Swift/BAT Discovery of the Orbital Period of IGR J16320-4751
ATel #649; R. Corbet (GSFC/USRA), L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (UMD), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS), J. Tueller (GSFC), on behalf of the Swift-Survey team
on 2 Nov 2005; 19:50 UT
Credential Certification: Robin Corbet (firstname.lastname@example.org)
Subjects: X-ray, Gamma Ray, Binary, Neutron Star, Transient, Pulsar
Referred to by ATel #: 2588
The Swift/Burst Alert Telescope (BAT) light curve of the X-ray pulsar
IGR J16320-4751 obtained between 2004 Dec 21 and 2005 Sep 17 shows a
strong modulation at a period of 8.96 days.
The mean BAT count rate of IGR J16320-4751 in the range 14 - 200 keV
is 5.7E-4 counts/s which corresponds to approximately 13 mCrab. Most
photons are detected below 50 keV.
The Fourier amplitude of the modulation is 3.5(+/- 0.3)E-4 counts/s.
A sine wave fit to the BAT light curve gives parameters of period =
8.96 +/- 0.01 days and epoch of maximum flux = MJD 53507.1 +/- 0.1.
We interpret this modulation as revealing the orbital period of a
binary system. This source has a pulsation period of ~1300s
(Lutovinov et al., 2005, A&A, 433, L41) and the location of this
system on the pulse/orbital period diagram (Corbet, 1986, MNRAS, 220,
1047) suggests that it consists of a neutron star accreting from the
wind of an early spectral type supergiant.