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PCA Discovery of a New 11 Minute X-ray Pulsar, XTE J1716-379

ATel #2148; C. B. Markwardt (U. Maryland & NASA/GSFC), J. H. Swank (NASA/GSFC), T. E. Strohmayer (NASA/GSFC), E. A. Smith (Wyle IS), D. M. Pereira (Wyle IS)
on 6 Aug 2009; 01:37 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)

Subjects: X-ray, Request for Observations, Binary, Cataclysmic Variable, Neutron Star, Transient, Pulsar

RXTE PCA scans of the galactic ridge region on 2009-07-25 detected a new source. Follow-up RXTE PCA observations have occurred approximately daily since 2009-07-27, including a scan for position. Initial observations showed that the source was "pulsed" with a period of approximately 11 minutes.

A dedicated PCA scan yielded a position of R.A. = 259.119, Decl. = -37.960 (J2000), and thus we designate the source XTE J1716-379. Because of the variability of the source, and contributions from the galactic plane, it is difficult to estimate a position uncertainty. We de-weighted the counts due of the source in order to account approximately for the variability. The estimated 2-sigma error contour is an ellipse with extents (-9,+6) arcmin in R.A. and (-7,+5) arcmin in Decl. There are no obvious counterparts in Simbad.

A Lomb-Scargle periodogram of a barycentered lightcurve shows a X-ray period of 11.1744(1) minutes, where the quoted error is 3 sigma in the last digit. While the periodogram is heavily aliased, the strongest peak is significantly higher than other aliases. The pulsed flux varies considerably during the observation set, starting at about 23% (r.m.s.) and dropping to about 12% (r.m.s.).

The mean flux also varies, from about 12 mCrab, down to 8 mCrab (2-10 keV). Both the pulsed and unpulsed flux vary considerably during the observations. The energy spectrum is consistent with a power law with photon index 1.90. In the raw spectrum there is an excess at 6.3 keV (equivalent width ~ 300 eV), but we cannot rule out contamination from the galactic ridge. Recent fluxes are of order 10, 4 and 4 in the 2-10, 10-20 and 20-40 keV bands respectively, in units of 10^{-11} erg/s/cm2. For an object at ~10 kpc, the luminosity would be ~10^{36} erg/s.

While the orbital period alone suggests a possible identification as an X-ray pulsar with Be star companion or an intermediate polar, the X-ray variability suggests it is a Be pulsar.