Unveiling soft gamma-ray repeaters with INTEGRAL

Abstract

Thanks to INTEGRAL's long exposures of the Galactic Plane, the two brightest Soft Gamma-Ray Repeaters, SGR 1806-20 and SGR 1900+14, have been monitored and studied in detail for the first time at hard-X/soft gamma rays.This has produced a wealth of new scientific results, which we will review here. Since SGR 1806-20 was particularly active during the last two years, more than 300 short bursts have been observed with INTEGRAL and their characteristics have been studied with unprecedented sensitivity in the 15-200 keV range. A hardness-intensity anticorrelation within the bursts has been discovered and the overall Number-Intensity distribution of the bursts has been determined. In addition, a particularly active state, during which 100 bursts were emitted in 10 minutes, has been observed on October 5 2004, indicating that the source activity was rapidly increasing. This eventually led to the Giant Flare of December 27th 2004, for which a possible soft gamma-ray (>80 keV) early afterglow has been detected.

XMM–Newton observations of soft gamma-ray repeaters

“…On the other hand, the XMM-Newton data showed a doubling of the flux in SeptemberOctober 2004 followed by a gradual recovery to the "historical" level during the observations performed after the gi- ant flare. Interestingly, the same trend was seen above 20 keV with INTEGRAL (Mereghetti et al 2005b;Götz et al 2006a), as well as in the flux of the NIR counterpart Israel 2006). …”

“…Since spectral hardening, spin-down rate, and bursting rate increase with the twist angle, it is not surprising that these quantities varied in a correlated way in SGR 1806−20 (see Fig. 6 and Götz et al 2006a). However, as visible in Fig.…”

“…These observations, coupled with similar programs carried out with ESO telescopes in the infrared band (Israel 2006) and at hard X-ray energy with INTEGRAL (Götz et al 2006a) and Suzaku, can be used to study the connection between the persistent emission and the source activity level, as manifested by the emission of bursts and flares.…”

“…SGR 1806−20 is the target of an ongoing campaign of XMM-Newton observations aimed at studying in detail the long term variations in the properties of its persistent emission. These observations, coupled with similar programs carried out with ESO telescopes in the infrared band (Israel 2006) and at hard X-ray energy with INTEGRAL (Götz et al 2006a) and Suzaku, can be used to study the connection between the persistent emission and the source activity level, as manifested by the emission of bursts and flares.…”

The birthrate of magnetars

“…Recently, hard X-ray emission has been detected from three AXPs (4U 0142+61, 1E 1841-045, 1RXS J170849.0-400910) by INTEGRAL space telescope operating in the 15 keV -10 MeV energy range (Gotz et al 2006). Furthermore, an all sky survey, conducted by using the coded mask IBIS telescope on board INTEGRAL, has identified various high energy galactic sources, a few among them (∼ 42) are yet to be identified (Krivonos et al 2007).…”