RXTE OBSERVATIONS OF PROXIMA CENTAURI

We report on Rossi X-ray Timing Explorer (RXTE) observations of the dM 5e flare star Proxima Centauri. These were carried out using the Propo rtional Counter Array (PCA) in three segments totaling 50.87 ks on 199 6 February 20, 23 and 25. The star was detected in the three lowest-en ergy channels (1.75-3.9 keV, 3.9-5.75 keV, 5.75-8.7 keV) with a mean X -ray luminosity of < L-x > = 7 10(26) ergs s(-1). This is an order of magnitude higher than the mean non-flaring ASCA detection in a similar passband in March 1994. Previous Einstein Observatory, EXOSAT and ROS AT detections yielded similar L-x (similar to 10(27) ergs s(-1)) but a t lower energies. After compensating for passband differences the RXTE -PCA mean level of activity is found to be similarly enhanced with res pect to these observations. The star appears to be in a higher activit y state, but no major flares were detected. Owing to the high RXTE bac kground we cannot address the issue of solar-like, M-class flaring pre viously measured on Proxima by ASCA. Searches were carried out for sho rt-duration bursts - as on the Sun during the flare impulsive phase - at all PCA energies (1.75-65 keV) using statistical tests for any sign ificant clustering of 15, 25, 50 or 100 photons. Such events would be relatively insensitive to fluctuations and modeling limitations of the background. The number of photon clusters found was consistent with s tatistical fluctuations.