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Tue Dec 06, 2016

The last outburst of a millisecond pulsar?

The 599 Hz millisecond pulsar IGR J00291+5934 is a source I've been studying for more than a decade, having been involved in the discovery as well as observation of every transient outburst since. Although the first few outbursts displayed a remarkable predictability, the most recent, in 2015, was almost 3 years "late". In a detailed study of the INTEGRAL and Swift observations of the outburst, ISSI PhD student Vittorio De Falco examined the broad-band X-ray spectrum and the pulse properties, as well as data covering the first thermonuclear burst ever detected from the source. Remarkably, the estimated time-averaged accretion rate is decreasing on a timescale of only a few years, suggesting that we are unlikely to see another bright outburst in the next decade, if ever. Vittorio's paper was just accepted by A&A.

Read the paper arXiv:1611.08218

Labels: 2016, /pulsars

Mon Oct 31, 2016

Understanding burst oscillations

Some thermonuclear burst sources exhibit temporary "burst oscillations", periodic variations in the X-ray intensity at frequencies characteristic of each source. It has been shown that these oscillaions trace the neutron star spin, but much is still not known about the detailed mechanism, and many puzzles remain. UvA student Laura Ootes led a comprehensive study of the oscillations detected in the entire Rossi X-ray Timing Explorer sample, which has just been accepted for publication by ApJ. The paper presents a comprehensive comparison of the observed properties with burst oscillation models, as summarised in a series of 14 (!) tweets by co-author Anna Watts. Although we still cannot unambiguously identify the oscillation mechanism, this analysis is going to be definitive for many years, until a new X-ray timing mission is launched.

Read the paper arXiv:1610.08995

Labels: 2016, /thermonuclear bursts

Fri Oct 14, 2016

Seeking postdoctoral associates in gravitational wave astronomy

Following the approval of our Centre for Excellence in Gravitational-wave Astronomy, OzGRav, Monash has several postdoctoral positions available to contribute to research programs within the Centre. One of these is intended to work with the GOTO team hunting for optical counterparts to the hotly-anticipated mergers of neutron-star binaries detected by LIGO. Please visit the website to view the criteria and position description, or contact me if you have any enquiries. Applications close December 1st.

Labels: 2016, /opportunities

Thu Sep 08, 2016

ARC Centre of Excellence for Gravitational Wave Discovery approved

The Australian Research Council announced this morning the outcomes of the Centres of Excellence scheme, and I'm delighted to report that our Centre for Gravitational Wave Discovery, aka OzGRav, was approved! The Centre, led by Swinburne's Prof. Matthew Bailes, will support research into detecting gravitational waves with interferometric detectors like Advanced LIGO as well as the Parkes Pulsar Timing Array. Nineteen Chief Investigators from six Australian universities will join with 15 partners from Australia and all over the world, in a program extending for the next 7 years. A great time to be a gravitational wave astronomer!

Labels: 2016, /gravitational waves

Thu Jul 07, 2016

Intermittent dipping in an LMXB

Some years ago I noticed a peculiar dip in the X-ray intensity of a well-known transient, Aql X-1. Such dips have been seen from other systems, but there they occur once each orbital period, and are generally explained by material in the outer accretion disc coming into sight once each orbital period, and (partially) blocking the view of the neutron star. With the help of Honours sudents James Upjohn and Matthew Stuart, and vacation student Alishan Ajamyan, we made an exhaustive search of the available RXTE data on the source, and turned up another dip, six years earlier. We explained the behaviour as a new kind of "intermittent" dipping, which — due to it's apparent rarity — could be detectable in several tens of other systems. Our paper has now been published in MNRAS.

Labels: 2016, /transients

Thu Jun 30, 2016

Thermonuclear bursts in Japan

This June I visited Niigata, Japan for the 14th Nuclei in the Cosmos meeting. This biennial gathering attracts a mix of nuclear experimentalists, modelers, and astrophysicists. I presented a poster on our thermonuclear burst model-observation comparisons.
Following the meeting I stopped by RIKEN in Tokyo, where members of the MAXI instrument team were the very generous hosts of a meeting of our International Space Science Institute international team. The Monitor of All-Sky X-ray Image (MAXI) instrument, deployed on NASA's International Space Station, has been continuously monitoring the X-ray sky for several years, and has detected many rare, long-duration thermonuclear bursts, as well as transient outbursts of known and new sources.

Labels: 2016, /meetings

Mon May 30, 2016

JINA-CEE International Symposium on Neutron Stars in the Multi-Messenger Era: Prospects & Challenges

In May I travelled to Athens, OH for the JINA-CEE symposium on neutron stars. This was a great week of presentations on a very wide range of astrophysics topics relating to neutron stars, including my own presentation on thermonuclear bursts, but also discussions of new & upcoming missions like NICER and ASTROSAT, progress on mass-radius measurements from bursts and cooling transients, rotation-powered pulsars, gravitational waves, you name it. The week kicked off on Sunday with a satellite workshop on Experiments for X-ray Burst Nucleosynthesis, where we reviewed the prospects for better experimental constraints on the many nuclear reactions important to thermonuclear bursts. A big thank-you to JINA-CEE for supporting my trip!

Labels: 2016, /meetings

Tue May 03, 2016

Tuning up for Gravitational Wave Discoveries part II

Shakya Premachandra's paper on the orbital ephemeris of Cyg X-2, the next-best candidate LMXB (after Sco X-1) for continuous gravitational waves, has now been accepted by ApJ. Systems like Cyg X-2 and Sco X-1 may produce detectable gravitational radiation from "mountains" on the rapidly rotating neutron star, and precise knowledge of the system parameters (including the orbital period and neutron star spin frequency) may be critical for optimal GW searches with LIGO. However, many of the candidates are rather poorly known, so Shakya's analysis assembled the available data on the source to improve this situation. The accepted paper is available now at arXiv:1604.03233.

Labels: 2016, /gravitational waves

Fri Feb 12, 2016

First detection of gravitational waves

This morning, the LIGO Scientific Consortium has announced that it has made the first detection of gravitational waves. The signal was detected within 7 ms by both LIGO detectors in the US on September 14, 2015, and has been shown to be consistent with the merger of a pair of 30 solar mass black holes. The discovery was made possible by the enhanced capabilities of Advanced LIGO, a major upgrade that increases the sensitivity of the instruments compared to the first generation LIGO detectors. Amazingly, the detection was made prior to the first official observing run, instead being seen in an "engineering run" in which the instruments were otherwise operating optimally. This incredible achievement has kicked off an entirely new way of gathering information about the universe around us, and makes electromagnetic followup projects like our own Gravitational-wave Optical Transient Observer (GOTO) possible

Labels: 2016, /gravitational waves