This work reports the first discovery of（negative） spectral lags in X-ray emission below 10 ke V from the gamma ray binary LS I＋61？303 during large flaring episodes using Rossi X-ray Timing Explorer（RXTE） observ...This work reports the first discovery of（negative） spectral lags in X-ray emission below 10 ke V from the gamma ray binary LS I＋61？303 during large flaring episodes using Rossi X-ray Timing Explorer（RXTE） observations. It is found from the RXTE data that during the flares, low energy（3–5 ke V） variations lead the higher energy（8–10 ke V） variations by a 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 operating, 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, in which the flaring radiation may come from hot spots sitting above the black hole while steady state emissions are due to the jets.展开更多
The primary energy spectrum of cosmic rays exhibits a knee at about 3 PeV where a change in the spectral index occurs. Despite many efforts, the origin of such a feature in the spectrum is not satisfactorily solved ye...The primary energy spectrum of cosmic rays exhibits a knee at about 3 PeV where a change in the spectral index occurs. Despite many efforts, the origin of such a feature in the spectrum is not satisfactorily solved yet. Here it is proposed that the steepening of the spectrum beyond the knee may be a consequence of the mass distribution of the progenitor of the cosmic ray source. The proposed speculative model can account for all the major observed features of cosmic rays without invoking any fine tuning to match flux or spectra at any energy point. The prediction of the proposed model regarding the primary composition scenario beyond the knee is quite different from most of the prevailing models of the knee, and thereby can be discriminated from precise experimental measurement of the primary composition.展开更多
文摘This work reports the first discovery of（negative） spectral lags in X-ray emission below 10 ke V from the gamma ray binary LS I＋61？303 during large flaring episodes using Rossi X-ray Timing Explorer（RXTE） observations. It is found from the RXTE data that during the flares, low energy（3–5 ke V） variations lead the higher energy（8–10 ke V） variations by a 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 operating, 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, in which the flaring radiation may come from hot spots sitting above the black hole while steady state emissions are due to the jets.
基金partly supported by the Department of Science and Technology (Govt.of India) under the grant no.SR/S2/HEP-14/2007
文摘The primary energy spectrum of cosmic rays exhibits a knee at about 3 PeV where a change in the spectral index occurs. Despite many efforts, the origin of such a feature in the spectrum is not satisfactorily solved yet. Here it is proposed that the steepening of the spectrum beyond the knee may be a consequence of the mass distribution of the progenitor of the cosmic ray source. The proposed speculative model can account for all the major observed features of cosmic rays without invoking any fine tuning to match flux or spectra at any energy point. The prediction of the proposed model regarding the primary composition scenario beyond the knee is quite different from most of the prevailing models of the knee, and thereby can be discriminated from precise experimental measurement of the primary composition.
