Friday, 5 August 2011

A New Candidate Magnetar Located Outside the Galactic Plane

Magnetars!! I'm not a star person (they are useful kinematic tracers and stellar evolution [being on the Red Giant Branch] allows us to isolate stars in specific systems), but with ARC Postdoctoral Fellow, Sean Farrell, I'm an author on a paper on the detection of candidate magnetar outside the galactic plane.
The study uses mainly X-ray observations, plus a lack of an optical source (from the PAndAS survey; my contribution to the paper) to identify one of these weird objects. Basically, these are neutron stars which huge magnetic fields, and this results in some dramatic bursts of energy.

Co-author, Bryan Gaensler, and I gave some talks on "Music and the Cosmos" over the last could of years, and he recounts the story of SGR 1806-20; and I'm surprised that more people don't really know about it. Basically, this magnetar is 50,000 light-years away, and 50,000 years ago, it had a major energy burst, releasing, in one tenth of a second, the same amount of energy as the Sun outputs in 100,000 years (thank you wikipedia).

This outburst hit the Earth's atmosphere on December 27th, 2004. To directly quote wikipedia
The gamma rays struck the ionosphere and created more ionization which briefly expanded the ionosphere.
Remember, this is an outburst on a star on the other side of the Galaxy!! Pretty cool. On this new candidate magentar, well done Sean!!!

A New Candidate Magnetar Located Outside the Galactic Plane

Joseph R. Callingham (1), Sean A. Farrell (1,2), Bryan M. Gaensler (1,2), Geraint F. Lewis (1), Matthew J. Middleton (3) ((1) The University of Sydney, Australia, (2) ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), Australia, (3) University of Durham, UK)
In this paper we present detailed analysis of the transient X-ray source 2XMMi J003833.3+402133 detected by XMM-Newton in January 2008 during a survey of M31. This source has previously been identified as a black hole X-ray binary in M31, but here we argue that the X-ray spectra and timing data are inconsistent with this conclusion. We instead argue that 2XMMi J003833.3+402133 may be a new addition to the rare class of magnetars. The X-ray spectrum is well fitted by either a steep power law plus a blackbody model or a double blackbody model. Prior observations with XMM-Newton, Chandra, Swift and ROSAT spanning 1991 to 2007, as well as an additional Swift observation in 2011, all failed to detect this source. No counterpart was detected in deep optical imaging with the Canada France Hawaii Telescope down to a 3sigma lower limit of g = 26.5 mag. The transient behaviour, X-ray spectrum, and lack of an optical counterpart are all consistent with a magnetar. The derived luminosity and black body emitting radius at the distance of M31 argue against an extragalactic location, implying that it is located within the Milky Way but 22 deg out of the plane. The high Galactic latitude could be explained if 2XMMi J003833.3+402133 were an old magnetar, or if its progenitor was a runaway star that traveled away from the plane prior to going supernova.

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