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Astron. Astrophys. 324, 941-942 (1997)

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Research Note

X-ray variability in the quiescent state of Centaurus X-4

S. Campana 1, 2, S. Mereghetti 3, L. Stella 4, 2 and M. Colpi 5

1 Osservatorio Astronomico di Brera, Via Bianchi 46, I-22055 Merate (Lc), Italy
2 Affiliated to I.C.R.A.
3 Istituto di Fisica Cosmica del C.N.R., Via Bassini 15, I-20133 Milano, Italy
4 Osservatorio Astronomico di Roma, Via dell'Osservatorio 2, I-00040 Monteporzio Catone (Roma), Italy
5 Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, I-20133 Milano, Italy

Received 5 December 1996 / Accepted 29 January 1997

Abstract

We report on a ROSAT-HRI observation of the soft X-ray transient Cen X-4 during quiescence. We discover a variation in the flux by a factor of 3 in less than four days. This relatively fast variation, the first observed from a quiescent soft X-ray transient, rules out some of the emission mechanisms that have been proposed for the quiescent flux. Accretion either onto the neutron star surface or onto the magnetospheric boundary is clearly favored.

Key words: stars: individual: Cen X-4 – X-ray: stars

Send offprint requests to: Sergio Campana (campana@merate.mi.astro.it)

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© European Southern Observatory (ESO) 1997

Online publication: May 5, 1998

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