R. A. Burenin

CHANDRA CLUSTER COSMOLOGY PROJECT III: COSMOLOGICAL PARAMETER CONSTRAINTS

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 a structure-based dark energy probe. In this paper, we present cosmological parameter constraints obtained from Chandra observations of 37 clusters withz �= 0.55 derived from 400 deg 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 ΩΛ > 0 with a ∼ 5σ significance, and constrains the dark energy equation- of-state parameter to w0 =− 1.14 ± 0.21, assuming a constant w and a flat universe. Cluster information also significantly improves constraints when combined with other methods. Fitting our cluster data jointly with the latest supernovae, Wilkinson Microwave Anisotropy Probe, and baryonic acoustic oscillation 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 with constraints that can be obtained without clusters. The joint analysis of these four data sets puts a conservative upper limit on the masses of light neutrinos mν < 0.33 eV at 95% CL. We also present updated measurements of ΩMh and σ8 from the low-redshift cluster mass function.

Chandra Cluster Cosmology Project. II. Samples and X-Ray Data Reduction

We discuss the measurements of the galaxy cluster mass functions at z 0.05 and z 0.5 using high-quality Chandra observations of samples derived from the ROSAT PSPC All-Sky and 400 deg2 surveys. We provide a full reference for the data analysis procedures, present updated calibration of relations between the total cluster mass and its X-ray indicators (TX , M gas, and YX ) based on a subsample of low-z relaxed clusters, and present a first measurement of the evolving LX -M tot relation (with M tot estimated from YX ) obtained from a well defined statistically complete cluster sample and with appropriate corrections for the Malmquist bias applied. Finally, we present the derived cluster mass functions, estimate the systematic uncertainties in this measurement, and discuss the calculation of the likelihood function. We confidently measure the evolution in the cluster comoving number density at a fixed mass threshold, e.g., by a factor of 5.0 ? 1.2 at M 500 = 2.5 ? 1014 h ?1 M ? between z = 0 and 0.5. This evolution reflects the growth of density perturbations, and can be used for the cosmological constraints complementing those from the distance-redshift relation.

THE AFTERGLOWS OF SWIFT-ERA GAMMA-RAY BURSTS. I. COMPARING PRE-SWIFT AND SWIFT-ERA LONG/SOFT (TYPE II) GRB OPTICAL AFTERGLOWS

We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical high-luminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall.

The 400 Square Degree ROSAT PSPC Galaxy Cluster Survey: Catalog and Statistical Calibration

We present a catalog of galaxy clusters detected in a new ROSAT PSPC survey. The survey is optimized to sample, at high redshifts, the mass range corresponding to T > 5 keV clusters at z = 0. Technically, our survey is the extension of the 160 square degree survey (160d). We use the same detection algorithm, thus preserving high quality of the resulting sample; the main difference is a significant increase in sky coverage. The new survey covers 397 deg2 and is based on 1610 high Galactic latitude ROSAT PSPC pointings, virtually all pointed ROSAT data suitable for the detection of distant clusters. The search volume for X-ray luminous clusters within z 1.4 × 10-13 ergs s-1 cm-2 in the 0.5-2 keV energy band, of which 266 (93%) are optically confirmed as galaxy clusters, groups or individual elliptical galaxies. This paper provides a description of the input data, the statistical calibration of the survey via Monte Carlo simulations, and the catalog of detected clusters. We also compare the basic results to those from previous, smaller area surveys and find good agreement for the log N- log S distribution and the local X-ray luminosity function. Our sample clearly shows a decrease in the number density for the most luminous clusters at z > 0.3. The comparison of our ROSAT-derived fluxes with the accurate Chandra measurements for a subset of high-redshift clusters demonstrates the validity of the 400 square degree surveys statistical calibration.

ChaMP Serendipitous Galaxy Cluster Survey

We present a survey of serendipitous extended X-ray sources and optical cluster candidates from the Chandra Multiwavelength Project (ChaMP). Our main goal is to make an unbiased comparison of X-ray and optical cluster detection methods. In 130 archival Chandra pointings covering 13 deg 2 , we use a wavelet decomposition technique to detect 55 extended sources, of which 6 are nearby single galaxies. Our X-ray cluster catalog reaches a typical flux limit of about � 10 � 14 ergs cm � 2 s � 1 , with a median cluster core radius of 21 00 . For 56 of the 130 X-ray fields, we use the ChaMP’s deep NOAO 4 m MOSAIC g 0 , r 0 , and i 0 imaging to independently detect cluster candidates using a Voronoi tessellation and percolation (VTP) method. Red-sequence filtering decreases the galaxy fore- and background contamination and provides photometric redshifts to z � 0:7. From the overlapping 6.1 deg 2 X-ray/optical imaging, wefind115opticalclusters (ofwhich11%areintheX-raycatalog)and28X-rayclusters(ofwhich46%are in the optical VTP catalog). The median redshift of the 13 X-ray/optical clusters is 0.41, and their median X-ray luminosity (0.5‐2 keV) is LX ¼ 2:65 � 0:19 ðÞ ; 10 43 ergs s � 1 . The clusters in our sample that are only detected in our optical data are poorer on average (� 4 � ) than the X-ray/optically matched clusters, which may partially explain the difference in the detection fractions. Subject headingg galaxies: clusters: general — surveys — X-rays: galaxies: clusters

FOSSIL SYSTEMS IN THE 400d CLUSTER CATALOG

We report the discovery of seven new fossil systems in the 400d cluster survey. Our search targets nearby, z ≤ 0.2, and X-ray bright, LX ≥ 1043 erg s–1, clusters of galaxies. Where available, we measure the optical luminosities from Sloan Digital Sky Survey images, thereby obtaining uniform sets of both X-ray and optical data. Our selection criteria identify 12 fossil systems, out of which five are known from previous studies. While in general agreement with earlier results, our larger sample size allows us to put tighter constraints on the number density of fossil clusters. It has been previously reported that fossil groups are more X-ray bright than other X-ray groups of galaxies for the same optical luminosity. We find, however, that the X-ray brightness of massive fossil systems is consistent with that of the general population of galaxy clusters and follows the same LX -L opt scaling relation.

Discovery of heavily-obscured AGN among seven INTEGRAL hard X-ray sources observed by Chandra

Aims. We identify hard X-ray sources discovered by the INTEGRAL all-sky survey. We complete identification of a unique sample of active galactic nuclei (AGN) selected in the hard X-ray band (17−60 keV) with minimal effects from absorption. Subsequently, we determine the fraction of obscured AGN in the local Universe. Methods. We observed 7 INTEGRAL sources with the Chandra X-ray Observatory to refine their localization to ∼ 2a rcsec and to study their X-ray spectra. Results. Two sources are inferred to have a Galactic origin: IGR J08390−4833 is most likely a magnetic cataclysmic variable with a white dwarf spin period ∼1450 s; and IGR J21343+4738 is a high-mass X-ray binary. Five sources (IGR J02466−4222, IGR J09522−6231, IGR J14493−5534, IGR J14561−3738, and IGR J23523+5844) prove to be AGN with significant intrinsic X-ray absorption along the line of sight. Their redshifts and hard X-ray (17−60 keV) luminosities range from 0.025 to 0.25 and from ∼2×10 43 to ∼2 × 10 45 erg s −1 , respectively, with the distance to IGR J14493−5534 remaining unknown. The sources IGR J02466−4222 and IGR J14561−3738 are likely Compton-thick AGN with absorption column densities NH > 10 24 cm −2 , and the former further appears to be one of the nearest X-ray bright, optically-normal galaxies. Conclusions. With the newly-identified sources, the number of heavily-obscured (NH > 10 24 cm −2 ) AGN detected by INTEGRAL has increased to ∼10. Therefore, such objects constitute 10−15% of hard X-ray bright, non-blazar AGN in the local Universe. The small ratio (� 1%) of soft (0.5− 8.0 keV) to hard (17−60 keV) band fluxes (Chandra to INTEGRAL) and the non-detection of optical narrow-line emission in some of the Compton-thick AGN in our sample suggests that there is a new class of objects in which the central massive black hole may be surrounded by a geometrically-thick dusty torus with a narrow ionization cone.

Possible indication for non-zero neutrino mass and additional neutrino species from cosmological observations

The constraints on total neutrino mass and effective number of neutrino species based on CMB anisotropy power spectrum, Hubble constant, baryon acoustic oscillations and galaxy cluster mass function data are presented. It is shown that discrepancies between various cosmological data in Hubble constant and density fluctuation amplitude, measured in standard ΛCDM cosmological model, can be eliminated if more than standard effective number of neutrino species and non-zero total neutrino mass are considered. This extension of ΛCDM model appears to be ≈3σ significant when all cosmological data are used. The model with approximately one additional neutrino type, Neff ≈ 4, and with non-zero total neutrino mass, Σmν ≈ 0.5 eV, provide the best fit to the data. In the model with only one massive neutrino the upper limits on neutrino mass are slightly relaxed. It is shown that these deviations from ΛCDM model appearmainly due to the usage of recent data on the observations of baryon acoustic oscillations. The larger than standard number of neutrino species is measured mainly due to the comparison of the BAO data with direct measurements of Hubble constant, which was already noticed earlier. As it is shown below, the data on galaxy cluster mass function in this case give the measurement of non-zero neutrino mass.

New nearby active galactic nuclei among INTEGRAL and RXTE X-ray sources

We present the first results of a campaign to optically identify X-ray sources discovered in the all-sky surveys of the RXTE and INTEGRAL observatories. Six newly discovered sources proved to be hitherto unknown nearby active galactic nuclei (z < 0.1). Spectrophotometric studies of these sources were performed with the Russian-Turkish 1.5-m telescope (RTT150). We measured their redshifts and parameters of the strongest emission lines.We present first results of a campaign of optical identifications of X-ray sources discovered by RXTE and INTEGRAL observatories during their sky surveys. In this work we study six newly discovered nearby active galactic nuclei at z<0.1. The optical spectrophotometric data were obtained with Russian-Turkish 1.5-m telescope (RTT150). We present their redshifts and main parameters of brightest emission lines.

XSS J00564+4548 and IGR J00234+6141: New cataclysmic variables from the RXTE and INTEGRAL all-sky surveys

We present the results of our optical identification of two X-ray sources from the RXTE and INTEGRAL all-sky surveys: XSS J00564+4548 and IGR J00234+6141. Using optical observations with the 1.5-m Russian-Turkish Telescope (RTT150) and publicly accessible X-ray data from the SWIFT Orbital Observatory, we show that these sources are most likely intermediate polars, i.e., binary systems with accreting white dwarfs that possess a moderately strong magnetic field (≲10 MG). We have found periodic optical oscillations with periods of ≈480 and ≈570 s. These periods most likely correspond to the rotation periods of the white dwarfs in these systems. Further optical RTT150 observations of these systems will allow their parameters to be studied in more detail.