GOTO | MINBAR | high-energy group | MoCA | MIT/RXTE burst catalog | vcard | CV | wiki

Tue Apr 16, 2019

A brand-new bursting X-ray binary

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

Mon Nov 05, 2018

Measuring neutrino losses in thermonuclear bursts

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

Mon Mar 09, 2015

Hauke's thesis accepted; postdoctoral position

I am proud and pleased to report the award of Hauke Wörpel's PhD degree was approved last week. Hauke's thesis, entitled "Radiation drag on the accretion disk in type-I X-ray bursts" was submitted last October. His thesis involved analysis of a few thousand thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer, showing that the accretion rate seems to increase during the bursts, and by a substantial amount, up to a factor of 20. Hauke also undertook numerical SPH modelling of accretion disks under the influence of bursts, with a view to better understanding the dynamics of the disk. Hauke has already left these shores and is now undertaking postdoctoral work at the Leibniz-Institut für Astrophysik Potsdam, where, on arrival, he unexpectedly grew an umlaut. Congratulations Hauke!

Labels: 2015, /postgrads

Tue Feb 17, 2015

The remarkable RXTE observations of the Rapid Burster

The Rapid Burster is a neutron-star binary that exhibits singular behaviour; extremely frequent "type-II" X-ray bursts, which cannot be thermonuclear in origin. The standard explanation of these bursts is that they arise from episodic accretion onto the neutron star, and it is this accretion which also fuels the (mostly) independent thermonuclear (type-I) bursts. The Rossi X-ray Timing Explorer made many observations (totalling 2.4 Ms, or almost a month of continuous observing!) of the source over multiple transient outbursts throughout the mission lifetime, building up an impressive database of burst behaviour. SRON PhD student Tullio Bagnoli, having already made a detailed study of the thermonuclear events in this source, has now completed a study of the type-II events, examining the demographics of the almost 8500 bursts detected by RXTE. The singular behaviour of this source may be explained by a special combination of magnetic field strength, stellar spin period and alignment between the magnetic field and the spin axis. Tullio's paper was just accepted by MNRAS.

Read the paper arXiv:1502.03941

Labels: 2015, /postgrads

Mon Jan 12, 2015

Shakya's thesis accepted

I am pleased and proud to report that the award of Sammanani (Shakya) Premachandra's PhD degree was approved last week. Shakya's thesis, entitled "Precision ephemerides of neutron star binaries to assist gravitational wave searches: Sco X-1 & Cyg X-2" was submitted last September. Her thesis involved extensive analyses of optical data of candidate gravitational wave sources Scorpius X-1 and Cygnus X-2, with a view towards improving the precision of binary orbital parameters and hence making more sensitive searches for gravitational waves in future with advanced-LIGO. The system parameters she has established for the two best candidate sources have already been utilised by the LSC's continuous-wave group in a mock data challenge to compare various search algorithms. These parameters will also serve as crucial input parameters to the actual searches, expected as soon as advanced-LIGO comes on line later this year. Congratulations Shakya!

Labels: 2015, /postgrads