* Astronomy

Blobrana · L

RE: SGR 1627-41

Blobrana · L

XMM-Newton has caught the fading glow of a tiny celestial object, revealing its rotation rate for the first time. The new information confirms this particular object as one of an extremely rare class of stellar zombie - each one the dead heart of a star that refuses to die.
There are just five so-called Soft Gamma-ray Repeaters (SGRs) known, four in the Milky Way and one in our satellite galaxy, the Large Magellanic Cloud. Each is between 10 and 30 km across, yet contains about twice the mass of the Sun. Each one is the collapsed core of a large star that has exploded, collectively called neutron stars.
What sets the Soft Gamma-ray Repeaters apart from other neutron stars is that they possess magnetic fields that are up to 1000 times stronger. This has led astronomers to call them magnetars.
SGR 1627-41 was discovered in 1998 by NASA's Compton Gamma Ray Observatory when it burst into life emitting around a hundred short flares during a six-week period. It then faded before X-ray telescopes could measure its rotation rate. Thus, SGR 1627-41 was the only magnetar with an unknown period.
Last summer, SGR 1627-41 flared back into life. But it was located in a region of sky that ESA's XMM-Newton was unable to point at for another four months. This was because XMM-Newton has to keep its solar panels turned towards the Sun for power. So astronomers waited until Earth moved along its orbit, carrying XMM-Newton with it and bringing the object into view. During that time, SGR 1627-41 began fading fast. When it came into view in September 2008, thanks to the superior sensitivity of the EPIC instrument on XMM-Newton, it was still detectable.

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Blobrana · L

Title: XMM-Newton discovery of 2.6 s pulsations in the soft gamma-ray repeater SGR 1627-41
Authors: P. Esposito, A. Tiengo, S. Mereghetti, G. L. Israel, A. De Luca, D. Götz, N. Rea, R. Turolla, S. Zane

After nearly a decade of quiescence, the soft gamma-ray repeater SGR 1627-41 reactivated on 2008 May 28 with a bursting episode followed by a slowly decaying enhancement of its persistent emission. To search for the still unknown spin period of this SGR taking advantage of its high flux state, we performed on 2008 September 27-28 a 120 ks long X-ray observation with the xmm satellite. Pulsations with P=2.594578(6) s were detected at a >6-sigma confidence level, with a double-peaked pulse profile. The pulsed fraction in the 2-12 keV range is 19% ±3% and 24% ±3% for the fundamental and the second harmonic, respectively. The observed 2-10 keV flux is 3.4E-13 erg/cm^2/s, still a factor ~5 above the quiescent pre burst-activation level, and the spectrum is well fitted by an absorbed power law plus blackbody model (photon index Gamma = 0.6, blackbody temperature kT = 0.5 keV, and absorption nH = 1.2E+23 cm^-2). We also detected a shell of diffuse soft X-ray emission which is likely associated to the young supernova remnant G337.0-0.1.

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Blobrana · L

Position(2000): RA = 16 35 52, Dec -47 35.2

Blobrana · L

Title: The 2008 May burst activation of SGR 1627-41
Authors: P. Esposito, G. L. Israel, S. Zane, F. Senziani, R. L. C. Starling, N. Rea, D. M. Palmer, N. Gehrels, A. Tiengo, A. De Luca, D. Götz, S. Mereghetti, P. Romano, T. Sakamoto, S. D. Barthelmy, L. Stella, R. Turolla, M. Feroci, V. Mangano

In May 2008 the soft gamma-ray repeater SGR 1627-41 resumed its bursting activity after nearly a decade of quiescence. After detection of a bright burst, Swift pointed its X-ray telescope in the direction of the source in less than five hours and followed it for over five weeks. In this paper we present an analysis of the data from these Swift observations and an XMM-Newton one performed when SGR 1627-41 was still in a quiescent state. The analysis of the bursts detected with Swift/BAT shows that their temporal and spectral properties are similar to those found in previous observations of SGR 1627-41 and other soft gamma-ray repeaters. The maximum peak luminosity of the bursts was about 2E+41 erg/s. Our data show that the outburst was accompanied by a fast flux enhancement and by a hardening of the spectrum with respect to the persistent emission.

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