RXTE observations of 3C 279 during a high-energy flare

Abstract

ABSTRA C T We present details of a large X-ray flare in the blazar 3C 279 detected during a 3-week period of daily observations by the satellite RXTE in early 1996. The flare lasted for a total of 7 d. The shape of the flare is well described by a symmetrical, exponential rise and fall with e-folding time-scales in each case of 1.1 d. The peak measured flux is three times the quiescent level. The flare is superimposed on a well-defined quiescent level and appears to represent a separate emission component. There is no statistically significant variability of the X-ray spectral index during the observations, but the errors are large and the data hint at a hardening of about 0.1 at the peak of the flare. Such a hardening is required to allow the X-ray flare spectrum to join on, in a single power law, to the g-ray flare that occurred at the same time. The exponential rise and decay most likely correspond to a variation in the acceleration of relativistic electrons or in the flux of seed photons, if the latter do not originate in the jet, as the energy loss time-scales are shorter than the rise and decay time-scales and the flare profile does not match that expected if light-travel delays determine the light curve.