Home About us Contact
|
Home About us Contact | ||
|
|
||
Erg Cm (erg + cm)
Selected AbstractsX-ray groups and clusters of galaxies in the Subaru,XMM Deep FieldMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010A. Finoguenov Abstract We present the results of a search for galaxy clusters in the Subaru,XMM Deep Field (SXDF). We reach a depth for a total cluster flux in the 0.5,2 keV band of 2 × 10,15 erg cm,2 s,1 over one of the widest XMM,Newton contiguous raster surveys, covering an area of 1.3 deg2. Cluster candidates are identified through a wavelet detection of extended X-ray emission. The red-sequence technique allows us to identify 57 cluster candidates. We report on the progress with the cluster spectroscopic follow-up and derive their properties based on the X-ray luminosity and cluster scaling relations. In addition, three sources are identified as X-ray counterparts of radio lobes, and in three further sources, an X-ray counterpart of the radio lobes provides a significant fraction of the total flux of the source. In the area covered by near-infrared data, our identification success rate achieves 86 per cent. We detect a number of radio galaxies within our groups, and for a luminosity-limited sample of radio galaxies we compute halo occupation statistics using a marked cluster mass function. We compare the cluster detection statistics in the SXDF with that in the literature and provide the modelling using the concordance cosmology combined with current knowledge of the X-ray cluster properties. The joint cluster log(N) , log(S) is overpredicted by the model, and an agreement can be achieved through a reduction of the concordance ,8 value by 5 per cent. Having considered the dn/dz and the X-ray luminosity function of clusters, we conclude that to pin down the origin of disagreement a much wider (50 deg2) survey is needed. [source] Probing the nature of IGR J16493,4348: spectral and temporal analysis of the 1,100 keV emissionMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008A. B. Hill ABSTRACT IGR J16493,4348 was one of the first new sources to be detected by the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) ,-ray telescope in the 18,100 keV energy band. Based on spatial coincidence, the source was originally associated with the free radio pulsar PSR J1649,4349. Presented here are the results of 2.8 Ms of observations made by the INTEGRAL mission and a 5.6-ks observation with the Swift/X-ray Telescope (XRT). Spectral analysis indicates that the source is best modelled by an absorbed power law with a high energy cut-off at Ecut, 15 keV and a hydrogen absorbing column of NH= 5.4+1.3,1× 1022 cm,2. Analysis of the light curves indicates that the source is a weak, persistent ,-ray emitter showing indications of variability in the 2,9 and 22,100 keV bands. The average source flux is ,1.1 × 10,10 erg cm,2 s,1 in the 1,100 keV energy band. No coherent timing signal is identified at any time-scale in the INTEGRAL or Swift data. The refined source location and positional uncertainty of IGR J16493,4348 places PSR J1649,4349 outside the 90 per cent error circle. We conclude that IGR J16493,4348 is not associated with PSR J1649,4349. Combining the INTEGRAL observations with Swift/XRT data and information gathered by RXTE and Chandra, we suggest that IGR J16493,4348 is an X-ray binary, and that the source characteristics favour a high-mass X-ray binary although a low-mass X-ray binary nature cannot be ruled out. [source] The XMM-SSC survey of hard-spectrum XMM,Newton sources , I. Optically bright sourcesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007M. J. Page ABSTRACT We present optical and X-ray data for a sample of serendipitous XMM,Newton sources that are selected to have 0.5,2 versus 2,4.5 keV X-ray hardness ratios which are harder than the X-ray background. The sources have 2,4.5 keV X-ray flux ,10,14 erg cm,2 s,1, and in this paper we examine a subsample of 42 optically bright (r < 21) sources; this subsample is 100 per cent spectroscopically identified. All but one of the optical counterparts are extragalactic, and we argue that the single exception, a Galactic M star, is probably a coincidental association rather than the correct identification of the X-ray source. The X-ray spectra of all the sources are consistent with heavily absorbed power laws (21.8 < log NH < 23.4), and all of them, including the two sources with 2,10 keV intrinsic luminosities of <1042 erg s,1, appear to be absorbed active galactic nuclei (AGN). The majority of the sources show only narrow emission lines in their optical spectra, implying that they are type 2 AGN. Three sources have 2,10 keV luminosities of >1044 erg s,1, and two of these sources have optical spectra which are dominated by narrow emission lines, that is, are type 2 QSOs. Only a small fraction of the sources (7/42) show broad optical emission lines, and all of these have NH < 1023 cm,2. This implies that ratios of X-ray absorption to optical/ultraviolet extinction equivalent to >100 times the Galactic gas-to-dust ratio are rare in AGN absorbers (at most a few per cent of the population), and may be restricted to broad absorption line QSOs. Seven objects appear to have an additional soft X-ray component in addition to the heavily absorbed power law; all seven are narrow emission-line objects with z < 0.3 and 2,10 keV intrinsic luminosities <1043 erg s,1. We consider the implications of our results in the light of the AGN unified scheme. We find that the soft components in narrow-line objects are consistent with the unified scheme provided that >4 per cent of broad-line AGN (BLAGN) have ionized absorbers that attenuate their soft X-ray flux by >50 per cent. In at least one of the X-ray-absorbed BLAGN in our sample the X-ray spectrum requires an ionized absorber, consistent with this picture. [source] The GRB early optical flashes from internal shocks: application to GRB 990123, GRB 041219a and GRB 060111bMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007D. M. Wei ABSTRACT With the successful launch of the Swift Gamma-ray Burst Explorer, it is widely expected that the prompt optical flashes like GRB 990123 would be easily detected. However, the observations show that for a number of Gamma-ray bursts (GRBs) no early optical flash has been detected, which indicates that the reverse shock emission must be suppressed. Here we explore the possibility that the optical flash may arise from the internal shock emission. For GRB 990123 and GRB 060111b, although their optical emission are not correlated with the gamma-ray emission, we propose here that their optical and gamma-ray emission may arise from different internal shocks (which can be formed by collision of different shells), and find that, under certain circumstances, the optical flashes of GRB 990123 and GRB 060111b can well be explained by the internal shock model. For GRB 041219a, the prompt optical emission was correlated with the gamma-ray emission, which can also be explained by the internal shock model if we assume the optical emission was the low-energy extension of the gamma-ray emission, and we find its redshift is about z, 0.2. As for GRB 050904, we have shown in previous paper that the optical flash was produced by synchrotron radiation and the X-ray flare was produced by the synchrotron,self-Compton (SSC) mechanism. Therefore we conclude that the early optical flashes of GRBs can usually arise from the internal shock emission. Meanwhile in our model since the shells producing the optical flashes would be easily disrupted by other shells, so we suggest that the bright optical flash should not be common in GRBs. In addition, we also discussed the SSC emission in the internal shock model, and find that for different values of parameters, there would be several kinds of high-energy emission (at ,100 keV, ,10 MeV or GeV) accompanying the optical flash. For a burst like GRB 990123, a GeV flare with fluence about 10,8 erg cm,2 s,1 is expected, which might be detected by the GLAST satellite. [source] The XMM,Newton Needles in the Haystack Survey: the local X-ray luminosity function of ,normal' galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005I. Georgantopoulos ABSTRACT In this paper we estimate the local (z < 0.22) X-ray luminosity function of ,normal' galaxies derived from the XMM,Newton Needles in the Haystack Survey. This is an on-going project that aims to identify X-ray-selected normal galaxies (i.e. non-AGN dominated) in the local Universe. We are using a total of 70 XMM,Newton fields covering an area of 11 deg2 which overlap with the Sloan Digital Sky Survey Data Release 2. Normal galaxies are selected on the basis of their resolved optical light profile, their low X-ray-to-optical flux ratio [log (fx/fo) < , 2] and soft X-ray colours. We find a total of 28 candidate normal galaxies to the 0.5,8 keV band flux limit of ,2 × 10,15 erg cm,2 s,1. Optical spectra are available for most sources in our sample (82 per cent). These provide additional evidence that our sources are bona fide normal galaxies with X-ray emission coming from diffuse hot gas emission and/or X-ray binaries rather than a supermassive black hole. 16 of our galaxies have narrow emission lines or a late-type spectral energy distribution (SED) while the remaining 12 present only absorption lines or an early-type SED. Combining our XMM,Newton sample with 18 local (z < 0.22) galaxies from the Chandra Deep Field North and South surveys, we construct the local X-ray luminosity function of normal galaxies. This can be represented with a Schechter form with a break at L,, 3+1.4,1.0× 1041 erg s,1 and a slope of ,, 1.78 ± 0.12. Using this luminosity function and assuming pure luminosity evolution of the form ,(1 +z)3.3 we estimate a contribution to the X-ray background from normal galaxies of ,10,20 per cent (0.5,8 keV). Finally, we derive, for the first time, the luminosity functions for early- and late-type systems separately. [source] A deep Chandra survey of the Groth Strip , I. The X-ray dataMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005K. Nandra ABSTRACT We present the results of a 200-ks Chandra observation of part of the Groth Strip region, using the ACIS-I instrument. We present a relatively simple method for the detection of point sources and calculation of limiting sensitivities, which we argue is at least as sensitive and more self-consistent than previous methods presented in the literature. A total of 158 distinct X-ray sources are included in our point-source catalogue in the ACIS-I area. The number counts show a relative dearth of X-ray sources in this region. For example, at a flux limit of 10,15 erg cm,2 s,1, around 20 per cent more soft-band sources are detected in the HDF-N and almost 50 per cent more in the ELAIS-N1 field, which we have analysed by the same method for comparison. We find, however, that these differences are consistent with Poisson variations at <2, significance, and therefore there is no evidence for cosmic variance based on these number counts alone. We determine the average spectra of the objects and find a marked difference between the soft-band-selected sources, which have ,= 1.9 typical of unobscured active galactic nuclei (AGN), and the hard-band-selected sources, which have ,= 1.0. Reassuringly, the sample as a whole has a mean spectrum of ,= 1.4 ± 0.1, the same as the X-ray background. None the less, our results imply that the fraction of sources with significant obscuration is only ,25 per cent, much less than predicted by standard AGN population synthesis models. This is confirmed by direct spectral fitting, with only a handful of objects showing evidence for absorption. After accounting for absorption, all objects are consistent with a mean intrinsic spectrum of ,= 1.76 ± 0.08, very similar to local Seyfert galaxies. The survey area is distinguished by having outstanding multiwaveband coverage. Comparison with these observations and detailed discussion of the X-ray source properties will be presented in future papers. [source] Extended X-ray emission in the high-redshift quasar GB 1508+5714 at z= 4.3MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2003W. Yuan ABSTRACT We report the discovery of extended X-ray emission around the powerful high-redshift quasar GB 1508+5714 at z= 4.3, revealed in a long Chandra ACIS observation. The emission feature is 3,4 arcsec away from the quasar core, which corresponds to a projected distance of about 25 kpc. The X-ray spectrum is best fitted with a power law of photon index 1.92 ± 0.35 (90 per cent confidence limit). The X-ray flux and luminosity reach 9.2 × 10,15 erg cm,2 s,1 (0.5,8 keV) and 1.6 × 1045 erg s,1 (2.7,42.4 keV rest frame, ,,= 0.73, ,m= 0.27, H0= 71 km s,1 Mpc,1), which is about 2 per cent of the total X-ray emission of the quasar. We interpret the X-ray emission as inverse Compton scattering of cosmic microwave background photons. The scattering relativistic electron population could either be a quasi-static diffuse cloud fed by the jet, or an outer extension of the jet with a high bulk Lorentz factor. We argue that the lack of an obvious detection of radio emission from the extended component could be a consequence of Compton losses on the electron population, or of a low magnetic field. Extended X-ray emission produced by inverse Compton scattering may be common around high-redshift radio galaxies and quasars, demonstrating that significant power is injected into their surroundings by powerful jets. [source] A star-forming galaxy at z= 5.78 in the Chandra Deep Field SouthMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2003Andrew J. Bunker ABSTRACT We report the discovery of a luminous z= 5.78 star-forming galaxy in the Chandra Deep Field South. This galaxy was selected as an ,i -drop' from the GOODS public survey imaging with the Hubble Space Telescope/Advanced Camera for Surveys (object 3 in the work of Stanway, Bunker & McMahon 2003). The large colour of (i,,z,)AB= 1.6 indicated a spectral break consistent with the Lyman , forest absorption shortward of Lyman , at z, 6. The galaxy is very compact (marginally resolved with ACS with a half-light radius of 0.08 arcsec, so rhl < 0.5 h,170 kpc). We have obtained a deep (5.5 h) spectrum of this z,AB= 24.7 galaxy with the DEIMOS optical spectrograph on the Keck Telescope, and here we report the discovery of a single emission line centred on 8245 Å detected at 20, with a flux of f, 2 × 10,17 erg cm,2 s,1. The line is clearly resolved with detectable structure at our resolution of better than 55 km s,1, and the only plausible interpretation consistent with the ACS photometry is that we are seeing Lyman , emission from a z= 5.78 galaxy. This is the highest redshift galaxy to be discovered and studied using HST data. The velocity width (,vFWHM= 260 km s,1) and rest-frame equivalent width (WLy,rest= 20 Å) indicate that this line is most probably powered by star formation, as an AGN would typically have larger values. The starburst interpretation is supported by our non-detection of the high-ionization N v,1240- Å emission line, and the absence of this source from the deep Chandra X-ray images. The star formation rate inferred from the rest-frame UV continuum is 34 h,270 M, yr,1 (,M= 0.3, ,,= 0.7). This is the most luminous starburst known at z > 5. Our spectroscopic redshift for this object confirms the validity of the i,-drop technique of Stanway et al. to select star-forming galaxies atz, 6. [source] The ROSAT Brightest Cluster Sample , IV.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2000The extended sample We present a low-flux extension of the X-ray-selected ROSAT Brightest Cluster Sample (BCS) published in Paper I of this series. Like the original BCS and employing an identical selection procedure, the BCS extension is compiled from ROSAT All-Sky Survey (RASS) data in the northern hemisphere (,,0°) and at high Galactic latitudes (|b|,20°). It comprises 99 X-ray-selected clusters of galaxies with measured redshifts z,0.3 (as well as eight more at z>0.3) and total fluxes between 2.8×10,12 and 4.4×10,12 erg cm,2 s,1 in the 0.1,2.4 keV band (the latter value being the flux limit of the original BCS). The extension can be combined with the main sample published in 1998 to form the homogeneously selected extended BCS (eBCS), the largest and statistically best understood cluster sample to emerge from the RASS to date. The nominal completeness of the combined sample (defined with respect to a power-law fit to the bright end of the BCS log N,log S distribution) is relatively low at 75 per cent (compared with 90 per cent for the high-flux sample of Paper I). However, just as for the original BCS, this incompleteness can be accurately quantified, and thus statistically corrected for, as a function of X-ray luminosity and redshift. In addition to its importance for improved statistical studies of the properties of clusters in the local Universe, the low-flux extension of the BCS is also intended to serve as a finding list for X-ray-bright clusters in the northern hemisphere which we hope will prove useful in the preparation of cluster observations with the next generation of X-ray telescopes such as Chandra and XMM-Newton. An electronic version of the eBCS can be obtained from the following URL: http://www.ifa.hawaii.edu/~ebeling/clusters/BCS.html. [source] Toward an unbiased sample of X-ray selected normal galaxies outside the local UniverseASTRONOMISCHE NACHRICHTEN, Issue 2 2008A. GeorgakakisArticle first published online: 14 FEB 200 Abstract This paper shows that our understanding of the statistical properties of X-ray selected normal galaxies (e.g. X-ray luminosity function) can be significantly improved by combining a wide-area XMM-Newton survey with the moderare resolution and high S/N optical spectroscopy of the SDSS. Such a combined dataset has the potential to minimise uncertainties that affect existing normal galaxy samples at X-rays, such as small number statistics, cosmic variance, AGN contamination and incompleteness at bright X-ray luminosities. It is demonstrated that a 100 deg2 XMM-Newton survey in the SDSS area to the limit fX(0.5,2 keV) , 5 × 10,15 erg cm,2 s,1 will detect over 400 X-ray selected normal galaxies with excellent control over systematic biases, thereby providing tight contraints on the X-ray luminosity function at z , 0.1. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Resolving the source populations that contribute to the X-ray background: The 2 Ms Chandra Deep Field-North SurveyASTRONOMISCHE NACHRICHTEN, Issue 1-2 2003D. M. Alexander Abstract With , 2 Ms of exposure, the Chandra Deep Field-North (CDF-N) survey provides the deepest view of the Universe in the 0.5,8.0 keV band. Five hundred and three (503) X-ray sources are detected down to on-axis 0.5,2.0 keV and 2,8 keV flux limits of , 1.5 × 10,17 erg cm,2 s,1 and , 1.0 × 10,16 erg cm,2 s,1, respectively. These flux limits correspond to L0.5,8.0 keV, 3 × 1041 erg s,1 at z = 1 and L0.5,8.0 keV, 2 × 1043 erg s,1 at z = 6; thus this survey is sensitive enough to detect starburst galaxies out to moderate redshift and Seyfert galaxies out to high redshift. We present the X-ray observations, describe the broad diversity of X-ray selected sources, and review the prospects for deeper exposures. [source] The weak outnumbering the mighty: normal galaxies in deep Chandra surveysASTRONOMISCHE NACHRICHTEN, Issue 1-2 2003A. E. Hornschemeier Abstract Chandra is detecting a significant population of normal and starburst galaxies in extremely deep X-ray exposures. For example, approximately 15% of the sources arising in the 2 Ms Chandra Deep Field-North survey are fairly normal galaxies, where "normal" means "Milky Way-type" X-ray emission rather than simply exhibiting an "optically normal" spectrum. Many of these galaxies are being detected at large look-back times (z , 0.1,0.5), allowing the study of the evolution of X-ray binary populations over significant cosmological timescales. We are also detecting individual off-nuclear ultraluminous X-ray sources (e.g., X-ray binaries), providing the first direct constraints on the prevalence of lower-mass black holes at significantly earlier times. The X-ray emission from such "normal" galaxies may also be a useful star-formation rate indicator, based on radio/X-ray cross-identifications. We describe the contribution of normal galaxies to the populations which make up the X-ray background and present their directly measured X-ray number counts. We find that normal and starburst galaxies should dominate the 0.5,2 keV number counts at X-ray fluxes fainter than , 7 × 10,18 erg cm,2 s,1 (thus they will outnumber the "mighty" AGN). Finally, we look to the future, suggesting that it is important that the population of X-ray faint normal and starburst galaxies be well constrained in order to design the next generation of X-ray observatories. [source] | ||||||||||