Deep Chandra Observations of the Compact Starburst Galaxy Henize 2-10:
  X-rays from the Massive Black Hole
  We present follow-up X-ray observations of the candidate massive black hole
(BH) in the nucleus of the low-mass, compact starburst galaxy Henize 2-10.
Using new high-resolution observations from the Chandra X-ray Observatory
totaling 200 ks in duration, as well as archival Chandra observations from
2001, we demonstrate the presence of a previously unidentified X-ray point
source that is spatially coincident with the known nuclear radio source in
Henize 2-10 (i.e., the massive BH). We show that the hard X-ray emission
previously identified in the 2001 observation is dominated by a source that is
distinct from the nucleus, with the properties expected for a high-mass X-ray
binary. The X-ray luminosity of the nuclear source suggests the massive BH is
radiating significantly below its Eddington limit (~10^-6 L_Edd), and the soft
spectrum resembles other weakly accreting massive BHs including Sagittarius A*.
Analysis of the X-ray light curve of the nucleus reveals the tentative
detection of a ~9-hour periodicity, although additional observations are
required to confirm this result. Our study highlights the need for sensitive
high-resolution X-ray observations to probe low-level accretion, which is the
dominant mode of BH activity throughout the Universe.
