We present ongoing Rossi X-ray Timing Explorer (RXTE) monitoring observations of the 377.3 Hz accretion-powered pulsar, HETE J1900.1-2455 Activity continues in this system more than 3 years after discovery, at a mean luminosity of 4.4e36 erg/s (for d=5 kpc), although pulsations were present only within the first 70 days. X-ray variability has increased each year, notably with a brief interval of nondetection in 2007, during which the luminosity dropped to below 1e-3 of the mean level. A deep search of data from the intervals of nondetection in 2005 revealed evidence for extremely weak pulsations at an amplitude of 0.29% rms, a factor of ten less than the largest amplitude seen early in the outburst. X-ray burst activity continued through 2008, with bursts typically featuring strong radius expansion. Spectral analysis of the most intense burst detected by RXTE early in the outburst revealed unusual variations in the inferred photospheric radius, as well as significant deviations from a blackbody. We obtained much better fits instead with a comptonisation model.
Download