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Author(s): Whalen, Thomas J; Hickox, Ryan C; Reines, Amy E; Greene, Jenny E.; Sivakoff, Gregory R; et al

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Abstract: We present an analysis of the X-ray spectrum and long-term variability of the nearby dwarf starburst galaxy Henize 2-10. Recent observations suggest that this galaxy hosts an actively accreting black hole (BH) with mass. similar to 10(6) M-circle dot. The presence of an active galactic nucleus (AGN) in a low-mass starburst galaxy marks a new environment for AGNs, with implications for the processes by which “seed” BHs may form in the early universe. In this paper, we analyze four epochs of X-ray observations of Henize 2-10, to characterize the long-term behavior of its hard nuclear emission. We analyze observations with Chandra from 2001 and XMM-Newton from 2004 and 2011, as well as an earlier, less sensitive observation with ASCA from 1997. Based on a detailed analysis of the source and background, we find that the hard (2-10 keV) flux of the putative AGN has decreased by approximately an order of magnitude between the 2001 Chandra observation and exposures with XMM-Newton in 2004 and 2011. The observed variability confirms that the emission is due to a single source. It is unlikely that the variable flux is due to a supernova or ultraluminous X-ray source, based on the observed long-term behavior of the X-ray and radio emission, while the observed X-ray variability is consistent with the behavior of well-studied AGNs.
Publication Date: 10-Jun-2015
Electronic Publication Date: 5-Jun-2015
Citation: Whalen, Thomas J, Hickox, Ryan C, Reines, Amy E, Greene, Jenny E, Sivakoff, Gregory R, Johnson, Kelsey E, Alexander, David M, Goulding, Andy D. (2015). VARIABLE HARD-X-RAY EMISSION FROM THE CANDIDATE ACCRETING BLACK HOLE IN DWARF GALAXY HENIZE 2-10. ASTROPHYSICAL JOURNAL, 806 (10.1088/0004-637X/806/1/37
DOI: doi:10.1088/0004-637X/806/1/37
ISSN: 0004-637X
EISSN: 1538-4357
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Type of Material: Journal Article
Journal/Proceeding Title: ASTROPHYSICAL JOURNAL
Version: Final published version. Article is made available in OAR by the publisher's permission or policy.

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