135 research outputs found
Long Fading Mid-Infrared Emission in Transient Coronal Line Emitters: Dust Echo of Tidal Disruption Flare
The sporadic accretion following the tidal disruption of a star by a
super-massive black hole (TDE) leads to a bright UV and soft X-ray flare in the
galactic nucleus. The gas and dust surrounding the black hole responses to such
a flare with an echo in emission lines and infrared emission. In this paper, we
report the detection of long fading mid-IR emission lasting up to 14 years
after the flare in four TDE candidates with transient coronal lines using the
WISE public data release. We estimate that the reprocessed mid-IR luminosities
are in the range between and erg~s
and dust temperature in the range of 570-800K when WISE first detected these
sources three to five years after the flare. Both luminosity and dust
temperature decreases with time. We interpret the mid-IR emission as the
infrared echo of the tidal disruption flare. We estimate the UV luminosity at
the peak flare to be 1 to 30 times erg s and for warm dust
masses to be in the range of 0.05-1.3 Msun within a few parsecs. Our results
suggest that the mid-infrared echo is a general signature of TDE in the
gas-rich environment
Mid-infrared variability of changing-look AGN
It is known that some active galactic nuclei (AGNs) transited from type 1 to
type 2 or vice versa. There are two explanations for the so-called changing
look AGNs: one is the dramatic change of the obscuration along the
line-of-sight, the other is the variation of accretion rate. In this paper, we
report the detection of large amplitude variations in the mid-infrared
luminosity during the transitions in 10 changing look AGNs using WISE and newly
released NEOWISE-R data. The mid-infrared light curves of 10 objects echoes the
variability in the optical band with a time lag expected for dust reprocessing.
The large variability amplitude is inconsistent with the scenario of varying
obscuration, rather supports the scheme of dramatic change in the accretion
rate.Comment: Published by ApjL, 7 pages, 3 figures, 2 table
Discovery of a Mid-infrared Echo from the TDE candidate in the nucleus of ULIRG F01004-2237
We present the mid-infrared (MIR) light curves (LCs) of a tidal disruption
event (TDE) candidate in the center of a nearby ultraluminous infrared galaxy
(ULIRG) F01004-2237 using archival {\it WISE} and {\it NEOWISE} data from 2010
to 2016. At the peak of the optical flare, F01004-2237 was IR quiescent. About
three years later, its MIR fluxes have shown a steady increase, rising by 1.34
and 1.04 mag in and m up to the end of 2016. The host-subtracted
MIR peak luminosity is \,erg\,s. We interpret the MIR
LCs as an infrared echo, i.e. dust reprocessed emission of the optical flare.
Fitting the MIR LCs using our dust model, we infer a dust torus of the size of
a few parsecs at some inclined angle. The derived dust temperatures range from
\,K, and the warm dust mass is . Such a large mass
implies that the dust cannot be newly formed. We also derive the UV luminosity
of \,erg\,s. The inferred total IR energy is
\,erg, suggesting a large dust covering factor. Finally, our
dust model suggests that the long tail of the optical flare could be due to
dust scattering
Mid-infrared flare of TDE candidate PS16dtm: dust echo and implications for the spectral evolution
PS16dtm was classified as a candidate tidal disruption event (TDE) in a dwarf
Seyfert 1 galaxy with low-mass black hole () and has presented
various intriguing photometric and spectra characteristics. Using the archival
WISE and the newly released NEOWISE data, we found PS16dtm is experiencing a
mid-infrared (MIR) flare which started days before the first optical
detection. Interpreting the MIR flare as a dust echo requires close
pre-existing dust with a high covering factor, and suggests the optical flare
may have brightened slowly for some time before it became bright detectable
from the ground. More evidence is given at the later epochs. At the peak of the
optical light curve, the new inner radius of the dust torus has grown to much
larger size, a factor of 7 of the initial radius due to strong radiation field.
At days after the first optical detection, the dust temperature has
dropped well below the sublimation temperature. Other peculiar spectral
features shown by PS16dtm are the transient, prominent FeII emission lines and
outflows indicated by broad absorption lines detected during the optical flare.
Our model explains the enhanced FeII emission from iron newly released from the
evaporated dust. The observed broad absorption line outflow could be explained
by accelerated gas in the dust torus due to the radiation pressure.Comment: Accepted by ApJ, 5 figure
Discovery of An Active Intermediate-Mass Black Hole Candidate in the Barred Bulgeless Galaxy NGC 3319
We report the discovery of an active intermediate-mass black hole (IMBH)
candidate in the center of nearby barred bulgeless galaxy . The
point X-ray source revealed by archival Chandra and XMM-Newton observations is
spatially coincident with the optical and UV galactic nuclei from Hubble Space
Telescope observations. The spectral energy distribution derived from the
unresolved X-ray and UV-optical flux is comparable with active galactic nuclei
(AGNs) rather than ultra-luminous X-ray sources, although its bolometric
luminosity is only . Assuming an Eddington
ratio range between 0.001 and 1, the black hole mass (M_\rm{BH}) will be
located at , placing it in the so-called
IMBH regime and could be the one of the lowest reported so far. Estimates from
other approaches (e.g., fundamental plane, X-ray variability) also suggest
M_\rm{BH}\lesssim10^5~M_{\odot}.Similar to other BHs in bulgeless galaxies,
the discovered IMBH resides in a nuclear star cluster with mass of
. The detection of such a low-mass BH offers us an
ideal chance to study the formation and early growth of SMBH seeds, which may
result from the bar-driven inflow in late-type galaxies with a prominent bar
such as .Comment: ApJ accepted, 2 tables, 6 figure
- …