23 research outputs found
An asymmetric arcsecond radio jet from Circinus X-1
In observations with the Australia Telescope Compact Array we have resolved
the radio counterpart of the unusual X-ray binary Cir X-1 into an asymmetric
extended structure on arcsecond scales. In order to quantify the asymmetry we
have redetermined as accurately as possible both the optical and radio
coordinates of the source. The extended emission can be understood as a
compact, absorbed core at the location of the X-ray binary, and extended
emission up to 2 arcsec to the southeast of the core. The arcsec-scale extended
emission aligns with the larger, more symmetric arcmin-scale collimated
structures in the surrounding synchrotron nebula. This suggests that the
transport of mass and/or energy from the X-ray binary to the synchroton nebula
is occurring via the arcsec-scale structures. The ratio of extended flux from
the southeast to that from the northwest of the core is at least 2:1.
Interpreted as relativistic aberration of an intrinsically symmetric jet from
the source, this implies a minimum outflow velocity of 0.1 c. Alternatively,
the emission may be intrinsically asymmetric, perhaps as a result of the high
space velocity of the system.Comment: Accepted for publication in ApJ Letters. Three figure
Quenching of the radio jet during the X-ray high state of GX 339-4
We have observed the black hole candidate X-ray binary GX 339-4 at radio
wavelengths before, during and after the 1998 high/soft X-ray state transition.
We find that the radio emission from the system is strongly correlated with the
hard X-ray emission and is reduced by a factor > 25 during the high/soft state
compared to the more usual low/hard state. At the points of state transition we
note brief periods of unusually optically-thin radio emission which may
correspond to discrete ejection events. We propose that in the low/hard state
black hole X-ray binaries produce a quasi-continuous outflow, in the high/soft
state this outflow is suppressed, and that state transitions often result in
one or more discrete ejection events. Future models for low/hard states, such
as ADAF/ADIOS solutions, need to take into account strong outflow of
relativistic electrons from the system. We propose that the inferred
Comptonising corona and the base of the jet-like outflow are the same thing,
based upon the strong correlation between radio and hard X-ray emission in GX
339-4 and other X-ray binaries, and the similarity in inferred location and
composition of these two components.Comment: Accepted for publication in ApJ Letter
ALMA observations of PKS 1549-79: A case of feeding and feedback in a young radio quasar
We present CO(1-0) and CO(3-2) ALMA observations of the molecular gas in PKS
1549-79, as well as mm and VLBI 2.3-GHz continuum observations of its radio
jet. PKS 1549-79 is one of the closest young, radio-loud quasars caught in an
on-going merger in which the AGN is in the first phases of its evolution. We
detect three structures tracing the accretion and the outflow of molecular gas:
kpc-scale tails of gas accreting onto PKS 1549-79, a circumnuclear disc (CND)
in the inner few hundred parsec, and a very broad (>2300 \kms) component
detected in CO(1-0) at the position of the AGN. Thus, in PKS 1549-79 we see the
co-existence of accretion and the ejection of gas. The line ratio
CO(1-0)/CO(3-2) suggests that the gas in the CND has both high densities and
high kinetic temperatures. We estimate a mass outflow rate of at least 650
msun/yr. This massive outflow is confined to r < 120 pc, which suggests that
the AGN drives the outflow. Considering the amount of molecular gas available
in CND and the observed outflow rate, we estimate a time scale of ~10^5 yr over
which the AGN would be able to destroy the CND, although gas from the merger
may come in from larger radii, rebuilding this disc at the same time. The AGN
appears to self-regulate gas accretion onto the super-massive black hole. From
a comparison with HST data, we find that the ionised gas outflow is more
extended. Nevertheless, the warm outflow is about two orders of magnitude less
massive than the molecular outflow. PKS 1549-79 does not seem to follow the
scaling relation between bolometric luminosity and the relative importance of
warm ionised and molecular outflows claimed to exist for other AGN. We argue
that, although PKS 1549-79 hosts a powerful quasar nucleus and an ultra-fast
outflow, the radio jet plays a significant role in producing the outflow.Comment: Accepted for A&A Main Journa
First geodetic observations using new VLBI stations ASKAP-29 and WARK12M
We report the results of a successful 7 hour 1.4 GHz VLBI experiment using
two new stations, ASKAP-29 located in Western Australia and WARK12M located on
the North Island of New Zealand. This was the first geodetic VLBI observing
session with the participation of these new stations. We have determined the
positions of ASKAP-29 and WARK12M. Random errors on position estimates are
150-200 mm for the vertical component and 40-50 mm for the horizontal
component. Systematic errors caused by the unmodeled ionosphere path delay may
reach 1.3 m for the vertical component.Comment: 11 pages, 6 flgures, 4 table
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
Baryons in the relativistic jets of the stellar-mass black-hole candidate 4U 1630-47
Accreting black holes are known to power relativistic jets, both in stellar-mass binary systems and at the centres of galaxies. The power carried away by the jets, and, hence, the feedback they provide to their surroundings, depends strongly on their composition. Jets containing a baryonic component should carry significantly more energy than electron–positron jets. Energetic considerations1, 2 and circular-polarization measurements3 have provided conflicting circumstantial evidence for the presence or absence of baryons in jets, and the only system in which they have been unequivocally detected is the peculiar X-ray binary SS 433 (refs 4, 5). Here we report the detection of Doppler-shifted X-ray emission lines from a more typical black-hole candidate X-ray binary, 4U 1630-47, coincident with the reappearance of radio emission from the jets of the source. We argue that these lines arise from baryonic matter in a jet travelling at approximately two-thirds the speed of light, thereby establishing the presence of baryons in the jet. Such baryonic jets are more likely to be powered by the accretion disk6 than by the spin of the black hole7, and if the baryons can be accelerated to relativistic speeds, the jets should be strong sources of γ-rays and neutrino emission