Orbital Parameters of SWIFT J1756.9-2508
ATel #1114; C. B. Markwardt (CRESST/U. Md./GSFC) and H. A. Krimm (CRESST/USRA/GSFC)
on 16 Jun 2007; 01:14 UT
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)
Subjects: X-ray, Gamma Ray, Binary, Neutron Star, Transient, Pulsar
We report on high time resolution properties of the 182 Hz X-ray
pulsar SWIFT J1756.9-2508 (ATEL #1105, #1107, #1108, #1111).
The RXTE PCA instrument has performed several observations of the
source since its discovery for a total of 13 ksec. Over 1.3 days, the
source has faded from 20 to 17 mCrab (2-10 keV).
Pulsations continue to be detectable in the PCA data, and the clear
signatures of orbital Doppler modulation are present. The orbital
period is 54 minutes, and the pulsar mass function is (1.66 +/- 0.25)
x 10^{-7} M_sun (i.e. minimum companion mass of ~0.007 M_sun). The
orbital period and mass function place J1756 as one of the
"ultra-compact" X-ray binary systems, and very similar to the
two other short orbital-period millisecond X-ray pulsars XTE J0929-314
and XTE J1807-294.
No strong high or low frequency QPOs are detected.
