Podcasts about lmxb

Broad-band spectral analysis of LMXB 2S 0921-63 with Suzaku by Prince Sharma et al. on Monday 26 September We present the broad-band spectral analysis of the low-mass X-ray binary 2S 0921-63 by using the Suzaku archival data covering the orbital phase between 0.31 and 1.16 during four close observations. It is the first time that a broad-band spectral analysis of 2S 0921-63 has been done up to 25 keV. The 0.5-10 keV XIS count rate varied between $sim$ 1 and $sim$ 5 counts s$^{-1}$ during the observations. A partial X-ray eclipse and broad post-eclipse intensity dip were observed during the observations. The X-ray emission hardened marginally during the intensity dip. We have modelled the source spectra by simultaneously fitting the XIS and HXD-PIN spectra for each of the four observations. The broad-band spectra of the source can be described by a model comprising a very hot blackbody having temperature, $kT_{rm BB} approx$ 1.66 - 2.13 keV, a high-energy cutoff power law, and an Fe emission line at $E_{rm line} sim$ 6.7 keV. A second model, accounting for the Comptonization of the thermal emission from accretion disc along with an Fe emission line, describes the broad-band spectra of 2S 0921-63 equally well. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2209.00282v2

Investigating the Lower Mass Gap with Low Mass X-ray Binary Population Synthesis by Jared C. Siegel et al. on Thursday 15 September Mass measurements from low-mass black hole X-ray binaries (LMXBs) and radio pulsars have been used to identify a gap between the most massive neutron stars (NS) and the least massive black holes (BH). BH mass measurements in LMXBs are typically only possible for transient systems: outburst periods enable detection via all-sky X-ray monitors, while quiescent periods enable radial-velocity measurements of the low-mass donor. We present the first quantitative study of selection biases due to the requirement of transient behavior for BH mass measurements. Using rapid population synthesis simulations (COSMIC), detailed binary stellar-evolution models (MESA), and the disk instability model of transient behavior, we demonstrate that transient LMXB selection effects do introduce biases into the observed sample. If a gap is not inherent in BH birth masses, mass growth through LMXB accretion and selection effects can suppress mass-gap BHs in the observed sample. Our results are robust against variations of binary evolution prescriptions. We further find that a population of transient LMXBs with mass-gap BHs form through accretion induced collapse of a NS during the LMXB phase. The significance of this population is dependent on the maximum NS birth mass $M_mathrm{NS, birth-max}$. For $M_mathrm{NS, birth-max}=3M_{odot}$, MESA and COSMIC models predict a similar fraction of mass gap LMXBs. However, for $M_mathrm{NS, birth-max}lesssim2M_{odot}$ and realistic models of the disk-instability, our MESA models produce a dearth of mass-gap LMXBs, more consistent with observations. This constraint on $M_mathrm{NS, birth-max}$ is independent of whether low-mass BHs form at core-collapse. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2209.06844v1

The aim of this thesis is to study the environmental dependence of populations of low-mass X-ray binaries (LMXBs) in early-type galaxies. The dissertation is mainly based on archival data of the Chandra observatory, complemented by the infrared data of the Spitzer observatory as well as by the results of the Hubble Space Telescope and ground based optical observations. The dissertation investigates the dependence of LMXB populations on the stellar density, velocity dispersion and the age of the stellar population. To investigate the LMXB dependence on the stellar density and velocity dispersion, we studied different sub populations of low-mass X-ray binaries -- dynamically formed systems in globular clusters and in the nucleus of M31, and presumably primordial X-ray binaries in the fields of galaxies. We found that the luminosity distributions of globular cluster and field LMXBs differ throughout the entire luminosity range. The fraction of faint (Lx < E37 erg/s) sources in globular clusters is ~ 4 times smaller than in the field population. This may present a challenge for the models suggesting that the entire LMXB population was formed dynamically in globular clusters and then expelled to the field due to dynamical interactions or as globular clusters dissolve. The luminosity function of dynamically formed sources in the nucleus of M31 is similar to that of globular cluster sources at the faint end but differs at the bright end, that the M31 nucleus hosting significantly fewer bright sources than globular clusters (and field population). The difference between their luminosity distributions is likely caused by the factor of ~ 10-20 difference in stellar velocities in globular clusters and galactic nuclei, which leads to different dynamical formation channels. In order to investigate the LMXB dependence on the stellar age we collected a sample of 20 nearby massive E/S0 galaxies covering a broad range of stellar ages from ~ 1 to > 10 Gyrs. We found statistically significant correlation of the specific frequency of LMXBs (number per unit stellar mass) with the age of the host galaxy and its globular cluster content. Overall, older galaxies tend to have more X-ray binaries per unit stellar mass than the younger ones. This can be explained as a combined effect of two factors. On one hand, there appears to be an intrinsic correlation of the specific number of low-mass X-ray binaries in the field with the age of the stellar population. On the other hand, the older galaxies tend to have richer globular cluster population and therefore a larger number of dynamically formed X-ray sources associated with them. We also found a significant difference in the luminosity functions of low-mass X-ray binaries in younger and older galaxies, with the former having a flatter luminosity distribution and hosting more bright sources. This behavior is unrelated to the difference between luminosity distributions of the globular cluster and field sources and reflects the intrinsic age dependence of the LMXB populations.

In this dissertation we study the properties of high-mass X-ray binaries (HMXBs) and hot inter-stellar medium in star-forming galaxies and their relation with the star formation rate (SFR), based on the data from Chandra, Spitzer, GALEX and 2MASS public archives. We constructed a large sample of galaxies for which we collected homogeneous sets of multiwavelength measurements in X-ray, ultraviolet (UV), far-infrared (FIR) and near-infrared (NIR) bands. The sample includes 45 star-forming galaxies in total, divided in two sub-samples: the primary sample, consisting of 29 nearby galaxies, having distance < 40 Mpc, so that Chandra can resolve their X-ray point-like source population; the high-SFR sample, including 16 more distant galaxies that allowed us to extend the dynamical range of SFRs by approximately two orders of magnitude. In this sample we detected 1057 compact X-ray sources, of which ~300 are expected to be background active galactic nuclei (AGN). The majority of remaining ~700 sources are young systems associated with star-formation in the host galaxy. Based on their high X-ray luminosities and analogy with the X-ray populations in the Milky Way and few other very nearby galaxies, we conclude that they are high-mass X-ray binaries, powered by accretion of matter from a massive donor star onto a compact object - a black hole or a neutron star. Such a large number of sources allowed us to perform the most detailed study of the population of HMXBs and its dependence on various properties of the host galaxy, as well as to obtain a very accurate calibration of the X-ray luminosity-SFR relation. The study of the population of HMXBs is based on their X-ray luminosity functions (XLF). To this end, we took a special care to minimize the contamination by LMXBs, background AGN and to control the incompleteness of the Chandra source lists. The shape of the HMXB luminosity function is similar in different galaxies with the power law indexes having rms=0.25 with respect to the average value of ~1.6. The XLF normalizations, on the contrary, show significantly larger dispersion with the rms=0.34 dex around the A-SFR law. Combining the data of all galaxies, which include ~700 X-ray sources, we produced the average XLF of high-mass X-ray binaries in nearby star-forming galaxies. Its statistical accuracy exceeds by far that achieved in any of the previous studies of the HMXB luminosity function. The HMXB XLF has a single power law shape in a broad luminosity range of logLx~35-40 and shows a moderately significant evidence for the high luminosity break or cut-off at logLx~40. We did not find any statistically significant features at the Eddington luminosity limits of neutron stars or a 10 Msun black hole. With the knowledge of the relation between the number of high-mass X-ray binaries and star formation rate of the host galaxy, we estimated that the fraction of compact objects that went through an X-ray active phase at least once in their lifetime, powered by accretion of matter from a massive donor star in a binary system is fx~0.2. This constrains the mass distribution of the secondary in massive binaries. For an independent mass distribution of the secondary, the power law index must be flatter than 0.3. In particular, an independent mass distribution of a Kroupa or Salpeter type is strongly excluded. Assuming that the masses of components in a binary are not independent, our results are consistent with the flat mass ratio distribution. For comparison, we obtained a similar estimate for the fraction of compact objects that become X-ray sources powered by accretion from a low-mass donor star in an LMXB. Based on the scaling-laws by Gilfanov (2004), the fraction of compact objects, X-ray active in LMXBs, is small, fx~1e-6, demonstrating that LMXBs are extremely rare objects. This result is in line with the conclusions of the binary population studies. The collective luminosity of high-mass X-ray binaries is a good tracer of the recent star formation activity in the host galaxy: L_XRB(0.5-8 keV)(erg/s) = 2.5 10^{39} SFR (Msun/yr) The rms of points around this relation is 0.4 dex. The observed dispersion is unlikely to be caused by any of the obvious contaminating factors such as CXB or LMXB sources and is likely to have a physical origin. In addition to the emission from XRB population, the X-ray emission from star-forming galaxies includes a hot diffuse gas component with a mean characteristic temperature of 2-3 10^{6} K. We show that its X-ray luminosity correlates with the star formation rate of the host galaxy. Finally we demonstrate that the total X-ray luminosity of a galaxy scales with the star formation rate: L_tot(0.5-8 keV)(erg/s) = 4.5 10^{39} SFR(Msun/yr) with a dispersion sigma = 0.32 dex. We obtained consistent scale factors for nearby galaxies from the resolved sample and galaxies from the high-SFR sample. Among the latter (eight out of 16) are Chandra Deep Field North galaxies, located at the red-shifts of z~0.2-1.3. This proves that the total X-ray luminosity of a galaxy is a powerful tool to measure the star formation rate in distant galaxies.

This dissertation presents the analysis of a large and deep XMM-Newton survey of the second large Local Group spiral galaxy M 31. The survey observations, taken between June 2006 and February 2008, together with re-analysed archival observations from June 2000 to July 2004 cover, for the first time, the whole D25 ellipse of M 31 with XMM-Newton down to a limiting luminosity of ~10^35 erg/s in the 0.2-4.5 keV band. The main goal of the thesis was a study of the different source populations of M 31 that can be observed in X-rays. Therefore a catalogue was created, which contains all 1948 sources detected in the 0.2-12.0 keV range. 961 of these sources were detected in X-rays for the first time. Source classification and identification was based on X-ray hardness ratios, spatial extent of the sources, and by cross correlating with catalogues in the X-ray, optical, infrared and radio wavelengths. An additional classification criterion was the long-term temporal variability of the sources in X-rays. This variability allows us to distinguish between X-ray binaries and active galactic nuclei. Furthermore, supernova remnant classifications of previous studies that did not use long-term variability as a classification criterion, could be validated. Including previous Chandra and ROSAT observations in the long-term variability study allowed me to detect additional transient or at least highly variable sources, which are good candidates for being X-ray binaries. Fourteen of the 40 supersoft source (SSS) candidates correlated with optical novae and therefore can be considered the supersoft emission of the optical novae. Among them is the first nova/SSS detected in a globular cluster of M 31. Correlations with previous ROSAT and Chandra studies revealed that only three SSSs are visible for at least one decade. This result underlines the strong long-term variability found for the class of SSSs. In addition the correlations demonstrated that strict selection criteria have to be applied to securely select SSSs. An investigation of the spatial distribution of the 25 supernova remnants (SNRs) and 37 SNR candidates showed that many of these sources are consistent with the location of the 10 kpc dust ring and other star forming regions in M 31. This connection between SNRs and star forming regions implies that most of the remnants are from type II supernovae. The brightest sources of M 31 belong to the class of X-ray binaries (XRBs). Ten low mass XRBs (LMXBs) and 26 LMXB candidates were identified based on their temporal variability. In addition 36 LMXBs and 17 LMXB candidates were identified due to correlations with globular clusters and globular cluster candidates. From the LMXBs located in globular clusters one is a black hole candidate and another a neutron star candidate. From optical and X-ray colour-colour diagrams, possible high mass XRB (HMXB) candidates were selected. Two of these candidates have an X-ray spectrum as is expected for an HMXB containing a neutron star primary. To investigate the logN-logS relations of sources in the field of M 31, a catalogue of sources detected in the 2.0-10.0 keV energy range was created. The slope of the logN-logS relation for the whole galaxy is consistent with the expectation for spiral galaxies (Colbert et al. 2004). Subtracting the background logN-logS relation, the region beyond the D25 ellipse still contains about 13 sources/deg^2 of M 31 with fluxes above the completeness limit of ~3.2x10^{-14} erg/cm^2/s (~2.3x10^36 erg/s at the distance of M 31). The radial dependence of the source distribution in M 31's disc can be well fitted with an exponential profile, for limiting fluxes of ~3.2x10^{-14} erg/cm^2/s and 10^{-13} erg/cm^2/s (~7.3x10^36 erg/s). About 60% of all sources with fluxes above 3.2x10^{-14} erg/cm^2/s are background sources. While the contribution of background sources lies at ~20% in the inner disc region, the fraction increases to >~80% in the outer areas of M 31. For the dust ring region, the slope of the logN-logS relation as well as the number of sources and their dependence on the star forming rate were consistent with the universal logN-logS relation predicted from theoretical considerations of HMXBs (Grimm et al. 2003). These findings propose that the dust ring region contains a population of HMXBs. A comparison of the number of X-ray binaries (XRBs) obtained from the logN-logS study to the ones listed in the source catalogue showed that many XRBs detected in the logN-logS study with fluxes between 10^{-13} erg/cm^2/s and 3.2x10^{-14} erg/cm^2/s, or (independent from the flux) those XRBs located in the inner disc of M 31, remain without XRB classification in the source catalogue. The results presented in this thesis gave us deeper insights in the properties of the population of X-ray sources in M 31. Nevertheless, about 65% of all sources detected in the field of M 31 can be classified as ``hard" sources only, i.e. it is not possible to decide whether these sources are X-ray binaries or Crab-like supernova remnants in M 31, or active galactic nuclei. Deeper observations in the X-ray and at other wavelengths are needed to classify these sources.

Die vorliegende Arbeit beschäftigt sich mit einem Modell, das Oszillationen der Massentransferrate in halbgetrennten, kompakten Doppelsternsystemen auf verhältnismäßig großen Zeitskalen erklären kann. Der kompakte Stern, ein Weißer Zwerg, Neutronenstern oder Schwarzes Loch akkretiert Materie von seinem ausgedehnteren Begleiter. Durch die entstehende Akkretionsleuchtkraft wird der masseverlierende Stern bestrahlt und seine äußersten, dem Begleiter zugewandten Schichten werden aufgeheizt. Besitzt der masseverlierende Stern eine konvektive Hülle, so ist sein thermischer Gleichgewichtsradius von der äußeren Bestrahlung abhängig, und der Stern reagiert auf Änderungen in der Bestrahlung auf der Kelvin-Helmholtz-Zeitskala der konvektiven Hülle. Da die Massentransferrate wiederum empfindlich vom Sternradius abhängt, kommt es zu einer Rückkopplung auf den Massentransfer. Dieser Effekt kann dazu führen, daß die stationäre Massentransferrate instabil wird und sich das System quasi immer entweder im "High State" bei erhöhtem Massentransfer oder im "Low State" bei verringertem oder sogar abgeschaltetem Massentransfer befindet. In Frage kommen hierfür Systeme mit einem massearmen Hauptreihenstern oder Riesen als Massegeber, also Kataklysmische Veränderliche (CV) und Massearme Röntgendoppelsterne (LMXB). Es gibt ein auf einfachen Sternmodellen beruhendes analytisches Modell für das Auftreten von Massentransferzyklen sowie einzelne numerische Entwicklungsrechnungen, die auf jenen vereinfachten Modellen basieren. Das Hauptziel der vorliegenden Arbeit besteht nun darin, dieses analytische Modell und insbesondere die Grenzen der Instabilitätsbereiche durch numerische Rechnungen mit vollen 1D-hydrostatischen Sternmodellen für den masseverlierenden Stern zu bestätigen. Es wird daher zunächst ein impliziter Algorithmus entwickelt, der es ermöglicht, insbesondere das Ein- und Ausschalten des Massentransfers numerisch mit der erforderlichen Genauigkeit zu verfolgen, und der für Langzeitrechnungen möglichst wenig Zeitschritte benötigt. Des weiteren wird das analytische Modell ausführlich mittels linearer Stabilitätsanalyse hergeleitet und diskutiert sowie durch Hinzunahme eines bisher vernachlässigten Terms verbessert. Es ergibt sich schließlich eine einfache Ungleichung als Bedingung für das Auftreten von bestrahlungsinduzierten Massentransferzyklen. Schließlich werden numerische Langzeitentwicklungen sowohl für nuklear unentwickelte als auch nuklear entwickelte Sterne gerechnet. Vergleiche mit dem analytischen Modell zeigen eine recht gute quantitative Übereinstimmung für unentwickelte Sterne. Für stark entwickelte Sterne, für die das analytische Modell formal nicht anwendbar ist, zeigen sich deutliche Unterschiede. Dennoch ist es mit dem verbesserten analytischen Modell nun möglich, für ein vorgegebenes System anzugeben, ob und für welche Parameter Massentransferzyklen auftreten sollten.