arXiv subjects

R. P. Fender

Publications and source records attributed to R. P. Fender.

At least 235 records · Page 13Linked to original sources

arXiv2000

Excess sub-millimetre emission from GRS 1915+105

We present the first detections of the black hole X-ray binary GRS 1915+105 at sub-millimetre wavelengths. We clearly detect the source at 350 GHz on two epochs, with significant variability over the 24 hr between epochs. Quasi-simultaneous radio monitoring indicates an approximately flat spectrum from 2 - 350 GHz, although there is marginal evidence for a minimum in the spectrum between 15 - 350 GHz. The flat spectrum and correlated variability imply that the sub-mm emission arises from the same synchrotron source as the radio emission. This source is likely to be a quasi-steady partially self-absorbed jet, in which case these sub-mm observations probe significantly closer to the base of the jet than do radio observations and may be used in future as a valuable diagnostic of the disc:jet connection in this source.

astro-ph↗

arXiv2000

Coupling of the X-ray and radio emission in the black hole candidate a nd compact jet source GX 339-4

We report the results of a long-term campaign of radio, soft- and hard- X-ray observations of the galactic black hole candidate GX 339-4. In the Low-Hard X-ray state the system displays a strong 3-way linear correlation between soft- and hard-X-rays and radio emission, implying a coupling between the Comptonising corona and a radio-emitting compact jet. In this state the radio emission is linearly polarised at a level of around 2 %, with an almost constant polarisation angle, indicative of a favored axis in this system probably related to the compact jet and/or black hole spin axis. In the Off X-ray state the radio emission declines with the X-ray emission to below detectable levels, suggesting that it is simply a lower-luminosity version of the Low-Hard state. In the High-Soft state both the hard-X-ray and radio emission are suppressed. We also note that the transitions from the Low-Hard state to the High-Soft state (and the reverse) are possibly associated with discrete ejection(s) of expanding relativistic plasma.

astro-ph↗

arXiv2000

The radio luminosity of persistent X-ray binaries

We summarise all the reported detections of, and upper limits to, the radio emission from persistent (i.e. non-transient) X-ray binaries. A striking result is a common mean observed radio luminosity from the black hole candidates (BHCs) in the Low/Hard X-ray state and the neutron-star Z sources on the horizontal X-ray branch. This implies a common mean intrinsic radio luminosity to within a factor of twenty five (or less, if there is significant Doppler boosting of the radio emission). Unless coincidental, these results imply a physical mechanism for jet formation which requires neither a black hole event horizon or a neutron star surface. As a whole the populations of Atoll and X-ray pulsar systems are less luminous by factors of >5 and >10 at radio wavelengths than the BHCs and Z sources (while some Atoll sources have been detected, no high-field X-ray pulsar has ever been reliably detected as a radio source). We suggest that all of the persistent BHCs and the Z sources generate, at least sporadically, an outflow with physical dimensions > 1e12cm, i.e. significantly larger than the binary separations of most of the systems. We compare the physical conditions of accretion in each of the types of persistent X-ray binary and conclude that a relatively low (<1e10 G) magnetic field associated with the accreting object, and a high (>0.1 Eddington) accretion rate and/or dramatic physical change in the accretion flow, are required for formation of a radio-emitting outflow or jet.

astro-ph↗

arXiv1999

Black hole states and radio jet formation

An empirical relation between `canonical' X-ray states in black hole X-ray binaries and radio emission is presented. In the Low/Hard state a quasi-continuous radio-emitting jet is produced. In the the High/Soft state the jet is not observed. In the Very High state and at major state transitions, which may correspond physically to rapid and/or significant changes in the inner accretion disc radius, discrete ejection events, which manifest themselves as radio flares, are observed. These relations appear to hold for both transient and persistent systems. Furthermore it is argued that the extremely strong coupling between hard X-rays and radio emission from black hole X-ray binaries implies that the Comptonising corona is simply the base of the jet.

astro-ph↗

arXiv1999

A comparison of radio emission from neutron star and black hole X-ray binaries

I compare the properties of radio emission from neutron star and black hole X-ray binaries. In both transient and persistent systems the ratio of X-ray : radio fluxes is comparable for (low field) neutron stars and black holes. It appears that, broadly speaking, the disc : jet coupling is independent of the nature of the accretor, (except for X-ray pulsars where the strong magnetic field prevents formation of an inner accretion disc and jet).

astro-ph↗

arXiv1999

The very flat radio - millimetre spectrum of Cygnus X-1

We present almost-simultaneous detections of Cygnus X-1 in the radio and mm regimes, obtained during the low/hard X-ray state. The source displays a flat spectrum between 2 and 220 GHz, with a spectral index flatter than 0.15 (3sigma). There is no evidence for either a low- or high-frequency cut-off, but in the mid-infrared (~30 microns) thermal emission from the OB-type companion star becomes dominant. The integrated luminosity of this flat-spectrum emission in quiescence is > 2 x 10^{31} erg/s (2 x 10^{24} W). Assuming the emission originates in a jet for which non-radiative (e.g. adiabatic expansion) losses dominate, this is a very conservative lower limit on the power required to maintain the jet. A comparison with Cyg X-3 and GRS 1915+105, the other X-ray binaries for which a flat spectrum at shorter than cm wavelengths has been observed, shows that the jet in Cyg X-1 is significantly less luminous and less variable, and is probably our best example to date of a continuous, steady, outflow from an X-ray binary. The emissive mechanism reponsible for such a flat spectral component remains uncertain. Specifically, we note that the radio-mm spectra observed from these X-ray binaries are much flatter than those of the `flat-spectrum' AGN, and that existing models of synchrotron emission from partially self-absorbed radio cores, which predict a high-frequency cut-off in the mm regime, are not directly applicable.

astro-ph↗

arXiv1999

Circinus X-1: survivor of a highly asymmetric supernova

We have analyzed the kinematical parameters of Cir X-1 to constrain the nature of its companion star, the eccentricity of the binary and the pre-supernova parameter space. We argue that the companion is most likely to be a low-mass (< 2.0 M_sun) unevolved star and that the eccentricity of the orbit is 0.94 +/- 0.04. We have evaluated the dynamical effects of the supernova explosion and we find it must have been asymmetric. On average, we find that a kick of 740 km/s is needed to account for the recently measured radial velocity of +430 km/s (Johnston, Fender & Wu) for this extreme system. The corresponding minimum kick velocity is 500 km/s. This is the largest kick needed to explain the motion of any observed binary system. If Cir X-1 is associated with the supernova remnant G321.9-0.3 then we find a limiting minimum age of this remnant of 60000 yr. Furthermore, we predict that the companion star has lost 10% of its mass as a result of stripping and ablation from the impact of the supernova shell shortly after the explosion.

astro-ph↗

arXiv1999

On the nature of XTE J0421+560/CI Cam

We present the results of the analysis of RXTE, BATSE and optical/infrared data of the 1998 outburst of the X-ray transient system XTE J0421+560 (CI Cam). The X-ray outburst shows a very fast decay (initial e-folding time ~0.5 days, slowing down to ~2.3 days). The X-ray spectrum in the 2-25 keV band is complex, softening considerably during decay and with strongly variable intrinsic absorption. A strong iron emission line is observed. No fast time variability is detected (<0.5 % rms in the 1-4096 Hz band at the outburst peak). The analysis of the optical/IR data suggests that the secondary is a B[e] star surrounded by cool dust and places the system at a distance of >~ 2 kpc. At this distance the peak 2-25 keV luminosity is ~4 x 10^37 erg/s. We compare the properties of this peculiar system with those of the Be/NS LMC transient A 0538-66 and suggest that CI Cam is of similar nature. The presence of strong radio emission during outburst indicates that the compact object is likely to be a black hole or a weakly magnetized neutron star.

astro-ph↗

arXiv1999

Orbital, precessional and flaring variability of Cygnus X-1

We present the results of a 2.5-year multiwavelength monitoring programme of Cygnus X-1, making use of hard and soft X-ray data, optical spectroscopy, UBVJHK photometry and radio data. In particular we confirm that the 5.6-day orbital period is apparent in all wavebands and note the existence of a wavelength-dependence to the modulation, in the sense that higher energies reach minimum first. We also find a strong modulation at a period of 142 +/- 7 days, which we suggest is due to precession and/or radiative warping of the accretion disc. Strong modulation of the hard and soft X-ray flux at this long period may not be compatible with simple models of an optically thin accretion flow and corona in the low state. We present the basic components required for more detailed future modelling of the system - including a partially optically thick jet, quasi-continuous in the low state, the base of which acts as the Comptonising corona. In addition, we find that there are a number of flares which appear to be correlated in at least two wavebands and generally in more. We choose two of these flares to study in further detail and find that the hard and soft X-rays are well-correlated in the first and that the soft X-rays and radio are correlated in the second. In general, the optical and infrared show similar behaviour to each other but are not correlated with the X-rays or radio.

astro-ph↗

arXiv1999

Infrared spectroscopic variability of Cygnus X-3 in outburst and quiescence

We present four epochs of high-resolution infrared spectroscopy of the peculiar X-ray binary Cygnus X-3. The observations cover quiescent, small flaring and outburst states of the system as defined by radio and X-ray monitoring. The underlying infrared spectrum of the source, as observed during radio and X-ray quiescence and small flaring states, is one of broad, weak HeII and NV emission. Spectral variability in this state is dominated by modulation at the 4.8 hr orbital period of the system. H-band spectra confirm the significant hydrogen depletion of the mass donor. The closest spectral match to the quiescent infrared spectrum of Cyg X-3 is an early-type WN Wolf-Rayet star. In outburst, the infrared spectrum is dramatically different, with the appearance of very strong twin-peaked HeI emission displaying both day-to-day variability and V(iolet)/R(ed) variations with orbital phase. The most likely explanation appears to be an enhanced stellar wind from the companion. Thus X-ray and radio outbursts in this system are likely to originate in mass-transfer, and not disc, instabilities, and the lengthening of the orbital period will not be smooth but will be accelerated during these outbursts. Furthermore, the appearance of these lines is suggestive of an asymmetric emitting region. We propose that the wind in Cyg X-3 is significantly flattened in the plane of the binary orbit. This may explain the observed twin-peaked HeI features as well as reconciling a massive Wolf-Rayet secondary with the relatively small optical depth to X-rays, if the disc wind is inclined at some angle to the line of sight.

astro-ph↗

arXiv1999

Multiple ejections during the 1975 outburst of A0620-00

The well-known black-hole X-ray transient A0620-00 was a bright radio source during the first part of its outburst in 1975. We have revisited the available data and find for the first time evidence that the source exhibited multiple jet ejections. Rapid radio spectral changes indicate the addition of at least three new components which are initially optically thick. From single baseline interferometry taken about three weeks after the start of the X-ray outburst we find that the source is extended on arcsec scales and infer a relativistic expansion velocity. Some of the other (soft) X-ray transients, such as GS 1124-68 and GS 2000+25, show very similar X-ray outburst light curve shapes to that of A0620-00, while their radio outburst light curve shapes are different. We suggest that this is due to the radio emission being strongly beamed in outburst, whereas the X-ray emission remains isotropic. Since this effect is stronger at higher jet velocities, this strengthens our conclusion that the jets in A0620-00 and other soft X-ray transients move with relativistic speeds.

astro-ph↗

arXiv1998

Observations of GX 339-4 in 1996

GX 339-4 is an unusual black hole candidate in that it is a persistent source, being detected by X-ray telescopes most of the time, but it also has nova-like flaring states. In 1996 we performed radio, optical, X-ray, and gamma-ray observations of GX 339-4 when it was in a hard state (= soft X-ray low state). Here we present a brief summary of some of the results.

astro-ph↗

arXiv1998

MERLIN observations of relativistic ejections from GRS 1915+105

We present high resolution MERLIN radio images of multiple relativistic ejections from GRS 1915+105 in 1997 October / November. The observations were made at a time of complex radio behaviour, corresponding to multiple optically-thin outbursts and several days of rapid radio flux oscillations. The radio imaging resolved four major ejection events from the system. As previously reported from earlier VLA observations of the source, we observe apparent superluminal motions resulting from intrinsically relativistic motions of the ejecta. However, our measured proper motions are significantly greater than those observed on larger angular scales with the VLA. Under the assumption of an intrinsically symmetric ejection, we can place an upper limit on the distance to GRS 1915+105 of 11.2 +/- 0.8 kpc. Solutions for the velocities unambiguously require a higher intrinsic speed by about 0.1c than that derived from the earlier VLA observations, whilst the angle to the line-of-sight is not found to be significantly different. At a distance of 11 kpc, we obtain solutions of v = 0.98 (-0.05,+0.02)c and theta = 66 +/- 2 degrees. The jet also appears to be curved on a scale which corresponds to a period of around 7 days. We observe significant evolution of the linear polarisation of the approaching component, with large rotations in position angle and a general decrease in fractional polarisation. The power input into the formation of the jet is very large, >10^38 erg/s at 11 kpc for a pair plasma. If the plasma contains a cold proton for each electron, then the mass outflow rate, >10^18 g/sec is comparable to inflow rates previously derived from X-ray spectral fits.

astro-ph↗

arXiv1998

Multiwavelength Observations of GX 339-4 in 1996. I. Daily Light Curves and X-ray and Gamma-Ray Spectroscopy

As part of our multiwavelength campaign of GX 339-4 observations in 1996 we present our radio, X-ray, and gamma-ray observations made in July, when the source was in a hard state (= soft X-ray low state). The radio observations were made at the time when there was a possible radio jet. We show that the radio spectrum was flat and significantly variable, and that the radio spectral shape and amplitude at this time were not anomalous for this source. Daily light curves from our pointed observation July 9-23 using OSSE, from BATSE, and from the ASM on RXTE also show that there was no significant change in the X- and gamma-ray flux or hardness during the time the possible radio jet-like feature was seen. The higher energy portion of our pointed RXTE observation made July 26 can be equally well fit using simple power law times exponential (PLE) and Sunyaev-Titarchuk (ST) functions. An additional soft component is required, as well as a broad emission feature centered on 6.4 keV. This may be an iron line that is broadened by orbital Doppler motions and/or scattering off a hot medium. Its equivalent width is 600 eV. Our simplistic continuum fitting does not require an extra reflection component. Both a PLE and a ST model also fit our OSSE spectrum on its own. Although the observations are not quite simultaneous, combining the RXTE and CGRO spectra we find that the PLE model easily fits the joint spectrum. However, the ST model drops off too rapidly with increasing energies to give an acceptable joint fit.

astro-ph↗

arXiv1998

X-Ray Spectral Behavior of the Relativistic Jet Source Cygnus X-3

Cyg X-3 is an unusual X-ray binary which shows remarkable correlative behavior between the hard X-ray, soft X-ray, and the radio. We present an analysis of these long term light curves in the context of spectral changes of the system. This analysis will also incorporate a set of pointed RXTE observations made during a period when Cyg X-3 made a transition from a quiescent radio state to a flaring state (including a major flare) and then returned to a quiescent radio state.

astro-ph↗

arXiv1998

RXTE Observations of Cygnus X-3

In the period between May 1997 and August 1997 a series of pointed RXTE observations were made of Cyg X-3. During this period Cyg X-3 made a transition from a quiescent radio state to a flare state (including a major flare) and then returned to a quiescent radio state. Analyses of the observations are made in the context of concurrent observations in the hard X-ray (CGRO/BATSE), soft X-ray (RXTE/ASM) and the radio (Green Bank Interferometer, Ryle Telescope, and RATAN-600). Preliminary analyses of the observations are presented.

astro-ph↗

arXiv1998

Orbital modulation and longer-term variability in the radio emission from Cygnus X-1

20 months of observations of the radio emission at 15 GHz from Cygnus X-1, starting in 1996 October, show variations at the binary period of 5.6 days, but with a phase offset from those at X-ray wavelengths. There are also longer-term variations on a time-scale of 150 days which are only loosely related to the soft X-ray flux. The source was in the hard/low X-ray state throughout this period. The mean 15-GHz flux density is 13 mJy, the radio spectrum is flat, and the semi-amplitude of the orbital modulation about 2 mJy. We discuss the possible origins of the modulation and the relationship to the soft X-ray emission.

astro-ph↗

arXiv1998

Magnetic field estimation in Cyg X-3's jet

Multi-wavelength photometric observations of Cygnus X-3 were carried out at 18 cm through to 450 um, complemented by X-ray (2-10 keV) observations. The system was mildly active with cm fluxes at 150 -- 250 mJy. We find the spectrum to be flat with a spectral index of zero. Using a modified Wolf-Rayet wind model, and assuming emission is generated in synchrotron emitting jets from the source, we find an upper-limit to the magentic field of 20 G at a distance of $5 \times 10^{12}$ cm is required.

astro-ph↗