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A&A 420, 527-532 (2004)
DOI: 10.1051/0004-6361:20040113
The high energy X-ray tail of
Car revealed by BeppoSAX
R. F. Viotti1, L. A. Antonelli2, C. Rossi3 and S. Rebecchi4
1 Istituto di Astrofisica Spaziale e Fisica Cosmica, CNR, Area di Ricerca Tor Vergata, Via del Fosso del Cavaliere 100, 00133 Roma, Italy
2 INAF-Osservatorio Astronomico di Roma, Via di Frascati 33, 00040 Monte Porzio Catone, Roma, Italy
3 Dipartimento di Fisica, Università La Sapienza, Piazzale Aldo Moro 3, 00185 Roma, Italy
4 ASI Science Data Center (ASDC), c/o ESA-ESRIN, Via Galileo Galilei, 00044 Frascati, Roma, Italy
(Received 27 December 2003 / Accepted 10 February 2004 )
Abstract
We report on the June 2000 long (100 ks) BeppoSAX exposure that unveiled
a new very high energy component of the X-ray spectrum
of
Car above 10 keV extending to at least 50 keV.
We find that the 2-150 keV spectrum is best reproduced
by a thermal + non-thermal model.
The thermal component dominates the 2-10 keV spectral
range with kTh
= 5.5
0.3 keV and log NH
h
= 22.68
0.01.
The spectrum displays a prominent iron emission line centred
at 6.70 keV. Its equivalent width of 0.94 keV,
if produced by the thermal source, gives a slightly
sub-solar iron abundance ([Fe/H]
= -0.15
0.02).
The high energy tail above 10 keV is best fitted by a power law
with a photon index of 2.42
0.04.
The integrated 13-150 keV luminosity of ~12
is
comparable to that of the 2-10 keV thermal component (19
).
The present result can be explained,
in the
Car binary star scenario,
by Comptonisation of low frequency radiation by high energy
electrons, probably generated in the colliding wind shock front,
or in instabilities in the wind of the S Dor primary star.
It is possible that the high energy tail had
largely weakened near the minimum of the 5.53 yr cycle.
Probably, the thermal component has a longer recovery time like
that of the highest excitation optical emission lines.
Both features can be associated with the large absorption
measured by BeppoSAX at phase 0.05.
Key words: radiation mechanisms: non-thermal -- stars: individual:
Car -- stars: winds, outflows - X-rays: stars
Offprint request: R. Viotti, uvspace@rm.iasf.cnr.it
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