Variable Hard-X-Ray Emission from the Candidate Accreting Black Hole in Dwarf Galaxy Henize 2-10

Whalen, T.J.; Hickox, R.C.; Reines, A.E.; Greene, J.E.; Sivakoff, G.R.; Johnson, K.E.; Alexander, D.M.; Goulding, A.D.

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 ~106 ${{M}_{\odot }}$. 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.

Citation

Whalen, T., Hickox, R., Reines, A., Greene, J., Sivakoff, G., Johnson, K., …Goulding, A. (2015). Variable Hard-X-Ray Emission from the Candidate Accreting Black Hole in Dwarf Galaxy Henize 2-10. Astrophysical Journal, 806(1), Article 37. https://doi.org/10.1088/0004-637x/806/1/37

• Journal Article Type: Article
• Online Publication Date: Jun 5, 2015
• Publication Date: Jun 5, 2015
• Deposit Date: May 31, 2016
• Publicly Available Date: Jul 15, 2016
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 806
• Issue: 1
• Article Number: 37
• DOI: https://doi.org/10.1088/0004-637x/806/1/37
• Public URL: https://durham-repository.worktribe.com/output/1403368
• Related Public URLs: http://adsabs.harvard.edu/abs/2015ApJ...806...37W