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Swift/XRT non-detection of HETE J1900.1-2455

ATEL # 1098; N. Degenaar, R. Wijnands (UvA), S. Campana (OA Brera), D. Galloway (U. Melbourne), W. Lewin, J. Homan, D. Chakrabarty (MIT), P.Jonker (SRON/CfA), E. Cackett, J. Miller (University of Michigan)
on 7 Jun 2007; 14:32 UT
Password Certification: Rudy Wijnands (

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

During a ~0.8 ksec pointed Swift/XRT observation performed on June 6, 2007 (18:26-21:38 UT), we did not detect the accreting millisecond pulsar HETE J1900.1-2455. We can set a 2-10 keV upper limit on the source flux of ~(5-15)E-14 erg/cm2/s (depending on the assumed spectral model). This is more than a factor of 10 weaker than the X-ray flux observed with Swift/XRT last week, on May 31 (ATEL #1091). The distance to HETE J1900.1-2455 is ~5 kpc (inferred from type-I X-ray bursts; e.g., ATELs #534 and #657), which means that its X-ray luminosity is currently below ~5E32 erg/s. The current low flux and its rapid decay strongly indicate that HETE J1900.1-2455 is now back in quiescence or will very soon be.

We would like to thank the Swift-team for making these XRT observations possible.

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R. E. Rutledge , Editor
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