1998A&A...335L.101H

We report on Rossi X-ray Timing Explorer (RXTE) observations of the dM5e flare star Proxima Centauri. These were carried out using the Proportional Counter Array (PCA) in three segments totaling 50.87 ks on 1996 February 20, 23 and 25. The star was detected in the three lowest-energy channels (1.75-3.9keV, 3.9-5.75keV, 5.75-8.7keV) with a mean X-ray luminosity of <L_x≥7x10²⁶ergs/s. 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 ROSAT detections yielded similar L_x (∼10²⁷ergs/s) but at lower energies. After compensating for passband differences the RXTE-PCA mean level of activity is found to be similarly enhanced with respect to these observations. The star appears to be in a higher activity state, but no major flares were detected. Owing to the high RXTE background we cannot address the issue of solar-like, M-class flaring previously measured on Proxima by ASCA. Searches were carried out for short-duration bursts - as on the Sun during the flare impulsive phase - at all PCA energies (1.75-65keV) using statistical tests for any significant 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 statistical fluctuations.