810 research outputs found
The variable radio counterpart and possible large-scale jet of the new Z-source XTE J1701-462
We report radio observations, made with the Australia Telescope Compact
Array, of the X-ray transient XTE J1701-462. This system has been classified as
a new `Z' source, displaying characteristic patterns of behaviour probably
associated with accretion onto a low magnetic field neutron star at close to
the Eddington limit. The radio counterpart is highly variable, and was detected
in six of sixteen observations over the period 2006 January -- April. The
coupling of radio emission to X-ray state, despite limited sampling, appears to
be similar to that of other `Z' sources, in that there is no radio emission on
the flaring branch. The mean radio and X-ray luminosities are consistent with
the other Z sources for a distance of 5--15 kpc. The radio spectrum is
unusually flat, or even inverted, in contrast to the related sources, Sco X-1
and Cir X-1, which usually display an optically thin radio spectrum. Deep
wide-field observations indicate an extended structure three arcminutes to the
south which is aligned with the X-ray binary. This seems to represent a
significant overdensity of radio sources for the field and so, although a
background source remains a strong possibility, we consider it plausible that
this is a large-scale jet associated with XTE J1701-462.Comment: Accepted for publication as a Letter in MNRA
A decelerating jet observed by the EVN and VLBA in the X-ray transient XTE J1752-223
The recently discovered Galactic X-ray transient XTE J1752-223 entered its
first known outburst in 2010, emitting from the X-ray to the radio regimes. Its
general X-ray properties were consistent with those of a black hole candidate
in various spectral states, when ejection of jet components is expected. To
verify this, we carried out very long baseline interferometry (VLBI)
observations. The measurements were carried out with the European VLBI Network
(EVN) and the Very Long Baseline Array (VLBA) at four epochs in 2010 February.
The images at the first three epochs show a moving jet component that is
significantly decelerated by the last epoch, when a new jet component appears
that is likely to be associated with the receding jet side. The overall picture
is consistent with an initially mildly relativistic jet, interacting with the
interstellar medium or with swept-up material along the jet. The brightening of
the receding ejecta at the final epoch can be well explained by initial Doppler
deboosting of the emission in the decelerating jet.Comment: Accepted for publication in MNRAS Letters. 5 pages, 2 figure
A transient large-scale relativistic radio jet from GX 339-4
We report on the formation and evolution of a large-scale,
synchrotron-emitting jet from the black hole candidate and X-ray binary system
GX 339-4. In 2002 May, the source moved from a low/hard to a very high X-ray
state, contemporaneously exhibiting a very bright optically thin radio flare.
Further observations with the Australia Telescope Compact Array have tracked
the formation of a collimated structure extending to about 12 arcsec, with
apparent velocity greater than 0.9c. The luminosity of the outflow seems to be
rapidly decreasing; these observations confirm that transient large-scale jets
are likely to be common events triggered by X-ray state transitions in black
hole X-ray binaries.Comment: accepted for publication as a letter in MNRA
High-energy gamma-ray observations of the accreting black hole V404 Cygni during its June 2015 outburst
We report on Fermi/Large Area Telescope observations of the accreting black
hole low-mass X-ray binary V404 Cygni during its outburst in June-July 2015.
Detailed analyses reveal a possible excess of -ray emission on 26 June
2015, with a very soft spectrum above MeV, at a position consistent with
the direction of V404 Cyg (within the confidence region and a chance
probability of ). This emission cannot be associated with any
previously-known Fermi source. Its temporal coincidence with the brightest
radio and hard X-ray flare in the lightcurve of V404 Cyg, at the end of the
main active phase of its outburst, strengthens the association with V404 Cyg.
If the -ray emission is associated with V404 Cyg, the simultaneous
detection of keV annihilation emission by INTEGRAL requires that the
high-energy rays originate away from the corona, possibly in a
Blandford-Znajek jet. The data give support to models involving a
magnetically-arrested disk where a bright -ray jet can re-form after
the occurrence of a major transient ejection seen in the radio.Comment: 5 pages, 3 figures, accepted for publication in MNRA
Stellar Mass Black Holes and Ultraluminous X-Ray Sources
We review the likely population, observational properties, and broad
implications of stellar-mass black holes and ultraluminous x-ray sources. We
focus on the clear empirical rules connecting accretion and outflow that have
been established for stellar-mass black holes in binary systems in the past
decade and a half. These patterns of behavior are probably the keys that will
allow us to understand black hole feedback on the largest scales over
cosmological time scales.Comment: Review for Science Special Issue on black holes, 2012 August 3. 8
pages, 2 figure
Studying the X-ray hysteresis in GX 339-4: the disc and iron line over one decade
We report on a comprehensive and consistent investigation into the X-ray
emission from GX 339-4. All public observations in the 11 year RXTE archive
were analysed. Three different types of model - single powerlaw, broken
powerlaw and a disc + powerlaw - were fitted to investigate the evolution of
the disc, along with a fixed gaussian component at 6.4 keV to investigate any
iron line in the spectrum. We show that the relative variation in flux and
X-ray colour between the two best sampled outbursts are very similar. The decay
of the disc temperature during the outburst is clearly seen in the soft state.
The expected decay is S_Disc \propto T^4; we measure T^4.75\pm0.23. This
implies that the inner disc radius is approximately constant in the soft state.
We also show a significant anti-correlation between the iron line significant
width and the X-ray flux in the soft state while in the hard state the EW is
independent of the flux. This results in hysteresis in the relation between
X-ray flux and both line flux and EW. To compare the X-ray binary outburst to
the behaviour seen in AGN, we construct a Disc Fraction Luminosity Diagram for
GX 339-4, the first for an X-ray binary. The shape qualitatively matches that
produced for AGN. Linking this with the radio emission from GX 339-4 the change
in radio spectrum between the disc and power-law dominated states is clearly
visible.Comment: Accepted for publication in MNRAS, 20 pages, 17 figures. For high-res
version see http://www.astro.soton.ac.uk/~r.j.dunn/publications.htm
Limits on the quiescent radio emission from the black hole binaries GRO J1655-40 and XTE J1550-564
We present the results of radio observations of the black hole binaries GRO
J1655-40 and XTE J1550-564 in quiescence, with the upgraded Australia Telescope
Compact Array. Neither system was detected. Radio flux density upper limits (3
sigma) of 26 micro Jy (at 5.5 GHz), 47 micro Jy (at 9 GHz) for GRO J1655-40,
and 1.4 mJy (at 1.75 GHz), 27 micro Jy (at 5.5 GHz), 47 micro Jy (at 9 GHz) for
XTE J1550-564 were measured. In conjunction with quasi-simultaneous Chandra
X-ray observations (in the case of GRO J1655-40) and Faulkes Telescope optical
observations (XTE J1550-564) we find that these systems provide the first
evidence of relatively `radio quiet' black hole binaries at low luminosities;
indicating that the scatter observed in the hard state X-ray:radio correlation
at higher luminosities may also extend towards quiescent levels.Comment: Accepted for publication in MNRA
The Distance to the Soft Gamma Repeater SGR 1627-41
We report millimeter observations of the line of sight to the recently
discovered Soft Gamma Repeater, SGR 1627-41, which has been tentatively
associated with the supernova remnant SNR G337.0-0.1 Among the eight molecular
clouds along the line of sight to SGR 1627-41, we show that SNR G337.0-0.1 is
probably interacting with one of the most massive giant molecular clouds (GMC)
in the Galaxy, at a distance of 11 kpc from the sun. Based on the high
extinction to the persistent X-ray counterpart of SGR 1627-41, we present
evidence for an association of this new SGR with the SNR G337.0-0.1; they both
appear to be located on the near side of the GMC. This is the second SGR
located near an extraordinarily massive GMC. We suggest that SGR 1627-41 is a
neutron star with a high transverse velocity (~ 1,000 \kms) escaping the young
(~ 5,000 years) supernova remnant G337.0-0.1Comment: 17 pages, including 2 figures. Accepted for publication in the
Astrophysical Journal Letter
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