XMM-Newton: pulsed heartbeat of a weird new type of star (Forwarded)

ESA News
http://www.esa.int

21 December 2007

XMM-Newton: pulsed heartbeat of a weird new type of star

XMM-Newton has detected periodic X-ray emission, or the pulsed heartbeat of
a weird new type of star. Collecting the X-rays from the so-called rotating
radio transient has confirmed the nature of the underlying celestial object
and given astronomers a new insight into these exotic objects.

The observations were made using XMM-Newton's European Photon Imaging Camera
(EPIC), which targeted the celestial object RRAT J18191458. Astronomers
observed the object for around 12 hours and detected pulsations in the X-ray
data that show the source to be rotating once every 4.26 seconds.

Previously, astronomers had only seen radio outbursts from this object. It
erupts every three minutes or so with a brief burst of radio emission
lasting just 3 milliseconds. Such behaviour defines the object as a rotating
radio transient (RRAT).

The RRATs were announced in February 2006. Eleven objects were found using
the Parkes radio telescope. Astronomers suspected that RRATs were neutron
stars, the compact remnants of dead stars made of neutrons and measuring
just 1012 km across yet containing more matter than the Sun. They are
therefore extremely dense. Most observed neutron stars are radio pulsars;
rotating quickly and sweeping lighthouse beams of radiation across space
that make them appear to pulsate. The RRATs, however, were only detected
through their radio bursts.

The new XMM-Newton observations show that periodic emission, linked to the
object's rotation, can be detected in X-rays. "It is now definite that RRATs
are rotating neutron stars as we can see the 4.26-second rotation period of
the RRAT in the X-ray data," says Maura McLaughlin, West Virginia
University, USA, who took the lead in the research.

In addition to the identification of the underlying celestial object from
the discovery of the X-ray pulsations, XMM-Newton also revealed another
facet of the RRAT's behaviour. Something appears to be absorbing certain
frequencies of the X-rays after they are emitted from the surface of the
neutron star.

The absorption could either be happening in an atmosphere of gases
surrounding the neutron star or by particles trapped in the neutron star's
magnetic field. If the second reason is the cause of the absorption, it
would indicate that the magnetic field of this RRAT is strong.

"We can't say for sure where the absorption is coming from with these
observations," says Nanda Rea, University of Amsterdam, Netherlands. She
estimates that an observation twice as long would collect enough data to
determine where the absorption is taking place.

She also hopes to follow-up this observation by targeting other RRATs.
Before that can happen, however, the team must refine the positions they
have for these objects. To do this, they continue to observe the RRATs with
radio telescopes across the world, timing the outbursts. From careful
measurements of the arrival times of the bursts over the course of the year,
their positions in the sky can be determined more accurately. Once these
locations are known, X-ray telescopes can be pointed in their direction.

Since the original discovery of 11 RRATs, McLaughlin's team has found an
additional 10. This indicates that they may form a substantial population in
the Milky Way, with over 100 000 of them dotted around our galaxy.

Notes for editors:

Discovery of pulsations and a possible spectral feature in the X-Ray
emission from rotating radio transient J18191458 by M. McLaughlin, N. Rea,
B. Gaensler, S. Chatterjee, F. Camilo, M. Kramer, D. Lorimer, A. Lyne, G.
Israel, and A. Possenti is published in The Astrophysical Journal.

For more information:

Maura McLaughlin, West Virginia University, USA
Email: maura.mclaughlin @ mail.wvu.edu

Nanda Rea, University of Amsterdam, the Netherlands
Email: nrea @ science.uva.nl,

Andrew Lyne, Jodrell Bank Observatory, UK
Email: andrew.lyne @ manchester.ac.uk

Bryan Gaensler, University of Sydney, Australia
Email: bgaensler @ usyd.edu.au

Norbert Schartel, ESA XMM-Newton Project Scientist
Email: Norbert.Schartel @ esa.int

[NOTE: Images supporting this release are available at
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