High energy observations of blazars-archival analysis

Abstract

We are conducting a systematic study of the archival data of 14 AGNs observed simultaneously by RXTE and EGRET. The sample includes eight flat spectrum radio quasars, three high-energy-peaked BL Lacs (HBLs), and three low-energy peaked BL Lacs (LBLs). Four sources have been observed for at least two consecutive EGRET observation periods (14 days). We have extracted spectral indices using the power-law models in both XTE and EGRET energy ranges and we are studying the X-ray-to-gamma-ray spectral energy distributions and their variability as a function of classification. Preliminary results show that FSRQs and LBLs have X-ray photon indices in the energy band 3.0-20 keV in the range 1.3-2.0, while HBLs have indices in the range 1.8-2.9. Several blazars were repeatedly observed in X-rays with XTE, enabling us to study flux and spectral variation on the time scales of half a day. Correlated variations between the photon index and flux are observed in HBLs with a trend of flatter slopes for increasing fluxes. In LBLs and FSRQs, both the flux and slope vary, but with no clear trends. The results are overall consistent with the current unification schemes for blazars where HBLs are dominated in X-rays by the variable tail of synchrotron emission, while in FSRQs and LBLs the XTE spectra are dominated by the inverse Compton emission extending to higher energies.