XMM-Newton TOO observation of the SMC field around XTE J0055-727: Two transient X-ray pulsars in outburst (XMMU J005455.4-724512 and XMMU J005517.9-723853).

ATel #219; F. Haberl (MPE), W. Pietsch (MPE), N. Schartel (ESA, Vilspa), P. Rodriguez (ESA, Vilspa) and R. H.D. Corbet (GSFC and USRA)
on 22 Jan 2004; 08:15 UT
Credential Certification: Frank Haberl (fwh@mpe.mpg.de)

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An XMM-Newton target of opportunity observation of the field around the transient pulsar XTE J0055-727 (ATEL #214) in the Small Magellanic Cloud was performed on 2003-12-18 between 14:32 UT and 19:48 UT. Two bright X-ray sources were detected by the EPIC instruments. XMMU J005455.4-724512 is consistent in position with CXOU J005455.6-724510 = RX J0054.9-7245 = AX J0054.8-7244 (ATEL #217) and a pulse period of 499.2 +/- 0.7 s was derived. A preliminary spectral analysis reveals a spectrum typical for a (Be) high mass X-ray binary pulsar with a luminosity of 4.3 x 10^35 erg/s (0.5 - 10 keV) for an assumed SMC distance of 60 kpc. The second source XMMU J005517.9-723853 shows a similar X-ray spectrum with a luminosity of 2.9 x 10^35 erg/s (0.5 - 10 keV) and pulsations with a period of 701.6 +/- 1.4 s were discovered. The position of this new pulsar is R.A. = 00h55m17.9s Decl. = -72d38m53s (equinox 2000) with a 3 arcsec systematic 90% confidence error and is located within the 9 arcsec error radius of the ROSAT source RX J0055.2-7238 (Haberl et al. 2000, A&AS 142, 41). Several other weak sources were seen in the EPIC images but the fluxes of these sources are too low for pulsations to be detected. The 18.37 s pulsations from XTE J0055-727 were still detected from an RXTE observation on 2003-12-15 but not seen during an RXTE observation on 2003-12-20 which, together with the XMM-Newton observation, indicates that XTE J0055-727 faded between 2003-12-15 and 2003-12-18.