87 research outputs found
The large-scale jet-powered radio nebula of Circinus X-1
We present multi-epoch observations of the radio nebula around the neutron
star X-ray binary Circinus X-1 made at 1.4 and 2.5 GHz with the Australia
Telescope Compact Array between October 2000 and September 2004. The nebula can
be seen as a result of the interaction between the jet from the system and the
interstellar medium and it is likely that we are actually looking toward the
central X-ray binary system through the jet-powered radio lobe. The study of
the nebula thus offers a unique opportunity to estimate for the first time
using calorimetry the energetics of a jet from an object clearly identified as
a neutron star. An extensive discussion on the energetics of the complex is
presented: a first approach is based on the minimum energy estimation, while a
second one employs a self-similar model of the interaction between the jets and
the surrounding medium. The results suggest an age for the nebula of \leq 10^5
years and a corresponding time-averaged jet power \geq 10^{35} erg s^{-1}.
During periodic flaring episodes, the instantaneous jet power may reach values
of similar magnitude to the X-ray luminosity.Comment: Accepted to MNRA
Revisiting the relativistic ejection event in XTE J1550-564 during the 1998 outburst
We revisit the discovery outburst of the X-ray transient XTE J1550â564 during which relativistic jets were observed in 1998 September, and review the radio images obtained with the Australian Long Baseline Array, and light curves obtained with the Molonglo Observatory Synthesis Telescope and the Australia Telescope Compact Array. Based on Hi spectra, we constrain the source distance to between 3.3 and 4.9 kpc. The radio images, taken some 2 d apart, show the evolution of an ejection event. The apparent separation velocity of the two outermost ejecta is at least 1.3c and may be as large as 1.9c; when relativistic effects are taken into account, the inferred true velocity is â„ 0.8c. The flux densities appear to peak simultaneously during the outburst, with a rather flat (although still optically thin) spectral index of â0.2
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
Chandra Detections of Two Quiescent Black Hole X-Ray Transients
Using the Chandra X-ray Observatory, we have detected the black hole
transients V4641 Sgr and XTE J1859+226 in their low luminosity, quiescent
states. The 0.3-8 keV luminosities are (4.0^(+3.3)_(-2.4))E31 (d/7 kpc)^2 erg/s
and (4.2^(+4.8)_(-2.2))E31 (d/11 kpc)^2 erg/s for V4641 Sgr and XTE J1859+226,
respectively. With the addition of these 2 systems, 14 out of the 15 transients
with confirmed black holes (via compact object mass measurements) now have
measured quiescent luminosities or sensitive upper limits. The only exception
is GRS 1915+105, which has not been in quiescence since its discovery in 1992.
The luminosities for V4641 Sgr and XTE J1859+226 are consistent with the median
luminosity of 2E31 erg/s for the systems with previous detections. Our analysis
suggests that the quiescent X-ray spectrum of V4641 Sgr is harder than for the
other systems in this group, but, due to the low statistical quality of the
spectrum, it is not clear if V4641 Sgr is intrinsically hard or if the column
density is higher than the interstellar value. Focusing on V4641 Sgr, we
compare our results to theoretical models for X-ray emission from black holes
in quiescence. Also, we obtain precise X-ray positions for V4641 Sgr and XTE
J1859+226 via cross-correlation of the X-ray sources detected near our targets
with IR sources in the 2 Micron All-Sky Survey catalog.Comment: 4 pages, Accepted by ApJ Letter
The Radio Variability of the Gravitational Lens PMN J1838-3427
We present the results of a radio variability study of the gravitational lens
PMN J1838-3427. Our motivation was to determine the Hubble constant by
measuring the time delay between variations of the two quasar images. We
monitored the system for 4 months (approximately 5 times longer than the
expected delay) using the Australia Telescope Compact Array at 9 GHz. Although
both images were variable on a time scale of a few days, no correlated
intrinsic variability could be identified, and therefore no time delay could be
measured. Notably, the fractional variation of the fainter image (8%) was
greater than that of the brighter image (4%), whereas lensed images of a point
source would have the same fractional variation. This effect can be explained,
at least in part, as the refractive scintillation of both images due to the
turbulent interstellar medium of the Galaxy.Comment: To appear in AJ (8 pages, including 4 figures
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