D. Campbell-Wilson

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 of ≥25 during the high/soft state compared with the more usual low/hard state. At the points of state transition, we note brief periods of unusually optically thin radio emission that may correspond to discrete ejection events. We propose that in the low/hard state, black hole X-ray binaries produce a quasi-continuous outflow, that 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 advection-dominated solutions, need to take into account the strong outflow of relativistic electrons from the system. We propose that the inferred Comptonizing corona and the base of the jetlike outflow are the same thing, based on the strong correlation between radio and hard X-ray emission in GX 339-4 and other X-ray binaries and on the similarity in inferred location and composition of these two components.

X-Ray States and Radio Emission in the Black Hole Candidate XTE J1550–564

We report on radio and X-ray observations of the black hole candidate (BHC) XTE J1550-564 performed during its 2000 X-ray outburst. Observations were conducted with the Australia Telescope Compact Array and allowed us to sample the radio behavior of XTE J1550-564 in the X-ray low hard and intermediate/very high states. We observed optically thin radio emission from XTE J1550-564 5 days after a transition to an intermediate/very high state, but we observed no radio emission 6 days later, while XTE J1550-564 was still in the intermediate/very high state. In the low hard state, XTE J1550-564 is detected with an inverted radio spectrum. The radio emission in the low hard state most likely originates from a compact jet; optical observations suggest that the synchrotron emission from this jet may extend up to the optical range. The total power of the compact jet might therefore be a significant fraction of the total luminosity of the system. We suggest that the optically thin radio emission detected 5 days after the transition to the intermediate/very high state is due to a discrete ejection of relativistic plasma during the state transition. Subsequent to the decay of the optically thin radio emission associated with the state transition, it seems that in the intermediate/very high state the radio emission is quenched by a factor greater than 50, implying a suppression of the outflow. We discuss the properties of radio emission in the X-ray states of BHCs.

Canadian Hydrogen Intensity Mapping Experiment (CHIME) pathfinder

A pathfinder version of CHIME (the Canadian Hydrogen Intensity Mapping Experiment) is currently being commissioned at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, BC. The instrument is a hybrid cylindrical interferometer designed to measure the large scale neutral hydrogen power spectrum across the redshift range 0.8 to 2.5. The power spectrum will be used to measure the baryon acoustic oscillation (BAO) scale across this poorly probed redshift range where dark energy becomes a significant contributor to the evolution of the Universe. The instrument revives the cylinder design in radio astronomy with a wide field survey as a primary goal. Modern low-noise amplifiers and digital processing remove the necessity for the analog beam forming that characterized previous designs. The Pathfinder consists of two cylinders 37m long by 20m wide oriented north-south for a total collecting area of 1,500 square meters. The cylinders are stationary with no moving parts, and form a transit instrument with an instantaneous field of view of ~100 degrees by 1-2 degrees. Each CHIME Pathfinder cylinder has a feedline with 64 dual polarization feeds placed every ~30 cm which Nyquist sample the north-south sky over much of the frequency band. The signals from each dual-polarization feed are independently amplified, filtered to 400-800 MHz, and directly sampled at 800 MSps using 8 bits. The correlator is an FX design, where the Fourier transform channelization is performed in FPGAs, which are interfaced to a set of GPUs that compute the correlation matrix. The CHIME Pathfinder is a 1/10th scale prototype version of CHIME and is designed to detect the BAO feature and constrain the distance-redshift relation. The lessons learned from its implementation will be used to inform and improve the final CHIME design.

Light Curves and Radio Structure of the 1999 September Transient Event in V4641 Sagittarii (=XTE J1819-254=SAX J1819.3-2525)

We report on radio observations of the 1999 September event of the X-ray transient V4641 Sgr (=XTE J1819-254=SAX J1819.3-2525). This event was extremely rapid in its rise and decay across radio, optical, and X-ray wavelengths; the X-rays rose to 12 crab within 8 hr and faded to below 0.1 crab in less than 2 hr. Radio observations were made with seven telescopes during the first day following the onset of the strong X-ray event, revealing a strong radio source that was detected for 3 further weeks by the more sensitive telescopes. The radio source was resolved even in the first Very Large Array (VLA) images (September 16.027 UT), being ~025 long with an axis ratio of at least 10 : 1. The total flux density decayed by a factor of ~4 over the first day, and by September 17.94 UT the radio emission was confined to a slowly decaying, marginally resolved remnant located at one side of the early elongated emission. The H I absorption spectrum gives a minimum kinematic distance of about 400 pc; various other arguments suggest that the true distance is not much greater than this. The inferred proper motions for the early extended emission (04-11 day-1) correspond to v/c ~ 1.0-3.2 (d/0.5 kpc), and this together with the radio morphology argues that this is a relativistic jet source like GRS 1915+105 and GRO J1655-40. The proper motion of the late-time remnant is at least 100 times smaller. One simple interpretation posits the ejection of a single short-lived jet segment, followed by a more slowly decaying, optically thin jet segment ejection. These two components can explain both the multifrequency radio light curves and the radio images. The most likely parameters for the fast-jet system with net-averaged proper motion of ~04 day-1, assuming d = 0.5 kpc, are v ~ 0.85c and i ~ 63°, where i is the inclination to the line of sight. The corresponding apparent velocities are 1.4c and 0.6c for the approaching and receding jets, making V4641 Sgr the closest superluminal jet source known.

SPECTRAL AND TIMING EVOLUTION OF THE BLACK HOLE X-RAY NOVA 4U 1543-47 DURING ITS 2002 OUTBURST

We present an X-ray spectral and timing analysis of 4U 1543-47 during its 2002 outburst based on 49 pointed observations obtained using the Rossi X-ray Timing Explorer (RXTE). The outburst reached a peak intensity of 4.2 Crab in the 2-12 keV band and declined by a factor of 32 throughout the month-long observation. A 21.9 +- 0.6 mJy radio flare was detected at 1026.75 MHz two days before the X-ray maximum; the radio source was also detected late in the outburst, after the X-ray source entered the low hard state. The X-ray light curve exhibits the classic shape of a rapid rise and an exponential decay. The spectrum is soft and dominated by emission from the accretion disk. The continuum is fit with a multicolor disk blackbody (kT_{max} = 1.04 keV) and a power-law (Gamma ~ 2.7). Midway through the decay phase, a strong low-frequency QPO (nu = 7.3-8.1 Hz) was present for several days. The spectra feature a broad Fe K alpha line that is asymmetric, suggesting that the line is due to relativistic broadening rather than Comptonization. Relativistic Laor models provide much better fits to the line than non-relativistic Gaussian models, particularly near the beginning and end of our observations. The line fits yield estimates for the inner disk radius that are within 6 R_g; this result and additional evidence indicates that this black hole may have a non-zero angular momentum.We present an X-ray spectral and timing analysis of 4U 1543-47 during its 2002 outburst based on 49 pointed observations obtained using the Rossi X-ray Timing Explorer (RXTE). The outburst reached a peak intensity of 4.2 Crab in the 2-12 keV band and declined by a factor of 32 throughout the month-long observation. A 21.9 +- 0.6 mJy radio flare was detected at 1026.75 MHz two days before the X-ray maximum; the radio source was also detected late in the outburst, after the X-ray source entered the low hard state. The X-ray light curve exhibits the classic shape of a rapid rise and an exponential decay. The spectrum is soft and dominated by emission from the accretion disk. The continuum is fit with a multicolor disk blackbody (kT_{max} = 1.04 keV) and a power-law (Gamma ~ 2.7). Midway through the decay phase, a strong low-frequency QPO (nu = 7.3-8.1 Hz) was present for several days. The spectra feature a broad Fe K alpha line that is asymmetric, suggesting that the line is due to relativistic broadening rather than Comptonization. Relativistic Laor models provide much better fits to the line than non-relativistic Gaussian models, particularly near the beginning and end of our observations. The line fits yield estimates for the inner disk radius that are within 6 R_g; this result and additional evidence indicates that this black hole may have a non-zero angular momentum.

The 1998 outburst of xte j1550-564: a model based on multiwavelength observations

The 1998 September outburst of the black hole X-ray binary XTE J1550-564 was monitored at X-ray, optical, and radio wavelengths. We divide the outburst sequence into five phases and discuss their multiwavelength properties. The outburst starts with a hard X-ray spike, while the soft X-ray flux rises with a longer timescale. We suggest that the onset of the outburst is determined by an increased mass transfer rate from the companion star, but the outburst morphology is determined by the distribution of specific angular momentum in the accreting matter. The companion in XTE J1550-564 is likely to be an active magnetic star, with a surface field strong enough to influence the dynamics of mass transfer. We suggest that its magnetic field can create a magnetic bag capable of confining gas inside the Roche lobe of the primary. The impulsive rise in the hard X-rays is explained by the inflow of material with low angular momentum onto the black hole, on a free-fall timescale, when the magnetic confinement breaks down. At the same time, high angular momentum matter, transferred via ordinary Roche lobe overflow, is responsible for the formation of a disk.

XTE J1550–564: a superluminal ejection during the September 1998 outburst

In 1998 September, the X-ray transient XTE J1550–564 underwent amajor outburst in soft and hard X-rays, followed by a radio flare. Australian Long Baseline Array imagesobtained shortly after the peak in the radio flare showed evolving structure.The components observed have an apparent separation velocity of >2c.

The first interferometric detections of fast radio bursts

We present the first interferometric detections of Fast Radio Bursts (FRBs), an enigmatic new class of astrophysical transient. In a 180-day survey of the Southern sky we discovered 3 FRBs at 843 MHz with the UTMOST array, as part of commissioning science during a major ongoing upgrade. The wide field of view of UTMOST (

Fast Radio Transient searches with UTMOST at 843 MHz

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The Nearest GHz Peaked-Spectrum Radio Galaxy, PKS 1718-649

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