EDP Sciences
Free access
Volume 372, Number 1, June II 2001
Page(s) 241 - 244
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20010490

A&A 372, 241-244 (2001)
DOI: 10.1051/0004-6361:20010490

A BeppoSAX view of transient black hole candidates in quiescence

S. Campana1, A. N. Parmar2 and L. Stella3

1  Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (Lecco), Italy
2  Astrophysics Division, Space Science Department of ESA, ESTEC, PO Box 299, 2200 AG Noordwijk, The Netherlands
3  Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monteporzio Catone (Roma), Italy

(Received 5 March 2001 / Accepted 2 April 2001 )

We report BeppoSAX observations of five transient black hole candidates during their quiescent phase. We confirm that these sources are X-ray faint, improving on and complementing existing upper limits. We derive 1-10 keV upper limits for GRO J0422+32, GRS 1009-45, 4U 1630-47 and XTE J1748-288, which range from $2\times 10^{32}\rm erg s^{-1}$ to $5\times 10^{34}\rm erg s^{-1}$. We positively detect GS 2023+338. Its X-ray spectrum can be fit by a power law (photon index $\Gamma=1.9$) or a thermal bremsstrahlung (with $k T_{\rm br}= 7$ keV), converting in both cases to a 1-10 keV unabsorbed luminosity of ~ $10^{33}\rm erg s^{-1}$. These values are comparable to the ones derived during an ASCA observation in 1994, indicating that the source remains stable over a ~5 yr baseline.

Key words: binaries: general -- black hole physics -- X-rays: stars

Offprint request: S. Campana, campana@mera te.mi.astro.it

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© ESO 2001