Searches for very high energy gamma rays from blazars with CANGAROO-III telescope in 2005-2009

TL;DR

This study used the CANGAROO-III telescope to search for very high energy gamma rays from four blazars between 2005 and 2009, finding no significant detections but providing valuable upper limits and spectral modeling insights.

Contribution

It presents a new analysis method to suppress position dependence effects in Cherenkov images and applies it to multi-year observations of four blazars, combining results with Fermi/LAT data for spectral modeling.

Findings

No significant VHE gamma-ray emission detected from the four blazars.

Spectral energy distributions modeled with SSC and EC models.

Results consistent with the blazar sequence regarding magnetic field and component size.

Abstract

We have searched for very high energy (VHE) gamma rays from four blazars using the CANGAROO-III imaging atmospheric Cherenkov telescope. We report the results of the observations of H 2356-309, PKS 2155-304, PKS 0537-441, and 3C 279, performed from 2005 to 2009, applying a new analysis to suppress the effects of the position dependence of Cherenkov images in the field of view. No significant VHE gamma ray emission was detected from any of the four blazars. The GeV gamma-ray spectra of these objects were obtained by analyzing Fermi/LAT archival data. Non-simultaneous wide range (radio to VHE gamma-ray bands) spectral energy distributions (SEDs) including CANGAROO-III upper limits, GeV gamma-ray spectra, and archival data are discussed using a one-zone synchrotron self-Compton (SSC) model in combination with a external Compton (EC) radiation. The HBLs (H 2356-309 and PKS 2155-304) can be explained by a simple SSC model, and PKS 0537-441 and 3C 279 are well modeled by a combination of SSC and EC model. We find a consistency with the blazar sequence in terms of strength of magnetic field and component size.