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A&A 433, L9-L12 (2005)
DOI: 10.1051/0004-6361:200500088
Letter
INTEGRAL discovery of persistent hard X-ray emission from the Soft Gamma-ray Repeater SGR 1806-20
S. Mereghetti1, D. Götz1, I. F. Mirabel2 and K. Hurley31 Istituto di Astrofisica Spaziale e Fisica Cosmica - Sezione di Milano "G. Occhialini" - INAF, via Bassini 15, 20133 Milano, Italy
e-mail: sandro@mi.iasf.cnr.it
2 European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile
3 University of California at Berkeley, Space Sciences Laboratory, Berkeley, CA 94720-7450, USA
(Received 26 November 2004 / Accepted 27 December 2004 )
Abstract
We report the discovery of persistent hard X-ray
emission extending up to 150 keV from the soft gamma-ray repeater
SGR 1806-20 using data obtained with the INTEGRAL satellite in
2003-2004. Previous observations of hard X-rays from objects of
this class were limited to short duration bursts and rare
transient episodes of strongly enhanced luminosity ("flares").
The emission observed with the IBIS instrument above 20 keV has a
power law spectrum with photon index in the range 1.5-1.9 and a
flux of 3 milliCrabs, corresponding to a 20-100 keV luminosity of
~1036 erg s-1 (for a distance of 15 kpc). The
spectral hardness and the luminosity correlate with the level of
source activity as measured from the number of emitted bursts.
Key words: gamma rays: bursts -- pulsars: general -- stars: individual: SGR 1806-20
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