Kavli Affiliate: John D. Silverman
| First 5 Authors: Jia-Lai Kang, Chris Done, Scott Hagen, Mai Liao, Matthew J. Temple
| Summary:
Accretion flows in both stellar and supermassive black holes show a distinct
spectral transition. This is seen directly in binaries and changing look AGN,
and also in a recent sample of eROSITA X-ray selected, unobscured AGN where the
stacked spectral energy distributions (SEDs) for a single black hole mass bin
(log $M/M_{odot} =8-8.5$) clearly show the UV bright disk appearing as the
luminosity increases. In binaries, this transition is associated with a change
in radio jet, from coupling to the X-ray hot flow with $L_R propto L_X^{0.7}$
(Fundamental Plane relation), to collapsing when the X-ray hot flow collapses
into a disc. We explore the radio behaviour across the transition in our AGN
sample by stacking VLASS images. We significantly detect weak radio emission
even after subtracting the contribution from star formation in the host galaxy.
The residual radio emission remains relatively constant across the transition,
despite the mean mass accretion rate changing by a factor 6 and UV flux
changing by a factor 100. However, the X-rays change by only a factor 2, giving
a constant radio to X-ray flux ratio as predicted by the ‘fundamental plane’.
We show that this is consistent with these AGN having the same compact radio
jet coupling to the X-ray hot flow (not the disc) as in the binaries. The most
significant difference is the persistence of the coronal X-rays across the
spectral transition in AGN, whereas in binaries the coronal X-rays can be very
weak in the disc dominated state.
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