On the nature of XTE J0421+560/CI camelopardalis

T. Belloni, S. Dieters, M. E. Van Den Ancker, R. P. Fender, D. W. Fox, B. A. Harmon, M. Van Der Klis, J. M. Kommers, W. H.G. Lewin, J. Van Paradijs

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39 Scopus citations


We present the results of an analysis of RXTE, BATSE, and optical/infrared data of the 1998 outburst of the X-ray transient system XTE J0421 + 560 (CI Cam). The X-ray outburst shows a very fast decay (initial e-folding time ∼0.5 days, slowing down to ∼2.3 days). The X-ray spectrum in the 2-25 keV band is complex, softening considerably during decay and with strongly variable intrinsic absorption. A strong iron emission line is observed. No fast time variability is detected (<0.5% rms in the 1-4096 Hz band at the outburst peak). The analysis of the optical/IR data suggests that the secondary is a B[e] star surrounded by cool dust, and places the system at a distance of ≳2 kpc. At this distance, the peak at 2-25 keV luminosity is ∼4 × 1037 ergs s-1. We compare the properties of this peculiar system with those of the Be/NS LMC transient A 0538-66 and suggest that CI Cam is of similar nature. The presence of strong radio emission during outburst indicates that the compact object is likely to be a black hole or a weakly magnetized neutron star.

Original languageEnglish (US)
Pages (from-to)345-352
Number of pages8
JournalAstrophysical Journal
Issue number1 PART 1
StatePublished - Dec 10 1999

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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