SPATIALLY RESOLVING A STARBURST GALAXY AT HARD X-RAY ENERGIES: NuSTAR, CHANDRA, AND VLBA OBSERVATIONS OF NGC 253

Journal Article · Sat Dec 20 00:00:00 EST 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/797/2/79· OSTI ID:22364866

Wik, D. R.; Lehmer, B. D.; Hornschemeier, A. E.; Yukita, M.; Ptak, A.; Venters, T.; Zhang, W. W. ^[1]; Zezas, A. ^[2]; Antoniou, V. ^[3]; Argo, M. K. ^[4]; Bechtol, K. ^[5]; Boggs, S.; Craig, W.; Krivonos, R. ^[6]; Christensen, F. ^[7]; Hailey, C. ^[8]; Harrison, F. ^[9]; Maccarone, T. J. ^[10]; Stern, D. ^[11]

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1. NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771 (United States)
2. Physics Department, University of Crete, Heraklion (Greece)
3. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
4. ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, 7990-AA Dwingeloo (Netherlands)
5. Kavli Institute for Cosmological Physics, Chicago, IL 60637 (United States)
6. U.C. Berkeley Space Sciences Laboratory, Berkeley, CA (United States)
7. National Space Institute, Technical University of Denmark, DK-2100 Copenhagen (Denmark)
8. Columbia University, New York, NY (United States)
9. Caltech Division of Physics, Mathematics and Astronomy, Pasadena, CA (United States)
10. Department of Physics, Texas Tech University, Lubbock, TX 79409 (United States)
11. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

Prior to the launch of NuSTAR, it was not feasible to spatially resolve the hard (E > 10 keV) emission from galaxies beyond the Local Group. The combined NuSTAR data set, comprised of three ∼165 ks observations, allows spatial characterization of the hard X-ray emission in the galaxy NGC 253 for the first time. As a follow up to our initial study of its nuclear region, we present the first results concerning the full galaxy from simultaneous NuSTAR, Chandra, and Very Long Baseline Array monitoring of the local starburst galaxy NGC 253. Above ∼10 keV, nearly all the emission is concentrated within 100'' of the galactic center, produced almost exclusively by three nuclear sources, an off-nuclear ultraluminous X-ray source (ULX), and a pulsar candidate that we identify for the first time in these observations. We detect 21 distinct sources in energy bands up to 25 keV, mostly consisting of intermediate state black hole X-ray binaries. The global X-ray emission of the galaxy—dominated by the off-nuclear ULX and nuclear sources, which are also likely ULXs—falls steeply (photon index ≳ 3) above 10 keV, consistent with other NuSTAR-observed ULXs, and no significant excess above the background is detected at E > 40 keV. We report upper limits on diffuse inverse Compton emission for a range of spatial models. For the most extended morphologies considered, these hard X-ray constraints disfavor a dominant inverse Compton component to explain the γ-ray emission detected with Fermi and H.E.S.S. If NGC 253 is typical of starburst galaxies at higher redshift, their contribution to the E > 10 keV cosmic X-ray background is <1%.

• OSTI ID: 22364866
• Journal Information: Astrophysical Journal, Vol. 797, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
BLACK HOLES
COSMIC PHOTONS
COSMIC X-RAY SOURCES
HARD X RADIATION
INTERMEDIATE STATE
KEV RANGE
LIMITING VALUES
MORPHOLOGY
PULSARS
RED SHIFT
STAR CLUSTERS
STARS
X-RAY GALAXIES