The first accretion-powered millisecond pulsar ever found, SAX 1808.4—3658 is a remarkable object, also showing thermonuclear bursts during it's infrequent outbursts. Over several years PhD student Adelle Goodwin has been trying to match the bursts observed during it's 2002 outburst with the predictions of a numerical model. This exercise can be thought of as searching exhaustively for a set of parameters which (in the model) reproduce the observed properties of the bursts. Now that we have an improved formula for determining the energy of these bursts, she built a Markov-chain Monte-Carlo (MCMC) code to constrain system parameters including neutron star mass and radius for the source. Her paper describing the study, and it's results, has now been published by MNRAS

Read the paper (MNRAS 490, 2228, 2019)

Labels: 2019, /postgrads

In June I attended the Lorentz Center workshop Bursting the Bubble: Connecting Thermonuclear Burst Research to a Wider Community in Leiden, NL. This meeting is the continuation of a series of meetings on the same topic, most recently with the BERN'18 meeting, but originally a series of ISSI international teams since about 2010. This year's meeting featured a selected group of attendees with the goal of bringing our burst research to a wider community, most notably those observers interested in novae, the WD analogues of thermonuclear bursts. A highlight for me was Bill Wolf's tutorial session on simulating bursts and novae with MESA. The centre proved terrific facilities and support for the great presentations and discussions we had over the week. As with previous meetings, JINA-CEE was a generous sponsor of the event, with support specifically aimed at enabling attendance by early-career scientists. Thanks also go to the dedicated team of organisers led by the irrepressible Anna Watts!

Labels: 2019, /meetings

While examining RXTE data for the MINBAR project two summers ago, Jean in 't Zand unexpectedly discovered a brand-new bursting source, XMMU J181227.8—181234. Now PhD student Adelle Goodwin's paper on the source has been accepted by MNRAS. The source is quite unusual; distant and hence low-intensity, but apparently a high accretion rate leading to frequent (but weak) bursts. The shape of the bursts strongly implies H-poor accreted composition, but we also found evidence for short recurrence-time bursts, which previously have been seen only in H-rich accretors. Hopefully the source will go into outburst again sometime soon and we can gather more information on it's properties.

Read the paper (MNRAS 486, 4149, 2019)

Labels: 2019, /postgrads

The 5^th Australia-China Workshop on Astrophysics was held in Healesville, VIC at RACV's Country Club resort this April. The meeting continues a series of events intended to foster cooperation between the two countries, and as my first attendance, I was very impressed with the level of cooperation alredy. A host of prominent Chinese and Australian astronomers were in attendance, and presentations were also made by students undertaking projects enabled made possible via cooperative programs. I gave a talk on X-ray binaries and the possibilities for joint observational programs, particularly with Insight-HXMT and the proposed eXTP. Exciting times ahead for cross-country cooperation!

Labels: 2019, /meetings

Longtime collaborator and friend of bursts Yuri Cavecchi visited Monash this month, supported by the MoCA Distinguished Visitor Program. Yuri and I have been working for a few years now on the global properties of thermonuclear bursts, particuarly the ignition conditions and how they respond to changes in accretion rate, motivated by observations with MINBAR. Yuri had already come up with a possible explanation for the drop in burst rates that is observed as accretion rates increase in some sources; during the visit we plan to work on matching the models in more detail to the observations. Stay tuned for exciting results coming soon!

Labels: 2019, /visits

PhD student Adelle Goodwin has been working hard trying to reconcile results of our 1-D time-dependent thermonuclear burst code Kepler with those of a much simpler (and much faster) code while trying to model the bursts from a millisecond pulsar, SAX 1808.4—3658. Continuing failure of this effort led to suspicion about the formula for the nuclear energy yield, and some careful experiments with Kepler revealed that the widely-used approximation for the energy generation adopted for the simpler code substantially overestimated the contribution lost as neutrinos. Adelle's paper on the study has now been published by ApJ. Adelle's work was also highlighted in the 2018 December edition of the JINA-CEE Newsletter.

Read the paper (ApJ 870, 64, 2019)

Labels: 2018, /postgrads

The Large Synoptic Survey Telescope (LSST) is a truly impressive instrument for the next decade. The 8.4m telescope will illuminate a 3200 Mpix camera, and carry out a 10-year survey of the sky expected to provide millions of transient alerts... every night. Many astronomers in Australia are keen to get their hands on the data which is expected to start flowing around 2023. The Australian Science Lead, Sarah Brough (UNSW) along with Astronomy Australia Ltd. is coordinating a joint national membership which would allow access to the data for Australian astronomers, and this week my application to be one of the Principal Investigators was approved! Next step is to join one (or more) of the science groups and think about all the fun we can have when the telescope comes on-line. I'm also hoping to attend theaupcoming LSST@Asia meeting in Sydney, 20—23 May 2019.

Labels: 2018, /transients

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