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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

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

Fri Dec 18, 2015

Kepler predictions for thermonuclear bursts

Monash researcher Alexander Heger has been for many years exploring the dependence of thermonuclear burst properties on the source conditions, including accretion rate and fuel composition. A year or two back Honours student Nathanael Lampe took all of the models Alexander had compiled over the years, and performed a common analysis, measuring the burst recurrence time and energetics, for the purposes of comparing broadly to observations, as well as understanding the stability properties of the bursts. As part of this analysis, Nathanael assembled a table giving the properties of bursts in each available run. Nathanal's paper has now been accepted by ApJ, and it is anticipated that the burst table will become a useful resource for observers (and theorists) in years to come.

Read the paper arXiv:1512.05769

Labels: 2015, /thermonuclear bursts

First meeting of new ISSI burst team

In December we kicked off a new international team supported by Bern's International Space Science Institute. This team is focussed on reconciling experimental, observational and numerical investigations on thermonuclear (X-ray) bursts and the nuclear reactions that power them. Due to the strong gravity and high temperature, these bursts probe nuclear physics and reactions not encountered elsewhere in nature, and are also influenced by the properties of the underlying neutron star - and hence the properties of matter at these extreme conditions. Our goals include identifying the key nuclear reactions which influence the burst lightcurve; taking advantage of new rare-isotope accelerator-based experiments and satellite observations to provide stringent tests of numerical models; identifying specific cases of ignition and burning from observation-model comparisons; and (ultimately) providing qualitatively new constraints on the properties of neutron stars and nuclear matter.

Although this is the third such team for me, it's the first I've led. Bern itself was once again celebrating Christmas, with the Weihnachtsmarkt in full swing, including the always popular gluhwein shack.

See the team home page for more information

Labels: 2015, /meetings