Spectral lags of flaring events in $LSI +61^{o} $ 303 from RXTE Observations

Abstract

This work reports the first discovery of (negative) spectral lags in the X-ray emission below 10 keV from the gamma ray binary $LSI +61^{o} $ 303 during large flaring episodes using the Rossi X-ray Timing Explorer (RXTE) observations. It is found from the RXTE data that during the flares, low energy (3-5 KeV) variations lead the higher energy (8-10 keV) variations by few tens of seconds whereas no significant time lag is observed during the non-flaring states. The observed spectral lag features for flaring events suggest that inverse Compton scattering may be operative, at least in some part of the system. Another possibility is that the sites of particle acceleration may be different for flaring and non-flaring events such as in the microquasar model the flaring radiation may come from hot spots sitting above the black hole while steady state emissions are due to the jets.