Perez, Kerstin M. Krivonos, Roman Wik, Daniel R Massachusetts Institute of Technology. Department of Physics The diffuse hard X-ray emission that fills the Galactic center, bulge, and ridge is believed to arise from unresolved populations of X-ray binary systems. However, the identity of the dominant class of accreting objects in each region remains unclear. Recent studies of Fe line properties and the low-energy (<10 keV) X-ray continuum of the bulge indicate a major population fraction of nonmagnetic cataclysmic variables (CVs), in particular quiescent dwarf novae (DNe). This is in contrast to previous high-energy (>10 keV) X-ray measurements of the bulge and ridge, which indicate a dominant population of magnetic CVs, in particular intermediate polars. In addition, NuSTAR broadband measurements have uncovered a much heavier intermediate polar population in the central ∼100 pc than previously assumed, raising the possibility that some fraction of this population extends further from the center. Here we use NuSTAR's large aperture for unfocused photons and its broadband X-ray range to probe the diffuse continuum of the inner ∼1°-3° of the Galactic bulge. This allows us to constrain possible multitemperature components of the spectrum, such as could indicate a mixture of soft and hard populations. Our emissivity is consistent with previous hard X-ray measurements in the bulge and ridge, with the diffuse X-ray luminosity tracing the stellar mass. The spectrum is well described by a singleerature thermal plasma with kT ≈ 8 keV, with no significant emission above 20 keV. This supports that the bulge is dominated by quiescent DNe; we find no evidence of a significant intermediate polar population in the hard X-ray band. ©2019. The American Astronomical Society. All rights reserved.. Russian Science Foundation (grant 19-12-00369) NASA Astrophysics Data Analysis grant (80NSSC18K0686) 2020-12-21T15:24:26Z 2020-12-21T15:24:26Z 2019-10 2019-09 2020-11-09T15:31:00Z Article http://purl.org/eprint/type/JournalArticle 1538-4357 https://hdl.handle.net/1721.1/128869 Perez, Kerstin et al., "The Galactic Bulge Diffuse Emission in Broadband X-Rays with NuSTAR." Astrophysical Journal 884, 2 (October 2019): 153 doi. 10.3847/1538-4357/ab4590 ©2019 Authors en https://dx.doi.org/10.3847/1538-4357/AB4590 Astrophysical Journal Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf American Astronomical Society The American Astronomical Society |
| spellingShingle | Perez, Kerstin M. Krivonos, Roman Wik, Daniel R The Galactic Bulge Diffuse Emission in Broadband X-Rays with NuSTAR |
| title | The Galactic Bulge Diffuse Emission in Broadband X-Rays with NuSTAR |
| title_full | The Galactic Bulge Diffuse Emission in Broadband X-Rays with NuSTAR |
| title_fullStr | The Galactic Bulge Diffuse Emission in Broadband X-Rays with NuSTAR |
| title_full_unstemmed | The Galactic Bulge Diffuse Emission in Broadband X-Rays with NuSTAR |
| title_short | The Galactic Bulge Diffuse Emission in Broadband X-Rays with NuSTAR |
| title_sort | galactic bulge diffuse emission in broadband x rays with nustar |
| url | https://hdl.handle.net/1721.1/128869 |
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