Kavli Affiliate: Luis C. Ho
| First 5 Authors: Jeremiah D. Paul, Richard M. Plotkin, W. N. Brandt, Christopher H. Ellis, Elena Gallo
| Summary:
The supermassive black holes ($M_{rm BH} sim 10^{6}$$-$$10^{10}~M_odot$)
that power luminous active galactic nuclei (AGNs), i.e., quasars, generally
show a correlation between thermal disk emission in the ultraviolet (UV) and
coronal emission in hard X-rays. In contrast, some "massive" black holes (mBHs;
$M_{rm BH} sim 10^{5}$$-$$10^{6}~M_odot$) in low-mass galaxies present
curious X-ray properties with coronal radiative output up to 100$times$ weaker
than expected. To examine this issue, we present new and archival 10 GHz Very
Large Array observations of a sample of high-accretion-rate (Eddington ratios
$L_{rm bol}/L_{rm Edd} > 0.1$), mBH-powered AGNs with Chandra X-ray coverage.
Empirical correlations previously revealed in samples of radio-quiet,
high-Eddington AGNs indicate that the radio$-$X-ray luminosity ratio, $L_{rm
R}/L_{rm X}$, is approximately constant. Through multiwavelength analysis, we
instead find that the X-ray-weaker mBHs in our sample tend toward larger values
of $L_{rm R}/L_{rm X}$ even though they remain radio-quiet per their
optical$-$UV properties. This trend results in a tentative but highly
intriguing correlation between $L_{rm R}/L_{rm X}$ and X-ray weakness, which
we argue is consistent with a scenario in which X-rays may be preferentially
obscured from our line of sight by a "slim" accretion disk. We compare this
observation to weak emission-line quasars (AGNs with exceptionally weak
broad-line emission and a significant X-ray-weak fraction) and conclude by
suggesting that our results may offer a new observational signature for finding
high-accretion-rate AGNs.
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