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Fri Oct 30, 2009

It's deja vu, all over again

Our recent discovery of 552 Hz burst oscillations in the well-known binary EXO 0748-676 was fairly unremarkable, except perhaps for the extreme rarity of the oscillations (detected in only 2 of ~160 bursts observed by RXTE). However, oscillations had already been detected in this source back in 2004, at 45 Hz. The 552 Hz signal is much stronger, recommending it as the neutron star spin; unfortunately, the Doppler broadening that would be expected by such a spin means that the narrow spectral features previously identified as arising from the neutron star surface, could not have. Our paper has now (Feb '10) been accepted by ApJL.

Read the paper (arXiv.org/0910.5546)

Labels: 2009, /thermonuclear bursts

Tue Sep 01, 2009

The apparent neutron-star radius during bursts

Measuring the radius of neutron stars is hard — ask anyone. (They're really small, and really far away; imagine trying to measure something the width of a human hair... on Pluto). The X-ray emission during the bursts seems to come from the entire surface, and is consistent with a blackbody, so it should be possible to infer the radius indirectly, but the apparent radius behaves in very unexpected ways — usually increasing or decreasing during the burst. Sudip Bhattacharyya & Cole Miller found a correlation between the slope of the radius evolution and the duration of the burst (a proxy for the burst fuel composition), based on the data from the RXTE burst catalog. Our paper was just accepted by MNRAS.

Read the paper (arXiv.org:0908:4245)
Astronomers get neutron star's measure @ ABC Science

Labels: 2009, /thermonuclear bursts

Thu Jul 09, 2009

Thermonuclear bursts at the ASA

The Astronomical Society of Australia held it's meeting this week at U. Melbourne. This annual event brings astronomers from all over the country (and the world) together for a week to catch up, present their research, and also award prizes to researchers and students. I gave a poster describing work on using mixed H/He thermonuclear bursts to deduce the neutron star redshift. Zdenka gave a talk on preliminary results from her comparisons of burst properties and models in the candidate He accretor 4U 1728-34. It was nice to be back on campus at U.Melbourne for a week — great location and even better coffee!

Measuring neutron star parameters from mixed H/He thermonuclear bursts (1.1MB PDF)

Labels: 2009, /neutron star EOS

Mon May 25, 2009

Defining the neutron star crust meeting

I just got back from a terrific meeting in Santa Fe on the subject of the neutron star crust, and attended by a wide range of nuclear theorists and experimentalists as well as astrophysicists. There were many interesting talks, and I learned a lot; one of the overarching themes was the need for better communication between the various groups — Bob Rutledge was remarkably persistent in asking after almost every talk, "what one thing would you like the other groups represented here to take away from your work?" (to paraphrase a little). The meeting was also one of the most "wired" that I have been to, with a blog including twitter updates, and culminating in the creation of a reddit group called neutronstarstructure to collect relevant papers on the subject.
I gave a talk on some of the recent work I've been doing with determining neutron star redshifts and mass, radius from mixed H/He thermonuclear bursts, which prompted quite a response.

Defining the Neutron Star Crust: X-ray Bursts, Superbursts and Giant Flares
Measuring neutron star parameters from mixed H/He thermonuclear bursts (3.2 MB PPT or 1.5 MB PDF)

Labels: 2009, /thermonuclear bursts

Mon Mar 02, 2009

International Year of Astronomy 2009

2009 has been designated the International Year of Astronomy by the International Astronomical Union (IAU) and UNESCO. I think I can speak for most astronomers when I say that we think astronomy is too much fun to keep to ourselves! There is a lot going on throughout the year, and a group here at Monash have been planning a bunch of fun and interesting activities. Check out the website iya09.monash.edu.au to find out more

Labels: 2009, /outreach