Search

We present results of X-ray spectral and time-domain variability analyses of 4 faint, "quiescent" blazars from the Swift-BAT 105-month catalog. We use observations from a recent, 5-month long NICER campaign, as well as archival BAT data. Variations in the 0.3-2 keV flux are detected on minute, $\sim$weekly, and monthly timescales, but we find that the fractional variability $F_{\rm var}$ on these timescales is $, Accepted for publication in MNRAS. 11 pages, 7 figures

Changing-look (CL) AGN are unique probes of accretion onto supermassive black holes (SMBHs), especially when simultaneous observations in complementary wavebands allow investigations into the properties of their accretion flows. We present the results of a search for CL behaviour in 412 Swift-BAT detected AGN with multiple epochs of optical spectroscopy from the BAT AGN Spectroscopic Survey (BASS). 125 of these AGN also have 14-195 keV ultra-hard X-ray light-curves from Swift-BAT which are contemporaneous with the epochs of optical spectroscopy. Eight CL events are presented for the first time, where the appearance or disappearance of broad Balmer line emission leads to a change in the observed Seyfert type classification. Combining with known events from the literature, 21 AGN from BASS are now known to display CL behaviour. Nine CL events have 14-195 keV data available, and five of these CL events can be associated with significant changes in their 14-195 keV flux from BAT. The ultra-hard X-ray flux is less affected by obscuration and so these changes in the 14-195 keV band suggest that the majority of our CL events are not due to changes in line-of-sight obscuration. We derive a CL rate of 0.7-6.2 per cent on 10-25 year time-scales, and show that many transitions happen within at most a few years. Our results motivate further multi-wavelength observations with higher cadence to better understand the variability physics of accretion onto SMBHs., 14 pages, 7 figures, plus appendix. v2: updated references. Published in MNRAS

We constrain the intrinsic Eddington ratio (λ Edd) distribution function for local active galactic nuclei (AGN) in bins of low and high obscuration [ log ( N H / cm − 2 ) ≤ 22 and 22 < log ( N H / cm − 2 ) < 25 ], using the Swift Burst Alert Telescope 70 month/BASS DR2 survey. We interpret the fraction of obscured AGN in terms of circumnuclear geometry and temporal evolution. Specifically, at low Eddington ratios ( log λ Edd < −2), obscured AGN outnumber unobscured ones by a factor of ∼4, reflecting the covering factor of the circumnuclear material (0.8, or a torus opening angle of ∼34°). At high Eddington ratios ( log λ Edd > −1), the trend is reversed, with 22 , which we suggest is mainly due to the small fraction of time spent in a highly obscured state. Considering the Eddington ratio distribution function of narrow-line and broad-line AGN from our prior work, we see a qualitatively similar picture. To disentangle temporal and geometric effects at high λ Edd, we explore plausible clearing scenarios such that the time-weighted covering factors agree with the observed population ratio. We find that the low fraction of obscured AGN at high λ Edd is primarily due to the fact that the covering factor drops very rapidly, with more than half the time spent with, The Astrophysical Journal Letters, 939 (1), ISSN:1967-2014, ISSN:2041-8213

Theory predicts that a supermassive black hole binary (SMBHB) could be observed as a luminous active galactic nucleus (AGN) that periodically varies on the order of its orbital timescale. In X-rays, periodic variations could be caused by mechanisms including relativistic Doppler boosting and shocks. Here we present the first systematic search for periodic AGNs using $941$ hard X-ray light curves (14-195 keV) from the first 105 months of the Swift Burst Alert Telescope (BAT) survey (2004-2013). We do not find evidence for periodic AGNs in Swift-BAT, including the previously reported SMBHB candidate MCG+11$-$11$-$032. We find that the null detection is consistent with the combination of the upper-limit binary population in AGNs in our adopted model, their expected periodic variability amplitudes, and the BAT survey characteristics. We have also investigated the detectability of SMBHBs against normal AGN X-ray variability in the context of the eROSITA survey. Under our assumptions of a binary population and the periodic signals they produce which have long periods of hundreds of days, up to $13$% true periodic binaries can be robustly distinguished from normal variable AGNs with the ideal uniform sampling. However, we demonstrate that realistic eROSITA sampling is likely to be insensitive to long-period binaries because longer observing gaps reduce their detectability. In contrast, large observing gaps do not diminish the prospect of detecting binaries of short, few-day periods, as 19% can be successfully recovered, the vast majority of which can be identified by the first half of the survey., 17 pages, including 8 figures and 4 tables. Accepted for publication in ApJ

We study the ${r}_{31}={L}_{\mathrm{CO}(3\mbox{--}2)}^{{\prime} }/{L}_{\mathrm{CO}(1\mbox{--}0)}^{{\prime} }$ luminosity line ratio in a sample of nearby (z 104 cm−3). We find a mild tightening of the Kennicutt–Schmidt relation when we use the molecular gas mass surface density traced by CO(3–2) (Pearson correlation coefficient R = 0.83), instead of the molecular gas mass surface density traced by CO(1–0) (R = 0.78), but the increase in correlation is not statistically significant (p-value = 0.06). This suggests that the CO(3–2) line can be reliably used to study the relation between SFR and molecular gas for normal SFGs at high redshift and to compare it with studies of low-redshift galaxies, as is common practice.

Located at the center of the Perseus cluster, 3C 84 is an extremely bright and nearby radio galaxy. Because of the strong diffuse thermal emission from the cluster in X-rays, the detailed properties and the origin of a power-law component from the central active galactic nucleus (AGN) remains unclear in the source. We report here the first NuSTAR observations of 3C 84. The source was observed for 24.2 and 32 ks on February 01 and 04, 2018, respectively. NuSTAR observations spectrally decompose the power-law AGN component above 10 keV. The power-law component dominates the spectrum above 20 keV with a photon index $\sim$1.9 and an energy flux F$_{20-30 keV}$ = 1.0 $\times$10$^{-11}$ erg cm$^{-2}$ s$^{-1}$, corresponding to an isotropic luminosity, $L_{20-30 keV}$ = 7.4$\times$10$^{42}$ erg s$^{-1}$. We discuss possible emitting sites for the power-law component. The expected thermal emission from the accretion disk is not hot enough to account for the hard X-rays detected from the source. Similar X-ray and $\gamma$-ray photon indices and long-term flux variations, the absence of cutoff energy in the hard X-ray spectrum of the source, correlated hard X-ray flux and hardness ratio variations, and the similarity of optical-X-ray slope to blazar rather than Seyfert galaxies supports the hard X-ray power-law component originating from the jet., Comment: accepted for publication in ApJ Letters

Arcus, a Medium Explorer (MIDEX) mission, was selected by NASA for a Phase A study in August 2017. The observatory provides high-resolution soft X-ray spectroscopy in the 12-50 A bandpass with unprecedented sensitivity: effective areas of >350 cm^2 and spectral resolution >2500 at the energies of O VII and O VIII for z=0-0.3. The Arcus key science goals are (1) to measure the effects of structure formation imprinted upon the hot baryons that are predicted to lie in extended halos around galaxies, groups, and clusters, (2) to trace the propagation of outflowing mass, energy, and momentum from the vicinity of the black hole to extragalactic scales as a measure of their feedback and (3) to explore how stars, circumstellar disks and exoplanet atmospheres form and evolve. Arcus relies upon the same 12m focal length grazing-incidence silicon pore X-ray optics (SPO) that ESA has developed for the Athena mission; the focal length is achieved on orbit via an extendable optical bench. The focused X-rays from these optics are diffracted by high-efficiency Critical-Angle Transmission (CAT) gratings, and the results are imaged with flight-proven CCD detectors and electronics. The power and telemetry requirements on the spacecraft are modest. Arcus will be launched into an ~ 7 day 4:1 lunar resonance orbit, resulting in high observing efficiency, low particle background and a favorable thermal environment. Mission operations are straightforward, as most observations will be long (~100 ksec), uninterrupted, and pre-planned. The baseline science mission will be completed in

We present a Hubble Space Telescope (HST) survey of extended [O III] {\lambda}5007 emission for a sample of 12 nearby (z < 0.12), luminous Type 2 quasars (QSO2s), which we use to measure the extent and kinematics of their AGN-ionized gas. We find the size of the observed [O III] regions scale with luminosity in comparison to nearby, less luminous Seyfert galaxies and radially outflowing kinematics to exist in all targets. We report an average maximum outflow radius of $\sim$600 pc, with gas continuing to be kinematically influenced by the central AGN out to an average radius of $\sim$1130 pc. These findings question the effectiveness of AGN being capable of clearing material from their host bulge in the nearby universe and suggest that disruption of gas by AGN activity may prevent star formation without requiring evacuation. Additionally, we find a dichotomy in our targets when comparing [O III] radial extent and nuclear FWHM, where QSO2s with compact [O III] morphologies typically possess broader nuclear emission-lines., Comment: 24 pages, 18 figures, accepted for publication in ApJ

Major galaxy mergers are thought to play an important part in fuelling the growth of supermassive black holes

The Swift/BAT 9-month catalogue of active galactic nuclei (AGN) provides an unbiased census of local supermassive black hole accretion, and probes to all but the highest levels of absorption in AGN. We explore a method for characterising the bolometric output of both obscured and unobscured AGN by combining the hard X-ray data from Swift/BAT (14-195keV) with the reprocessed IR emission as seen with the IRAS all-sky surveys. This approach bypasses the complex modifications to the SED introduced by absorption in the optical, UV and 0.1-10 keV regimes and provides a long-term, average picture of the bolometric output of these sources. We broadly follow the approach of Pozzi et al. for calculating the bolometric luminosities by adding nuclear IR and hard X-ray luminosities, and consider different approaches for removing non-nuclear contamination in the large-aperture IRAS fluxes. Using mass estimates from the M_BH-L_bulge relation, we present the Eddington ratios \lambda_Edd and 2-10 keV bolometric corrections for a subsample of 63 AGN (35 obscured and 28 unobscured) from the Swift/BAT catalogue, and confirm previous indications of a low Eddington ratio distribution for both samples. Importantly, we find a tendency for low bolometric corrections (typically 10-30) for the obscured AGN in the sample (with a possible rise from ~15 for \lambda_Edd, Comment: 19 pages, 16 figures, 2 tables. Accepted for publication in MNRAS

The Swift Burst Alert Telescope (BAT) survey of Active Galactic Nuclei (AGN) is providing an unprecedented view of local AGNs ( = 0.03) and their host galaxy properties. In this paper, we present an analysis of the optical spectra of a sample of 64 AGNs from the 9-month survey, detected solely based on their 14-195 keV flux. Our analysis includes both archived spectra from the Sloan Digital Sky Survey and our own observations from the 2.1-m Kitt Peak National Observatory telescope. Among our results, we include line ratio classifications utilizing standard emission line diagnostic plots, [O III] 5007 A luminosities, and H-beta derived black hole masses. As in our X-ray study, we find the type 2 sources to be less luminous (in [O III] 5007 A and 14-195 keV luminosities) with lower accretion rates than the type 1 sources. We find that the optically classified LINERs, H II/composite galaxies, and ambiguous sources have the lowest luminosities, while both broad line and narrow line Seyferts have similar luminosities. From a comparison of the hard X-ray (14-195 keV) and [O III] luminosities, we find that both the observed and extinction-corrected [O III] luminosities are weakly correlated with X-ray luminosity. In a study of the host galaxy properties from both continuum fits and measurements of the stellar absorption indices, we find that the hosts of the narrow line sources have properties consistent with late type galaxies.

We present a study of the radial velocity offsets between narrow emission lines and host galaxy lines (stellar absorption and H I 21-cm emission) in Seyfert galaxies with observed redshifts less than 0.043. We find that 35% of the Seyferts in the sample show [O III] emission lines with blueshifts with respect to their host galaxies exceeding 50 km/s, whereas only 6% show redshifts this large, in qualitative agreement with most previous studies. We also find that a greater percentage of Seyfert 1 galaxies show blueshifts than Seyfert 2 galaxies. Using HST/STIS spatially-resolved spectra of the Seyfert 2 galaxy NGC 1068 and the Seyfert 1 galaxy NGC 4151, we generate geometric models of their narrow-line regions (NLRs) and inner galactic disks, and show how these models can explain the blueshifted [O III] emission lines in collapsed STIS spectra of these two Seyferts. We conclude that the combination of mass outflow of ionized gas in the NLR and extinction by dust in the inner disk (primarily in the form of dust spirals) is primarily responsible for the velocity offsets in Seyfert galaxies. More exotic explanations are not needed. We discuss the implications of this result for the velocity offsets found in higher redshift AGN., 25 pages, 7 figures, accepted for publication in the Astrophysical Journal

(Abridged) We present simultaneous optical--to--X-ray spectral energy distributions (SEDs) from Swift's X-ray and UV--optical telescopes (XRT and UVOT) for a well-selected sample of 26 low-redshift (z, Comment: 25 pages, 22 figures, 4 tables, accepted for publication in MNRAS

著者人数：13名, Accepted: 2009-06-17, 資料番号: SA1001466000

The fraction of Compton-thick sources is one of the main uncertainties left in understanding the active galactic nucleus (AGN) population. The Swift Burst Alert Telescope (BAT) all-sky survey for the first time gives us an unbiased sample of AGNs for all but the most heavily absorbed sources N H > 1025 cm–2). Still, the BAT spectra (14-195 keV) are time averaged over months of observations and therefore hard to compare with softer spectra from the Swift XRT or other missions. This makes it difficult to distinguish between Compton-thin and Compton-thick models. With Suzaku, we have obtained simultaneous hard (>15 keV) and soft (0.3-10 keV) X-ray spectra for five Compton-thick candidate sources. We report on the spectra and a comparison with the BAT and earlier XMM observations. Based on both flux variability and spectral shape, we conclude that these hidden sources are not Compton thick. We also report on a possible correlation between excess variance and Swift BAT luminosity from the 16 day binned light curves, which holds true for a sample of both absorbed (four sources), unabsorbed (eight sources), and Compton-thick (Circinus) AGNs, but is weak in the 64 day binned BAT light curves.

We report on Suzaku observations of four unidentified sources from the INTEGRAL and Swift BAT Galactic plane surveys. All the sources have a large neutral hydrogen column density and are likely members of an emerging class of heavily absorbed high mass X-ray binary (HMXB) first identified in INTEGRAL observations. Two of the sources in our sample are approximately constant flux sources, one source shows periodic variation and one source exhibited a short, bright X-ray outburst. The periodicity is transient, suggesting it is produced by a neutron star in an elliptical orbit around a stellar wind source. We analyze the flaring source in several segments to look for spectral variation and discuss the implications of the findings for the nature of the source. We conclude that all four sources in our sample can be identified with the emerging class of highly absorbed HMXBs, that one is a newly identified transient X-ray pulsar and that at least one is a newly identified supergiant fast X-ray transient (SFXT)., 22 pages, 5 figures, submitted to ApJ

We use 3 years of data from the Swift/BAT survey to select a complete sample of X-ray blazars above 15 keV. This sample comprises 26 Flat-Spectrum Radio Quasars (FSRQs) and 12 BL Lac objects detected over a redshift range of 0.03, Comment: Accepted for publication in The Astrophysical Journal. 59 pages, 18 figures, 5 tables

We present a systematic spectral analysis with Suzaku of six active galactic nuclei (AGNs) detected in the Swift/BAT hard X-ray (15-200 keV) survey: Swift J0138.6–4001, J0255.2–0011, J0350.1–5019, J0505.7–2348, J0601.9–8636, and J1628.1–5145. This is considered to be a representative sample of new AGNs without X-ray spectral information before the BAT survey. We find that the 0.5-200 keV spectra of these sources can be uniformly fitted with a base model consisting of heavily absorbed (log N H > 23.5 cm–2) transmitted components, scattered lights, a reflection component, and an iron-K emission line. There are two distinct groups: three "new-type" AGNs (including the two sources reported by Ueda et al.) with an extremely small scattered fraction (f scat 0.5% and R 0.8. The spectral parameters suggest that the new type has an optically thick torus for Thomson scattering (N H ~ 1025 cm–2) with a small opening angle θ ~ 20° viewed in a rather face-on geometry, while the classical type has a thin torus (N H ~ 1023-24 cm–2) with θ 30°. We infer that a significant number of new-type AGNs with an edge-on view are missing in the current all-sky hard X-ray surveys.

We measure the correlation between sky coordinates of the Swift BAT catalogue of active galactic nuclei with the arrival directions of the highest energy cosmic rays detected by the Auger Observatory. The statistically complete, hard X-ray catalogue helps to distinguish between AGN and other source candidates that follow the distribution of local large-scale structure. The positions of the full catalogue are marginally uncorrelated with the cosmic ray arrival directions, but when weighted by their hard X-ray flux, AGN within 100 Mpc are correlated at a significance level of 98 per cent. This correlation sharply decreases for sources beyond ~100 Mpc, suggestive of a GZK suppression. We discuss the implications for determining the mechanism that accelerates particles to these extreme energies in excess of 10^19 eV., 5 pages, 2 figures. Accepted for publication in MNRAS

The SWIFT gamma ray observatory's Burst Alert Telescope (BAT) has detected a sample of active galactic nuclei (AGN) based solely on their hard X-ray flux (14-195 keV). In this paper, we present for the first time {\it XMM-Newton} X-ray spectra for 22 BAT AGNs with no previously analyzed X-ray spectra. If our sources are a representative sample of the BAT AGN, as we claim, our results present for the first time global X-ray properties of an unbiased towards absorption (n$_H = 0.03$), AGN sample. We find 9/22 low absorption (n$_H 2.0$ keV. Five of the complex sources are classified as Compton-thick candidates. Further, we find four more sources with properties consistent with the hidden/buried AGN reported by Ueda {\it et al.} (2007). Finally, we include a comparison of the {\it XMM-Newton} EPIC spectra with available SWIFT X-ray Telescope (XRT) observations. From these comparisons, we find 6/16 sources with varying column densities, 6/16 sources with varying power law indices, and 13/16 sources with varying fluxes, over periods of hours to months. Flux and power law index are correlated for objects where both parameters vary.

著者人数: 16名, Accepted: 2006-12-28, 資料番号: SA1000323000

著者人数: 16名, Accepted: 2006-09-13, 資料番号: SA1000359000

(abridged) In this paper, we examined XMM Newton EPIC spectra of 14 ultra-luminous X-ray sources (ULXs)in addition to the XMM RGS spectra of two sources (Holmberg II X-1 and Holmberg IX X-1). We determined oxygen and iron abundances of the host galaxy's interstellar medium (ISM) using K-shell (O) and L-shell (Fe) X-ray photo-ionization edges towards these ULXs. We found that the oxygen abundances closely matched recent solar abundances for all of our sources, implying that ULXs live in similar local environments despite the wide range of galaxy host properties. Also, we compare the X-ray hydrogen column densities (n_H) for 8 ULX sources with column densities obtained from radio H I observations. The X-ray model n_H values are in good agreement with the H I n_H values, implying that the hydrogen absorption towards the ULXs is not local to the source (with the exception of the source M81 XMM1). In order to obtain the column density and abundance values, we fit the X-ray spectra of the ULXs with a combined power law and one of several accretion disk models. We tested the abundances obtained from the XSPEC models bbody, diskbb, grad, and diskpn along with a power law, finding that the abundances were independent of the thermal model used. We comment on the physical implications of these different model fits. We also note that very deep observations allow a breaking of the degeneracy noted by Stobbart et al. (2006) favoring a high mass solution for the absorbed grad + power law model.

We have conducted an archival XMM-Newton study of the bright X-ray point sources in 32 nearby galaxies. From our list of approximately 100 point sources, we attempt to determine if there is a low-state counterpart to the Ultraluminous X-ray (ULX) population. Indeed, 16 sources in our sample match the criteria we set for a low-state ULX, namely, L(sub X) greater than 10(exp 38 ergs per second) and a spectrum best fit with an absorbed power law. Further, we find evidence for 26 high-state ULXs which are best fit by a combined blackbody and a power law. As in Galactic black hole systems, the spectral indices, GAMMA, of the low-state objects, as well a s the luminosities, tend to be lower than those of the high-state objects. The observed range of blackbody temperatures is 0.1-1 keV with the most luminous systems tending toward the lowest temperatures. We also find a class of object whose properties (luminosity, blackbody temperature, and power law slopes) are very similar to those of galactic stellar mass black holes. In addition, we find a subset of these objects that can be best fit by a Comptonized spectrum similar to that used for Galactic black holes in the very high state, when they are radiating near the Eddington limit.

We present the spatial correlation function analysis of non-stellar X-ray point sources in the Chandra Large Area Synoptic X-ray Survey of Lockman Hole Northwest (CLASXS). Our 9 ACIS-I fields cover a contiguous solid angle of 0.4 deg^2 and reach a depth of 3x10^-15 c.g.s in the 2-8 keV band. We supplement our analysis with data from the Chandra Deep Field North (CDFN). The addition of this field allows better probe of the correlation function at small scales. A total of 233 and 252 sources with spectroscopic information are used in the study of the CLASXS and CDFN fields respectively. We calculate both redshift-space and projected correlation functions in comoving coordinates, averaged over the redshift range of 0.1, Comment: ApJ accepted. A missing hubble constant h has been noticed in one of the equations and hence corrected. Tables, figures affected are changed. The results and conclusions however are not significantly affected

We present measurements of the oxygen abundance of the Milky Way's ISM by observing the K-shell X-ray photoionization edge towards galaxy clusters. This effect is most easily observed towards objects with galactic columns (n_H) of a few times 1e21 cm^-2. We measure X-ray column densities towards 11 clusters and find that at high galactic columns above approximately 1e21 cm^-2 the X-ray columns are generally 1.5--3.0 times greater than the 21 cm H II columns, indicating that molecular clouds become an important contributor to n_H at higher columns. We find the average ISM oxygen abundance to be (O/H) = (4.85 +/- 0.06) x 10^-4, or 0.99 solar when using the most recent solar photospheric values. Since X-ray observations are sensitive to the total amount of oxygen present (gas + dust), these results indicate a high gas to dust ratio. Also, the oxygen abundances along lines of sight through high galactic columns (n_H) are the same as abundances through low columns, suggesting that the composition of denser clouds is similar to that of the more diffuse ISM., Comment: submitted to ApJ

We report the detection of radio emission coincident with the ultraluminous X-ray source (ULX) in Holmberg II. The radio emission is diffuse and resolved, covering an area ~60 by 40 pc in extent and well-matched to the recently discovered HeII nebula surrounding the X-ray source. Comparison of the radio and optical properties of this extended radio emission argue against its association with either an HII region or supernova remnant. This is additional evidence that this ULX is not powered by a stellar-mass object whose emission is relativistically beamed towards the observer, and thus is either a super-Eddington source or intermediate mass black hole as suggested by optical observations. Implications of this result to future and existing radio studies of ULXs are discussed.

We have identified the optical counterpart of the Ultra-Luminous X-ray source Ml0l ULX-1 (CX- OKM101 J140332.74+542102), by comparing HST ACS images with Chandra ACIS-S images. The optical counterpart has V= 23.75 and colours consistent with those for a mid-B supergiant. Archival WFPC2 observations show that the source brightness is constant to within approximately 0.1 mag. The physical association of this source with the ULX is confirmed by Gemini GMOS spectroscopic observations which show spatially unresolved He II lambda4686 and He I lambda5876 emission. These results suggest that M10l ULX-1 is a HMXB but deep spectroscopic monitoring observations are needed to determine the detailed properties of this system.

We have studied the candidate optical counterparts and the stellar population in the star-forming complex around a bright ULX in NGC4559, using HST/WFPC2, XMM-Newton/OM, and ground-based data. We find that the ULX is located near a small group of OB stars. The brightest point source in the Chandra error circle is consistent with a single blue supergiant of mass ~ 20 M_sun and age ~ 10 Myr. A few other stars are resolved inside the error circle: mostly blue and red supergiants with masses ~ 10-15 M_sun and ages ~ 20 Myr. This is consistent with the interpretation of this ULX as a black hole (BH) accreting from a high-mass donor star in its supergiant phase, via Roche-lobe overflow. The observed optical colors and the blue-to-red supergiant ratio suggest a low metal abundance: 0.2 50 M_sun) than typical Milky Way BH candidates. The optical data favour a ``young'' BH originating in the recent episode of massive star formation; however, they also rule out an association with young massive star clusters. We speculate that other mechanisms may lead to the formation of relatively massive BHs (~ 50-100 M_sun) from stellar evolution processes in low-metallicity environments, or when star formation is triggered by galactic collisions.

We present the X-ray catalog and basic results from our Chandra Large Area Synoptic X-ray Survey (CLASXS) of the Lockman Hole-Northwest field. Our 9 ACIS-I fields cover a contiguous solid angle of ~0.4 sq. deg. and reach fluxes of 5E-16 cgs (0.4-2 keV) and 3E-15 cgs (2-8keV). Our survey bridges the gap between ultradeep pencil-beam surveys, such as the Chandra Deep Fields (CDFs), and shallower, large area surveys, allowing a better probe of the X-ray sources that contribute most of the 2-10 keV cosmic X-ray background (CXB). We find a total of 525 X-ray point sources and 4 extended sources. At ~10E-14 cgs 2-8 keV, our number counts are significantly higher than those of several non-contiguous, large area surveys. On the other hand, the integrated flux from the CLASXS field, combined with ASCA and Chandra ultradeep surveys, is consistent with results from other large area surveys, within the variance of the CXB. Spectral evolution is seen in the hardening of the sources at fluxes below 1E-14 cgs Above 4E1-14 cgs(0.4-8 keV), ~60 of the sources are variable. Four extended sources in CLASXS is consistent with the previously measured LogN-LogS of galaxy clusters. We report the discovery of a gravitational lensing arc associated with one of these sources. (Abridged), 67 pages, 26 figures, accepted for publication in the Astronomical Journal

We present the results from a ~53 ksec XMM observation of NGC 2276. This galaxy has an unusual optical morphology with the disk of this spiral appearing to be truncated along the western edge. This XMM observation shows that the X-ray source at the western edge is a bright Intermediate X-ray Object (IXO). Its spectrum is well fit by a multi-color disk blackbody model used to fit optically thick standard accretion disks around black holes. The luminosity derived for this IXO is 1.1x10^41 erg/s in the 0.5 - 10 keV band making it one of the most luminous discovered to date. The large source luminosity implies a large mass black hole if the source is radiating at the Eddington rate. On the other hand, the inner disk temperature determined here is too high for such a massive object given the standard accretion disk model. In addition to the IXO we find that the nuclear source in this galaxy has dimmed by at least a factor of several thousand in the eight years since the ROSAT HRI observations.

We present an XMM observation of the radio jet and diffuse halo of the nearby radio galaxy NGC6251. The EPIC spectrum of the galaxy's halo is best-fitted by a thermal model with temperature kT~1.6 keV and subsolar abundances. Interestingly, an additional hard X-ray component is required to fit the EPIC spectra of the halo above 3 keV, and is independently confirmed by an archival Chandra observation. However, its physical origin is not clear. Contribution from a population of undetected Low Mass X-ray Binaries seems unlikely. Instead, the hard X-ray component could be due to inverse Compton scattering of the CMB photons off relativistic electrons scattered throughout the halo of the galaxy, or non-thermal bremsstrahlung emission. The IC/CMB interpretation, together with limits on the diffuse radio emission, implies a very weak magnetic field, while a non-thermal bremsstrahlung origin implies the presence of a large number of very energetic electrons. We also detect X-ray emission from the outer (~3.5') jet, confirming previous ROSAT findings. Both the EPIC and ACIS spectra of the jet are best-fitted by a power law with photon index \~1.2. A thermal model is formally ruled out by the data. Assuming an origin of the X-rays from the jet via IC/CMB, as suggested by energetic arguments, and assuming equipartition implies a large Doppler factor (delta~10). Alternatively, weaker beaming is possible for magnetic fields several orders of magnitude lower than the equipartition field., Comment: 11 pages, 7 figures, accepted for publication in A&A; typos corrected