NuSTAR Discovery of Dead Quasar Engine in Arp 187. (arXiv:1908.10864v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Ichikawa_K/0/1/0/all/0/1">Kohei Ichikawa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kawamuro_T/0/1/0/all/0/1">Taiki Kawamuro</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shidatsu_M/0/1/0/all/0/1">Megumi Shidatsu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ricci_C/0/1/0/all/0/1">Claudio Ricci</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bae_H/0/1/0/all/0/1">Hyun-Jin Bae</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Matsuoka_K/0/1/0/all/0/1">Kenta Matsuoka</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shin_J/0/1/0/all/0/1">Jaejin Shin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Toba_Y/0/1/0/all/0/1">Yoshiki Toba</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ueda_J/0/1/0/all/0/1">Junko Ueda</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ueda_Y/0/1/0/all/0/1">Yoshihiro Ueda</a>
Recent active galactic nucleus (AGN) and quasar surveys have revealed a
population showing rapid AGN luminosity variability by a factor of $sim10$.
Here we present the most drastic AGN luminosity decline by a factor of $gtrsim
10^{3}$ constrained by a NuSTAR X-ray observation of the nearby galaxy Arp 187,
which is a promising “dead” quasar whose current activity seems quiet but whose
past activity of $L_mathrm{bol} sim 10^{46}$ erg s$^{-1}$ is still observable
at a large scale by its light echo. The obtained upper bound of the X-ray
luminosity is $log (L_{rm 2-10 keV}/{rm erg} {rm s}^{-1}) < 41.2$,
corresponding to $log (L_mathrm{bol}/{rm erg} {rm s}^{-1}) < 42.5$,
indicating an inactive central engine. Even if a putative torus model with
$N_mathrm{H} sim 1.5 times 10^{24}$ cm$^{-2}$ is assumed, the strong
upper-bound still holds with $log (L_{rm 2-10 keV}/{rm erg} {rm s}^{-1}) <
41.8$ or $log (L_mathrm{bol}/{rm erg} {rm s}^{-1}) < 43.1$. Given the
expected size of the narrow line region, this luminosity decrease by a factor
of $gtrsim 10^3$ must have occurred within $lesssim 10^4$ yr. This extremely
rapid luminosity/accretion shutdown is puzzling and it requires one burst-like
accretion mechanism producing a clear outer boundary for an accretion disk. We
raise two possible scenarios realizing such an accretion mechanism: a mass
accretion 1) by the tidal disruption of a molecular cloud and/or 2) by the gas
depletion as a result of vigorous nuclear starformation after rapid mass inflow
to the central engine.
Recent active galactic nucleus (AGN) and quasar surveys have revealed a
population showing rapid AGN luminosity variability by a factor of $sim10$.
Here we present the most drastic AGN luminosity decline by a factor of $gtrsim
10^{3}$ constrained by a NuSTAR X-ray observation of the nearby galaxy Arp 187,
which is a promising “dead” quasar whose current activity seems quiet but whose
past activity of $L_mathrm{bol} sim 10^{46}$ erg s$^{-1}$ is still observable
at a large scale by its light echo. The obtained upper bound of the X-ray
luminosity is $log (L_{rm 2-10 keV}/{rm erg} {rm s}^{-1}) < 41.2$,
corresponding to $log (L_mathrm{bol}/{rm erg} {rm s}^{-1}) < 42.5$,
indicating an inactive central engine. Even if a putative torus model with
$N_mathrm{H} sim 1.5 times 10^{24}$ cm$^{-2}$ is assumed, the strong
upper-bound still holds with $log (L_{rm 2-10 keV}/{rm erg} {rm s}^{-1}) <
41.8$ or $log (L_mathrm{bol}/{rm erg} {rm s}^{-1}) < 43.1$. Given the
expected size of the narrow line region, this luminosity decrease by a factor
of $gtrsim 10^3$ must have occurred within $lesssim 10^4$ yr. This extremely
rapid luminosity/accretion shutdown is puzzling and it requires one burst-like
accretion mechanism producing a clear outer boundary for an accretion disk. We
raise two possible scenarios realizing such an accretion mechanism: a mass
accretion 1) by the tidal disruption of a molecular cloud and/or 2) by the gas
depletion as a result of vigorous nuclear starformation after rapid mass inflow
to the central engine.
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