RXTE detects a coherent signal at ~ 401 Hz from IGR J17498-2921.
ATel #3556; A. Papitto (Univ. Cagliari), C. Ferrigno, E. Bozzo, L. Gibaud (ISDC, Switzerland), L. Burderi (Univ. Cagliari), T. Di Salvo (Univ. Palermo), A. Riggio (INAF OAC)
on 13 Aug 2011; 10:54 UT
Credential Certification: Carlo Ferrigno (Carlo.Ferrigno@unige.ch)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
Referred to by ATel #: 3558, 3560, 3561, 3563, 3568, 3601, 3606, 3622, 3638, 3643, 3646, 3661
A RXTE Target of Opportunity pointed observation of the newly
discovered transient IGR J17498-2921 (ATsLs #3551, #3555) began at roughly
2011-09-13 02:19 UTC, for an exposure of 1.8 ks. The observed flux in
the 2-30 keV energy band is 1.1(1)e-9 erg/s/cm2. Such a value is
probably an over-estimate of the source flux, because of the
contribution by the emission of the Galactic ridge.
Power density spectra produced every 256s reveal the presence of a
signal at a frequency between 400.95 and 401.0 Hz, making this source
a candidate accreting millisecond pulsar. Taking into account the
number of frequencies searched in each of the intervals (2**20), the
signal is detected at a significance in excess of 4.7 sigma in all but
one of the 256s interval considered. The frequency is observed to vary
by ~0.05 Hz during the observation. Such a variation is possibly
caused by the uncorrected orbital motion of the spacecraft and/or of
the NS in the system. By considering only the intervals during which
the signal is significantly detected, we set a lower limit of 0.027 on
the RMS fractional amplitude of the signal (3 sigma confidence level).
Further observations at these and other wavelengths are strongly
We thank the RXTE team for the prompt scheduling of this observation.