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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 Space.com and Phys.org, 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