Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userReconciling the Quasar Microlensing Disc Size Problem with a Wind Model of Active Galactic Nucleus
42
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Many analyses have concluded that the accretion disc sizes measured from the microlensing variability of quasars are larger than the expectations from the standard thin disc theory by a factor of $sim4$. We propose a simply model by invoking a strong wind from the disc to flatten its radial temperature profile, which can then reconcile the size discrepancy problem. This wind model has been successfully applied to several microlensed quasars with a wind strength $slesssim1.3$ by only considering the inward decreasing of the mass accretion rate (where $s$ is defined through $dot{M}(R)propto({R}/{R_{0}})^{s}$ ). After further incorporating the angular momentum transferred by the wind, our model can resolve the disc size problem with an even lower wind parameter. The corrected disc sizes under the wind model are correlated with black hole masses with a slope in agreement with our modified thin disc model.
rate research
Read More
For most of their lifetime, super-massive black holes (SMBHs) commonly found in galactic nuclei obtain mass from the ambient at a rate well below the Eddington limit, which is mediated by a radiatively inefficient, hot accretion flow. Both theory and numerical simulations predict that a strong wind must exist in such hot accretion flows. The wind is of special interest not only because it is an indispensable ingredient of accretion, but perhaps more importantly, it is believed to play a crucial role in the evolution of the host galaxy via the so-called kinetic mode AGN feedback. Observational evidence for this wind, however, remains scarce and indirect. Here we report the detection of a hot outflow from the low-luminosity active galactic nucleus in M81, based on {it Chandra} high-resolution X-ray spectroscopy. The outflow is evidenced by a pair of Fe XXVI Ly$alpha$ lines redshifted and blueshifted at a bulk line-of-sight velocity of $pm2.8times10^3 rm~km~s^{-1}$ and a high Fe XXVI Ly$alpha$-to-Fe XXV K$alpha$ line ratio implying a plasma temperature of $1.3times10^8$ Kelvin. This high-velocity, hot plasma cannot be produced by stellar activity or the accretion inflow onto the SMBH. Our magnetohydrodynamical simulations show, instead, it is naturally explained by a wind from the hot accretion flow, propagating out to $gtrsim10^6$ times the gravitational radius of the SMBH. The kinetic energy and momentum of this wind can significantly affect the evolution of the circumnuclear environment and beyond.
We report the discovery of a luminous ultra-soft X-ray excess in a radio-loud narrow-line Seyfert1 galaxy, RXJ1633+4718, from archival ROSAT observations. The thermal temperature of this emission, when fitted with a blackbody, is as low as 32.5(+8.0,-6.0)eV. This is in remarkable contrast to the canonical temperatures of ~0.1-0.2keV found hitherto for the soft X-ray excess in active galactic nuclei (AGN), and is interestingly close to the maximum temperature predicted for a postulated accretion disc in this object. If this emission is indeed blackbody in nature, the derived luminosity [3.5(+3.3,-1.5)x10^(44)ergs/s] infers a compact emitting area with a size [~5x10^(12)cm or 0.33AU in radius] that is comparable to several times the Schwarzschild radius of a black hole at the mass estimated for this AGN (3x10^6Msun). In fact, this ultra-steep X-ray emission can be well fitted as the (Compton scattered) Wien tail of the multi-temperature blackbody emission from an optically thick accretion disc, whose parameters inferred (black hole mass and accretion rate) are in good agreement with independent estimates using optical emission line spectrum. We thus consider this feature as a signature of the long-sought X-ray radiation directly from a disc around a super-massive black hole, presenting observational evidence for a black hole accretion disc in AGN. Future observations with better data quality, together with improved independent measurements of the black hole mass, may constrain the spin of the black hole.
We use thirteen seasons of R-band photometry from the 1.2m Leonard Euler Swiss Telescope at La Silla to examine microlensing variability in the quadruply-imaged lensed quasar WFI 2026-4536. The lightcurves exhibit ${sim},0.2,text{mag}$ of uncorrelated variability across all epochs and a prominent single feature of ${sim},0.1,text{mag}$ within a single season. We analyze this variability to constrain the size of the quasars accretion disk. Adopting a nominal inclination of 60$^text{o}$, we find an accretion disk scale radius of $log(r_s/text{cm}) = 15.74^{+0.34}_{-0.29}$ at a rest-frame wavelength of $2043,unicode{xC5}$, and we estimate a black hole mass of $log(M_{text{BH}}/M_{odot}) = 9.18^{+0.39}_{-0.34}$, based on the CIV line in VLT spectra. This size measurement is fully consistent with the Quasar Accretion Disk Size - Black Hole Mass relation, providing another system in which the accretion disk is larger than predicted by thin disk theory.
The gravitationally lensed quasar APM 08279+5255 has the fastest claimed wind from any AGN, with velocities of 0.6-0.7c, requiring magnetic acceleration as special relativisitic effects limit all radiatively driven winds to v<0.3-0.5c. However, this extreme velocity derives from interpreting both the narrow and broad absorption features in the X-ray spectrum as iron absorption lines. The classic ultrafast outflow source PDS 456 also shows similar absorption systems, but here the higher energy, broader feature is generally interpreted as an absorption edge. We reanalyse all the spectra from APM 08279+5255 using a full 3-dimensional Monte Carlo radiative transfer disc wind model for the ionised wind at 0.1-0.2c, together with complex absorption from lower ionisation material, and find that this is a better description of the data. Thus there is no strong requirement for outflow velocities beyond 0.2c, which can be powered by radiation driving. We show that UV line driving is especially likely given the spectral energy distribution of this source which is intrinsically UV bright and X-ray weak. While the peak of this emission is unobservable, it must be luminous enough to power the observed hot dust, favouring at least moderate black hole spin.
This letter presents a revised radiative transfer model for the infrared (IR) emission of active galactic nuclei (AGN). While current models assume that the IR is emitted from a dusty torus in the equatorial plane of the AGN, spatially resolved observations indicate that the majority of the IR emission from 100 pc in many AGN originates from the polar region, contradicting classical torus models. The new model CAT3D-WIND builds upon the suggestion that the dusty gas around the AGN consists of an inflowing disk and an outflowing wind. Here, it is demonstrated that (1) such disk+wind models cover overall a similar parameter range of observed spectral features in the IR as classical clumpy torus models, e.g. the silicate feature strengths and mid-IR spectral slopes, (2) they reproduce the 3-5{mu}m bump observed in many type 1 AGN unlike torus models, and (3) they are able to explain polar emission features seen in IR interferometry, even for type 1 AGN at relatively low inclination, as demonstrated for NGC3783. These characteristics make it possible to reconcile radiative transfer models with observations and provide further evidence of a two-component parsec-scaled dusty medium around AGN: the disk gives rise to the 3-5{mu}m near-IR component, while the wind produces the mid-IR emission. The model SEDs will be made available for download.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
