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ATEL # 1770; G.L. Israel (INAF-OA Roma), P. Esposito (INAF-IASF, Milan), N. Rea (U. Amsterdam), H. A. Krimm (CRESST/GSFC/USRA), D. M. Palmer (LANL), N. Gehrels (GSFC), S. Mereghetti, A. Tiengo, F. Senziani (INAF/IASF-Milan), D. Gotz (CEA-Saclay), S. Zane (UCL-MSSL) report on behalf of a larger collaboration
on 8 Oct 2008; 10:28 UT
Password Certification: GianLuca Israel (firstname.lastname@example.org)
Subjects: X-ray, Neutron Stars, Pulsars, Soft Gamma-ray Repeaters, Transients, Variables
Swift XRT monitored 1E1547.0-5408 in the latest 5 days starting from about 90 seconds since the BAT trigger (Krimm et al. GCN 8311, 8312). During this period observations in the WT mode were carried out for a total exposure time of about 37ks. After having removed bursts and corrected the photon arrival times to the barycenter of the Solar System, the dataset was used to infer a phase-coherent timing solution including both a period and period derivative component.
According to our preliminary analysis the period and period derivative of 1E1547.0-5408 are: P=2.071335(1)s and Pdot=5.7(5) x 10^-11 s/s (1 sigma uncertainties are reported). We note that the period derivative inferred at the time of the previous outburst was 2.318(5)x10^-11 s/s, with a very high second derivative (Camilo et al. 2007, ApJ, 666, L93; Camilo et al. 2008, ApJ, 679, 681). Therefore, our inferred period derivative value is a factor of two larger than the historical one. The above reported period is within 1-sigma from our first measurement (Esposito et al. 2008, ATel #1763) and at about 7-sigma from the recently reported value inferred from RXTE observations (Dib et al. 2008, ATel #1769).
The Swift monitoring of 1E1547.0-5408 is still ongoing.