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1.
First studies of the X‐ray source population of M 31 were performed with the Einstein Observatory and ROSAT. High resolution Chandra Observatory images not only spatially resolved the center area but also supernova remnants (SNRs) in the galaxy. Source catalogues of restricted areas were presented with high astrometric accuracy. Also luminosity function studies and studies of individual sources based on Chandra and XMM‐Newton observations led to a better knowledge of the X‐ray source population. An XMM‐Newton source catalog based on archival observations revealed more than 850 sources down to a 0.2–4.5 keV luminosity of 1035 erg s–1. EPIC hardness ratios as well as informations from earlier X‐ray, optical, and radio catalogues were used to distinguish between different source classes (SNRs, supersoft sources (SSSs), X‐ray binaries (XRBs), globular cluster sources within M 31, and foreground stars and objects in the background). However, many sources could only be classified as “hard”. These sources may either be XRBs or Crab‐like SNRs in M 31 or background sources. Two of the globular cluster sources could be identified as low mass XRBs with a neutron star as compact object as they showed type I X‐ray bursts. Many of the SSSs were identified as optical novae. Inspired by these results an XMM‐Newton survey of the entire D25 disk of M 31 and a dedicated program to monitor X‐ray counterparts of optical novae in M 31 was started. We discuss implications for further nearby galaxy studies. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

2.
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)  相似文献   

3.
I review various phenomena associated with mass‐accreting white dwarfs (WDs) in the view of supersoft X‐ray sources. When the mass‐accretion rate is low (Ṁacc < a few × 10–7 M⊙yr–1), hydrogen nuclear burning is unstable and nova outbursts occur. A nova is a transient supersoft X‐ray source (SSS) in its later phase which timescale depends strongly on the WD mass. The X‐ray turn on/off time is a good indicator of the WD mass. At an intermediate mass‐accretion rate an accreting WD becomes a persistent SSS with steady hydrogen burning. For a higher mass‐accretion rate, the WD undergoes “accretion wind evolution” in which the WD accretes matter from the equatorial plane and loses mass by optically thick winds from the other directions. Two SSS, namely RX J0513‐6951 and V Sge, are corresponding objects to this accretion wind evolution. We can specify mass increasing WDs from light‐curve analysis based on the optically thick wind theory using multiwavelength observational data including optical, IR, and supersoft X‐rays. Mass estimates of individual objects give important information for the binary evolution scenario of type Ia supernovae (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

4.
Gamma‐ray bursts (GRBs) are the most powerful explosions since the formation of the Universe, associated with the death of massive stars or mergers of compact stellar objects. Several recent striking results strongly support the idea that host galaxies of GRBs are opening a new view on our understanding of galaxy formation and evolution, back to the very primordial universe at z ∼ 8. They form a unique sample of galaxies which cover a wide range of redshift, they are typically weak with low mass and unlike other methods they are not selected on luminosity. In recent years, thanks to the support of new generation instruments, multi‐band photometry and spectroscopy allow us to better investigate the properties of these host galaxies (e.g., stellar mass, age, SFR, metallicity), to study their possible evolution and to compare them with field galaxies and other classes of galaxies. GRB host spectroscopy is one of the main science drivers behind the X‐shooter spectrograph. In this paper, we present the first results of the program devoted to Italian‐French GTO multiband spectroscopy of GRB host galaxies with X‐shooter (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

5.
The landscape of Galactic X‐ray sources made of accreting binaries, isolated objects and active stellar coronae has been significantly modified by the advent of the Chandra, XMM‐Newton and INTEGRAL satellites. New types of relatively low X‐ray luminosity X‐ray binaries have been unveiled in the Galactic disc, while deep observations of the central regions have revealed large numbers of X‐ray binaries of so far poorly constrained nature. Because of the high spatial resolution needed and faint X‐ray luminosities generally emitted, studying the dependency of the X‐ray source composition with parent stellar population, Galactic disc, bulge, nuclear bulge, etc., is only practicable in our Galaxy. The evolutionary links between low LX X‐ray binaries and classical X‐ray luminous accreting systems are still open in many cases. In addition, the important question of the nature of the compact sources contributing to the Galactic ridge hard X‐ray emission remains unresolved. We review the most important results gathered by XMM‐Newton over the last years in this domain and show how future observations could be instrumental in addressing several of these issues. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

6.
Observations of present and future X‐ray telescopes include a large number of ipitous sources of unknown types. They are a rich source of knowledge about X‐ray dominated astronomical objects, their distribution, and their evolution. The large number of these sources does not permit their individual spectroscopical follow‐up and classification. Here we use Chandra Multi‐Wavelength public data to investigate a number of statistical algorithms for classification of X‐ray sources with optical imaging follow‐up. We show that up to statistical uncertainties, each class of X‐ray sources has specific photometric characteristics that can be used for its classification. We assess the relative and absolute performance of classification methods and measured features by comparing the behaviour of physical quantities for statistically classified objects with what is obtained from spectroscopy. We find that among methods we have studied, multi‐dimensional probability distribution is the best for both classifying source type and redshift, but it needs a sufficiently large input (learning) data set. In absence of such data, a mixture of various methods can give a better final result.We discuss some of potential applications of the statistical classification and the enhancement of information obtained in this way. We also assess the effect of classification methods and input data set on the astronomical conclusions such as distribution and properties of X‐ray selected sources. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

7.
In recent work it was demonstrated that narrow‐line Seyfert 1 galaxies, which possessed spectral complexity in the 2–10 keV band were at the same time X‐ray weak. In this contribution I show how X‐ray weakness can be understood in the context of reflection and light bending picture. In fact, X‐ray weakness should be expected from objects that are in a reflection dominated state. With simultaneous UV and X‐ray data available with most XMM‐Newton observations, an estimate of the X‐ray weakness is relatively straightforward. As such, it is an easy way to substantiate conclusions of reflection dominated spectra, and we use this method to examine recent claims. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

8.
Because of the intense brightness of the OB‐type multiple star system σ Ori, the low‐mass stellar and substellar populations close to the centre of the very young σ Orionis cluster is poorly know. I present an IJHKs survey in the cluster centre, able to detect from the massive early‐type stars down to cluster members below the deuterium burning mass limit. The near‐infrared and optical data have been complemented with X‐ray imaging. Ten objects have been found for the first time to display high‐energy emission. Previously known stars with clear spectroscopic youth indicators and/or X‐ray emission define a clear sequence in the I vs. I – Ks diagram. I have found six new candidate cluster members that follow this sequence. One of them, in the magnitude interval of the brown dwarfs in the cluster, displays X‐ray emission and a very red J – Ks colour, indicative of a disc. Other three low‐mass stars have excesses in the Ks band as well. The frequency of X‐ray emitters in the area is 80±20 %. The spatial density of stars is very high, of up to 1.6±0.1 arcmin–2. There is no indication of lower abundance of substellar objects in the cluster centre. Finally, I also report two cluster stars with X‐ray emission located at only 8000–11000 AU to σ Ori AB, two sources with peculiar colours and an object with X‐ray emission and near‐infrared magnitudes similar to those of previously‐known substellar objects in the cluster. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

9.
We review the most important findings on AGN physics and cosmological evolution as obtained by extragalactic X‐ray surveys and associated multiwavelength observations. We briefly discuss the perspectives for future enterprises and in particular the scientific case for an extremely deep (2–3 Ms) XMM survey. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

10.
In the last couple of decades hundreds of studies have explored the nature of star‐forming galaxies at different redshifts. This contribution focuses on X‐shooter observations of star‐burst galaxies at 0 < z < 6 from commissioning runs, science verification, and regular observations, and demonstrates the capability of the new instrument in this competitive field. Observations of gravitationally lensed galaxies show that X‐shooter has no limitation in the redshift desert (1.4 < z < 2) where the strong optical emission lines are shifted to the near‐IR region. Physical properties of galaxies, such as masses, metallicities, abundance ratios, and star formation rates can be derived from observations with relatively short integration times for faint galaxies. The simultaneous UV to near‐IR spectral coverage makes derivation of physical quantities more reliable because there are no differential slit losses as may occur when observations from different optical and near‐IR instruments are used. Over the entire redshift range, spectra of faint galaxies will allow us to better measure stellar ages and dominating ionisation sources compared to broad band spectral energy distribution measurements (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

11.
Classical novae (CNe) have recently been reported to represent the major class of supersoft X‐ray sources (SSSs) in the central area of our neighbouring galaxy M 31. This paper presents a review of results from recent X‐ray observations of M 31 with XMM‐Newton and Chandra. We carried out a dedicated optical and X‐ray monitoring program of CNe and SSSs in the central area ofM 31. We discovered the first SSSs in M 31 globular clusters (GCs) and their connection to the very first discovered CN in a M 31 GC. This result may have an impact on the CN rate in GCs. Furthermore, in our optical and X‐ray monitoring data we discovered the CN M3 1N 2007‐11a, which shows a very short SSS phase of 29–52 days. Short SSS states (durations ≤ 100 days) of CNe indicate massive white dwarfs (WDs) that are candidate progenitors of supernovae type Ia. In the case of M31N 2007‐11a, the optical and X‐ray light curves suggest a binary containing a WD with MWD > 1.0 M⊙. Finally, we present the discovery of the SSS counterpart of the CN M31N 2006‐04a. The X‐ray light curve of M31N 2006‐04a shows short‐time variability, which might indicate an orbital period of about 2 hours (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

12.
We show that binned differential luminosity functions constructed using the 1/ V a method have a significant systematic error for objects close to the flux limit(s) of their parent sample. This is particularly noticeable when luminosity functions are produced for a number of different redshift ranges as is common in the study of AGN or galaxy evolution. We present a simple method of constructing a binned luminosity function which overcomes this problem and has a number of other advantages over the traditional 1/ V a method. We also describe a practical method for comparing binned and model luminosity functions, by calculating the expectation values of the binned luminosity function from the model.
Binned luminosity functions produced by the two methods are compared for simulated data and for the Large Bright QSO Survey (LBQS). It is shown that the 1/ V a method produces a very misleading picture of evolution in the LBQS. The binned luminosity function of the LBQS is then compared with a model two-power-law luminosity function undergoing pure luminosity evolution from Boyle et al. The comparison is made using a model luminosity function averaged over each redshift shell, and using the expectation values for the binned luminosity function calculated from the model. The luminosity function averaged in each redshift shell gives a misleading impression that the model over predicts the number of QSOs at low luminosity even for 1.0< z <1.5, when model and data are consistent. The expectation values show that there are significant differences between model and data: the model overpredicts the number of low luminosity sources at both low and high redshift. The luminosity function does not appear to steepen relative to the model as redshift increases.  相似文献   

13.
Our aim is to investigate tidal interaction in High‐Mass X‐ray Binary stars in order to determine in which objects the rotation of the mass donors is synchronized or pseudosynchronized with the orbital motion of the compact companion. We calculate the pseudosynchronization period (Pps) and compare it with the rotational period of the mass donors (Prot). We find that (1) the Be/X‐ray binaries are not synchronized, the mass donors rotate faster than the orbital period and the ratio Pps/Prot is 2–300; (2) the giant and supergiant systems are close to synchronization and for them the ratio Pps/Prot is 0.3–2 (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

14.
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15.
Charge‐transfer (CT) X‐ray emission may occur at interfaces between a partially neutral gas and gas possessing high ions, provided there is a relative motion between those two phases. The CTX surface brightness from distant objects must be taken into account if it is not far below other “classical” emission sources, especially the thermal emission from the hot phase. I discuss those conditions and potential spectroscopic or photometric diagnostics. I also mention potential indirect effects of the CT reactions by means of pickup ion production, acceleration and subsequent modification of interface and plasma properties (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

16.
We report the discovery of a bright blue quasar: SDSS J022218.03–062511.1. This object was discovered spectroscopically while searching for hot white dwarfs that may be used as calibration sources for large sky surveys such as the Dark Energy Survey or the Large Synoptic Survey Telescope project. We present the calibrated spectrum, spectral line shifts and report a redshift of z = 0.521±0.0015 and a rest‐frame g‐band luminosity of 8.71×1011 L⊙. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

17.
We describe the current status and recent results from our Swift/VLT legacy survey, a VLT Large Programme aimed at characterizing the host galaxies of a homogeneously selected sub‐sample of Swift gamma‐ray bursts (GRBs). The immediate goals are to determine the host luminosity function, study the effects of reddening, determine the fraction of Lyα emitters in the hosts, and obtain redshifts for targets without a reported one. We have defined a very carefully selected sample, obeying strict and well‐defined criteria: 68 targets in total. Among the preliminary results is a large optical detection rate, the lack of extremely red objects (only one possible case in the sample), and 10 new GRB redshifts with the mean redshift of the host sample assessed to be 〈z 〉 ≳ 2 (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

18.
The workshop “Supersoft X‐ray Sources – New Developments” brought together observers and theoretician to discuss the present status and unsolved problems of supersoft source research. A large part of the workshop was devoted to optical novae and their supersoft state. Large samples of supersoft X‐ray sources were presented from nearby galaxies, as well as extensive monitoring campaigns ofbright individual sources. The theoretical modelling oflight curves and high‐resolution X‐ray spectra are well underway, but details are often not yet understood (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

19.
By combining a model for the evolution of the radio luminosity of an individual source with the radio luminosity function, we perform a multidimensional Monte Carlo simulation to investigate the cosmological evolution of the Fanaroff–Riley type II (FR II) radio galaxy population by generating large artificial samples. The properties of FR II sources are required to evolve with redshift in the artificial samples to fit the observations. Either the maximum jet age or the maximum density of the jet environment or both evolve with redshift. We also study the distribution of FR II source properties as a function of redshift. From currently available data we cannot constrain the shape of the distribution of environment density or age, but jet power is found to follow a power-law distribution with an exponent of approximately −2. This power-law slope does not change with redshift out to   z = 0.6  . We also find the distribution of the pressure in the lobes of FR II sources to evolve with redshift up to   z ∼ 1.2  .  相似文献   

20.
We review some recent results on the identification and characterisation of Active Galactic Nuclei (AGN) obtained by cross correlating X‐ray surveys with infrared and submillimetre surveys. We also look toward the scientific gains that could be achieved from an XMM‐Newton survey of the medium‐deep legacy fields that are being observed at ≈ 1–850 μm. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

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