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We present the discovery of four absorption lines in the X-ray spectrum of the Seyfert Galaxy NGC 1365, at energies between 6.7 and 8.3 keV. The lines are detected with high statistical confidence (from >20sigma for the strongest to \~4sigma for the weakest) in two XMM-Newton observations 60 ksec long. We also detect the same lines, with lower signal-to-noise (but still >2sigma for each line) in two previous shorter (~10 ksec) XMM observations. The spectral analysis identifies these features as FeXXV and FeXXVI Kalpha and Kbeta lines, outflowing with velocities varying between ~1000 to ~5000 km/s among the observations. These are the highest quality detections of such lines so far. The high equivalent widths (EW(Kalpha)~100 eV) and the Kalpha/Kbeta ratios imply that the lines are due to absorption of the AGN continuum by a highly ionized gas with column density N_H~5x10^23 cm^{-2}, 15 pages, 4 figures. Accepted for publication in ApJ Letters

We present new X-ray spectral data for the Seyfert 1 nucleus in NGC 4151 observed with Chandra for {approx}200 ks. A significant ACIS pileup is present, resulting in a nonlinear count rate variation during the observation. With pileup corrected spectral fitting, we are able to recover the spectral parameters and find consistency with those derived from unpiled events in the ACIS readout streak and outer region from the bright nucleus. The absorption corrected 2-10 keV flux of the nucleus varied between 6 x 10{sup -11} erg s{sup -1} cm{sup -2} and 10{sup -10} erg s{sup -1} cm{sup -2} (L{sub 2-10{sub keV}} {approx} 1.3-2.1 x 10{sup 42} erg s{sup -1}). Similar to earlier Chandra studies of NGC 4151 at a historical low state, the photon indices derived from the same absorbed power-law model are {Gamma} {approx} 0.7-0.9. However, we show that {Gamma} is highly dependent on the adopted spectral models. Fitting the power-law continuum with a Compton reflection component gives {Gamma} {approx} 1.1. By including passage of non-uniform X-ray obscuring clouds, we can reproduce the apparent flat spectral states with {Gamma} {approx} 1.7, typical for Seyfert 1 active galactic nuclei. The same model also fits the hard spectra from previous ASCAmore » 'long look' observation of NGC 4151 in the lowest flux state. The spectral variability during our observation can be interpreted as variations in intrinsic soft continuum flux relative to a Compton reflection component that is from distant cold material and constant on short timescale, or variations of partially covering absorber in the line of sight toward the nucleus. An ionized absorber model with ionization parameter log {xi} {approx} 0.8-1.1 can also fit the low-resolution ACIS spectra. If the partial covering model is correct, adopting a black hole mass M{sub BH{approx}}4.6x10{sup 7} M{sub sun} we constrain the distance of the obscuring cloud from the central black hole to be r {approx_lt} 9 lt-day, consistent with the size of the broad emission line region of NGC 4151 from optical reverberation mapping.« less

We present a correlation between the 2-10 keV spectral slope {gamma} {sub X} and the Eddington ratio L/L{sub EDD} in a sample of {approx}400 Sloan Digital Sky Survey (SDSS) quasars with available hard X-ray spectra from XMM-Newton serendipitous observations. We find that the {gamma} {sub X}-L/L {sub EDD} correlation is strongest in objects with black hole (BH) masses determined from the H{beta} line, and weaker (but still present) for those based on Mg II. An empirical nonlinear correction of the Mg II-based masses, obtained by comparing the mass estimates in SDSS quasars having both H{beta} and Mg II measurements, significantly increases the strength of the correlation. No correlation is found among objects with BH masses derived from C IV, confirming that this line is not a reliable indicator of the BH mass. No significant correlation is found with the bolometric luminosity, while a {gamma} {sub X}-M {sub BH} relation is present, though with a lower statistical significance than between {gamma} {sub X} and L/L {sub EDD}. Our results imply a physical link between the accretion efficiency in the (cold) accretion disk of active galactic nuclei and the physical status of the (hot) corona responsible for the X-ray emission.

We have cross-correlated the SDSS DR3 Schneider et al. (2005) quasar catalog with the XMM-Newton archive. Color and redshift selections (g - r > 0.5 and 0.9 z =10,500 km s^{-1}), moderately flat, but unabsorbed X-ray spectra =1.66+/-0.08), and low accretion rates (mdot/mdot_{Edd}} ~ 0.01). We suggest low accretion rates as a possible physical explanation for quasars with intrinsically red optical continua. We find that 8 of 17 quasars can be classified as dust-reddened. Three of these have upper-limits on the absorption column from X-ray spectral fits of N_H = 3-13 x 10^{22} cm^2, while the other five quasars must be absorbed by at least N_H = 10^{23} cm^2 in order to be consistent with a comparably selected alpha_{ox}-l_{uv} distribution. Two objects in the sample are unclassified.

grisaliti@cfa.harvard.eduABSTRACTWe present multiple Chandra and XMM-Newton observations of the type 1.8Seyfert Galaxy NGC 1365, which shows the most dramatic X-rayspectral changesobserved so far in an AGN: the source switched from reflection dominated totransmission dominated and back in just 6 weeks. During this time the softthermal component, arising from a ∼ 1 kpc region around the center, remainedconstant. The reflection component is constant at all timescales, and its high fluxrelative to the primary component implies the presence of thick gas covering alarge fraction of the solid angle. The presence of this gas, and the fast variabilitytime scale, suggest that the Compton-thick to Compton thin change is due tovariation in the line-of-sight absorber, rather than to extreme intrinsic emissionvariability. We discuss a structure of the circumnuclear absorber/reflector whichcan explain the observed X-ray spectral and temporal properties.Subject headings: Galaxies: AGN — X-rays: galaxies — Galaxies: individual(NGC 1365)1. IntroductionAccording to the Unified Model of Active Galactic Nuclei (AGNs, see review by Urry &Padovani, 1995), an axisymmetric absorber/reflector is present around the central black holeof AGNs, with a size between that of the Broad Emission Line Region (BELR, ∼ 1000 R

We present two Rossi Xray Timing Explorer (RXTE) PCA observations of the type~2 Seyfert galaxy NGC 4388 caught in an unusual low X-ray absorption state. The observations were triggered by a detection in the 1.5-3 keV band of the RXTE All-Sky Monitor. NGC 4388 was found at a somewhat high continuum level (f(2-10 keV)=8x10(-11)erg cm(-2) s(-1)) and with a column density (N_H~3x10(22)cm(-2)), a factor ~10 lower than normal. The second PCA observation, four hours later, gave N_H

We present Chandra observations of 18 spectroscopically selected quasars, already known to be X-ray weak from previous ROSAT observations. All the sources but one are detected by Chandra, and spectral analysis suggests that most of them are intrinsically underluminous in the X-rays (by a factor from 3 to >100). These objects could represent a large population of quasars with a Spectral Energy Distribution different from that of standard blue quasars. We discuss the possibility that a significant fraction of the obscured AGN needed in Synthesis models of the X-ray background could be instead optically broad-line, X-ray weak quasars.

We present X-ray spectral analyses for three Seyfert 2 active galactic nuclei (AGNs), NGC 424, NGC 1320, and IC 2560, observed by NuSTAR in the 3-79 keV band. The high quality hard X-ray spectra allow detailed modeling of the Compton reflection component for the first time in these sources. Using quasi-simultaneous NuSTAR and Swift/XRT data, as well as archival XMM-Newton data, we find that all three nuclei are obscured by Compton-thick material with column densities in excess of similar to 5 x 10(24) cm(-2), and that their X-ray spectra above 3 keV are dominated by reflection of the intrinsic continuum on Compton-thick material. Due to the very high obscuration, absorbed intrinsic continuum components are not formally required by the data in any of the sources. We constrain the intrinsic photon indices and the column density of the reflecting medium through the shape of the reflection spectra. Using archival multi-wavelength data we recover the intrinsic X-ray luminosities consistent with the broadband spectral energy distributions. Our results are consistent with the reflecting medium being an edge-on clumpy torus with a relatively large global covering factor and overall reflection efficiency of the order of 1%. Given the unambiguous confirmation of the Compton-thick nature of the sources, we investigate whether similar sources are likely to be missed by commonly used selection criteria for Compton-thick AGNs, and explore the possibility of finding their high-redshift counterparts.

We use the integrated spectrum of the X-ray background and quasars Spectral Energy Distribution to derive the contribution of quasars to the energy output of the Universe. We find a lower limit for the energy from accretion onto black holes of 6%, of the total luminosity of the Universe and probably more, with 15% quite possible. Comparing these values with the masses of black holes in the center of nearby galaxies we show that the accretion process must be on average very efficient: at least 15% of the accreted mass must be transformed into radiated energy. This further implies that most supermassive black holes are rapidly rotating., 8 Pages, Astrophysical Journal Letters, in press

We have obtained a high spatial resolution X-ray image of the nucleus of NGC 1068 using the High Resolution Camera (HRC-I) on board the Chandra X-ray Observatory, which provides an unprecedented view of the innermost 1 arcsecond radius region of this galaxy. The HRC image resolves the narrow line region into X-ray emission clumps matching bright emission-line clouds in the HST [OIII]5007 images and allows comparison with sub-arcsecond scale radio jet for the first time. Two distinct X-ray knots are revealed at 1.3-1.4 arcsecond northeast and southwest of the nucleus. Based on the combined X-ray, [OIII], and radio continuum morphology, we identify the locations of intense radio jet-cloud interaction. The [OIII] to soft X-ray ratios show that some of these clouds are strongly affected by shock heating, whereas in other locations the jet simply thrusts through with no signs of strong interaction. This is further strengthened by the presence of a kT~1 keV collisionally ionized component in the ACIS spectrum of a shock heated cloud (HST-G). We estimate that the kinematic luminosity of the jet-driven shocks is 6x10^{38} erg/s, a negligible fraction (10^{-4}) of the estimated total jet power., Comment: Accepted for publication in ApJ. 16 pages, 4 figures, and 1 table

We have studied the X-ray emission within the inner 150 pc radius of NGC 4151 by constructing high spatial resolution emission line images of OVII, OVIII, and NeIX. These maps show extended structures that are spatially correlated with the radio outflow and optical [OIII] emission. We find strong evidence for jet--gas cloud interaction, including morphological correspondences with regions of X-ray enhancement, peaks of near-infrared [FeII] emission, and optical clouds. In these regions, moreover, we find evidence of elevated NeIX/OVII ratios; the X-ray emission of these regions also exceeds that expected from nuclear photoionization. Spectral fitting reveals the presence of a collisionally ionized component. The thermal energy of the hot gas suggests that >0.1% of the estimated jet power is deposited into the host interstellar medium through interaction between the radio jet and the dense medium of the circum-nuclear region. We find possible pressure equilibrium between the collisionally ionized hot gas and the photoionized line-emitting cool clouds. We also obtain constraints on the extended iron and silicon fluorescent emission. Both lines are spatially unresolved. The upper limit on the contribution of an extended emission region to the Fe Kalpha emission is, Accepted for publication in ApJ. 28 pages, 9 figures