VARIABLE HARD-X-RAY EMISSION FROM THE CANDIDATE ACCRETING BLACK HOLE IN DWARF GALAXY HENIZE 2-10

• Published in: The Astrophysical journal 2015-06, Vol.806 (1), p.1-7
• Main Authors: Whalen, Thomas J., Hickox, Ryan C., Reines, Amy E., Greene, Jenny E., Sivakoff, Gregory R., Johnson, Kelsey E., Alexander, David M., Goulding, Andy D.
• Format: Article
• Language: English
• Subjects: Active galactic nuclei; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BLACK HOLES; Black holes (astronomy); Dwarf galaxies; EMISSION; Flux; GALACTIC EVOLUTION; galaxies: active; galaxies: dwarf; galaxies: evolution; galaxies: individual (Henize 2-10); GALAXY NUCLEI; HARD X RADIATION; MASS; Starburst galaxies; UNIVERSE; X-RAY GALAXIES; X-RAY SPECTRA; X-rays; X-rays: galaxies; XMM (spacecraft)
• ISSN: 0004-637X; 1538-4357; 1538-4357
• DOI: 10.1088/0004-637X/806/1/37

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 . 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.