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RXTE observation of 2S 1553-542 at the time of recent flare

ATEL # 1373; Sabyasachi Pal (NCRA) and Mayukh Pahari (Pune University, NCRA)
on 29 Jan 2008; 17:48 UT
Password Certification: Sabyasachi Pal (

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

RXTE PCA has observed the transient X-ray pulsar 2S 1553-542, almost every day, from 6th January 2008, after Swift/BAT detected an increased activity from it (ATEL #1345, ATEL #1371). The fitted flux between 2 and 10 keV is varying between 9.6276e-10 ergs/cm^2/s and 2.2155e-09 ergs/cm^2/s excepting on 9th Jan 2008 (Observation Id 93426-01-02-03) when the flux was found to be 3.4483e-09 ergs/cm^2/s. The pulse period is found to be 9.29+-0.01s which indicates that the pulse period is almost constant from the June 1975 outburst (Kelly et al., 1983, ApJ, 274, 765). The pulse profile has one strong and one weak components, both in 2-10 and 50-100 keV range.

The spectrum is well fitted with a broken power law with break energy varying between 13.3 to 14.1 keV. The fitted hydrogen column density was varying between 3.66e22 to 4.75e22, with exception on 9th and 15th January 2008, where the best fitted column density was found to be 2.21e22 and 2.23e22 respectively. The low energy and high energy power law photon indexes were varying between 1.40 to 1.51 and 3.15 to 3.87 respectively. We detected iron line with 1.3+-0.1 keV equivalent width.

Further observation is planned by RXTE.

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R. E. Rutledge , Editor
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