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Identification of the Be/X-ray binary transient XMMU J004911.4-724939 in the SMC with the pulsar XTE J0055-727

ATEL # 1453; P. Eger, F. Haberl (Max-Planck-Institut fuer extraterrestrische Physik)
on 1 Apr 2008; 14:23 UT
Password Certification: Frank Haberl (

Subjects: X-ray, Binaries, Neutron Stars, Pulsars, Transients

During a 39 ks XMM-Newton observation on 2007 March 12-13 of the emission nebula N19 in the Small Magellanic Cloud (SMC) a bright X-ray transient at (J2000) R.A. = 00 49 11.4 Dec. = -72 49 39 was observed. Our timing analysis revealed X-ray pulsations with a period of 18.3814(1) s, which identifies the source, designated XMMU J004911.4-724939, with XTE J0055-727 = SXP18.3 (Corbet et al. 2003, ATEL #214), which was discovered with a period of 18.37 s +/- 0.1 s. The EPIC X-ray spectra are well represented by an absorbed powerlaw with photon index 0.65 +/- 0.05 and a column density of (2.0 +/- 0.2)E22 cm-2. The 0.5-10.0 keV flux was 1.2E-11 erg s-1 cm-2, corresponding to a source luminosity of 5.5E36 erg s-1, for a distance of 60 kpc. The X-ray position (systematic uncertainty ~2 arsec) is consistent with that of a V=16.0 mag star with typical properties of a Be star (Zaritsky et al. 2002, AJ 123, 855). Analysis of the extracted MACHO and OGLE light curves shows two optical outbursts, lasting about 330 and 270 days with brightness increases by ~0.55 and ~0.50 mag (in B), ~0.8 mag and ~0.6 (in R) for the two outbursts, respectively, and ~0.75 mag (in I) for the second outburst. Similar behaviour is also observed from other Be stars (Mennickent et al. 2002, A&A 393, 887). We conclude that XMMU J004911.4-724939 is a Be/X-ray binary pulsar in the SMC, and identical to XTE J0055-727.

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