1998A&A...337..772C

We report the discovery of a ∼96s period X-ray pulsar in the direction of the Large Magellanic Cloud (LMC). The BeppoSAX X-ray spectrum is well fitted by an absorbed power-law model with photon index ∼0.5. The unabsorbed luminosity in the 2-10keV energy range is ∼9x10³⁵erg/s. The BeppoSAX position (40" uncertainty radius) of 3C 273 was found to be consistent with that of the ASCA source AX J0448-70.4 and WGACAT (ROSAT PSPC) source 1WGA J0544.1-710. The source was detected four times between 1991 and 1996 at luminosity levels from ∼3x10³⁵ to 9x10³⁵erg/s (2-10keV), while during a relatively deep ROSAT HRI observation an extrapolated 2-10keV luminosity upper limit of ∼1x10³⁵erg/s was obtained. Timing analysis of the ASCA data confirmed the BeppoSAX period discovery. Long-term flux variability is evident in the ROSAT and Einstein data. We revealed a pronounced Hα activity from a bright (V≃15) likely Be-type star within the 8" ROSAT PSPC error circle. Its optical spectrum shows it is located in the LMC. These results strongly suggest that 3C 273 is a transient X-ray pulsar in a massive binary system.