We present theoretical models for the formation and evolution of populations of low-mass X-ray binaries (LMXBs) in the two elliptical galaxies NGC 3379 and NGC 4278. The models are calculated with the recently updated StarTrack code, assuming only a primordial galactic field LMXB population. StarTrack is an advanced population synthesis code that has been tested and calibrated using detailed binary star calculations and incorporates all the important physical processes of binary evolution. The simulations are targeted to modeling and understanding the origin of the X-ray luminosity functions (XLFs) of point sources in these galaxies. For the first time we explore the population XLF in luminosities below 10 37 ergs s À1 , as probed by the most recent observational results. We consider models for the formation and evolution of LMXBs in galactic fields with different CE efficiencies, stellar wind prescriptions, magnetic braking laws, and IMFs. We identify models that produce XLFs consistent with the observations both in shape and absolute normalization, suggesting that a primordial galactic field LMXB population can make a significant contribution to the total population of an elliptical galaxy. We also find that the treatment of the outburst luminosity of transient systems remains a crucial factor for the determination of the XLF, since the modeled populations are dominated by transient X-ray systems.

We present a statistical study of the low-mass X-ray binary (LMXB) populations of three nearby, old elliptical galaxies: NGC 3379, NGC 4278, and NGC 4697. With a cumulative ~1 Ms Chandra ACIS observing time, we detect 90-170 LMXBs within the D 25 ellipse of each galaxy. Cross-correlating Chandra X-ray sources and HST optical sources, we identify 75 globular cluster (GC) LMXBs and 112 field LMXBs with L X > 10 36 erg s -1 (detections of these populations are 90% complete down to luminosities in the range of 6 x 10 36 -1.5 x10 37 erg s -1 ). At the higher luminosities explored with previous studies, the statistics of this sample are consistent with the properties of GC-LMXBs reported in the literature. In the low luminosity range allowed by our deeper data (L X < 5 x 10 37 erg s -1 ), we find a significant relative lack of GC-LMXBs, when compared with field sources. Using the co-added sample from the three galaxies, we find that the incompletenesscorrected X-ray luminosity functions (XLFs) of GC and field LMXBs differ at ~4σ significance at L X < 5 x 10 37 erg s -1 . As previously reported, these XLFs are consistent at higher luminosities. The presently available theoretical models for LMXB formation and evolution in clusters are not sophisticated enough to provide a definite explanation for the shape of the observed GC-LMXB XLF. Our observations may indicate a potential predominance of GC-LMXBs with donors evolved beyond the main sequence, when compared to current models, but their efficient formation requires relatively high initial binary fractions in clusters. The field LMXB XLF can be fitted with either a single power-law model plus a localized excess at a luminosity of 5-6 x 10 37 erg s -1 , or a broken power-law with a similar low-luminosity break. This XLF may be explained with NSred-giant LMXBs, contributing to ~15% of total LMXBs population at ~5x10 37 erg s -1 . The difference in the GC and field XLFs is consistent with different origins and/or evolutionary paths between the two LMXB populations, although a fraction of the field sources are likely to have originated in GCs.

From a Chandra survey of nine interacting galaxy systems the evolution of X-ray emission during the merger process has been investigated. It is found that the X-ray luminosity peaks ~300Myr before nuclear coalescence, and then dips, even though we know that rapid and increasing activity is still taking place at this time. It is likely that this drop in X-ray luminosity is a consequence of outflows breaking out of the galactic discs of these systems. In this work it is also shown that, for the systems close to the point of nuclear coalescence, LFIR becomes massively enhanced compared to the X-ray luminosity of these systems. We suggest that this enhancement may indicate a `top heavy' initial mass function (IMF), with an enhanced fraction of massive stars. At a time ~1Gyr after coalescence, the merger remnants in our sample are X-ray faint when compared to typical mature elliptical galaxies. However, we do see evidence that these systems will start to resemble typical elliptical galaxies at a greater dynamical age, given the properties of the 3-Gyr system within our sample, supporting the idea that halo regeneration will take place within low LX merger remnants. As a part of this survey, detailed Chandra observations for the double nucleus merger system Markarian266 (Mrk266) and the merger remnant Arp222 are presented for the first time. With the Mrk266 observation, in contrast to previous studies, we now have good spectral information of the individual components part seen with the ROSAT High Resolution Imager (HRI). Additionally, the structure of the emission to the north of the system can clearly be distinguished and there is also a suggestion of some extension of X-ray emission to the south-east of the nuclear region, indicating that this galaxy could just be on the verge of large-scale galactic winds breaking out. Within Arp222 an X-ray luminosity of 1.46 ?? 1040ergs-1 has been detected, this is the lowest value of LX within our sample. The diffuse gas of Arp222 has been modelled with a temperature of 0.6keV and, from CO observations it has been found to host very little molecular gas, indicating that, from current observations, Arp222 does not resemble a mature elliptical

We present new deep Chandra observations of the Centaurus A jet, with a combined on-source exposure time of 719 ks. These data allow detailed X-ray spectral measurements to be made along the jet out to its disappearance at 4.5 kpc from the nucleus. We distinguish several regimes of high-energy particle acceleration: while the inner part of the jet is dominated by knots and has properties consistent with local particle acceleration at shocks, the particle acceleration in the outer 3.4 kpc of the jet is likely to be dominated by an unknown distributed acceleration mechanism. In addition to several compact counterjet features we detect probable extended emission from a counterjet out to 2.0 kpc from the nucleus, and argue that this implies that the diffuse acceleration process operates in the counterjet as well. A preliminary search for X-ray variability finds no jet knots with dramatic flux density variations, unlike the situation seen in M87.

We present here the first study of the X‐ray properties of an evolutionary sample of merging galaxies. Both ROSAT PSPC and HRI data are presented for a sample of eight interacting galaxy systems, each believed to involve a similar encounter between two spiral discs of approximately equal size. The mergers span a large range in age, from completely detached to fully merged systems. A great deal of interesting X‐ray structure is seen, and the X‐ray properties of each individual system are discussed in detail. Along the merging sequence, several trends are evident: in the case of several of the infrared bright systems, the diffuse emission is very extended, and appears to arise from material ejected from the galaxies. The onset of this process seems to occur very soon after the galaxies first encounter one another, and these ejections soon evolve into distorted flows. More massive extensions (perhaps involving up to 1010 M⊙ of hot gas) are seen at the ‘ultraluminous’ peak of the interaction, as the galactic nuclei coalesce. The amplitude of the evolution of the X‐ray emission through a merger is markedly different from that of the infrared and radio emission, however. Although the X‐ray luminosity rises and falls along the sequence, the factor by which the X‐ray luminosity increases, relative to the optical, appears to be only about a tenth of that seen in the far‐infrared. This, we believe, may well be linked with the large extensions of hot gas observed. The late, relaxed remnants appear relatively devoid of gas, and possess an X‐ray halo very different from that of typical ellipticals, a problem for the ‘merger hypothesis’, whereby the merger of two disc galaxies results in an elliptical galaxy. However, these systems are still relatively young in terms of total merger lifetime, and they may still have a few Gyr of evolution to go through before they resemble typical elliptical galaxies.