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A 44 Day Period in AX J1700.2-4220 from Swift/BAT Observations

ATEL # 2559; Robin H.D. Corbet (UMBC/NASA GSFC), Hans A. Krimm (USRA/NASA GSFC), Gerald K. Skinner (UMCP/NASA GSFC)
on 14 Apr 2010; 14:10 UT
Password Certification: Robin Corbet (

Subjects: X-ray, Binaries, Black Holes, Neutron Stars, Stars

AX J1700.2-4220 is a poorly studied X-ray source that may be a high-mass X-ray binary (Negueruela & Schurch, 2007, A&A, 461, 631; Bird et al., 2010, ApJ Supp., 186, 1). An analysis of the 15 - 50 keV light curve of this source obtained with the Swift/BAT covering 2005-02-12 through 2010-03-30 (MJD 53,413 to 55,285) reveals highly significant modulation at a period near 44 days.

In order to characterize the modulation we fitted a sine wave to the light curve and derived:
Tmax (MJD) = 54342.0 (+/- 0.5) + n x 44.12 (+/- 0.04)
where Tmax is the time of maximum flux.

The mean flux is 0.0004 cts/cm2/s, equivalent to approximately 2 mCrab, and the flux is close to 100% modulated on the 44 day period. An inspection of the folded light curve suggests that the peak flux may actually occur slightly later than is derived from the sine wave fit.

The presence of this periodic modulation is consistent with an HMXB classification for the source. Additional X-ray observations near predicted flux maximum are encouraged to search for X-ray pulsations.

This telegram made use of Swift/BAT transient monitor results provided by the Swift/BAT team.

Scaled Map Transient Analysis for AX J1700.2-4220

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