Issue |
A&A
Volume 418, Number 3, May II 2004
|
|
---|---|---|
Page(s) | 1061 - 1072 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20034550 | |
Published online | 16 April 2004 |
Discovery of X-ray absorption features from the dipping low-mass X-ray binary XB 1916-053 with XMM-Newton
1
Astrophysics Missions Division, Research and Scientific Support Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands
2
Centre d'Etude Spatiale des Rayonnements, CNRS/UPS, 9 Av. du Colonel Roche, 31028 Toulouse Cedex 4, France
3
Laboratoire d'Astrophysique de Marseille, Traverse du Siphon, BP 8, 13376 Marseille Cedex 12, France
4
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street Cambridge, MA 02138, USA
Corresponding author: L. Boirin, L.Boirin@sron.nl
Received:
21
October
2003
Accepted:
3
February
2004
We report the discovery of narrow
and
Kα X-ray absorption lines at 6.65
and 6.95
keV in the persistent emission of the
dipping low-mass X-ray binary (LMXB) XB 1916-053 during an XMM-Newton
observation performed in September 2002. In addition,
there is marginal evidence for absorption features at 1.48 keV,
2.67 keV, 7.82 keV and 8.29 keV consistent with
,
,
Kα and
Kβ transitions, respectively. Such absorption lines from
highly ionized ions are now observed in a number of high inclination
(i.e. close to edge-on) LMXBs, such as XB 1916-053, where the inclination
is estimated to be between 60–80°. This, together with the
lack of any orbital phase dependence of the features (except during
dips), suggests that the highly ionized plasma responsible for the
absorption lines is located in a cylindrical geometry around the
compact object. Using the ratio of
and
column densities, we estimate the photo-ionization
parameter of the absorbing material, ξ, to be 103.92 . Only the
line is observed during dipping intervals
and the upper-limits to the
column density are consistent
with a decrease in the amount of ionization during dipping intervals.
This implies the presence of cooler material in the line of sight
during dipping. We also report the discovery of a 0.98 keV absorption
edge in the persistent emission spectrum. The edge energy decreases
to 0.87 keV during deep dipping intervals. The detected feature may
result from edges of moderately ionized Ne and/or Fe with the average
ionization level decreasing from persistent emission to deep
dipping. This is again consistent with the presence of cooler material
in the line of sight during dipping.
Key words: accretion, accretion disks / stars: individual: XB 1916-053 / X-rays: binaries
© ESO, 2004
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