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Chandra Non-Detection of the Eclipsing Millisecond X-ray Pulsar SWIFT J1749.4-2807

ATEL # 2585; Deepto Chakrabarty (MIT), Peter G. Jonker (SRON), and Craig B. Markwardt (NASA/GSFC)
on 26 Apr 2010; 20:29 UT
Password Certification: Deepto Chakrabarty (

Subjects: X-ray, Neutron Stars, Pulsars, Transients

We report on a Chandra/ACIS-S observation of the eclipsing accretion-powered millisecond pulsar SWIFT J1749.4-2807, which has recently been reported in a fading outburst during 2010 April 11-21 (ATels #2548, #2561, #2565, #2569, #2576, #2579). Our 1080 s observation was made on April 25 (12:25 TT). Using the pulsar orbital parameters (ATel #2569), the observation midpoint was at an orbital mean longitude of 217 degrees, placing the entire observation well outside of the X-ray eclipse region.

No X-ray sources were detected within 5 arcsec of the improved Swift X-ray position (1.9 arcsec radius, ATel #2579). The 95%-confidence upper limit on the source count rate is <0.008 count/s, corresponding to an absorbed source flux of <1.8e-13 erg/cm^2/s (0.5-10 keV) assuming a power-law spectrum with photon index of 1.64 and hydrogen column density of 2.8e22 cm^(-2) (ATel #2579). For the distance upper limit of 6.7 kpc derived by Campana (2009, ApJ, 699, 1144), this implies an X-ray luminosity of <1.6e33 erg/s.

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