Search

著者人数: 42名, Accepted: 2016-01-18, 資料番号: SA1160090000

The compact configuration of Phase II of the Murchison Widefield Array (MWA) consists of both a redundant subarray and pseudo-random baselines, offering unique opportunities to perform sky-model and redundant interferometric calibration. The highly redundant hexagonal cores give improved power spectrum sensitivity. In this paper, we present the analysis of nearly 40 hours of data targeting one of the MWA's EoR fields observed in 2016. We use both improved analysis techniques presented in Barry et al. (2019) as well as several additional techniques developed for this work, including data quality control methods and interferometric calibration approaches. We show the EoR power spectrum limits at redshift 6.5, 6.8 and 7.1 based on our deep analysis on this 40-hour data set. These limits span a range in $k$ space of $0.18$ $h$ $\mathrm{Mpc^{-1}}$ $

We present the 24 micron rest-frame luminosity function (LF) of star-forming galaxies in the redshift range 0.0 < z < 0.6 constructed from 4047 spectroscopic redshifts from the AGN and Galaxy Evolution Survey of 24 micron selected sources in the Bootes field of the NOAO Deep Wide-Field Survey. This sample provides the best available combination of large area (9 deg^2), depth, and statistically complete spectroscopic observations, allowing us to probe the evolution of the 24 micron LF of galaxies at low and intermediate redshifts while minimizing the effects of cosmic variance. In order to use the observed 24 micron luminosity as a tracer for star formation, active galactic nuclei (AGNs) that could contribute significantly at 24 micron are identified and excluded from our star-forming galaxy sample based on their mid-IR spectral energy distributions or the detection of X-ray emission. The evolution of the 24 micron LF of star-forming galaxies for redshifts of z < 0.65 is consistent with a pure luminosity evolution where the characteristic 24 micron luminosity evolves as (1+z)^(3.8+/-0.3). We extend our evolutionary study to encompass 0.0 < z < 1.2 by combining our data with that of the Far-Infrared Deep Extragalactic Legacy Survey. Over this entire redshift range the evolution of the characteristic 24 micron luminosity is described by a slightly shallower power law of (1+z)^(3.4+/-0.2). We find a local star formation rate density of (1.09+/-0.21) x 10^-2 Msun/yr/Mpc^-3, and that it evolves as (1+z)^(3.5+/-0.2) over 0.0 < z < 1.2. These estimates are in good agreement with the rates using optical and UV fluxes corrected for the effects of intrinsic extinction in the observed sources. This agreement confirms that star formation at z, Comment: ApJ, in press, 16 pages 9 figures

Chandra observations of large samples of galaxy clusters detected in X-rays by ROSAT provide a new, robust determination of the cluster mass functions at low and high redshifts. Statistical and systematic errors are now sufficiently small, and the redshift leverage sufficiently large for the mass function evolution to be used as a useful growth of structure based dark energy probe. In this paper, we present cosmological parameter constraints obtained from Chandra observations of 36 clusters with =0.55 derived from 400deg^2 ROSAT serendipitous survey and 49 brightest z=~0.05 clusters detected in the All-Sky Survey. Evolution of the mass function between these redshifts requires Omega_Lambda>0 with a ~5sigma significance, and constrains the dark energy equation of state parameter to w0=-1.14+-0.21, assuming constant w and flat universe. Cluster information also significantly improves constraints when combined with other methods. Fitting our cluster data jointly with the latest supernovae, WMAP, and baryonic acoustic oscillations measurements, we obtain w0=-0.991+-0.045 (stat) +-0.039 (sys), a factor of 1.5 reduction in statistical uncertainties, and nearly a factor of 2 improvement in systematics compared to constraints that can be obtained without clusters. The joint analysis of these four datasets puts a conservative upper limit on the masses of light neutrinos, Sum m_nu, ApJ, in press (Feb 10, 2009 issue)

We present preliminary results from a deep (600 ks) {\em Chandra} observation of the hot interstellar medium of the nearby early-type galaxy Centaurus A (Cen A). We find a surface brightness discontinuity in the gas $\sim$3.5 kpc from the nucleus spanning a 120$^\circ$ arc. The temperature of the gas is 0.60$\pm$0.05 and 0.68$\pm$0.10 keV, interior and exterior to the discontinuity, respectively. The elemental abundance is poorly constrained by the spectral fits, but if the abundance is constant across the discontinuity, there is a factor of 2.3$\pm$0.4 pressure jump across the discontinuity. This would imply that the gas is moving at 470$\pm$100 km s$^{-1}$, or Mach 1.0$\pm$0.2 (1.2$\pm$0.2) relative to the sound speed of the gas external (internal) to the discontinuity. Alternatively, pressure balance could be maintained if there is a large (factor of $\sim$7) discontinuity in the elemental abundance. We suggest that the observed discontinuity is the result of non-hydrostatic motion of the gas core (i.e. sloshing) due to the recent merger. In this situation, both gas motions and abundance gradients are important in the visibility of the discontinuity. Cen A is in the late stages of merging with a small late-type galaxy, and a large discontinuity in density and abundance across a short distance demonstrates that the gas of the two galaxies remains poorly mixed even several hundred million years after the merger. The pressure discontinuity may have had a profound influence on the temporal evolution of the kpc-scale jet. The jet could have decollimated crossing the discontinuity and thereby forming the northeast radio lobe.

We built an optimal basis of low resolution templates for galaxies over the wavelength range from 0.2 to 10 $\mu$m using a variant of the algorithm presented by Budavari et al. (2000). We derived them using eleven bands of photometry from the NDWFS, FLAMEX, zBo\"otes and IRAC Shallow surveys for 16033 galaxies in the NDWFS Bo\"otes field with spectroscopic redshifts measured by the AGN and Galaxy Evolution Survey. We also developed algorithms to accurately determine photometric redshifts, K corrections and bolometric luminosities using these templates. Our photometric redshifts have an accuracy of $\sigma_z/(1+z) = 0.04$ when clipped to the best 95%. We used these templates to study the spectral type distribution in the field and to estimate luminosity functions of galaxies as a function of redshift and spectral type. In particular, we note that the 5-8$\mu$m color distribution of galaxies is bimodal, much like the optical g--r colors.

We present results from deeper {\em Chandra} observations of the southwest radio lobe of Centaurus A, first described by Kraft et al. (2003). We find that the sharp X-ray surface brightness discontinuity extends around $\sim$75% of the periphery of the radio lobe, and detect significant temperature jumps in the brightest regions of this discontinuity nearest to the nucleus. This demonstrates that this discontinuity is indeed a strong shock which is the result of an overpressure which has built up in the entire lobe over time. Additionally, we demonstrate that if the mean free path for ions to transfer energy and momentum to the electrons behind the shock is as large as the Spitzer value, the electron and proton temperatures will not have equilibrated along the SW boundary of the radio lobe where the shock is strongest. Thus the proton temperature of the shocked gas could be considerably larger than the observed electron temperature, and the total energy of the outburst correspondingly larger as well. We investigate this using a simple one-dimensional shock model for a two-fluid (proton/electron) plasma. We find that for the thermodynamic parameters of the Cen A shock the electron temperature rises rapidly from $\sim$0.29 keV (the temperature of the ambient ISM) to $\sim$3.5 keV at which point heating from the protons is balanced by adiabatic losses. The proton and electron temperatures do not equilibrate in a timescale less than the age of the lobe. We note that the measured electron temperature of similar features in other nearby powerful radio galaxies in poor environments may considerably underestimate the strength and velocity of the shock.

We present Chandra observations of two nearby radio galaxies in group environments, 3C285 and 3C442A. The host galaxies of both sources are involved in mergers with nearby massive galaxies, and the hot gas in the systems is extended along lines joining the interacting galaxies. Both sources show strong evidence for interactions between the radio lobes and the asymmetrical hot gas. We argue that the structure in the hot gas is independent of the existence of the radio lobes in these systems, and argue that hot gas shaped by an ongoing massive galaxy merger may play an important role in the dynamics of radio lobes in other objects. For 3C442A, our observations show that gas is being driven out of both members of the host interacting galaxy pair, and the implied constraints on galaxy velocities are consistent with mildly supersonic motions with respect to the group-scale hot gas. The previously known filamentary radio structure in the center of 3C442A may be a result of the interaction between hot gas expelled from these galaxies and pre-existing radio-emitting plasma. In 3C285, where there is no ongoing galaxy merger, the powerful radio source is probably having a significant effect on the energetics of the host group., 43 pages, 8 figures. Accepted by ApJ. Some figures reduced in quality

Accurate photometric redshifts are calculated for nearly 200,000 galaxies to a 4.5 micron flux limit of ~13 uJy in the 8.5 deg^2 Spitzer/IRAC Shallow survey. Using a hybrid photometric redshift algorithm incorporating both neural-net and template-fitting techniques, calibrated with over 15,000 spectroscopic redshifts, a redshift accuracy of \sigma = 0.06(1+z) is achieved for 95% of galaxies at 01) galaxy clusters. We present one such spectroscopically confirmed cluster at =1.24, ISCS J1434.5+3427. Finally, we present a measurement of the 4.5 micron-selected galaxy redshift distribution., Comment: 14 pages, 9 Figures, 5 Tables. ApJ in press. For a version with full-resolution figures, please see http://www.astro.utoronto.ca/~brodwin/papers/0607450.pdf

A Chandra observation of the intermediate luminosity (M_B=-20) elliptical galaxy NGC 3379 resolves 75% of the X-ray emission within the central 5kpc into point sources. Spectral analysis of the remaining unresolved emission within the central 770pc indicates that 90% of the emission probably arises from undetected point sources, while 10% arises from thermal emission from kT=0.6keV gas. Assuming a uniform density distribution in the central region of the galaxy gives a gas mass of 5.0e5 Mo.Such a small amount of gas can be supplied by stellar mass loss in only 1.0e7 years. Thus, the gas must be accreting into the central supermassive black hole at a very low radiative efficiency as in the ADAF or RIAF models, or is being expelled in a galactic wind driven by the same AGN feedback mechanism as that observed in cluster cooling flows. If the gas is being expelled in an AGN driven wind, then the ratio of mechanical to radio power of the AGN must be 1.0e4, which is comparable to that measured in cluster cooling flows which have recently been perturbed by radio outbursts. The brightest point source in NGC 3379 is located 360pc from the central AGN with a peak luminosity of 3.5e39 ergs/s, which places it in the class of ultra-luminous X-ray point sources (ULX). Analysis of an archival ROSAT HRI observation of NGC 3379 shows that this source was at a comparable luminosity 5 years prior to the Chandra observation. During the Chandra observation, the source intensity smoothly varies by a factor of two with the suggestion of an 8-10 hour period.

We compare new maps of the hot gas, dark matter, and galaxies for 1E0657-56, a cluster with a rare, high-velocity merger occurring nearly in the plane of the sky. The X-ray observations reveal a bullet-like gas subcluster just exiting the collision site. A prominent bow shock gives an estimate of the subcluster velocity, 4500 km/s, which lies mostly in the plane of the sky. The optical image shows that the gas lags behind the subcluster galaxies. The weak-lensing mass map reveals a dark matter clump lying ahead of the collisional gas bullet, but coincident with the effectively collisionless galaxies. From these observations, one can directly estimate the cross-section of the dark matter self-interaction. That the dark matter is not fluid-like is seen directly in the X-ray -- lensing mass overlay; more quantitative limits can be derived from three simple independent arguments. The most sensitive constraint, sigma/m, Text clarified; some numbers changed slightly for consistency with final version of the accompanying lensing paper. 6 pages, uses emulateapj. ApJ in press

We describe an observation of the X-ray luminous SN1978K in NGC 1313 using the ACIS detector on Chandra and an archival Newton EPIC observation. The models that provided good fits to the ASCA SIS and GIS and the ROSAT PSPC spectra no longer do so for the ACIS or EPIC spectra. The best-fit model to the ACIS and EPIC spectra are dual hot plasma model (vmekal); one component is soft (T = 0.61+0.04-0.05 keV, 90% errors) and the other is harder (T=3.16+0.44-0.40 keV). For the varying abundances permitted within the model, only the Si abundance of the soft component differs from solar, with a value n(Si)(SN78K)/n(Si)(solar) = 3.20+1.80-1.90 (90% errors). From a ratio of the low- and high-T model fits to the Chandra and XMM-Newton spectra, we infer an exponent n of the ejecta density distribution, rho_ejecta ~ r^(-n), of ~5.2, adopting a circumstellar matter distribution exponent of s = 2 (rho_cs ~ r^(-s)). The 0.5-2 keV light curve shows essentially no decline; the 2-10 keV light curve, constructed only of the ASCA, XMM-Newton, and Chandra observations, shows a drop of 1.5 from the ASCA epoch. The hard band decline, together with the apparently enhanced Si emission, signal the start of the X-ray decline of SN1978K., 12 pages, 8 figures, returned to ApJ following referee's report

The red quasar 3C212 (z = 1.049) is one of the most distant and most luminous AGN which has shown evidence of an X-ray warm absorber. In order to further investigate this unusual quasar, we used Chandra/ACIS-S to observe 3C212 for 19.5 ksec, resulting in a net detection of � 4000 counts. The Chandra data confirm the presence of an excess absorbing column NH � 4 × 10 21 cm −2 at the quasar redshift, but we find no compelling evidence for a warm absorber. Using both the Chandra and archival ROSAT PSPC data, we obtain very good fits for both a partially covered neutral absorber and a low-ionization (U = 0.03) photo-ionized absorber. In the ultraviolet, 3C212 shows a strong associated Mg ii absorber. Based on a moderate resolution (80kms −1 ) MMT spectrum we show that the absorber is highly saturated and has a covering fraction less than 60%, implying that the absorber is truly intrinsic to the quasar. Photo-ionization modeling of the Mg ii absorber yields a constraint on the ionization parameter of U < 0.03, inconsistent with a warm UV/X-ray absorber. In addition to our spectral analysis, we find evidence in the ACIS image data for weak extended emission surrounding the quasar as well as emission corresponding to the radio lobes at a distance of 5 ′′ from 3C212. The statistical significance of these features is low, but we briefly explore the implications if the detections are valid. Subject headings: quasars: absorption lines — quasars:individual (3C212) — ultraviolet: galaxies — X-rays: galaxies

We present results from two {\em Chandra}/ACIS-I observations and one {\em XMM-Newton} observation of X-ray emission from the ISM and the inner radio lobes of the nearby radio galaxy Centaurus A. The ISM has an average radial surface brightness profile that is well described by a $\beta$-model profile with index $\beta$=0.40$\pm$0.04 and a temperature of $k_BT_{ISM}\sim$0.29 keV beyond 2 kpc from the nucleus. We find that diffuse X-ray emission is coincident with the outer half of the southwest radio lobe, and a bright X-ray enhancement is detected along the edge of the lobe. On the basis of energetic and lifetime arguments, we reject a nonthermal explanation for this emission. We model this emission as a thin, hot shell or cap of X-ray emitting plasma surrounding the radio lobe that was created by the supersonic inflation of the lobe. This plasma shell is both hotter than ($k_BT_{SH}\sim$2.9 keV) and greatly overpressurized relative to the ambient ISM indicating supersonic expansion. We estimate that the lobe is expanding into the ISM at approximately Mach 8.5 or 2400 km s$^{-1}$. We are not directly observing the bow shock, but rather the cooler, denser material that is accumulating ahead of the contact discontinuity. The thermal energy in the shell is a significant fraction of the thermal energy of the hot ISM, demonstrating the possibility that the hot ISM of early galaxies can be re-energized by outflows from nuclear activity. Interestingly, no similarly bright X-ray emission is detected in or along the edge of the NE lobe, implying that there are differences in the dynamics and evolution of the kpc-scale radio components.

We present a technique for determining the number of X-ray sources per flux density interval, the log N-log S relationship, that is mathematically analogous to spectral fitting. This technique is ideal for X-ray source counts obtained using the Chandra X-ray Observatory since the telescope and the focal plane instruments have been well modeled. This technique is of general applicability. In this paper, we apply it to a wavelet source-detect analysis of a Chandra Advanced CCD Imaging Spectrometer (ACIS-I) mosaic image of a 1.35 deg2 survey of the Lockman Hole. We verify the technique via Monte Carlo simulations.

We report on \chandra observations of the central region of M31. By combining eight \chandra ACIS-I observations taken between 1999 and 2001, we have identified 204 X-ray sources within the central $\sim 17'\times17'$ region of M31, with a detection limit of $\sim 2\times10^{35}$\lum. Of these 204 sources, 22 are identified with globular clusters, 2 with supernova remnants, 9 with planetary nebula, and 9 as supersoft sources. By comparing individual images, about 50% of the sources are variable on time scales of months. We also found 13 transients, with light curves showing a variety of shapes. We also extracted the energy spectra of the 20 brightest sources; they can be well fit by a single power-law with a mean photon index of 1.8. The spectral shapes of 12 sources are shown to be variable, suggesting that they went through state changes. The luminosity function of all the point sources is consistent with previous observations (a broken power-law with a luminosity break at $1.7\times10^{37}$\lum). However, when the X-ray sources in different regions are considered separately, different luminosity functions are obtained. This indicates that the star-formation history might be different in different regions., 42 pages, 9 figures, ApJ, accepted, Higher-resolution figures available on request

We investigate the nature of the luminous X-ray source population detected in a (72 ks) Chandra ACISS observation of NGC 4038/39, the Antennae galaxies. We derive the average X-ray spectral properties of sources in different luminosity ranges, and we correlate the X-ray positions with radio, IR, and optical (HST) data. The X-ray sources are predominantly associated with young stellar clusters, indicating that they belong to the young stellar population. Based on both their co-added X-ray spectrum, and on the lack of associated radio emission, we conclude that the Ultra Luminous X-ray sources (ULXs), with LX ≥ 10 39 ergs s −1 , are not young compact Supernova Remnants (SNR), but accretion binaries. While their spectrum is consistent with those of ULXs studied in nearby galaxies, and interpreted as the counterparts of intermediate mass black-holes (M> 10 − 1000 M⊙ ), comparison with the position of star-clusters suggests that some of the ULXs may be runaway binaries, thus suggesting lower-mass binary systems. The co-added spectrum of the sources in the 3 × 10 38 − 10 39 erg s −1 luminosity range is consistent with those of Galactic black-hole candidates. These sources are also on average displaced from neighboring star clusters. The softer spectrum of the less luminous sources suggests the presence of SNRs or of hot interstellar medium (ISM) in the Chandra source extraction area. Comparison with HI and CO observations shows that most sources are detected in the outskirts of large concentrations of gas. The absorbing columns inferred from these observations would indeed absorb X-rays up to 5 keV, so there may be several hidden X-ray sources. Associated with these obscured regions we find 6 sources with heavily absorbed X-ray spectra and absorption-corrected luminosities in the ULX range. We detect the nuclei of both galaxies with luminosities in the 10 39 ergs s −1 range and soft, possibly thermal, X-ray

NGC 1448 is one of the nearest luminous galaxies ($L_{8-1000\mu m} >$ 10$^{9} L_{\odot}$) to ours ($z$ $=$ 0.00390), and yet the active galactic nucleus (AGN) it hosts was only recently discovered, in 2009. In this paper, we present an analysis of the nuclear source across three wavebands: mid-infrared (MIR) continuum, optical, and X-rays. We observed the source with the Nuclear Spectroscopic Telescope Array (NuSTAR), and combined this data with archival Chandra data to perform broadband X-ray spectral fitting ($\approx$0.5-40 keV) of the AGN for the first time. Our X-ray spectral analysis reveals that the AGN is buried under a Compton-thick (CT) column of obscuring gas along our line-of-sight, with a column density of $N_{\rm H}$(los) $\gtrsim$ 2.5 $\times$ 10$^{24}$ cm$^{-2}$. The best-fitting torus models measured an intrinsic 2-10 keV luminosity of $L_{2-10\rm{,int}}$ $=$ (3.5-7.6) $\times$ 10$^{40}$ erg s$^{-1}$, making NGC 1448 one of the lowest luminosity CTAGNs known. In addition to the NuSTAR observation, we also performed optical spectroscopy for the nucleus in this edge-on galaxy using the European Southern Observatory New Technology Telescope. We re-classify the optical nuclear spectrum as a Seyfert on the basis of the Baldwin-Philips-Terlevich diagnostic diagrams, thus identifying the AGN at optical wavelengths for the first time. We also present high spatial resolution MIR observations of NGC 1448 with Gemini/T-ReCS, in which a compact nucleus is clearly detected. The absorption-corrected 2-10 keV luminosity measured from our X-ray spectral analysis agrees with that predicted from the optical [OIII]$\lambda$5007\AA\ emission line and the MIR 12$\mu$m continuum, further supporting the CT nature of the AGN., Comment: Accepted for publication in ApJ on Dec. 27th, 2016; 14 pages; 9 figures and 2 tables

We present results from two Chandra X-ray Observatory observations of the X-ray point source population in the nearby radio galaxy Centaurus A (NGC 5128). Using a wavelet decomposition detection algorithm, we detect 246 individual point sources above a limiting luminosity of ~2 × 1036 ergs s-1, 82 of which are detected in both data sets where the fields of view overlap. Thirty-eight sources were detected in only one observation but were within the field of view of both pointings, implying considerable variability. We identify eight foreground stars in our observations. We also identify nine of the sources with known globular clusters in Centaurus A. All previously observed ROSAT sources within our field of view are detected. The number of luminous (Lx > 1037 ergs s-1) X-ray binaries per unit optical luminosity in Cen A is roughly consistent with that observed for the M31 bulge. There are approximately 50% more X-ray binaries per unit optical luminosity in Centaurus A than in the whole of M31, however. We find considerably fewer luminous X-ray binaries per unit optical luminosity in Cen A than in two other elliptical galaxies, M84 and NGC 4697, recently observed by Chandra. This result directly confirms the variance in the X-ray binary population with host galaxy optical luminosity previously inferred from spectral analysis of ROSAT and ASCA observations of elliptical galaxies.

We report deep near-infrared and optical observations of the X-ray point source in the Cassiopeia A supernova remnant, CXO J232327.9+584842. We have identified a J = 21.4 ± 0.3 mag and a Ks = 20.5 ± 0.3 mag source within the 1 σ error circle, but we believe this source is a foreground Population II star with Teff = 2600-2800 K at a distance of ≈2 kpc that could not be the X-ray point source. We do not detect any sources in this direction at the distance of Cas A and therefore place 3 σ limits of R 25 mag, F675W 27.3 mag, J 22.5 mag, and Ks 21.2 mag (and roughly H 20 mag) on emission from the X-ray point source, corresponding to MR 8.2 mag, MF675W 10.7 mag, MJ 8.5 mag, MH 6.5 mag, and M 8.0 mag, assuming a distance of 3.4 kpc and an extinction of AV = 5 mag.

We report new observations of emission line intensity ratios of Fe XVII under controlled experimental conditions, using the National Institute of Standards and Technology electron beam ion trap (EBIT) with a microcalorimeter detector. We compare our observations with collisional-radiative models using atomic data computed in distorted wave and R-matrix approximations, which follow the transfer of the polarization of level populations through radiative cascades. Our results for the intensity ratio of the 2p6 1S0-2p53d 1P1 15.014 A line to the 2p6 1S0-2p53d 3D1 15.265 A line are 2.94 ± 0.18 and 2.50 ± 0.13 at beam energies of 900 and 1250 eV, respectively. These results are not consistent with collisional-radiative models and support conclusions from earlier EBIT work at the Lawrence Livermore National Laboratory that the degree of resonance scattering in the solar 15.014 A line has been overestimated in previous analyses. Further observations assess the intensity ratio of the three lines between the 2p6-2p53s configurations to the three lines between the 2p6-2p53d configurations. Both R-matrix and distorted wave approximations agree with each other and our experimental results much better than most solar and stellar observations, suggesting that other processes not present in our experiment must play a role in forming the Fe XVII spectrum in solar and astrophysical plasmas.

We present first results from a Chandra X-Ray Observatoryobservation of the radio galaxy Centaurus A with the High-Resolution Camera. All previously reported major sources of X-ray emission including the bright nucleus, the jet, individual point sources, and diffuse emission are resolved or detected. The spatial resolution of this observation is better than 10 in the center of the field of view and allows us to resolve X-ray features of this galaxy not previously seen. In particular, we resolve individual knots of emission in the inner jet and diffuse emission between the knots. All of the knots are diffuse at the 10 level, and several exhibit complex spatial structure. We find the nucleus to be extended by a few tenths of an arcsecond. Our image also suggests the presence of an X-ray counterjet. Weak X-ray emission from the southwest radio lobe is also seen, and we detect 63 pointlike galactic sources (probably X-ray binaries and supernova remnants) above a luminosity limit of » ergs s 21 . 37 1.7 # 10 Subject headings: galaxies: active — galaxies: individual (Centaurus A, NGC 5128) — galaxies: jets — X-rays: galaxies

The UV sensitivity to bright stars observed during operations of the high-resolution imager (HRI) on the X-ray-XUV Roentgen Satellite (ROSAT) has been commonly interpreted as a result of enhanced transmission solely in the wavelength range 1500-1700 A of the HRI's UV/ion shield. We report on recent laboratory UV transmission measurements of HRI flight spare filters that show transmissions much higher than previously assumed for wavelengths longward of approximately 2000 A. We present a model for the UV response of the HRI based on these measurements. Using this model and the known UV spectra of the A stars Vega (α Lyrae, V = +0.03) and β Carinae (V = +1.68), we successfully predict the observed HRI count rates for these two stars.

SPT-CLJ2040-4451 -- spectroscopically confirmed at z = 1.478 -- is the highest redshift galaxy cluster yet discovered via the Sunyaev-Zel'dovich effect. SPT-CLJ2040-4451 was a candidate galaxy cluster identified in the first 720 deg^2 of the South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey, and confirmed in follow-up imaging and spectroscopy. From multi-object spectroscopy with Magellan-I/Baade+IMACS we measure spectroscopic redshifts for 15 cluster member galaxies, all of which have strong [O II] 3727 emission. SPT-CLJ2040-4451 has an SZ-measured mass of M_500,SZ = 3.2 +/- 0.8 X 10^14 M_Sun/h_70, corresponding to M_200,SZ = 5.8 +/- 1.4 X 10^14 M_Sun/h_70. The velocity dispersion measured entirely from blue star forming members is sigma_v = 1500 +/- 520 km/s. The prevalence of star forming cluster members (galaxies with > 1.5 M_Sun/yr) implies that this massive, high-redshift cluster is experiencing a phase of active star formation, and supports recent results showing a marked increase in star formation occurring in galaxy clusters at z >1.4. We also compute the probability of finding a cluster as rare as this in the SPT-SZ survey to be >99%, indicating that its discovery is not in tension with the concordance Lambda-CDM cosmological model., 14 pages, 8 figures, 4 tables, Accepted to ApJ

Over approximately the last five years, we have identified ∼35 black hole candidates (BHCs) in M31 from their X-ray spectra. Our BHCs exhibited 0.3-10 keV spectra consistent with the X-ray binary (XB) hard state at luminosities that are above the upper limit for neutron star (NS) XBs. When our BHC spectra were modeled with a disk blackbody + blackbody model for comparison with bright NS XBs, we found that the BHCs inhabited a different parameter space than the NS XBs. However, BH XBs may also exhibit a thermally dominated (TD) state that has never been seen in NS XBs; this TD state is most often observed in X-ray transients. We examined the ∼50 X-ray transients in our Chandra survey of M31 and found 13 with spectra suitable for analysis. We also examined two BHCs outside the field of view of our survey in the globular clusters B045 and B375. We have 42 strong BHCs and 8 plausible BHCs that may benefit from further observation. Of our 15 BHCs in globular clusters, 12 differ from NS spectra by >5σ. Due to improvements in our analysis, we have upgraded 10 previously identified plausible BHCs to strong BHCs. The mean maximum duty cyclemore » of the 33 X-ray transients within 6' of M31* is 0.13; we estimate that >40% of the XBs in this region contain BH accretors. Remarkably, we estimate that BHCs contribute >90% of those XBs >10{sup 38} erg s{sup –1}.« less

We present first results on the cooling properties derived from Chandra X-ray observations of 83 high-redshift (0.3 < z < 1.2) massive galaxy clusters selected by their Sunyaev-Zel'dovich signature in the South Pole Telescope data. We measure each cluster's central cooling time, central entropy, and mass deposition rate, and compare to local cluster samples. We find no significant evolution from z~0 to z~1 in the distribution of these properties, suggesting that cooling in cluster cores is stable over long periods of time. We also find that the average cool core entropy profile in the inner ~100 kpc has not changed dramatically since z ~ 1, implying that feedback must be providing nearly constant energy injection to maintain the observed "entropy floor" at ~10 keV cm^2. While the cooling properties appear roughly constant over long periods of time, we observe strong evolution in the gas density profile, with the normalized central density (rho_0/rho_crit) increasing by an order of magnitude from z ~ 1 to z ~ 0. When using metrics defined by the inner surface brightness profile of clusters, we find an apparent lack of classical, cuspy, cool-core clusters at z > 0.75, consistent with earlier reports for clusters at z > 0.5 using similar definitions. Our measurements indicate that cool cores have been steadily growing over the 8 Gyr spanned by our sample, consistent with a constant, ~150 Msun/yr cooling flow that is unable to cool below entropies of 10 keV cm^2 and, instead, accumulates in the cluster center. We estimate that cool cores began to assemble in these massive systems at z ~ 1, which represents the first constraints on the onset of cooling in galaxy cluster cores. We investigate several potential biases which could conspire to mimic this cool core evolution and are unable to find a bias that has a similar redshift dependence and a substantial amplitude., Comment: 17 pages with 15 figures, plus appendix. Published in ApJ

XMMU J004243.6+412519 is a transient X-ray source in M31, first discovered 2012 January 15. Different approaches to fitting the brightest follow-up observation gave luminosities 1.3-2.5 Multiplication-Sign 10{sup 39} erg s{sup -1}, making it the second ultraluminous X-ray source (ULX) in M31, with a probable black hole accretor. These different models represent different scenarios for the corona: optically thick and compact, or optically thin and extended. We obtained Chandra ACIS and Hubble Space Telescope Advanced Camera for Surveys observations of this object as part of our transient monitoring program, and also observed it serendipitously in a 120 ks XMM-Newton observation. We identify an optical counterpart at J2000 position 00:42:43.70 +41:25:18.54; its F435W ({approx}B band) magnitude was 25.97 {+-} 0.03 in the 2012 March 7 observation, and >28.4 at the 4{sigma} level during the 2012 September 7 observation, indicating a low-mass donor. We created two alternative light curves, using the different corona scenarios, finding linear decay for the compact corona and exponential decay for the extended corona; linear decay implies a disk that is >5 mag brighter than we observed. We therefore favor the extended corona scenario, but caution that there is no statistical preference for this model in the X-ray spectramore » alone. Using two empirical relations between the X-ray to optical ratio and the orbital period, we estimate a period of {approx}9-30 hr; this period is consistent with that of the first ULX in M31 (18{sup +5}{sub -6} hr)« less

The fraction of cluster galaxies that host luminous AGN is an important probe of AGN fueling processes, the cold ISM at the centers of galaxies, and how tightly black holes and galaxies co-evolve. We present a new measurement of the AGN fraction in a sample of 13 clusters of galaxies (M >= 10^{14} Msun) at 1 = 10^{44} erg/s. This fraction is measured relative to all cluster galaxies more luminous than M*_{3.6}(z)+1, where M*_{3.6}(z) is the absolute magnitude of the break in the galaxy luminosity function at the cluster redshift in the IRAC 3.6um bandpass. The cluster AGN fraction is 30 times greater than the 3sigma upper limit on the value for AGN of similar luminosity at z~0.25, as well as more than an order of magnitude greater than the AGN fraction at z~0.75. AGN with L_{X,H} >= 10^{43} erg/s exhibit similarly pronounced evolution with redshift. In contrast with the local universe, where the luminous AGN fraction is higher in the field than in clusters, the X-ray and MIR-selected AGN fractions in the field and clusters are consistent at 1

Almost all Galactic black hole (BH) binaries with low-mass donor stars are transient X-ray sources; we expect most of the X-ray transients observed in external galaxies to be BH binaries also. Obtaining period estimates for extragalactic transients is challenging, but the resulting period distribution is an important tool for modeling the evolution history of the host galaxy. We have obtained periods, or upper limits, for 12 transients in M31, using an updated relation between the optical and X-ray luminosities. We have monitored the central region of M31 with Chandra for the last ~12 years, and followed up promising transients with the Hubble Space Telescope; 4σ B-magnitude limits for optical counterparts are 26-29, depending on crowding. We obtain period estimates for each transient for both neutron star and BH accretors. Periods range from

We present one of the most precise measurement to date of the spatial clustering of X-ray selected AGNs using a sample derived from the Chandra X-ray Observatory survey in the Bootes field. The real-space two-point correlation function over a redshift interval from z=0.17 to z~3 is well described by the power law, xi(r)=(r/r0)^-gamma, for comoving separations r =0.37 and r0=6.9+-1.0 h^-1 Mpc for =1.28). Further, we are able to measure the projections of the two-point correlation function both on the sky plane and in the line of sight. We use these measurements to show that the Chandra/Bootes AGNs are predominantly located at the centers of dark matter halos with the circular velocity Vmax>320 km/s or M_200 > 4.1e12 h^-1 Msun, and tend to avoid satellite galaxies in halos of this or higher mass. The halo occupation properties inferred from the clustering properties of Chandra/Bootes AGNs --- the mass scale of the parent dark matter halos, the lack of significant redshift evolution of the clustering length, and the low satellite fraction --- are broadly consistent with the Hopkins et al. scenario of quasar activity triggered by mergers of similarly-sized galaxies.

All IPC exposures in the Einstein Extended Deep X-ray Survey program have been reanalyzed. The current survey covers about 2.3 sq deg with a typical limiting sensitivity of about 5 x 10 to the -14th ergs/sq cm/s in the energy range from 0.8-3.5 keV. A total of 25 IPC sources are detected above a threshold of 4.5 sigma. A total of 18 are detected independently in the HRI, leading to the identification of six with stars and 11 with extragalactic objects. The remaining sources are classified as extragalactic. The population of identified extragalactic objects is dominated by QSOs, with one or two possible clusters. The basic conclusions of the original survey remain unchanged.

Cas A was observed with the imaging detectors on the Einstein X-ray Observatory. The mass of the expanding shell due to the interaction of the blast wave and the ambient medium is determined. This indicates that Cas A is probably not in the free expansion phase, but has not yet reached the adiabatic phase of expansion. Detailed comparison of X-ray, optical, and radio images shows various degrees of correlation, indicating that several processes for emission are present. An upper limit of 1,500,000 K is established for any stellar remnant that is below the expected temperature of a neutron star by a factor of about 5. The total mass of the SNR is found to be 10-30 solar masses

A comparison of high resolution radio, optical, and X-ray images of two young supernova remnants (SNR), Cas A and Tycho, shows significant differences between them. Cas A probably broke into many small knots at the time of the initial explosion, whereas Tycho's SNR appears to be a more uniformly expanding blast wave.

Observations of the structure of the X-ray emission from 12 nearby rich clusters of galaxies are presented and interpreted in terms of dynamic cluster evolution. X-ray structures revealed by the Einstein Observatory imaging proportional counter in the range 0.25 to 3.0 keV were analyzed and used to classify the clusters based on their X-ray morphologies. Four categories are observed, consisting of spiral-rich clusters with low X-ray temperatures and velocity dispersions with broad and highly clumped emission, spiral-poor clusters with high X-ray temperatures and velocity dispersions with smoothly varying emission broadly or sharply peaked around a dominant galaxy, and clusters with emission typical of a cD galaxy in a poor cluster or group. The broad, highly clumped cluster emission is interpreted as a result of an early evolutionary stage, while the cD and centrally enhanced emissions represent successive later stages in X-ray galactic cluster evolution.

The precise positions of the luminous X-ray sources in eight globular clusters have been measured with the Einstein X-Ray Observatory. When combined with similarly precise measurements of the dynamical centers and core radii of the globular clusters, the distribution of the X-ray source mass is determined to be in the range 0.9-1.9 solar mass. The X-ray source positions and the detailed optical studies indicate that (1) the sources are probably all of similar mass, (2) the gravitational potentials in these high-central density clusters are relatively smooth and isothermal, and (3) the X-ray sources are compact binaries and are probably formed by tidal capture.

X-rays in the 2-11-keV band were detected from LMC X-4 using the rotating modulation collimator system on SAS-3. The derived X-ray luminosity of LMC X-4 is of the order of 10 to the 38th power ergs/s. A transition to a high-intensity state which lasted about 40 minutes was detected during which short-time-scale flares (about 20 s) were observed. The temporal and spectral behavior of LMC X-4 is found to be similar to that of several X-ray binaries. A derived 90% error circle with a radius of 1 arcmin is also presented.

The paper presents results of an X-ray survey of about 50 sq deg of the high galactic latitude sky at sensitivities in the range of 7 x 10 to the -14 to 5 x 10 to the -12 ergs/sq cm/s. The number-flux relation is derived for the extragalactic population to yield a best-fit power-law slope of 1.53 + or - 0.16, and the content of the sample is analyzed in terms of types of sources, appearing to be significantly different from the content of similar samples selected at higher fluxes. The medium sensitivity sample of extragalactic sources is dominated by active galactic nuclei, while samples selected at higher fluxes and higher energies are dominated by clusters of galaxies. Thus, the number-flux relation for extragalactic sources may be interpreted to a first approximation as the sum of the two different distributions with flatter and steeper slopes describing clusters and AGNs, respectively.

It is found that the unidentified high latitude UHURU sources can have either of two very different explanations. They must either reside at great distances with luminosity equivalent to or greater than 10 to the 46th power ergs/sec, or be contained in the galaxy with luminosity equivalent to or less than 10 to the 34th power ergs/sec. The two possibilities are indistinguishable with the available data.

About one-third of the Uhuru sources with galactic latitude vertical-barbvertical-bar>20degree are identified with extra-galactic objects. The predicted level of fluctuations is based on assuming that all the unidentified high-galactic-latitude sources form a homogeneous volume distribution of extragalactic sources. The discrepancy between measured and predicted fluctuations does not easily disappear if all the unidentified sources are galactic. Therefore, we conclude that a portion of the unidentified sources represents a class of objects at cosmological distances. (AIP)

The paper reports the first extensive detection of X-ray emission from clusters of galaxies at cosmological distances. The properties of these objects are similar to those observed in objects at low redshifts. The 0.5-4.5 keV luminosities are in the range of less than 1 x 10 to the 43rd to 2 x 10 to the 45th ergs/s; the core radii are on the order of 0.5 Mpc; and Bautz-Morgan type I clusters are more luminous than types II or III. The observations are consistent with models assuming an evolving cluster potential and moderately efficient galaxy formation, but do not require them when observational selection is considered. X-ray observations of the 3C 295 cluster indicate that there is sufficient intergalactic medium to cause stripping of the cluster spirals, but the colors of these galaxies imply that they have not been stripped. A possible explanation of this discrepancy is discussed.

X-ray emission from three class 2 clusters of rich clusters of galaxies has been detected. A definition for these objects based in part on Abell's (1961) description is used, and 12 candidate superclusters of distance class 5 and six clusters are found within the area of sky covered by the 4U catalog. The probability that these three X-ray sources accidentally coincide with the superclusters is less than 0.003. Equally low probabilities are found that the X-ray emission is due to either a single luminous cluster or to the combined emission of all members of the supercluster. A possible explanation of these sources is thermal bremsstrahlung emission from a hot tenuous gas pervading the supercluster. The mass of the gas can be as much as 10 times the mass of the galaxies in the supercluster and comparable to the virial mass necessary to bind the supercluster gravitationally. Should such regions of enhanced gas density be found to be associated with all groups of clusters (multiplicity of at least 2), this gas may provide a significant fraction of the mass required to close the universe.

Uhuru observations of 22 unidentified high-galactic-latitude X-ray sources over the period from December 1970 to April 1973 are analyzed. The results confirm the existence of at least 19 sources, improve the positions for several of them, and yield evidence that some are variable. Two sources, 3U 0042+32 and 3U 1809-50, are found to be variable at the 3-sigma level. The improved positions for 3U 1555+27 and 3U 0405+10 confirm that these sources are, respectively, the Abell galaxies A2142 and A478.

The Einstein (HEAO 2) X-ray Observatory, launched in 1978, includes a fully imaging focusing X-ray telescope with an angular resolution of a few arc sec, a field of view of up to one deg, and a sensitivity several hundred times greater than previously available in any X-ray astronomy experiment. A high-resolution imager, an imaging proportional counter, a focal plane crystal spectrometer, and a monitor proportional counter are among the principal instruments on board the Einstein X-ray Observatory. About 20% of the total effective observing time in the first year of the X-ray astronomy experiment has been reserved for guest observers.