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)

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)

ASA 2008, Perth WA

The annual meeting of the Astronomical Society of Australia was held this July in Perth, WA. I've never spent much time in Perth, so it was good to spend a little time over there. The UWA campus at Crawley is beautiful, right on the shore of the Swan river, and with fantastic architecture and gardens. We stayed at St. George's College, which is also very picturesque, and backs onto King's Park. The meeting was very well attended and a lot of fun. I gave an invited talk on searches for spectral features from radius-expansion bursts observed by RXTE

ASA 2008, Perth WA
ASA talk (2.9MB PDF)

US/Netherlands tour

I just got back from a very busy trip around the US, with a stop in Amsterdam on the way home. I presented a couple of posters at the AAS/High Energy Astrophysics Division Meeting in Los Angeles, and went on to visit Ed Brown at JINA, where I gave a lunch talk on the following Monday.

Then it was on to Boston for a brief visit to MIT to catch up with collaborators and friends, as well as a pilgrimage to Toscaninis (sadly the Harvard Square location has closed). After that I had a couple of nights in St. Louis for the APS meeting, and gave an invited talk on burst observations in a special session on the physics of X-ray bursts (L3).

Finally I headed home via Amsterdam for another invited talk at the Decade of Accreting Millisecond X-ray Pulsars workshop at UvA.

HEAD posters 1 2 (0.24/1.22 MB PDF)
APS talk (10.2 MB PPT)
AMSPs workshop talk (1.5 MB PPT) and the proceedings paper

SINS summer school

Last week I spent two days at the first Stellar Interiors and Nucleosynthesis summer school, hosted by the CSPA at Monash U. I gave a talk on nuclear processes in thermonuclear bursts, which was good since it forced me to actually learn a little bit more about this subject. Most of the other talks were pretty hard-core stellar physics, but Jordi Jose gave a nice series of talks on classical novae and type 1a supernovae.

Nuclear burning on the surface of accreting neutron stars (6.7 Mb .ppt)

Texas in Australia

The XXIIIth Texas Symposium, held here in Melbourne, concluded last week. All in all a terrific success, with a very interesting program full of great talks by stellar (sorry) attendees. There were plenty of international visitors, many of whom commented on how much they enjoyed their visit despite the long trip. I managed to catch up with quite few people I hadn't seen for a while, but for most the social highlight was Thursday's dinner at the NGV's Garden Restaurant.

Magnetic Field Burial Observed in an Accretion-Powered Millisecond Pulsar? (poster presented at the symposium, .PDF format)

HEAT is... well, hot

We just had the first High-Energy Astrophysics Teleconference (HEAT) this afternoon, hosted by yours truly. The idea is to bring observers and theorists interested in high-energy astrophysics together on a regular basis, to share information, present new results, and generally build our small, diverse, and highly dispersed community. We had a round of introductions followed by a little science discussion, and suggestions for future topics and presentations; everthing went very well. The next meeting is scheduled for Friday October 13th at noon — please email me if you are interested in taking part.

MIRAX workshop proceedings

Here's the paper "Accretion-powered Millisecond Pulsar Outbursts" I submitted to the proceedings of the MIRAX workshop last December.

>> Click for the abstract Abstract: The population of accretion-powered millisecond pulsars has grown rapidly over the last four years, with the discovery of six new examples to bring the total sample to seven. While the first six discovered are transients active for a few weeks every two or more years, the most recently-discovered source HETE J1900.1-2455, has been active for more than 8 months. We summarise the transient behaviour of the population to estimate long-term time-averaged fluxes, and equate these fluxes to the expected mass transfer rate driven by gravitational radiation in order to constrain the distances. We also estimate an upper limit of 6 kpc to the distance of IGR J00291+5934 based on the non-detection of bursts from this source.

X-ray data analysis

For those in the local Astro group who may have an interest or a need to analyse some X-ray data from Chandra or RXTE, I have installed some analysis software (Linux machines only) and related calibration files in /data/software. For Chandra data analysis I have installed CIAO version 3.3.0.1, as well as the ISIS spectral fitting package version 1.3.1 and the CALDB files. For RXTE analysis I have installed HEASOFT version 6.0.3 and the appropriate CALDB files.

If you missed the introduction to X-ray astronomy I gave on April 5^th, here is a PDF file of the slides and notes

>> Read more To initialise CIAO:

source /data/software/ciao/bin/ciao.csh

For ISIS, add /data/software/isis/bin to your path and invoke with "isis". See the CXC for analysis threads and other documentation.

To initialise HEASOFT (which also has general tools to manipulate FITS files) for analysis of RXTE data:

setenv HEADAS /data/software/headas/i686-pc-linux-gnu-libc2.2.4
source $HEADAS/headas-init.csh
setenv CALDB /data/software/caldb
source $CALDB/software/tools/caldbinit.csh

HEASOFT also includes the popular spectral fitting package Xspec. See the HEASARC site for more info or RXTE data analysis recipes

I also plan to install the SAS software for analysis of XMM-Newton data. Let me know if you are interested in getting started with these packages or need any help.

MIRAX workshop, Brazil

In December I attended the MIRAX workshop at INPE in São José dos Campos, Brazil. This is a nice, small-scale mission to be launched in 2010/11 which will use the BeppoSAX flight spare WFC camera, as well as a wide-field hard X-ray detector to be built by UCSD. Lots of interesting talks about X-ray transients and the science you can do with dedicated, long-term monitoring. Amongst the current and past monitoring projects mentioned are

• INTEGRAL source light-curves at http://isdc.unige.ch/index.cgi?Data+sources
• INTEGRAL galactic bulge monitoring at http://isdc.unige.ch/Science/BULGE
• INTEGRAL HMXB monitoring at http://pulsar.astro.warwick.ac.uk/gps
• BATSE earth occultation monitoring at http://f64.nsstc.nasa.gov/batse/occultation/

Observations of transient LMXB pulsars (PDF file)

Korea | Sydney | 4U 1636-536

A busy few weeks, with a trip to Seoul to attend the 7th Pacific Rim Conference on Stellar Astrophysics. I gave a talk (PDF file) on accretion-powered millisecond pulsars, highlighting the recent observations of the latest discovery, HETE J1900.1-2455. Returned via Sydney where I visited a collaborator at U. Sydney and caught up with friends and family.
In the meantime, the long awaited paper on the radius-expansion bursts from 4U 1636-536 was finally accepted. In a study of all the bursts observed by RXTE, we found a bimodal distribution of peak radius-expansion burst fluxes, separated by a factor of 1.7. This is exactly what you would expect if the fainter bursts reach the Eddington limit in an atmosphere containing hydrogen at approximately solar abundances, while the brighter bursts instead occur in a pure helium environment. It remains a mystery exactly how the accreted hydrogen is eliminated from the atmosphere in the brighter radius-expansion bursts.
Read the paper

Australia-Italy Workshop on GW Detection

The workshop, organised by the UWA Gravity Wave group, was held at the Gingin observatory site, home also to the Gravity Discovery Centre. Attendees included members of all the major interferometer groups around the world - LIGO, VIRGO, GEO and TAMA, as well as representatives of the Italian government (co-sponsors) and the WA Minister for Science and the Environment, Judy Edwards. It was a pretty technical meeting, a lot of it over my head, but I learned quite a bit about some of the details of interferometric GW detectors, as well as the current status and prospects for the detectors around the world. Although the proposed Australian instrument will not be as sensitive as LIGO, for example, it will play an important role in the worldwide effort because of it's southern location and the correspondingly maximal baseline with the US LIGO detectors.
Accreting Neutron Stars as Gravitational Wave Sources (PDF file)

Texas in Australia 2006

The increasingly poorly-named Texas Symposium on Relativistic Astrophysics will be held in Melbourne between 11-15 December 2006. Program and attendees TBA, but keep your calendars clear!
Download the poster

ASA 2005

The Astronomical Society of Australia just held its 2005 meeting in Sydney, which was a lot of fun. One of the highlights was the launch, and review discussion, of the NCA's Decadal Plan for the period 2006-15. I presented a talk on some millisecond pulsar work, as well as Jasmina's talk on G347.3-0.5 (she unfortunately couldn't attend).
Link to PDF file

AAS #206, Minneapolis MN

Greetings from the 206^th AAS meeting, all this week in Minneapolis. I presented a talk in Special Session 17: Fundamental Physics with Millisecond Pulsars about the newest accretion-powered millisecond pulsar, IGR J00291+5934
Link to PDF file
I also mentioned the outburst history to date of SAX J1808.4-3658, and commented that we were overdue for the next one; two days later a new outburst was detected in the PCA bulge scans.

HEAD meeting 2004

Just got back from New Orleans, where I attended the eighth High-Energy Astrophysics Divisional meeting. The highlight was almost certainly the detection of 45 Hz burst oscillations in EXO 0748-676 (see also astro-ph/0409384), a much lower frequency than the previous minimum of 270 Hz (for 4U 1916-053). There was lots of other fun stuff going on, as usual. I presented two posters (links to PS files):
Thermonuclear bursts observed by RXTE: The MIT catalog
Thermonuclear bursts from millisecond X-ray pulsars