Discovery of soft and hard X-ray time lags in low-mass AGNs. (arXiv:2101.09594v2 [astro-ph.HE] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Mallick_L/0/1/0/all/0/1">Labani Mallick</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wilkins_D/0/1/0/all/0/1">Daniel R. Wilkins</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Alston_W/0/1/0/all/0/1">William N. Alston</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Markowitz_A/0/1/0/all/0/1">Alex Markowitz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Marco_B/0/1/0/all/0/1">Barbara De Marco</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Parker_M/0/1/0/all/0/1">Michael L. Parker</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lohfink_A/0/1/0/all/0/1">Anne M. Lohfink</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stalin_C/0/1/0/all/0/1">C. S. Stalin</a>
The scaling relations between the black hole (BH) mass and soft lag
properties for both active galactic nuclei (AGNs) and BH X-ray binaries
(BHXRBs) suggest the same underlying physical mechanism at work in accreting BH
systems spanning a broad range of mass. However, the low-mass end of AGNs has
never been explored in detail. In this work, we extend the existing scaling
relations to lower-mass AGNs, which serve as anchors between the normal-mass
AGNs and BHXRBs. For this purpose, we construct a sample of low-mass AGNs
($M_{rm BH}<3times 10^{6} M_{rm odot}$) from the XMM-Newton archive and
measure frequency-resolved time delays between the soft (0.3-1 keV) and hard
(1-4 keV) X-ray emissions. We report that the soft band lags behind the hard
band emission at high frequencies $sim[1.3-2.6]times 10^{-3}$ Hz, which is
interpreted as a sign of reverberation from the inner accretion disc in
response to the direct coronal emission. At low frequencies ($sim[3-8]times
10^{-4}$ Hz), the hard band lags behind the soft band variations, which we
explain in the context of the inward propagation of luminosity fluctuations
through the corona. Assuming a lamppost geometry for the corona, we find that
the X-ray source of the sample extends at an average height and radius of $sim
10r_{rm g}$ and $sim 6r_{rm g}$, respectively. Our results confirm that the
scaling relations between the BH mass and soft lag amplitude/frequency derived
for higher-mass AGNs can safely extrapolate to lower-mass AGNs, and the
accretion process is indeed independent of the BH mass.
The scaling relations between the black hole (BH) mass and soft lag
properties for both active galactic nuclei (AGNs) and BH X-ray binaries
(BHXRBs) suggest the same underlying physical mechanism at work in accreting BH
systems spanning a broad range of mass. However, the low-mass end of AGNs has
never been explored in detail. In this work, we extend the existing scaling
relations to lower-mass AGNs, which serve as anchors between the normal-mass
AGNs and BHXRBs. For this purpose, we construct a sample of low-mass AGNs
($M_{rm BH}<3times 10^{6} M_{rm odot}$) from the XMM-Newton archive and
measure frequency-resolved time delays between the soft (0.3-1 keV) and hard
(1-4 keV) X-ray emissions. We report that the soft band lags behind the hard
band emission at high frequencies $sim[1.3-2.6]times 10^{-3}$ Hz, which is
interpreted as a sign of reverberation from the inner accretion disc in
response to the direct coronal emission. At low frequencies ($sim[3-8]times
10^{-4}$ Hz), the hard band lags behind the soft band variations, which we
explain in the context of the inward propagation of luminosity fluctuations
through the corona. Assuming a lamppost geometry for the corona, we find that
the X-ray source of the sample extends at an average height and radius of $sim
10r_{rm g}$ and $sim 6r_{rm g}$, respectively. Our results confirm that the
scaling relations between the BH mass and soft lag amplitude/frequency derived
for higher-mass AGNs can safely extrapolate to lower-mass AGNs, and the
accretion process is indeed independent of the BH mass.
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