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Astron. Astrophys. 360, L31-L34 (2000)


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Letter to the Editor

Unusual quiescent X-ray activity from XTE J0421+560 (CI Cam)

A.N. Parmar 1, T. Belloni 2, M. Orlandini 3, D. Dal Fiume 3, A. Orr 1 and N. Masetti 3

1 Astrophysics Division, Space Science Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands
2 Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate, Italy
3 Istituto Tecnologie e Studio Radiazioni Extraterrestri, CNR, Via Gobetti 101, 40129 Bologna, Italy

Received 23 May 2000 / Accepted 30 May 2000

Abstract

We report on BeppoSAX observations of the X-ray transient XTE J0421+560 in quiescence 156, 541, and [FORMULA]690 days after the maximum of the 1998 April outburst. In the first observation the source was soft with a power-law photon index, [FORMULA], of [FORMULA] and absorption, [FORMULA], of [FORMULA] atom cm-2. In the second observation, the source brightened by a factor [FORMULA]15 in the 1-10 keV energy range, became significantly harder with [FORMULA] and was strongly absorbed with [FORMULA]. There is evidence for a narrow emission line in both spectra at [FORMULA]7 keV. In the third observation, the source had faded by a factor [FORMULA]8 from the previous observation to below the BeppoSAX detection level. It is possible that these variations result from orbital motion of a compact object around the B[e] star companion with the intense, absorbed, spectrum arising during passage through dense circumstellar material. If this is the case, the system may be continuing to exhibit periodic activity.

Key words: stars: binaries: symbiotic – stars: individual: – stars: novae, cataclysmic variables – X-rays: stars

Send offprint requests to: A.N.Parmar (aparmar@astro.estec.esa.nl)

© European Southern Observatory (ESO) 2000

Online publication: August 23, 2000

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