Issue |
A&A
Volume 433, Number 2, April II 2005
|
|
---|---|---|
Page(s) | L13 - L16 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361:200500087 | |
Published online | 22 March 2005 |
Letter to the Editor
The broad-band spectrum of the persistent emission from SGR 1806-20*
1
Space Research Institute, Russian Academy of Sciences, Profsouznaya 84/32, 117997 Moscow, Russia e-mail: molkov@hea.iki.rssi.ru
2
Max-Plank-Institute für Astrophysik, Karl-Schwarzschild-Str. 1, 85740 Garching-bei-München, Germany
3
University of California at Berkeley, Space Sciences Laboratory, 7 Gauss Way, Berkeley, CA 94720-7450, USA
4
National Space Science Technology Center, NASA/MSFC, XD-12, Huntsville, AL 35805, USA
Received:
26
November
2004
Accepted:
16
February
2005
We present the results of an analysis of the quiescent X-ray
emission from the
Soft Gamma-Ray Repeater SGR 1806-20, taken during an INTEGRAL ultra-deep
survey of the
Galactic center region in Aug.-Sep. 2003. The total effective exposure time
spent on the source by the IBIS telescope during these observations
was 1.6 million seconds. Combining the INTEGRAL results with
results from the XMM-Newton observatory, we present the broad
band (1-200 keV) spectrum of the quiescent emission from this source.
This is the first spectrum of the persistent emission
from an SGR in the broad energy range up to 200 keV.
The spectrum of the source is very hard and has a power law
shape () without any trace of a high energy cutoff
up to ~160 keV.
No strong cyclotron line was detected in the persistent
spectrum. The luminosity of SGR 1806-20 in this range (1-200 keV) was
erg s-1 for an assumed distance of 15 kpc.
We show that weak undetected bursts should
not contribute significantly to the quiescent emission.
During our next observations
in August 2004 the source went into an active phase and its average
flux between powerful bursts was 2-3 times higher than in 2003.
During Aug.-Sep. 2003, two other SGR candidates, SGR 1801-23 and SGR 1808-20,
were in the field of view. Neither persistent hard X-ray emission nor
bursts were detected from them. The upper limit on the persistent flux
from each of them in the energy band
18-100 keV is about
erg s-1 cm-2.
Key words: gamma rays: bursts / pulsars: general / stars: individual: SGR 1806-20
© ESO, 2005
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