If the disappearance of the broad emission lines observed in changing-look quasars were caused by the obscuration of the quasar core through moving dust clouds in the torus, high linear polarization ...typical of type 2 quasars would be expected. We measured the polarization of the changing-look quasar J1011+5442 in which the broad emission lines have disappeared between 2003 and 2015. We found a polarization degree compatible with null polarization. This measurement suggests that the observed change of look is not due to a change of obscuration hiding the continuum source and the broad line region, and that the quasar is seen close to the system axis. Our results thus support the idea that the vanishing of the broad emission lines in J1011+5442 is due to an intrinsic dimming of the ionizing continuum source that is most likely caused by a rapid decrease in the rate of accretion onto the supermassive black hole.
We present results obtained from the time-resolved X-ray spectral analysis of the Narrow-Line-Seyfert 1 galaxy SWIFT J2127.4+5654 during a ∼130 ks XMM-Newton observation. We reveal large spectral ...variations, especially during the first ∼90 ks of the XMM-Newton exposure. The spectral variability can be attributed to a partial eclipse of the X-ray source by an intervening low-ionization/cold absorbing structure (cloud) with column density
cm−2 which gradually covers and then uncovers the X-ray emitting region with covering fraction ranging from zero to ∼43 per cent. Our analysis enables us to constrain the size, number density and location of the absorbing cloud with good accuracy. We infer a cloud size (diameter) of D
c ≤ 1.5 × 1013 cm, corresponding to a density of n
c ≥ 1.5 × 109 cm−3 at a distance of R
c ≥ 4.3 × 1016 cm from the central black hole. All of the inferred quantities concur to identify the absorbing structure with one single cloud associated with the broad line region of SWIFT J2127.4+5654. We are also able to constrain the X-ray emitting region size (diameter) to be D
s ≤ 2.3 × 1013 cm which, assuming the black hole mass estimated from single-epoch optical spectroscopy (1.5 × 107 M), translates into D
s ≤ 10.5 gravitational radii (r
g) with larger sizes (in r
g) being associated with smaller black hole masses, and vice versa. We also confirm the presence of a relativistically distorted reflection component off the inner accretion disc giving rise to a broad relativistic Fe K emission line and small soft excess (small because of the high Galactic column density), supporting the measurement of an intermediate black hole spin in SWIFT J2127.4+5654 that was obtained from a previous Suzaku observation.
Context.
Outflows play a major role in the evolution of galaxies. However, we do not yet have a complete picture of their properties (extension, geometry, orientation, and clumpiness). For ...low-luminosity active galactic nuclei (AGNs), in particular low-ionisation nuclear emission line regions (LINERs), the rate of outflows and their properties are largely unknown.
Aims.
The main goal of this work is to create the largest up-to-date atlas of ionised gas outflow candidates in a sample of 70 nearby LINERs. We aim to use narrowband imaging data to analyse the morphological properties of the ionised gas nuclear emission of these galaxies and to identify signatures of extended emission with distinctive outflow morphologies.
Methods.
We obtained new imaging data from Alhambra Faint Object Spectrograph and Camera (ALFOSC)/Nordic Optical Telescope (NOT) for a total of 32 LINERs, and complemented it with
Hubble
Space Telescope archival data (HST) for six objects. We extracted the H
α
emission of the galaxies and used it to morphologically classify the circumnuclear emission. We combined our results with those from the literature for additional 32 targets. We additionally obtained soft X-ray data from
Chandra
archive to compare this emission with the ionised gas.
Results.
The distribution of the ionised gas in these LINER indicates that ∼32% show Bubble emission, ∼28% show Core-halo unresolved emission, and ∼21% of the sample have a Disky distribution. Dust lanes prevent any detailed classification for ∼11% of the sample, which we call Dusty. The soft X-ray emission is in most cases (∼60%) co-spatial with the ionised gas. If we account for the kinematical information which is available for a total of 60 galaxies, we end up with a total of 48% of the LINERs with detected outflows or inflows in the emission lines (50% considering only kinematical information based on Integral Field Spectroscopic data).
Conclusions.
Our results suggest that the incidence of outflows in LINERs may vary from 41% to 56%, based on both the H
α
morphology and the kinematical information from the literature. The ionised gas seems to be correlated with the soft X-ray emission, so that they may have a common origin. We discuss the use of H
α
imaging for the pre-selection of candidates likely hosting ionised gas outflows.
We present a model of the dust environment of Main-Belt Comet P/2010 R2 (La Sagra) from images acquired during the period 2010 October-2011 January. The tails are best simulated by anisotropic ...ejection models, with emission concentrated near the nucleus south pole, the spin axis having an obliquity near 90?, indicative of a possible seasonally driven behavior. The dust mass loss rate increases rapidly shortly before perihelion, reaching a maximum value of ~4 kg s--1, and maintaining a sustained, cometary-like, activity of about 3-4 kg s--1 up to at least 200 days after perihelion, the date of the latest observation. The size distribution function is characterized by particles in the 5 X 10--4 cm to 1 cm radius range, assuming a time-constant power-law distribution with an index of --3.5. The ejection velocities are compatible with water-ice sublimation activity at the heliocentric distance of 2.7 AU, with values of 10-20 cm s--1 for particle radius of 1 cm, and inverse square root dependence on particle size, typical of hydrodynamical gas drag.
We report on the long- and short-term X-ray spectral analysis of the polar-scattered Seyfert 1.2 galaxy ESO 323−G77, observed in three epochs between 2006 and 2013 with Chandra and XMM–Newton. Four ...high-resolution Chandra observations give us a unique opportunity to study the properties of the absorbers in detail, as well as their short time-scale (days) variability. From the rich set of absorption features seen in the Chandra data, we identify two warm absorbers with column densities and ionizations that are consistent with being constant on both short and long time-scales, suggesting that those are the signatures of a rather homogeneous and extended outflow. A third absorber, ionized to a lesser degree, is also present and it replaces the strictly neutral absorber that is ubiquitously inferred from the X-ray analysis of obscured Compton-thin sources. This colder absorber appears to vary in column density on long time-scales, suggesting a non-homogeneous absorber. Moreover, its ionization responds to the nuclear luminosity variations on time-scales as short as a few days, indicating that the absorber is in photoionization equilibrium with the nuclear source on these time-scales. All components are consistent with being co-spatial and located between the inner and outer edges of the so-called dusty, clumpy torus. Assuming co-spatiality, the three phases also share the same pressure, suggesting that the warm / hot phases confine the colder, most likely clumpy, medium. We discuss further the properties of the outflow in comparison with the lower resolution XMM–Newton data.
We report results from multi-epoch (2006-2013) X-ray observations of the polar-scattered Seyfert 1 galaxy ESO 323-G77. The source exhibits remarkable spectral variability from months to years ...timescales. The observed spectral variability is entirely due to variations of the column density of a neutral absorber towards the intrinsic nuclear continuum. The column density is generally Compton-thin ranging from a few times 1022 cm−2 to a few times 1023 cm−2. However, one observation reveals a Compton-thick state with column density of the order of 1.5 × 1024 cm−2. The observed variability offers a rare opportunity to study the properties of the X-ray absorber(s) in an active galaxy. We identify variable X-ray absorption from two different components, namely (i) a clumpy torus whose individual clumps have a density of ≤1.7 × 108 cm−3 and an average column density of ∼4 × 1022 cm−2, and (ii) the broad-line region (BLR), comprising individual clouds with density of 0.1-8 × 109 cm−3 and column density of 1023-1024 cm−2. The derived properties of the clumpy torus can also be used to estimate the torus half-opening angle, which is of the order of 47°. We also confirm the previously reported detection of two highly ionized warm absorbers with outflow velocities of 1000-4000 km s−1. The observed outflow velocities are consistent with the Keplerian/escape velocity at the BLR. Hence, the warm absorbers may be tentatively identified with the warm/hot intercloud medium which ensures that the BLR clouds are in pressure equilibrium with their surroundings. The BLR line-emitting clouds may well be the cold, dense clumps of this outflow, whose warm/hot phase is likely more homogeneous, as suggested by the lack of strong variability of the warm absorber(s) properties during our monitoring.
We have obtained new spectropolarimetric observations at visible wavelengths of the changing-look active galactic nucleus (AGN) Mrk 1018. The AGN direct spectrum shows an extremely weak continuum ...with faint broad H
β
and H
α
emission lines. Both lines can be fit with a single very broad emission line component of full width at half maximum
FWHM
≃ 7200 km s
−1
, with no evidence of the additional 3000 km s
−1
-wide component that was previously detected. While this is in agreement with line formation in a Keplerian disk, the line profile variability suggests that the broad emission line region is likely more complex. The continuum polarization of Mrk 1018 is low; it is not higher in the current faint state compared to the past bright state, confirming that dust obscuration is not the mechanism at the origin of the change of look. The polarization profile of the H
α
line is asymmetric with no rotation of the polarization angle, which possibly reveals line formation in a polar outflow. Alternatively, the polarization profile may be the consequence of a time delay between the direct and the polarized light. Interestingly, the polarization signatures predicted for broad lines emitted around supermassive binary black holes are not observed.
Polarization of changing-look quasars Hutsemékers, D.; Agís González, B.; Marin, F. ...
Astronomy and astrophysics (Berlin),
05/2019, Letnik:
625
Journal Article, Web Resource
Recenzirano
Odprti dostop
If the disappearance of the broad emission lines observed in changing-look quasars originates from the obscuration of the quasar core by dusty clouds moving in the torus, high linear optical ...polarization would be expected in those objects. We then measured the rest-frame UV-blue linear polarization of a sample of 13 changing-look quasars, 7 of them being in a type 1.9-2 state. For all quasars but one the polarization degree is lower than 1%. This suggests that the disappearance of the broad emission lines cannot be attributed to dust obscuration, and supports the scenario in which changes of look are caused by a change in the rate of accretion onto the supermassive black hole. Such low polarization degrees also indicate that these quasars are seen under inclinations close to the system axis. One type 1.9-2 quasar in our sample shows a high polarization degree of 6.8%. While this polarization could be ascribed to obscuration by a moving dusty cloud, we argue that this is unlikely given the very long time needed for a cloud from the torus to eclipse the broad emission line region of that object. We propose that the high polarization is due to the echo of a past bright phase seen in polar-scattered light. This interpretation raises the possibility that broad emission lines observed in the polarized light of some type 2 active galactic nuclei can be echoes of past type 1 phases and not evidence of hidden broad emission line regions.
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