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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

Mon Nov 16, 2015

Hunting Gravitational Waves with Multi-Messenger Counterparts: Australia's Role

The first observations by a worldwide network of advanced interferometric gravitational wave detectors offer a unique opportunity for the astronomical community. At design sensitivity, these facilities will be able to detect coalescing binary neutron stars to distances approaching 400 Mpc, and neutron star-black hole systems to 1 Gpc. Eric Howell's paper, recently accepted by the Publications of the Astronomical Society of Australia, describes how Australian astronomical facilities and collaborations with the gravitational wave community can contribute to this new era of discovery, via contemporaneous follow-up observations from the radio to the optical and high energy. The preprint is now available at arXiv:1511.02959

Labels: 2015, /gravitational waves

Tue Nov 10, 2015

AEI-ICTS workshop on gravitational wave astronomy

It's an exciting time for Indian science at the moment, with the September 28th launch of the ASTROSAT multiwavelength astronomy mission, and the development of a new interferometric gravitational-wave detector, IndIGO. Motivated by these developments, the International Centre for Theoretical Sciences hosted a joint worshop between November 4th—6th with the Albert Einstein Institute, at the new ICTS campus north of Bengaluru (Bangalore). The meeting featured a range of talks on searches for gravitational waves as well as X-ray, radio and optical followup. I gave an invited talk on our knowledge of the orbital parameters of the best continuous-wave candidate source, Scorpius X-1, based on our 2014 paper.

Labels: 2015, /meetings

Tue Sep 01, 2015

Explainer: what is a neutron star? | The Conversation

Neutron stars are arguably the most exotic objects in the universe. Like one of those annoying friends who seemingly must overachieve in every aspect of life, neutron stars exceed in almost every category: surface gravity; magnetic field strength; density; and temperature.

>> Read more @ The Conversation

Labels: 2015, /outreach