27 research outputs found
Comments on the superluminal motion in Cygnus X-3
Following the recent discovery that Cyg X-3 exhibits superluminal motion, the
implications of superluminal expansion and contraction are investigated. We
propose that the effect is due to either a propagating photon pattern or to
outwardly moving shells illuminated by an intense beam of radiation.Comment: accepted for publication in MNRAS; 5 pages, 3 figure
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.Comment: 5 pages, 3 figures, accepted for publication in MNRA
Spectral evidence for a powerful compact jet from XTE J1118+480
We present observations of the X-ray transient XTE J1118+480 during its
Low/Hard X-ray state outburst in 2000, at radio and sub-millimetre wavelengths
with the VLA, Ryle Telescope, MERLIN and JCMT. The high-resolution MERLIN
observations reveal all the radio emission (at 5 GHz) to come from a compact
core with physical dimensions smaller than 65*d(kpc) AU. The combined radio
data reveal a persistent and inverted radio spectrum, with spectral index
\~+0.5. The source is also detected at 350 GHz, on an extrapolation of the
radio spectrum. Flat or inverted radio spectra are now known to be typical of
the Low/Hard X-ray state, and are believed to arise in synchrotron emission
from a partially self-absorbed jet. Comparison of the radio and sub-millimetre
data with reported near-infrared observations suggest that the synchrotron
emission from the jet extends to the near-infrared, or possibly even optical
regimes. In this case the ratio of jet power to total X-ray luminosity is
likely to be P_J/L_X >> 0.01, depending on the radiative efficiency and
relativistic Doppler factor of the jet. Based on these arguments we conclude
that during the period of our observations XTE J1118+480 was producing a
powerful outflow which extracted a large fraction of the total accretion power.Comment: Accepted for publication as a Letter in MNRA
Radio flares and plasmon size in Cygnus X-3
We have observed a number of minor radio flares in Cyg X-3 using the MERLIN
array. Photometric observations show the system to be highly active with
multiple flares on hourly timescales over the one month observing programme.
Analysis of the source's power spectrum show no persistent periodicities in
these data, and no evidence of the 4.8 hr orbital period. An upper limit of 15
mJy can be placed on the amplitude of any sinusoidal varaition of source flux
at the orbital period. The brightness temperature of a flare is typically T >
10^{9}- 10^{10} K, with a number of small flares of 5 minute duration having
brightness temperatures of T > few x 10^{11} K. For such a change in flux to
occur within a typical 10 minute timescale, the radiation must originate from
plasmons with a size < 1.22 AU. This emission is unlikely to originate close to
the centre of the system as both the jets and compact object are buried deep
within an optically thick stellar wind. Assuming a spherically symmetric wind,
plasmons would become visible at distances ~ 13 AU from the core.Comment: Accepted for publication in MNRA
A relativistic jet from Cygnus X-1 in the low/hard X-ray state
We present the detection of a radio-emitting jet from the black-hole
candidate and X-ray binary source Cygnus X-1. Evidence of a bright core with a
slightly extended structure was found on milliarcsecond resolution observations
with the VLBA at 15.4 GHz. Later observations with the VLBA (and including the
phased up VLA) at 8.4 GHz show an extended jet-like feature extending to
approx. 15 mas from a core region, with an opening angle of < 2 degrees. In
addition, lower resolution MERLIN observations at 5 GHz show that the source
has < 10 per cent linear polarization. The source was in the low/hard X-ray
state during the observations, and the results confirm the existence of
persistent radio emission from an unresolved core and a variable relativistic
(> 0.6c) jet during this state.Comment: Accepted for publication in MNRA
Cygnus X-3 with ISO: investigating the wind
We observed the energetic binary Cygnus X-3 in both quiescent and flaring
states between 4 and 16 microns using the ISO satellite. We find that the
quiescent source shows the thermal free-free spectrum typical of a hot, fast
stellar wind, such as from a massive helium star. The quiescent mass-loss rate
due to a spherically symmetric, non-accelerating wind is found to be in the
range 0.4-2.9 x 10E-4 solar masses per year, consistent with other infrared and
radio observations, but considerably larger than the 10E-5 solar masses per
year deduced from both the orbital change and the X-ray column density. There
is rapid, large amplitude flaring at 4.5 and 11.5 microns at the same time as
enhanced radio and X-ray activity, with the infrared spectrum apparently
becoming flatter in the flaring state. We believe non-thermal processes are
operating, perhaps along with enhanced thermal emission.Comment: Accepted for publication in MNRAS, 11 pages, 6 figure
IGR J16318-4848: an X-ray source in a dense envelope?
The hard X-ray source IGR J16318-4848 was recently discovered by the INTEGRAL
observatory (Courvoisier et al.) and subsequently uncovered in archival data of
ASCA observations in 1994 (Murakami et al.). We present results of a detailed
analysis of the ASCA data. The spectrum of the source in the 0.5--10 keV band
is extraordinarily hard and is virtually unobservable below 4 keV because of
strong photoabsorption NHL L>4e23 cm^-2. The 4--10 keV emission is dominated by
a Kalpha line of neutral or weakly ionized iron with an equivalent width of
\~2.5 keV. There is also an indication for a second line at ~7 keV. Our
analysis of archival observations of the IGR J16318-4848 infrared counterpart,
discovered by Foschini et al., shows that the point source is detected at
different wavelengths in the 1--15 micron range. The available data suggest
that IGR J16318-4848 is an X-ray binary system enshrouded by a dense envelope.
It is possible that the source is a wind-fed high-mass X-ray binary similar to
GX 301-2. We argue that IGR J16318-4848 might be the first representative of a
previously unknown population of highly absorbed galactic X-ray sources, which
remained undetected with X-ray missions before INTEGRAL.Comment: Accepted for publication in Astronomy Letter