Volume 474, Number 2, November I 2007
|Page(s)||575 - 578|
|Section||Stellar structure and evolution|
|Published online||10 September 2007|
Swift/XRT monitoring of five orbital cycles of LS I +61° 303
Università degli Studi di Pavia, Dipartimento di Fisica Nucleare e Teorica and INFN-Pavia, via Bassi 6, 27100 Pavia, Italy e-mail: firstname.lastname@example.org
2 INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica Milano, via Bassini 15, 20133 Milano, Italy
3 NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
Accepted: 16 August 2007
Context.LS I +61° 303 is one of the most interesting high-mass X-ray binaries owing to its spatially resolved radio emission and its TeV emission, generally attributed to non-thermal particles in an accretion-powered relativistic jet or in the termination shock of the relativistic wind of a young pulsar. Also, the nature of the compact object is still debated. Only LS 5039 and PSR B1259-63 (which hosts a non-accreting millisecond pulsar) have similar characteristics.
Aims.We study the X-ray emission from LS I +61° 303 covering both short-term and orbital variability. We also investigate the source spectral properties in the soft X-ray (0.3–10 keV) energy range.
Methods.Twenty-five snapshot observations of LS I +61° 303 were collected in 2006 with the XRT instrument on-board the Swift satellite over a period of four months, corresponding to about five orbital cycles. Since individual data sets have too few counts for a meaningful spectral analysis, we extracted a cumulative spectrum.
Results.The count rate folded at the orbital phase shows a clear modulation pattern at the 26.5 days period and suggests that the X-ray peak occurs around phase 0.65. Moreover, the X-ray emission appears to be variable on a timescale of ~1 ks. The cumulative spectrum is well described by an absorbed power-law model, with hydrogen column density cm-2 and photon index . No accretion disk signatures, such as an iron line, are found in the spectrum.
Key words: X-rays: individual: LS I +61° 303 / X-rays: binaries
© ESO, 2007
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.