Black Hole Candidate X-ray Binaries Research Articles

X-ray emission from the Sculptor galaxy NGC 300

We report here the results of a full analysis of all the ROSAT PSPC spectral imaging observations and all the ROSAT HRI high resolution imaging observations of the very nearby ( Mpc) Sculptor galaxy, NGC 300. Many point sources are detected within the field, several of them showing evidence for variability, and we present full source lists detailing their X-ray properties, and attempt to classify them on the basis of their temporal, spectral and multi-wavelength characteristics. A black hole X-ray binary candidate, a supersoft source and several supernova remnants and H ii regions are detected in X-rays, as is unresolved, possibly diffuse emission, accounting for perhaps ~20% of the total NGC 300 X-ray (0.1-2.4 keV) luminosity ( erg s-1). We compare the X-ray source luminosity distribution of NGC 300 with that of other nearby galaxies, and we also compare NGC 300 with its Sculptor neighbours, concluding that it is a quite an unremarkable system, showing no unusual X-ray (or other multi-wavelength) properties. It may be one of the best examples of a completely typical normal quiescent late-type spiral galaxy.

A jet model for the broadband spectrum of XTE J1118+480

Observations have revealed strong evidence for powerful jets in the Low/Hard states of black hole candidate X-ray binaries. Correlations, both temporal and spectral, between the radio - infrared and X-ray bands suggest that jet synchrotron as well as inverse Compton emission could also be significantly contributing at higher frequencies. We show here that, for reasonable assumptions about the jet physical parameters, the broadband spectrum from radio through X-rays can be almost entirely fit by synchrotron emission. We explore a relatively simple model for a relativistic, adiabatically expanding jet combined with a truncated thermal disk conjoined by an ADAF, in the context of the recently discovered black hole binary XTE J1118+480. In particular, the X-ray power-law emission can be explained as optically thin synchrotron emission from a shock acceleration region in the innermost part of the jet, with a cutoff determined by cooling losses. For synchrotron cooling-limited particle acceleration, the spectral cutoff is a function only of dimensionless plasma parameters and thus should be around a "canonical"value for sources with similar plasma properties. It is therefore possible that non-thermal jet emission is important for XTE J1118+480 and possibly other X-ray binaries in the Low/Hard state.

Jets in XRB Low/Hard States: Models of XTE J1118+480 Suggest a Strong Signature from Radio through X-Ray

Observations reveal the presence of powerful jets in the Low/Hard states of several black hole candidate X-ray binaries, so it is important to consider what signatures these outflows will have in the broadband Low/Hard spectrum. Correlations between the radio and X-rays, as well as in at least one case the optical, suggest that emission from a jet, via either synchrotron or inverse Compton (IC) processes, may play a role. The recently discovered X-ray transient XTE Jl 118+480 (Remillard et al., 2000), a black hole candidate in the Low/Hard X-ray state, provides an excellent opportunity for multi-wavelength modeling, since it has been observed not only in the radio through X-rays (see Fender et al., 2000, and references therein), but is also at high enough Galactic latitude to allow the first ever EUV detections of an X-ray transient (Hynes et al., 2000, hereafter H00).

X‐Ray Spectral and Timing Evolution during the Decay of the 1998 Outburst from the Recurrent X‐Ray Transient 4U 1630−47

We report on the X-ray spectral and timing behavior of the recurrent X-ray transient 4U 1630-47 for 51 Rossi X-Ray Timing Explorer (RXTE) observations made during the decay of its 1998 outburst. The observations began when the source was still relatively bright, and during one of the early observations, a quasi-periodic oscillation (QPO) with a non-Lorentzian profile occurred near 6 Hz. As the source decayed, the X-ray flux dropped exponentially with an e-folding time of 14.4 days. The exponential decay was interrupted by an increase in the X-ray flux, and a secondary maximum occurred 89 days after the onset of the outburst. A transition marked by significant changes in the timing and spectral properties of the source occurred 104 days after the start of the outburst. The transition is similar to soft-to-hard state transitions observed in other black hole candidate X-ray binaries. Most of the changes associated with the transition occurred in less than 2 days. The timing changes include an increase in the continuum noise level from less than 4% rms to greater than 10% rms and the appearance of a QPO at 3.4 Hz with an rms amplitude of 7.3% in the 2-21 keV energy band. At the transition, the energy spectrum also changed with an abrupt drop in the soft component flux in the RXTE bandpass. A change in the power-law photon index from 2.3 to 1.8, also associated with the transition, occurred over a time period of 8 days. After the transition, the source flux continued to decrease, and the QPO frequency decayed gradually from 3.4 Hz to about 0.2 Hz.

Time variabilities of X-ray binary stars

The hard and the soft power law components and the disk blackbody component of the black hole candidate X-ray binaries have their inherent normalized power spectrum densities and phase lags. These short term variabilities are also similar to those of the X-ray energy spectral components of the non-pulsating neutron star X-ray binaries, although X-ray energy spectra of these two kinds of X-ray binaries are different in their high X-ray intensity state. There are two states in the black hole candidate X-ray binaries; the power law hard state and the power law soft state. Some of the black hole candidate-X-ray binaries show large hysteretic behavior between the states and the X-ray intensity. There seems to be no observation of large hysteretic behavior of this sort in the non-pulsating neutron star X-ray binaries. A model is assumed that in the X-ray emitting region of the accretion disk, the power law hard state corresponds to the advection dominated optically thin accretion disk and the power law soft state corresponds to the cooling dominated optically thick accretion disk, and this model is compared with observations and discussed. It is concluded that to describe long term variabilities of X-rays from the black hole candidate-X-ray binaries and the non-pulsating neutron star-X-ray binaries, other factors such as magnetic field seem to be necessary.

Time Variation of X-Rays from GX 5–1

Long- and short-term variations of X-rays from GX 5–1 (a neutron-star X-ray binary) were investigated based on the Eastern energy spectral model: a disk-blackbody component plus a blackbody component model. In the horizontal branch (HB), an increase in the X-ray intensity is mainly due to the disk component; this increase is mainly due to an increase in Rin (the inner radius of the accretion disk), although Tin (the temperature of the inner edge of the accretion disk) decreases slightly. A fraction of the blackbody component decreases with the X-ray intensity in HB. In the normal branch (NB), an increase in the X-ray intensity is due to both components. The hardening of the X-ray energy spectrum with the X-ray intensity in NB is mainly due to an increase in the blackbody component: the fraction of the blackbody component increases with the X-ray intensity. The X-ray intensities of the disk component and the blackbody component show different long-term variations from each other, which are similar to the case of the disk component and the power-law component of black-hole candidate X-ray binaries (BHCXBs); GX 339–4 and GS 1124–683. It is possible that the behavior of the Z source from HB to NB is due to hysteretic behavior, such as that shown by the BHCXBs. Short-term variations of X-rays from GX 5–1 were investigated using normalized power spectral density functions (NPSDs), and were compared with those of a BHCXB, GS 1124–683. NPSD of the disk component has a power-law shape, and has an energy dependence: the higher is the X-ray energy, the larger is the variation. NPSD of the blackbody component has a flat-top shape, and has no energy dependence. These are the same as that of the disk component and the power-law energy spectral component of GS 1124–683, in spite of their different energy spectra and different category of X-ray stars. The very-low-frequency noise (VLFN) of GX 5–1 has minimum values in the transition part between HB and NB, where the total X-ray intensity has its maximum value. VLFN seems to be related to a variation of the mass-accretion rate.

Polarization from magnetized accretion discs in active galactic nuclei

Polarization of radiation emerging from magnetized, electron-scattering-dominated accretion discs in active galactic nuclei (AGN) may be strongly affected by Faraday rotation. We present fully self-consistent Monte Carlo calculations of the resulting polarization in plane-parallel electron-scattering atmospheres for magnetic fields of constant strength and both vertical and random topology. We provide analytic fits to our results and apply them to simple accretion disc models. We find that Faraday rotation by an equipartition magnetic field may be of major importance in determining the polarization at optical and ultraviolet wavelengths in AGN. It may also be important for future X-ray polarization measurements of black hole candidate X-ray binaries.

Large hysteretic behavior of stellar black hole candidate X-ray binaries

Large hysteretic behavior of stellar black hole candidate X-ray binaries