Issue |
A&A
Volume 420, Number 2, June III 2004
|
|
---|---|---|
Page(s) | 527 - 532 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20040113 | |
Published online | 28 May 2004 |
The high energy X-ray tail of
Car revealed by BeppoSAX*
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
Corresponding author: R. Viotti, uvspace@rm.iasf.cnr.it
Received:
27
December
2003
Accepted:
10
February
2004
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 η 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 NHh = 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 η 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: η Car / stars: winds, outflows - X-rays: stars
© ESO, 2004
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