Implications of the X-ray Variability for the Mass of MCG-6-30-15

The bright Seyfert 1 galaxy \mcg shows large variability on a variety of time scales. We study the \aproxlt 3 day time scale variability using a set of simultaneous archival observations that were obtained from \rxte and the {\it Advanced Satellite for Cosmology and Astrophysics} (\asca). The \rxte\ observations span nearly $10^6$ sec and indicate that the X-ray Fourier Power Spectral Density has an rms variability of 16%, is flat from approximately 10^{-6} - 10^{-5} Hz, and then steepens into a power law $\propto f^{-\alpha}$ with \alpha\aproxgt 1. A further steepening to $\alpha \approx 2$ occurs between 10^{-4}-10^{-3} Hz. The shape and rms amplitude are comparable to what has been observed in \ngc and \cyg, albeit with break frequencies that differ by a factor of 10^{-2} and 10^{4}, respectively. If the break frequencies are indicative of the central black hole mass, then this mass may be as low as $10^6 {\rm M}_\odot$. An upper limit of $\sim 2$ ks for the relative lag between the 0.5-2 keV \asca band compared to the 8-15 keV \rxte band was also found. Again by analogy with \ngc and \cyg, this limit is consistent with a relatively low central black hole mass.Comment: 5 pages, 3 figures, LaTeX, uses emulateapj.sty and apjfonts.sty, revised version, accepted for publication in ApJ Letter

Large Scale Fluctuations in the X-Ray Background

We present an attempt to measure the large angular scale fluctuations in the X-Ray Background (XRB) from the HEAO1-A2 data, expressed in terms of spherical harmonics. We model the harmonic coefficients assuming a power spectrum and an epoch-dependent bias parameter, and using a phenomenological scenario describing the evolution of the X-ray sources. From the few low-order multipoles detected above shot noise, we estimate the power-spectrum normalization on scales intermediate between those explored by local galaxy redshift surveys (~ 100 Mpc) and by the COBE Microwave Background measurements (~ 1000 Mpc). We find that the HEAO1 harmonics are consistent with present epoch rms fluctuations of the X-ray sources bx(0)sigma8 ~ 1-2 in 8 Mpc spheres. Therefore the observed fluctuations in the XRB are roughly as expected from interpolating between the local galaxy surveys and the COBE CMB experiment. We predict that an X-ray all-sky surface brightness survey resolving sources a factor of 10 fainter than HEAO1, may reveal fluctuations to significantly larger angular scales and therefore more strongly constrain the large scale structure of the Universe on scales of hundreds of Mpcs.Comment: 14 pages, 3 Postscript figures, uses aaspp4.sty and psfig. Revised following referee's report. Accepted for publication in Ap

X-ray Fluctuation Power Spectral Densities of Seyfert 1 Galaxies

By combining complementary monitoring observations spanning long, medium and short time scales, we have constructed power spectral densities (PSDs) of six Seyfert~1 galaxies. These PSDs span $\gtrsim$4 orders of magnitude in temporal frequency, sampling variations on time scales ranging from tens of minutes to over a year. In at least four cases, the PSD shows a "break," a significant departure from a power law, typically on time scales of order a few days. This is similar to the behavior of Galactic X-ray binaries (XRBs), lower mass compact systems with breaks on time scales of seconds. NGC 3783 shows tentative evidence for a doubly-broken power law, a feature that until now has only been seen in the (much better-defined) PSDs of low-state XRBs. It is also interesting that (when one previously-observed object is added to make a small sample of seven), an apparently significant correlation is seen between the break time scale $T$ and the putative black hole mass $M_{\rm BH}$, while none is seen between break time scale and luminosity. The data are consistent with the linear relation T = M_{\rm BH}/10^{6.5} \Msun; extrapolation over 6--7 orders of magnitude is in reasonable agreement with XRBs. All of this strengthens the case for a physical similarity between Seyfert~1s and XRBs.Comment: 27 pages, 13 figures. Accepted for publication in ApJ. Typo correcte

Frenkel line and solubility maximum in supercritical fluids

This research utilised Queen Mary’s MidPlus computational facilities, supported by QMUL Research-IT and funded by EPSRC Grant EP/K000128/1. K.T. is grateful to EPSRC, C.Y. to CSC. V.V.B. is grateful to RSF (14-2200093) for financial support

The HST Survey of BL Lacertae Objects. I. Surface Brightness Profiles, Magnitudes, and Radii of Host Galaxies

We report on a large HST imaging survey of BL Lac objects, at spatial resolution ~10 times better than previous ground-based surveys. We focus on data reduction and analysis, describing the procedures used to model the host galaxy surface brightness radial profiles. A total of 69 host galaxies were resolved out of 110 objects observed, including almost all sources at z < 0.5. We classify them morphologically by fitting with either an exponential disk or a de~Vaucouleurs profile; when one fit is preferred over the other, in 58 of 69 cases, it is invariably the elliptical morphology. This is a very strong result given the large number of BL Lac objects, the unprecedented spatial resolution, and the homogeneity of the data set. With the present reclassification of the host galaxy of 1418+546 as an elliptical, there remain no undisputed examples of a disk galaxy hosting a BL Lac nucleus. This implies that, at 99% confidence, fewer than 7% of BL Lacs can be in disk galaxies. The apparent magnitude of the host galaxies varies with distance as expected if the absolute magnitudes are approximately the same, with a spread of +-1 mag, out to redshift z < 0.5. At larger redshifts, only 6 of 23 BL Lacs are resolved so the present data do not constrain possible luminosity evolution of the host galaxies. The collective Hubble diagram for BL Lac host galaxies and radio galaxies strongly supports their unification.Comment: Accepted for publication on ApJS. 43 pages. 10 figures. Figure 1 can also be downloaded from http://icarus.stsci.edu/~scarpa/tmp/hst_figure1.ta

Optical and X-ray characteristics of a newly discovered narrow-line QSO : RX J1334.2+3759

We report the discovery of a narrow-line QSO (NLQSO) RX J1334.2+3759 with a steep soft X-ray spectrum. Soft X-ray emission from the NLQSO is highly variable. Changes in the intensity by a factor of about 2 have been detected in the ROSAT PSPC observations of RX J1334.2+3759 on time scales of 20000-40000s. Rapid variability events have also been observed from RX J1334.2+3759. The most extreme variable event has Delta L/Delta t = (1.95+/-1.02)E42 erg/s/s corresponding to a change in intensity by a factor of about 4 within 400s. The PSPC spectra of the NLQSO can be well represented by a power-law of photon index 3.8, modified by an absorbing column local to the source over and above that due to our own Galaxy. The intrinsic soft X-ray luminosity of RX J1334.2+3759 is estimated to be 2.2E44 erg/s in the energy band of 0.1-2.0 keV. The optical spectrum of RX J1334.2+3759 is typical of the NLS1 galaxies showing strong Balmer Hbeta, Halpha, and forbidden line [O III]5007. Fe II multiplets, usually present in the optical spectra of NLS1 galaxies, are also detected from RX J1334.2+3759. Decomposition of the Hbeta and Halpha line profiles shows the presence of narrow (FWHM = 880 km/s) and broad (FWHM = 2850 km/s) components in the spectrum of RX J1334.2+3759. The narrow-line region of RX J1334.2+3759 appears to be significantly different from those of normal Seyfert galaxies. A possible explanation for the observed properties of the narrow line region and the broad line region is suggested in terms of density enhancements.Comment: 13 pages with 9 figures, LaTex. To appear in MNRA

Ram-Pressure Stripping of Galaxies in High-Redshift Clusters and Influence of ICM Heating

We have investigated the ram-pressure stripping of disk galaxies in clusters at various redshifts and in cluster progenitors; the clusters grow up on a hierarchical clustering scenario. We consider a radially infalling galaxy whose initial position and velocity are given by a spherical collapse model of structure formation. Moreover, since observations show that the intracluster medium (ICM) of nearby clusters is non-gravitationally heated, we study the effect of the non-gravitational heating on the ram-pressure stripping. For a given redshift, we find that ram-pressure stripping has more influence on galaxies in more massive clusters. On the other hand, for a given mass, it has more influence on galaxies in the clusters at higher redshifts. In particular, we predict that in rich clusters at z ~> 1, most of the galaxies are affected by the ram-pressure stripping. While the non-gravitational heating significantly reduces the influence of ram-pressure stripping on galaxies in clusters with mass smaller than 1-5 10^13 M_sun, it does not affect the influence in richer clusters. If the ICM is heated non-gravitationally at z>>1, ram-pressure stripping does not occur at z ~ 1-2 in the progenitors of clusters observed at 0 ~< z ~< 0.5, because the heat makes the ICM fraction of the cluster progenitors small. On the other hand, if the ICM is heated non-gravitationally at z ~ 0 for the first time, the ram-pressure stripping occurs even at z ~ 3. We compare the results with the observations of galaxies in clusters at various redshifts.Comment: 22 pages, 7 figures, to be published in Ap

Computing welfare losses from data under imperfect competition with heterogeneous goods

We study the percentage of welfare losses (PWL) yielded by imperfect competition under product differentiation. When demand is linear, if prices, outputs, costs and the number of firms can be observed, PWL is arbitrary in both Cournot and Bertrand equilibria. If in addition, the elasticity of demand (resp. cross elasticity of demand) is known, we can calculate PWL in Cournot (resp. Bertrand) equilibrium. When demand is isoelastic and there are many firms, PWL can be computed from prices, outputs, costs and the number of .rms. In all these cases we find that price-marginal cost margins and demand elasticities may influence PWL in a counterintuitive way. We also provide conditions under which PWL increases or decreases with concentration

Ionized Absorbers in AGN: the Role of Collisional Ionization and Time-Evolving Photoionization

In this paper we explore collisional ionization and time-evolving photoionization in the, X-ray discovered, ionized absorbers in Seyfert galaxies. These absorbers show temporal changes inconsistent with simple equilibrium models. We develop a simple code to follow the temporal evolution of non-equilibrium photoionized gas. As a result several effects appear that are easily observable; and which, in fact, may explain otherwise paradoxical behavior. Specifically we find that: 1) In many important astrophysical conditions pure collisional and photoionization equilibria can be distinguished with moderate spectral resolution observations, due to a strong absorption structure between 1 and 3 keV. 2) In time-evolving non-equilibrium photoionization models the response of the ionization state of the gas to sudden changes of the ionizing continuum is smoothed and delayed at low gas densities, even when the luminosity increases. 3) If the changes of the ionizing luminosity are not instantaneous, and the electron density is low enough (the limit depends on the average ionization state of the gas), the ionization state of the gas can continue to increase while the source luminosity decreases, so a maximum in the ionization state of a given element may occur during a minimum of the ionizing intensity (the opposite of the prediction of equilibrium models). 4) Different ions of different elements reach their equilibrium configuration on different time-scales. These properties are similar to those seen in several ionized absorbers in AGN, properties which had hitherto been puzzling. We applied these models to a high S/N ROSAT PSPC observation of the Seyfert 1 galaxy NGC 4051.Comment: 36 pages, 10 figures, accepted for publication on Apj, in pres

A historic jet-emission minimum reveals hidden spectral features in 3C 273

Aims. The aim of this work is to identify and study spectral features in the quasar 3C 273 usually blended by its strong jet emission. Method. A historic minimum in the sub-millimetre emission of 3C 273 triggered coordinated multi-wavelength observations in June 2004. X-ray observations from the INTEGRAL, XMM-Newton and RXTE satellites are complemented by ground-based optical, infrared, millimetre and radio observations. The overall spectrum is used to model the infrared and X-ray spectral components. Results. Three thermal dust emission components are identified in the infrared. The dust emission on scales from 1 pc to several kpc is comparable to that of other quasars, as expected by AGN unification schemes. The observed weakness of the X-ray emission supports the hypothesis of a synchrotron self-Compton origin for the jet component. There is a clear soft-excess and we find evidence for a very broad iron line which could be emitted in a disk around a Kerr black hole. Other signatures of a Seyfert-like X-ray component are not detected.Comment: 4 pages. Accepted for publication in A&A Letter