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Register a new userExploring the high frequency emission of radio loud X-ray binaries
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We report millimetre-wave continuum observations of the X-ray binaries Cygnus X-3, SS 433, LSI+61 303, Cygnus X-1 and GRS 1915+105. The observations were carried out with the IRAM 30 m-antenna at 250 GHz (1.25 mm) from 1998 March 14 to March 20. These millimetre measurements are complemented with centimetre observations from the Ryle Telescope, at 15 GHz (2.0 cm) and from the Green Bank Interferometer at 2.25 and 8.3 GHz (13 and 3.6 cm). Both Cygnus X-3 and SS 433 underwent moderate flaring events during our observations, whose main spectral evolution properties are described and interpreted. A significant spectral steepening was observed in both sources during the flare decay, that is likely to be caused by adiabatic expansion, inverse Compton and synchrotron losses. Finally, we also report 250 GHz upper limits for three additional undetected X-ray binary stars: LSI+65 010, LSI+61 235 and X Per.
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The three basic ingredients - a spinning compact object, an accretion disc and a collimated relativistic jet - make microquasars a galactic scaled-down version of the radio-loud AGN. That explains the large interest attributed to this new class of objects, which up to now consists of less than 20 members. Microquasars belong to the much larger class of X-ray binary systems, where there exits a compact object together with its X-ray emitting accretion disc, but the relativistic jet is missing. When does an X-ray binary system evolve into a microquasar? Ideal for studying such kind of a transition is the periodic microquasar LSI+61deg303 formed by a compact object accreting from the equatorial wind of a Be star and with more than one event of super-critical accretion and ejection along the eccentric orbit. For ejections at periastron passage the relativistic electrons suffer severe inverse Compton losses by upscattering the UV photons of the Be star at high energy : At periastron passage Gamma-ray emission has been observed, whereas radio outbursts have never been observed in 20 years of radio flux monitoring. For ejections displaced from periastron passage the losses are less severe and radio outbursts are observed. The radio emission mapped on scales from a few AU to hundreds of AU shows a double-sided relativistic (beta=0.6c) S-shaped jet, similar to the well-known precessing jet of SS433.
The radio source 1146+596 is hosted by an elliptical/S0 galaxy NGC,3894, with a low-luminosity active nucleus. The radio structure is compact, suggesting a very young age of the jets in the system. Recently, the source has been confirmed as a high-energy (HE, $>0.1$,GeV) $gamma$-ray emitter, in the most recent accumulation of the {it Fermi} Large Area Telescope (LAT) data. Here we report on the analysis of the archival {it Chandra} X-ray Observatory data for the central part of the galaxy, consisting of a single 40,ksec-long exposure. We have found that the core spectrum is best fitted by a combination of an ionized thermal plasma with the temperature of $simeq 0.8$,keV, and a moderately absorbed power-law component (photon index $Gamma = 1.4pm 0.4$, hydrogen column density $N_{rm H}/10^{22}$,cm$^{-2}$,$= 2.4pm 0.7$). We have also detected the iron K$alpha$ line at $6.5pm 0.1$,keV, with a large equivalent width of EW,$= 1.0_{-0.5}^{+0.9}$,keV. Based on the simulations of the {it Chandra}s Point Spread Function (PSF), we have concluded that, while the soft thermal component is extended on the scale of the galaxy host, the hard X-ray emission within the narrow photon energy range 6.0--7.0,keV originates within the unresolved core (effectively the central kpc radius). The line is therefore indicative of the X-ray reflection from a cold neutral gas in the central regions of NGC,3894. We discuss the implications of our findings in the context of the X-ray Baldwin effect. NGC,3894 is the first young radio galaxy detected in HE $gamma$-rays with the iron K$alpha$ line.
We report spectral, imaging, and variability results from four new XMM-Newton observations and two new Chandra observations of high-redshift (z > 4) radio-loud quasars (RLQs). Our targets span lower, and more representative, values of radio loudness than those of past samples of high-redshift RLQs studied in the X-ray regime. Our spectral analyses show power-law X-ray continua with a mean photon index, Gamma =1.74 +/- 0.11, that is consistent with measurements of lower redshift RLQs. These continua are likely dominated by jet-linked X-ray emission, and they follow the expected anti-correlation between photon index and radio loudness. We find no evidence of iron Kalpha ~ emission lines or Compton-reflection continua. Our data also constrain intrinsic X-ray absorption in these RLQs. We find evidence for significant absorption (N_H ~ 10^22 cm^-2) in one RLQ of our sample (SDSS J0011+1446); the incidence of X-ray absorption in our sample appears plausibly consistent with that for high-redshift RLQs that have higher values of radio loudness. In the Chandra observation of PMN J221-2719 we detect apparent extended (~ 14 kpc) X-ray emission that is most likely due to a jet; the X-ray luminosity of this putative jet is ~2% that of the core. The analysis of a 4.9 GHz VLA image of PMN J221-2719 reveals a structure that matches the X-ray extension found in this source. We also find evidence for long-term (450-460 days) X-ray variability by 80-100% in two of our targets.
The X-ray emission of radio-loud (RL) AGNs is a powerful tool for probing the structure of the accretion flow in these objects. We review recent spectral and variability studies of RL AGNs, which show that these systems have systematically different X-ray properties than their radio-quiet (RQ) counterparts. Specifically, RL AGNs have weaker and narrower Fe K lines and weaker Compton reflection components above 10 keV. The nuclear continuum of RL AGNs in the 2--10 keV band is well described by a power law with photon indices $sim$ 1.8, similar to RQ AGNs of comparable X-ray luminosity. RL AGNs have little or no flux variability on short time scales (ltsima 0.5 days); however, flux and spectral variations are observed on time scales of weeks in two well-monitored objects, 3C~390.3 and 3C~120. These properties strongly suggest that the central engines of the two AGNs classes are different. We discuss the implications of these observational results, in particular the possibility that the central engines of RL AGNs are harbor an ion torus (also known as an Advection-Dominated Accretion Flow or ADAF). We show that a beamed component from the jet is unlikely in the majority of sources. Moreover, the X-ray data provide evidence that the circumnuclear environs of RL and RQ AGNs also differ: large amounts of cold gas are detected in BLRGs and QSRs, contrary to Seyfert galaxies of similar X-ray luminosity where an ionized absorber seems to be the norm. The role of future X-ray missions in advancing our understanding of the central engines of RL AGNs is briefly highlighted.
We have developed a clumpy stellar wind model for OB supergiants in order to compare predictions of this model with the X-ray behaviour of both classes of persistent and transient High Mass X-ray Binaries (HMXBs).
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