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Thu Jul 07, 2016

Intermittent dipping in an LMXB

Some years ago I noticed a peculiar dip in the X-ray intensity of a well-known transient, Aql X-1. Such dips have been seen from other systems, but there they occur once each orbital period, and are generally explained by material in the outer accretion disc coming into sight once each orbital period, and (partially) blocking the view of the neutron star. With the help of Honours sudents James Upjohn and Matthew Stuart, and vacation student Alishan Ajamyan, we made an exhaustive search of the available RXTE data on the source, and turned up another dip, six years earlier. We explained the behaviour as a new kind of "intermittent" dipping, which — due to it's apparent rarity — could be detectable in several tens of other systems. Our paper has now been published in MNRAS.

Labels: 2016, /transients

Sun Jan 29, 2012

Aspen winter transients meeting

This week I visited Aspen, CO for the Physics of Astronomical Transients meeting, at the remarkable Aspen Center for Physics. There is an increasing focus on transient astronomy at present, and astrophysicsts are racing to understand the physics of new phenomena that are being discovered by wide-field, automated instruments and observing programs such as NASA's Swift satellite, the Pan-STARRS program, and others. I presented a poster on the Variables and Slow Transients program for the Australian Square Kilometre Array Pathfinder (ASKAP) which is expected to uncover a wealth of new transient discoveries when it commences in 2013 or so.

Survey Science with ASKAP: Variables and Slow Transients (VAST) (8.5 MB vector PDF)

Labels: 2012, /transients

Wed Sep 01, 2010

Puzzling behaviour in IGR J17473-2721

A bunch of us have been working on the X-ray data from a quite remarkable transient, IGR J17473-2721, which went into a 6-month long outburst beginning in 2008. The source went through some dramatic changes in the burst behaviour, some of which we think we understand, but some of which we don't. In particular at the beginning and the end of the outburst completely different burst behaviour is observed at roughly the same intensity (accretion rate). This effect may be due to the heating of the neutron star core which has taken place during the outburst. Jerome's paper is out now on astro-ph at arXiv.org:1007.5201.

Labels: 2010, /transients

Thu Aug 14, 2008

New outburst of IGR J17473-2721

This system was discovered back in 2005, and was detected in outburst again this March. Since then, it's been observed by Swift, INTEGRAL and RXTE, and even SuperAGILE detected a thermonuclear burst (ATel #1445). Following reports of the bursting activity we triggered some observations with RXTE to search for burst oscillations; we caught some bursts, but no oscillations. Since then, public RXTE observations revealed kHz QPOs and radius expansion bursts, from which we estimated the distance (ATel #1651). Observations are continuing.
See also
INTEGRAL monitoring of IGR J17473-2721
Diego Altamirano's IGR J17473-2721 page
IGR J17473-2721 at SIMBAD

Labels: 2008, /transients

Sat Jul 31, 2004

The optical counterpart of XTE J1709-267

Jonker et al. report on Chandra and CTIO observations, as well as RXTE observations revealing bursts with an unusual precursor. A similar event occurred in the well-known burster 4U 1636-536
Accepted by MNRAS 22 July 2004

Labels: 2004, /transients