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

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 with mass ~10^6 M_sun. The presence of an AGN in a low-mass starburst galaxy marks a new environment for active galactic nuclei (AGNs), with implications for the processes by which "seed" black holes 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 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.

7 pages, 4 figures, 2 tables; accepted for publication in ApJ

References in corpus (10)

• X-ray spectral properties of AGN in the Chandra Deep Field South
• An actively accreting massive black hole in the dwarf starburst galaxy Henize 2-10
• The aftermath of the first stars: massive black holes
• X-ray observations of ultraluminous X-ray sources
• The XMM-Newton EPIC Background and the production of Background Blank Sky Event Files
• A Revised Broad-Line Region Radius and Black Hole Mass for the Narrow-Line Seyfert 1 NGC 4051
• A Candidate Massive Black Hole in the Low-metallicity Dwarf Galaxy Pair Mrk 709
• X-ray emission from active galactic nuclei with intermediate mass black holes
• An Optically Obscured AGN in a Low Mass, Irregular Dwarf Galaxy: A Multi-Wavelength Analysis of J1329+3234
• A VLBI Search for Radio Supernovae in Wolf Rayet Galaxies

Cited by in corpus (5)

• Observational Signatures of High-Redshift Quasars and Local Relics of Black Hole Seeds
• Deep Chandra Observations of the Compact Starburst Galaxy Henize 2-10: X-rays from the Massive Black Hole
• Do Some AGN Lack X-ray Emission?
• Microlensing of gravitational waves by dark matter structures
• The Luminosity and Stellar Mass Functions of Red W1-W2 Galaxies