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Mon Oct 18, 2021

Searching for X-ray pulsations from Sco X-1

Plot image from the paper Bright X-ray binaries are thought to be promising candidates for detecting continuous gravitational waves, because it is possible that the spin-up torques provided by accretion are offset by gravitational wave emission to maintain their equilibrium spin periods. A long-standing project led by Monash PhD student Shanika Galaudage has sought to use the most sensitive X-ray data available for the two best candidates, Sco X-1 and Cyg X-2, to make a deep search for pulsations that would measure the spin of the compact object in these systems. The analysis was extremely challenging, particularly for Sco X-1; that source is so bright that highly unusual data modes need to be selected for observations with the RXTE/PCA, which complicates the data reduction. Unfortunately we found no strong evidence of pulsations, but we did derive the deepest limits on pulse amplitudes ever. The paper describing our results has now been accepted by MNRAS.

Read the paper

Labels: 2021, /gravitational waves

Fri Aug 24, 2018

Mt. Kent (QLD) as a host for for GOTO-South?

Another possible site for the southern counterpart of our GOTO instrument on La Palma is USQ's Mt. Kent observatory. About 30 min drive from Toowoomba, Mt. Kent is significantly easier to get to compared to Siding Spring, via the recently-upgraded Wellcamp airport, and offers comparable observing conditions. Even better, they already have some spare concrete pads that might suit a GOTO-sized instrument! Earlier in the year we submitted a funding proposal to support development of the telescope from 2019 onwards. Fingers crossed!

Labels: 2018, /gravitational waves

Thu Jan 18, 2018

Surveying candidate sites for GOTO-South

This week I'm visiting Coonabarabran to check out Siding Spring Observatory as a possible site of the southern counterpart of our GOTO instrument on La Palma. Siting a second instrument in Australia willdramatically improve our ability to cover the large sky regions that LIGO produces in response to the detection of a binary neutron star or black hole merger. Later this year we plan to submit a funding proposal to support development of the telescope from 2019 onwards. Stay tuned!

Labels: 2018, /gravitational waves

Wed Oct 18, 2017

Detection of an optical counterpart to a binary neutron star merger

The milestones just keep coming this year for the burgeoning field of gravitational wave astronomy. Closely following the first "triple coincidence" detection of a black hole merger (with the two LIGO instruments joined by the Italian Virgo instrument), comes the announcement yesterday of the first detection of a binary neutron-star merger, which was — spectacularly — accompanied by a gamma-ray transient detected by Fermi GBM. Things just got more exciting when an optical counterpart was detected for the gamma-ray and gravitational-wave source, with the Swope Telescope in Chile. The counterpart, named SSS17a, was subsequently followed by an estimated 70 different observational groups (including a range of Australian facilities coordinated via the OzGRav Centre of Excellence). A literal frenzy of activity followed, culminating in the LIGO press release in the early hours (Australian time) yesterday, and followed by our own press event at Old Parliament House yesterday morning. It is hard to quantify the impact of this event; the announcement was accompanied by an estimated 76 papers (with likely more to come). Sadly, our own GOTO telescope missed out on this event, but the optical brightness indicates that future events will be easily detectable, and validates our instrumental design. The prospects for additional detections when O3 begins (in late 2018) are excellent.

Labels: 2017, /gravitational waves

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

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

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