Stereoscopic Observations of the Blazar 3C 66A with the MAGIC Telescopes

TL;DR

This paper reports the detection of gamma-ray emission from the blazar 3C 66A using MAGIC telescopes, providing spectral measurements and constraining its redshift to less than 0.68.

Contribution

First detection of VHE gamma-ray emission from 3C 66A with detailed spectral analysis and redshift constraint.

Findings

Gamma-ray signal confidently attributed to 3C 66A

Integral flux above 100 GeV is 8.3% of Crab Nebula flux

Redshift of the blazar constrained to z < 0.68

Abstract

3C 66A is an intermediate-frequency peaked BL Lacertae object of uncertain redshift. We report recent observations of the region around the blazar with the MAGIC telescopes. The source was observed and detected in 2009 December and 2010 January, in 2.3 h of good quality data. The signal could clearly be assigned to the blazar 3C 66A, statistically and systematically rejecting the nearby radio galaxy 3C 66B as a possible origin of the gamma-ray signal by 3.6 standard deviations. The derived integral flux above 100GeV is 8.3% of the Crab Nebula flux, and the energy spectrum is reproduced by a power law of photon index 3.64 \pm 0.39(stat.) \pm 0.25(sys.). Within the errors, this is compatible with the spectrum derived by VERITAS in 2009. From the spectra corrected for absorption by the extragalactic background light, we only find small differences between the four modellings that we applied, and constrain the redshift of the blazar to z < 0.68.