Issue |
A&A
Volume 459, Number 3, December I 2006
|
|
---|---|---|
Page(s) | 901 - 907 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20065933 | |
Published online | 12 September 2006 |
XMM-Newton observation of a spectral state transition in the peculiar radio/X-ray/γ-ray source LS I +61 303
1
Istituto di Astrofisica Spaziale e Fisica Cosmica, Sezione di Milano, INAF-IASF, Milano 20133, Italy e-mail: sidoli@iasf-milano.inaf.it
2
CIFS, Torino 10133, Italy
3
Istituto di Astrofisica Spaziale e Fisica Cosmica, Sezione di Roma, INAF-IASF, Roma 00133, Italy
4
Dipartimento di Fisica, Università di Tor Vergata, Roma 00133, Italy
Received:
29
June
2006
Accepted:
24
August
2006
We report the results of XMM-Newton and BeppoSAX observations of the
radio and X-ray emitting star LS I +61 303, likely associated with the gamma-ray
source 2CG 135+01 and recently detected also at TeV energies. The data
include a long XMM-Newton pointing carried out in January 2005,
which provides the
deepest look ever obtained for this object in the 0.3–12 keV range. During
this observation the source flux decreased from a high level of
~13 10-12 erg cm-2 s-1 to
4
10-12 erg cm-2 s-1 within 2–3 h.
This flux range is the same seen in shorter and less sensitive
observations carried out in the past, but the new data show for the first time that transitions between the two levels can occur on short time scales.
The flux decrease was accompanied by a significant softening of the
spectrum, which is well described by a power law with photon index
changing from 1.62 ± 0.01 to 1.83 ± 0.01.
A correlation between hardness and intensity is also found when comparing
different short observations spanning almost 10 years and covering various
orbital phases.
LS I +61 303 was detected in the 15–70 keV range with the PDS instrument in
one of the BeppoSAX observations, providing evidence for variability also
in the hard X-ray range. The X-ray spectra, discussed in the context of
multiwavelength observations, place some interesting constraints on the
properties and location of the high-energy emitting region.
Key words: X-rays: binaries / X-rays: individuals: LS I +61 303 / X-rays: individuals: GT 0236+610
© ESO, 2006
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