ABSTRACT Stars that pass within the Roche radius of a supermassive black hole will be tidally disrupted, yielding a sudden injection of gas close to the black hole horizon which produces an ...electromagnetic flare. A few dozen of these flares have been discovered in recent years, but current observations provide poor constraints on the bolometric luminosity and total accreted mass of these events. Using images from the Wide-field Infrared Survey Explorer, we have discovered transient 3.4 m emission from several previously known tidal disruption flares. The observations can be explained by dust heated to its sublimation temperature due to the intense radiation of the tidal flare. From the break in the infrared light curve we infer that this hot dust is located ∼0.1 pc from the supermassive black hole. Since the dust has been heated by absorbing UV and (potentially) soft X-ray photons of the flare, the reprocessing light curve yields an estimate of the bolometric flare luminosity. For the flare PTF-09ge, we infer that the most likely value of the luminosity integrated over frequencies at which dust can absorb photons is erg s−1, with a factor of 3 uncertainty due to the unknown temperature of the dust. This bolometric luminosity is a factor ∼10 larger than the observed blackbody luminosity. Our work is the first to probe dust in the nuclei of non-active galaxies on sub-parsec scales. The observed infrared luminosity implies a covering factor ∼1% for the nuclear dust in the host galaxies.
ABSTRACT
Multiwavelength variability studies of active galactic nuclei can be used to probe their inner regions that are not directly resolvable. Dust reverberation mapping (DRM) estimates the size ...of the dust emitting region by measuring the delays between the infrared (IR) response to variability in the optical light curves. We measure DRM lags of Zw229-015 between optical ground-based and Kepler light curves and concurrent IR Spitzer 3.6 and 4.5 µm light curves from 2010 to 2015, finding an overall mean rest-frame lag of 18.3 ± 4.5 d. Each combination of optical and IR light curve returns lags that are consistent with each other within 1σ, which implies that the different wavelengths are dominated by the same hot dust emission. The lags measured for Zw229-015 are found to be consistently smaller than predictions using the lag–luminosity relationship. Also, the overall IR response to the optical emission actually depends on the geometry and structure of the dust emitting region as well, so we use Markov chain Monte Carlo modelling to simulate the dust distribution to further estimate these structural and geometrical properties. We find that a large increase in flux between the 2011–2012 observation seasons, which is more dramatic in the IR light curve, is not well simulated by a single dust component. When excluding this increase in flux, the modelling consistently suggests that the dust is distributed in an extended flat disc, and finds a mean inclination angle of 49$^{+3}_{-13}$ deg.
PKS 1413+135 is one of the most peculiar blazars known. Its strange properties led to the hypothesis almost four decades ago that it is gravitationally lensed by a mass concentration associated with ...an intervening galaxy. It exhibits symmetric achromatic variability, a rare form of variability that has been attributed to gravitational milli-lensing. It has been classified as a BL Lac object, and is one of the rare objects in this class with a visible counterjet. BL Lac objects have jet axes aligned close to the line of sight. It has also been classified as a compact symmetric object-objects that have jet axes not aligned close to the line of sight. Intensive efforts to understand this blazar have hitherto failed to resolve even the questions of the orientation of the relativistic jet and the host galaxy. Answering these two questions is important because they challenge our understanding of jets in active galactic nuclei and the classification schemes we use to describe them. We show that the jet axis is aligned close to the line of sight and PKS 1413+135 is almost certainly not located in the apparent host galaxy, but is a background object in the redshift range 0.247 < z < 0.5. The intervening spiral galaxy at z = 0.247 provides a natural host for the putative lens responsible for symmetric achromatic variability and is shown to be a Seyfert 2 galaxy. We also show that, as for the radio emission, a "multizone" model is needed to account for the high-energy emission.
The Spitzer Deep, Wide-field Survey Ashby, M. L. N; Stern, D; Brodwin, M ...
The Astrophysical journal,
08/2009, Letnik:
701, Številka:
1
Journal Article
We estimate the relative contributions of the supermassive black hole (SMBH) accretion disk, corona, and obscuring torus to the bolometric luminosity of Seyfert galaxies, using Spitzer mid-infrared ...(MIR) observations of a complete sample of 68 nearby active galactic nuclei (AGNs) from the INTEGRAL all-sky hard X-ray (HX) survey. This is the first HX-selected (above 15 keV) sample of AGNs with complementary high angular resolution, high signal-to-noise, MIR data. Correcting for the host galaxy contribution, we find a correlation between HX and MIR luminosities: L sub(15 )mum is proportional to L super(0.74+ or -0.06) sub(HX). Assuming that the observed MIR emission is radiation from an accretion disk reprocessed in a surrounding dusty torus that subtends a solid angle decreasing with increasing luminosity (as inferred from the declining fraction of obscured AGNs), the intrinsic disk luminosity, L sub(Disk), is approximately proportional to the luminosity of the corona in the 2-300 keV energy band, L sub(Corona), with the L sub(Disk)/L sub(Corona) ratio varying by a factor of 2.1 around a mean value of 1.6. This ratio is a factor of ~2 smaller than for typical quasars producing the cosmic X-ray background. Therefore, over three orders of magnitude in luminosity, HX radiation carries a large, and roughly comparable, fraction of the bolometric output of AGNs. We estimate the cumulative bolometric luminosity density of local AGNs at ~(1-3) x 10 super(40) erg s super(-1) Mpc super(-3). Finally, the Compton temperature ranges between kT sub(c) approximately 2 and approximately 6 keV for nearby AGNs, compared to kT sub(c) approximately 2 keV for typical quasars, confirming that radiative heating of interstellar gas can play an important role in regulating SMBH growth.
We determine the contribution of AGN to the mid-IR emission of luminous infrared galaxies (LIRGs) at z > 0.6 by measuring the mid-IR dust continuum slope of 20,039 mid-IR sources. The 24 km sources ...are selected from a Spitzer MIPS survey of the NOAO Deep Wide-Field Survey Bootes field and have corresponding 8 km data from the IRAC Shallow Survey. There is a clear bimodal distribution in the 24 to 8 km flux ratio. The X-ray-detected sources fall within the peak corresponding to a flat spectrum in Vf sub(V) implying that it is populated by AGN-dominated LIRGs, whereas the peak corresponding to a higher 24 to 8 km flux ratio is likely due to LIRGs whose IR emission is powered by starbursts. The 24 km emission is increasingly dominated by AGN at higher 24 km flux densities (f sub(24)): the AGN fraction of the z > 0.6 sources increases from 9% at f sub(24) - 0.35 mJy to 74% c 20% at f sub(24) - 3 mJy, in good agreement with model predictions. Deep 24 km, small-area surveys, like GOODS, will be strongly dominated by starburst galaxies. AGN are responsible for 63%-7% of the total 24 km background.
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