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SWIFT J1729.9-3437: X-ray Position and Likely 530 sec Pulsations

ATEL # 2749; C. B. Markwardt (NASA/GSFC), H. A. Krimm (USRA & NASA/GSFC), J. H. Swank (NASA/GSFC)
on 21 Jul 2010; 3:39 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)

Subjects: X-ray, Gamma Ray, Binaries, Black Holes, Neutron Stars, Pulsars, Transients

Regarding the newly detected transient source SWIFT J1729.9-3437 (ATEL #2747), we report an X-ray position by Swift and the detection of possible pulsations at 530 sec by RXTE.

Swift observed the source with the X-ray Telescope (XRT) starting at 2010-07-20 at 15:00 UT for a total observation of 2.3 ks. The image shows a bright point source at coordinates R.A.=262.53746, Decl.=-34.61239 (J2000) with an uncertainty of 1.7" (90% confidence). This is 2.4' from the original Swift/BAT position.

RXTE observed the source starting at 2010-07-20 at 18:01 UT for a total good time of 1.5 ks. The 2-10 keV light curve is highly variable, with a suggested period of 530 sec. Given the exposure length, we would have detected fewer than 3 putative cycles, so such a detection should be viewed with caution. If confirmed, this detection would identify the source as an X-ray pulsar.

Analysis of the RXTE PCA data suggests a absorbed cut-off power-law model with nH = 4.1 +/- 0.5 x 10^22 cm^-2, a photon index of 0.84 +/- 0.1 and high energy cut-off of 13 keV. A weak line at 6.6 keV may be due to contamination from the galactic ridge in the field of view. The estimated fluxes in the 2-10, 10-20 and 20-40 keV bands are 2.4, 2.1 and 1.5 (in units of 1 x 10^-10 erg cm^-2 s^-1). Preliminary spectral analysis of the XRT data gives an absorbed power-law model gives a photon index of 1.91 0.45 and nH = 9.6 1.9 x 10^22 cm^-2. The observed 0.3-10 keV flux is 2.61 (+0.14, -1.66) x 10^-10 erg cm^-2 s^-1, and the unabsorbed flux is 9.7 x 10^-10 erg cm^-2 s^-1. The PCA and XRT parameters are different, likely because of different models and different instrumental pass-bands.

The most recent daily average rate in the Swift BAT (15-50 keV) is 0.0062 0.0011 ct cm^-2 s^-1 (~28 mCrab) on 2010-07-20, suggesting a slight increase compared to the results presented in ATel #2747.

The XRT work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester and the enhanced position was derived using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalog.


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