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ATEL # 2567; E. Bozzo (ISDC, Switzerland), T. Belloni (INAF-OAB, Italy), G. Israel (INAF-OAR, Italy), L. Stella (INAF-OAR, Italy)
on 16 Apr 2010; 1:48 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: Tomaso Belloni (email@example.com)
Subjects: X-ray, Request for Observations, Binaries, Neutron Stars, Transients
Referred to by ATEL #: 2568, 2569, 2576
Following the discovery of millisecond pulsations at ~518 Hz in the X-ray emission of Swift J1749-2807 (Atel 2565), a number of follow-up observations with RXTE have been triggered. We report here on the observation carried out on 15 April 2010 from 16:49:20UT to 17:44:48 (UT). The total effective exposure time was 3152 s. In this observation, the net 2-33 keV source count rate was 40 cts/s/PCU (with 2 PCUs active). The Fourier analysis in these data revealed the presence of pulsations at a mean (not barycentered) frequency of 1035.6 Hz. No evidence is found for the previously reported pulsation at 518 Hz (Atel 2565). Apparently, only the first overtone is now visible, indicating that most likely Swift J1749-2807 has switched to a two-pole accretion. Other Swift and RXTE observations of the source are already planned. Observations at other wavelength are strongly encouraged.