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Astron. Astrophys. 340, L19-L22 (1998)

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1. Introduction

Relativistic galactic jet sources are usually seen in X-ray binaries, where a black hole or neutron star is accreting from a "normal" star. Recently a new galactic jet source, XTE J0421+560, was discovered by the Rossi-XTE satellite as a bright and rapidly rising X-ray transient on 1998 March 31 (Smith et al. 1998). The source reached a peak intensity of [FORMULA]2 Crabs on April 1, before rapidly decaying. Radio observations quickly allowed the identification of the optical counterpart with the binary system CI Cam (= MWC 84). Miroshnichenko (1995) and Bergner et al. (1995) model CI Cam as a K0 II -B0 V system embedded in a hot circumstellar dust shell. Chkhikvadze (1970) estimates the interstellar extinction (1.5 mag.) and the distance (1 kpc) of CI Cam. Optical spectra before and after the outburst exhibit strong Balmer and He I emission lines (Merrill 1933). He II lines appeared after the outburst (Wagner & Starrfield 1998). Within a week of the X-ray outburst, extended radio emission appeared in the form of an S-shaped jet. If the X-ray and radio outbursts are assumed contemporaneous, for a distance of 1 kpc, the rate of expansion of the radio emission implies a tangential velocity of 0.15 c (Hjellming & Mioduszewski 1998).

In this Letter we describe the BeppoSAX spectra of XTE J0421+560 in the days following the 1998 March 31 outburst. X-ray and optical timing analysis and light curves are presented in Frontera et al. (1998).

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© European Southern Observatory (ESO) 1998

Online publication: November 9, 1998