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Swift and RXTE Discovery of a New X-ray Transient, SWIFT J1729.9-3437

ATEL # 2747; C. B. Markwardt (NASA/GSFC), H. A. Krimm (USRA & NASA/GSFC), J. H. Swank (NASA/GSFC)
on 20 Jul 2010; 3:01 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: Craig B. Markwardt (

Subjects: X-ray, Gamma Ray, Request for Observations, Binaries, Black Holes, Neutron Stars, Pulsars, Transients
Referred to by ATEL #: 2749

We report the discovery of a new X-ray transient, designated SWIFT J1729.9-3437, based on Swift BAT all-sky monitoring and RXTE PCA monitoring scans of the galactic center region.

Swift BAT detected a new source starting on 2010-07-13 at a count rate (15-50 keV) of 0.0033 0.0009 ct/cm2/s (~15 mCrab) and rising steadily to 0.0055 0.0013 ct/cm2/s (~25 mCrab) on 2010-07-18. The cumulative significance for the past eight days is 8.1 sigma. The best-fit BAT position is R.A. = 262.503, Decl. = -34.640 degrees (J2000), with 3.0 arcmin position uncertainty (95% confidence).

Independently, RXTE PCA monitoring scans of the galactic center region detected a new transient source. The position of the source is consistent with the Swift BAT position. After reprocessing the PCA data retrospectively with that position, the source was detected at 2-10 keV fluxes of 10 and 12 mCrab on dates 2010-07-14.7 and 2010-07-18.6, respectively, indicating a rising flux. Before that time, the flux was less than 1 mCrab (2-10 keV).

Given that the 2-50 keV spectrum appears harder than the Crab, it is possible that the source is an accreting X-ray pulsar or a black hole system in the "low hard" state.

Follow-up observations have been requested for Swift and RXTE.

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R. E. Rutledge , Editor
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