2003IAUC.8220....1L

R. C. Lamb and T. A. Prince, California Institute of Technology; D. J. Macomb, Boise State University; and W. A. Majid, Jet Propulsion Laboratory, report that the possible anomalous x-ray pulsar (AXP) designated CXOU J010043.1-721134 has a pulse period of 8.02 s, rather than the previously reported 5.4-s period (Lamb et al. 2002, Ap.J. 574, L29) from Chandra ACIS-I data, which yield a Nyquist frequency of 0.154 Hz (6.48-s period): "In the Fourier transform of these data, two strong peaks at 0.125 and 0.184 Hz were observed with power values of 40, where the average power is normalized to 1. ROSAT data for this same source favored the higher frequency. However, new data for this source, from the XMM- Newton satellite (observation 0018540101), clearly show that the correct frequency is near 0.125 Hz. The XMM data were obtained with the PN detector, which has a digitization interval of 0.0734 s, giving a Nyquist frequency of 6.8 Hz, well above the region of interest. The times of arrival of 4048 source photons, collected in the 27300-s observation (epoch 2001 Nov. 21.015 UTC), were corrected to the solar-system barycenter. The Fourier transform of these corrected times show a strong peak at 0.124699(5) Hz with a normalized power value of 28. Power peaks at the second and third harmonics are present as well. The luminosity of the source (0.2-10 keV), corrected to the 60000-pc distance of the Small Magellanic Cloud, is 2.6 x 10**35 erg/s. By combining this observation with the Chandra observation made 189.934 days earlier, we derive a frequency time derivative of -4 ± 3 x 10**-13 s. The relative constancy of the luminosity of this source, its magnitude, and its small spin-down rate [time scale P/(dP/dt) about 10000 yr] are consistent with the characteristics of AXPs (cf. Mereghetti et al. 2002, http://xxx.lanl.gov/abs/astro-ph/?0205122)."