doi:10.1038/nindia.2013.129 Published online 24 September 2013
A new model has proved promising in investigating 'extragalactic background light' or EBL, considered to have been produced by the first stars formed in the Universe . Researchers have used the model to estimate the fluxes of very high energy (VHE) gamma rays emitted by distant radio sources.
VHE gamma rays can provide a window into the processes of early star formation in the Universe. This is because they interact with the EBL, and subsequently carry information about it.
VHE gamma rays travelling from remote radio sources interact with the EBL via electron–positron pair production. Such interactions can result in photons in the EBL being absorbed, thus weakening the VHE gamma-ray signal. However, till now no model had probed the EBL based on energetic gamma rays from radio sources.
The researchers developed a homogenous one-zone model involving synchrotron and synchrotron-based emission mechanisms to estimate the values of VHE gamma-ray spectra. They considered three radio sources that emit VHE gamma rays and for which multi-wavelength data had been obtained by various observations.
They then compared the values predicted by the model for VHE gamma rays from the radio sources with data from the ground-based Cherenkov telescope array. This helped them determine the optical depth values of the VHE gamma rays. On comparison, the researchers found a relatively large systematic deviation for two radio sources at higher energies — especially for an EBL model proposed in a previous study.
The results of this study will provide unique information on the EBL density and the history of star and galaxy formation.