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Fri Dec 15, 2017

Thermonuclear bursts in the spotlight

It's been a few years now since a review of thermonuclear bursts came out, so a little while ago Tomaso Belloni and Mariano Mendez commissioned Laurens Keek and I to write one. It's a big job to try to cover the literature in such a broad field, and this took (unfortunately) a lot longer than we expected. Tomaso and Mariano were very patient, and I'm pleased to announce that the review is finally ready! You can read it for yourself on the arXiv, or wait for it as part of "Timing Neutron Stars: Pulsations, Oscillations and Explosions", in Springer's ASSL series, edited by Tomaso and Mariano

Read the paper arXiv:1712.06227

Labels: 2017, /thermonuclear bursts

Wed Nov 29, 2017

Cracking the code of burst rates

It's been a long-standing mystery, how for some burst sources, the burst rate decreases even as the accretion rate increases. Theory and numerical models both predict that as you dial up the accretion rate, the burst ignition point should be reached earlier and earlier (up to the point when burning becomes stable and bursts stop), so that the burst rate should always increase. Yuri Cavecchi recently came up with an alternative explanation, related to the way that the burst ignition point moves from the equator to higher latitudes at higher accretion rates. If this movement is sufficiently fast, a decrease in burst rate can result even as the accretion rate continues to increase. Yuri's paper (also with longtime burst expert Anna Watts) was just accepted by ApJ

Read the paper arXiv:1711.04389

Labels: 2017, /thermonuclear bursts

Fri Nov 24, 2017

IAU Symposium #339 on Time-Domain Astronomy

This month I visited South Africa (and the African continent for the first time!) to attend the Southern Horizons in Time-Domain Astronomy meeting in Stellenbosch. The programme featured an exhaustive roster of hot topics in the transient realm right now — from kilonovae through FRBs to supernovae and stellar pulsations. A wide range of instrument development activities were reported, both world-wide and in South Africa, which is of course the host of the Southern African Large Telescope (SALT) and the Square Kilometer Array precursor MeerKAT As well there were workshops on relevant topics including astroinformatics and machine learning. The setting, in the midst of SA's wine regions was pretty hard to beat, and the chance to visit Cape Town — surely one of the most geographically stunning cities in the world — was a nice bonus. The program and most of the talks are now online so check it out!

Labels: 2017, /meetings

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

Wed Oct 04, 2017

2017 Nobel Prize in Physics to LIGO team

Rainer Weiss, Barry Barish and Kip Thorne were last night awarded the 2017 Nobel Prize for Physics, "for decisive contributions to the LIGO detector and the observation of gravitational waves". This award caps a terrific year for the collaboration, which (by my observation) has scooped pretty much all the major science awards. Here at Monash we're celebrating our involvement in the project, and looking forward to the (hopefully many) surprises in store for the future.

Labels: 2017, /press

Tue Sep 05, 2017

Analysing the cooling tails of thermonuclear bursts

When the upper layer of an accreting neutron star experiences a thermonuclear runaway of helium and hydrogen, it exhibits an X-ray burst with a cool-down phase of typically 1 minute. Analysis of light curves of 1254 X-ray bursts observed by the Rossi X-ray Timing Explorer shows that the decay is described as a power-law with index in the range 1.3—2.1, with a Gaussian component also required for half of the bursts. The Gaussian appears consistent with being due to the rp process, which consists of rapid proton captures and slow beta-decays of proton-rich isotopes, and is expected to be prominent in bursts with a significant fraction of hydrogen in the fuel. The Gaussian fluence fraction suggests that the layer where the rp process is active is underabundant in H by a factor of at least five with respect to cosmic abundances. Jean's paper reporting the analysis is now accepted by A&A.

Read the paper arXiv:1708.08644

Labels: 2017, /thermonuclear bursts

Sat Jul 22, 2017

MINBAR meetings lead to new burst source

This (northern) summer I visited colleagues at DTU Space, Denmark and SRON, Netherlands to continue work on the Multi-INstrument Burst ARchive (MINBAR). We're currently preparing for the first data release (DR1), and we made a lot of progress with the data analysis and assembly of the companion paper. We also got to celebrate the deployment of NICER to the International Space Station, although because of a delay our celebration was a little early!

Unexpectedly, the careful eye of Jean in 't Zand identified a handful of bursts observed by RXTE from a 2008-9 transient, XTE J1812-182, that was not previously known to be a burster. We reported our discovery in Astronomer's Telegram #10567 and will shortly present a more detailed analysis via a paper. While this is a very pleasing outcome from the meeting, it now means there are even more bursts to analyse for MINBAR!

Labels: 2017, /thermonuclear bursts

Mon Jul 10, 2017

GOTO La Palma site inauguration

This month saw the official inauguration of Warwick's La Palma observing site, now hosting the Gravitational-wave Optical Transient Observer (GOTO) instrument. The July 3rd event celebrated the successful deployment of the GOTO prototype in the previous month. The press releases from Monash and Warwick were reposted in and, amongst other channels (TV La Palma!) The project is a collaboration between Warwick and Monash, along with UK partners Sheffield, Leicester, and Armagh Universities, and the National Astronomical Research Institute of Thailand (NARIT).

Labels: 2017, /press

Fri Mar 24, 2017

Reference bursts for model comparisons

Thermonuclear (type-I) X-ray bursts arise on the surface of neutron stars in binary systems, and offer a powerful probe of the neutron star environment as well as the nuclear reactions that power them. Efforts to match observed burst to numerical simulations have been fairly limited to date, partially because of the dearth of high-quality, well characterised burst measurements. To address this issue, we have assembled a set of "reference" bursts featuring examples of a number of different types of bursts, presented in a paper which has just been accepted by PASA. We also hope that the observed bursts will serve as test cases for numerical codes in order to assess the variations between those codes, in order to quantify the fundamental uncertainty of burst simulations.

Read the paper arXiv:1703.07485

Labels: 2017, /thermonuclear bursts