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ATEL # 1108; C. B. Markwardt (CRESST/U.Md./GSFC), H. A. Krimm (CRESST/USRA/GSFC), J. H. Swank (NASA/GSFC)
on 14 Jun 2007; 6:34 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Craig B. Markwardt (firstname.lastname@example.org)
Subjects: X-ray, Gamma Ray, Request for Observations, Binaries, Neutron Stars, Pulsars, Transients
Referred to by ATEL #: 1111
We report that the new transient SWIFT J1756.9-2508 (ATEL #1105) is the eighth known millisecond X-ray pulsar.
RXTE PCA observed the sources starting on 13 June 2007 (19:00 UTC) for about 1700 seconds. X-ray pulsations were detected at a (barycentered) frequency of 182.06 Hz, with an r.m.s. pulsed amplitude of a few percent. In a crude analysis, small changes in the pulse frequency are seen (of order mHz), which might be suggestive of orbital period modulation. However the current data span is far too short to capture a full orbital cycle, if such a cycle exists.
RXTE observations will continue for at least the next few days. Observations at other wavelengths are encouraged.