S. Collin

Intermediate resolution Hβ spectroscopy and photometric monitoring of 3C 390.3 I. Further evidence of a nuclear accretion disk

We have monitored the AGN 3C 390.3 between 1995 and 2000. A historical B-band light curve dating back to 1966 shows a large increase in brightness during 1970{1971, followed by a gradual decrease down to a minimum in 1982. During the 1995{2000 lapse the broad H emission and the continuum flux varied by a factor of 3. Two large amplitude outbursts, of dierent duration, in continuum and H light were observed i.e.: in October 1994 a brighter flare that lasted1000 days and in July 1997 another one that lasted700 days were detected. The response time lag of the emission lines relative to flux changes of the continuum has been found to vary with time i.e. during 1995{1997 a lag of about 100 days is evident, while during 1998{1999 a double valued lag of100 days and35 days is present in our data. The flux in the H wings and line core vary simultaneously, a behavior indicative of predominantly circular motions in the BLR. Important changes of the H emission proles were detected: at times, we found proles with prominent asymmetric wings, like those normaly seen in Sy1s, while at other times, we observe proles with weak, almost symmetrical wings, similar to those of Sy1.8s. We further dismiss the hypothesis that the double peaked H proles in this object originate in a massive binary BH. Instead, we found that the radial velocity dierence between the red and blue bumps is anticorrelated with the light curves of H and continuum radiation. This implies that the zone that contributes most of the energy to the emitted line changes in radius within the disk. The velocity dierence increases, corresponding to smaller radii, as the continuum flux decreases. When the continuum flux increases the hump velocity dierence decreases. These transient phenomena are expected to result from the variable accretion rate close to the central source. The optical continuum and the H flux variations might be related to changes in X-ray emission modulated by a variable accretion rate, changing the surface temperature of the disk, as a result of a variable X-ray irradiation (Ulrich 2000). Theoretical H proles were computed for an accretion disk, the observed proles are best reproduced by an inclined disk (25) whose region of maximum emission is located roughly at 200 Rg .T he mass of the black hole in 3C 390.3, estimated from the reverberation analysis is Mrev 2:1 10 9 M, 5 times larger than previous

A new model for the Warm Absorber in NGC 3783 : a single medium in total pressure equilibrium

Context. Many active galactic nuclei exhibit X-ray features typical of the highly ionized gas called “Warm Absorber” (WA). Such a material appears to be stratified, displaying zones of di fferent density, temperature, and ionization. In this paper, we investigate the possibility of modelling the WA gas in NGC 3783 as a single medium in total pressure equilibrium. Aims. Our goal is to demonstrate that the WA can be well modelled assuming constant total pressure, in contrast to the current de scriptions that are based on the presence of multiple regions, each in constant density. The assumption of total pressure equilibrium yields a more physical description of the WA, resulting in the natural stratificati on of the ionized gas, and providing an explanation for the presence of lines from different ionization states, as observed in WA spectra. Methods. We have used the photoionization code TITAN, developed by our team, to compute a grid of constant total pressure models with the purpose of fitting the WA in NGC 3783. We have compared our models to the 900 ks Chandra spectrum of NGC 3783 and to previous studies where the WA was described by multiple zones of constant density. Results. In the case of NGC 3783, the WA features can be well reproduced by a clumpy, ionized gas with cosmic abondances, ionization parameter� = 2500 erg cm s −1 , column density NH = 4 10 22 cm −2 , and constant total pressure. Conclusions. We have shown that the WA in NGC 3783 can be modelled by a single medium in total pressure equilibrium; this is probably the case for other WAs currently described by multi-zone, constant density models. In addition, our work demonstrates that the TITAN code is well adapted to the study of the WA in active galactic nuclei, opening new prospects for the use of TITAN by a larger community.

Reprocessing of X-rays in AGN - I. Plane parallel geometry – test of pressure equilibrium

We present a model of the vertical stratication and the spectra of an irradiated medium under the assumption of constant pressure. Such a solution has properties intermediate between constant density models and hydrostatic equilibrium models, and it may represent a flattened conguration of gas clumps accreting onto the central black hole. Such a medium develops a hot skin, thicker than hydrostatic models, but thinner than constant density models, under comparable irradiation. The range of theoretical values of the ox index is comparable to those from hydrostatic models and both are close to the observed values for Seyfert galaxies but lower than in quasars. The amount of X-ray Compton reflection is consistent with the observed range. The characteristic property of the model is a frequently multicomponent iron K line.

Thermal instability in X-ray photoionized media in active galactic nuclei: - influence on the gas structure and spectral features

Context. A photoionized gas in thermal equilibrium can display a thermal instability, with three or more solutions in the multi-branch region of the S-shape curve that gives the temperature versus the radiation-to-gas-pressure ratio. Many studies have been devoted to this curve and to its dependence on different parameters, always in the optically thin case. Aims. The subject of our study is the thermal instability in optically thick, stratified media in total pressure equilibrium. We are also interested in comparing photoionization models issued from the hot and cold stable solutions with the currently used models, which are computed with an approximate, intermediate solution. Methods. We developed a new algorithm that selects the hot/cold stable solution and therefrom computes a fully consistent photoionization model. We implemented it in the TITAN code and computed a set of models encompassing the range of conditions valid for the warm absorber in active galactic nuclei. Results. We demonstrate that the thermal instability problem is quite different in thin and thick media. Models computed with the hot/cold stable solution and with an intermediate solution differ throughout the gas slab, with the spectral distribution changing as the radiation progresses inside the ionized gas. These effects depend on the thickness of the medium and on its ionization. Conclusions. This has observational implications for the emitted/absorbed spectra, ionization states, and variability. However impossible it is to know what solution the plasma will adopt when attaining the multi-solution regime, we expect the emitted/absorbed spectrum to be intermediate between those resulting from pure cold and hot models; such a phase-mixed medium can be reproduced well by intermediate solution models. Large spectral fluctuations corresponding to the onset of a cold/hot solution could be observed in timescales on the order of the dynamical time. A strong turbulence implying supersonic velocities should permanently exist in the multi-branch region of thick, stratified, pressure equilibrium media.

Intermediate Resolution Hβ Spectroscopy and Photometric Monitoring of 3C 390.3

The BVR photometry of 3C 390.3 was carried out at three different observatories i.e. SAO RAS in North Caucasus (Russia), the Crimean Laboratory of the Sternberg Astronomical Institute (CL SAI, Russia) and the Abastumani Astrophysical Observatory (AAO) in Georgia. The observations at the SAO RAS were obtained with the 1 m and 60 cm Zeiss telescopes equipped with an offset guided automatic photometer. The VRI photometry at the Crimean Laboratory was obtained with the 60 cm telescope equipped with a CCD camera. BVRI observations at the AAO were obtained with the 70 cm menisk telescope equipped with a CCD camera.

The behavior of X‐ray emission lines from an accretion disk in flare model

We investigate the model of an accretion disk illuminated locally by hard X‐rays. The X‐ray source is in the form of the hot flares most probably produced via magnetic field reconnection. Flares are accompanied by hot spots created at the accretion disk surface by illumination. We compute the local reflected (spot) spectrum using the codes TITAN/NOAR. In our computations we are able to model the change of intensities of X‐ray emission lines from 0.1 keV up to the most prominent iron Kα line due to appearance of flares. The global spectrum is obtained assuming a distribution of flares, where each flare has assumed effective life time. In such a case we follow the line profile modified due to relativistic smearing in Kerr metric.

PROFILE VARIABILITY OF THE Hα AND Hβ BROAD EMISSION LINES IN NGC 5548

Between 1996 and 2002, we have carried out a spectral monitoring program for the Seyfert galaxy NGC 5548 with the 6 m and 1 m telescopes of SAO (Russia) and with the 2.1 m telescope of Guillermo Haro Observatory (GHO) at Cananea, México. High quality spectra with S/N> 50 in the continuum near Hα and Hβ were obtained, covering the spectral range ∼(4000 – 7500) Å with a (4.5 to 15) Å-resolution. We found that both the flux in the lines and the continuum gradually decreased, reaching minimum values during May-June 2002. In the minimum state, the wings of Hβ and Hα became extremely weak, corresponding to a Sy1.8 type, not to a Sy1, as observed previously when the nucleus was brighter. The line profiles were decomposed into variable and constant components. The variable broad component is well correlated with the continuum variation. It consists of a double peaked structure with radial velocities ∼ ±1000 km/s relative to the narrow component. A constant component, whose presence is independent of the continuum flux variations, shows only narrow emission lines.The mean, rms, and the averaged over years, observed and difference line profiles of Hβ and Hα reveal the same double peaked structure. The relative intensity of these peaks changes with time. During 1996, the red peak was the brightest, while in 1998 – 2002, the blue peak became the brighter one. Their radial velocities vary in the ∼ (500 – 1200) km/s range. In 2000 – 2002 a distinct third peak appeared in the red wing of Hα and Hβ line profiles. The radial velocity of this feature decreased between 2000 and 2002: from the observed profiles, from ∼ +(2500 – 2600) km/s to ∼ +2000 km/s and is clearly seen on the difference profiles. The fluxes of the various parts of the line profiles are well correlated with each other and also with the continuum flux. The blue and red parts of the line profiles at the same radial velocities vary in an almost identical manner. Shape changes of the different parts of the broad line are not correlated with continuum variations and, apparently, are not related to reverberation effects. Changes of the integral Balmer decrement are, on average, anticorrelated with the continuum flux variations. This is probably due to an increasing role of collisional excitation as the ionizing flux decreases. The behavior of the Balmer decrement of the various parts of the line profiles was different in 1996 – 2000 as compared with the 2001 behavior. Our results favor the formation of the broad Balmer lines in a turbulent accretion disc with large and moving ”optically thick” inhomogeneities, capable of reprocessing the central source continuum.

Double-peaked broad-line Hβ profiles of 3C390.3 FROM 1995–99. II. the accretion disk model

Abstract A preliminary fitting by the accretion disk model of the broad Hβ line profiles of 3C390.3 is presented.