NuSTAR Discovery of Dead Quasar Engine in Arp 187
Abstract
Recent active galactic nucleus (AGN) and quasar surveys have revealed a population showing rapid AGN luminosity variability by a factor of ∼10. Here we present the most drastic AGN luminosity decline by a factor of ≳103 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}bol}∼ {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}2-10{keV}/{erg} {{{s}}}-1)< 41.2, corresponding to {log}({L}bol}/{erg} {{{s}}}-1)< 42.5, indicating an inactive central engine. Even if a putative torus model with {N}{{H}}∼ 1.5× {10}24 cm-2 is assumed, the strong upper bound still holds with {log}({L}2-10{keV}/{erg} {{{s}}}-1)< 41.8 or {log}({L}bol}/{erg} {{{s}}}-1)< 43.1. Given the expected size of the narrow-line region, this luminosity decrease by a factor of ≳103 must have occurred within ≲104 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 star formation after rapid mass inflow to the central engine.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2019
- DOI:
- 10.3847/2041-8213/ab3ebf
- arXiv:
- arXiv:1908.10864
- Bibcode:
- 2019ApJ...883L..13I
- Keywords:
-
- Active galactic nuclei;
- X-ray active galactic nuclei;
- Quasars;
- 16;
- 2035;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 7 pages, 2 figures, accepted for publication in ApJL