Intrinsic VHE gamma-ray spectra of blazars as a probe for extragalactic background light

•Simple radiation emission model is used to extrapolate the MWL spectra of Blazars to VHE energies.•The intrinsic and the observed VHE spectra are used to estimate the optical depth at various redshifts.•The estimated optical depth values are then compared with the one predicted from different EBL models.•A systematic deviation of optical depth for z = 0.116 and 0.536 is observed for Finke et al. (2010) EBL model.

Very high energy (VHE) γγ-rays above 10’s of GeV energy, emitted from distant blazars, are attenuated by photons from the extragalactic background light (EBL). Unfortunately, neither the EBL nor the intrinsic blazar spectrum is accurately known to derive one quantity from the other. In this work we use a homogeneous one zone model involving synchrotron, synchrotron self Compton (SSC) and external Compton (EC) emission mechanisms to estimate the intrinsic VHE spectra of blazars. The model is applied on three VHE blazars, namely PKS2155-304, RGB J0710 + 591 and 3C 279, for which simultaneous multi-wavelength data are available from various observations. The predicted values of the intrinsic VHE fluxes are then compared with the observations by imaging atmospheric Cherenkov telescopes to determine the optical depth of VHE γγ-rays. On comparing these optical depth values with those predicted by four different EBL models, we observe a somewhat pronounced systematic deviation for PKS2155-304 and 3C 279 at higher energies, especially for the EBL model proposed by Finke et al. (2010). We attribute this deviation to be an outcome of either the failure of the extrapolation of blazar SED to VHE energies and/or due to various assumptions buried in the EBL models.