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

TL;DR

This paper reports the detection and spectral analysis of the blazar 3C 66A using MAGIC telescopes, demonstrating the importance of stereoscopic observations for source separation and constraining the blazar's redshift.

Contribution

First stereoscopic MAGIC observations of 3C 66A, showing effective source separation and providing spectral data consistent with previous measurements.

Findings

Detected significant gamma-ray signal from 3C 66A

Measured integral flux above 100 GeV at 8.3% of Crab flux

Constrained the blazar's redshift to less than 0.68

Abstract

We report new observations of the intermediate-frequency peaked BL Lacertae object 3C 66A with the MAGIC telescopes. The data sample we use were taken in 2009 December and 2010 January, and comprises 2.3 hr of good quality data in stereoscopic mode. In this period, we find a significant signal from the direction of the blazar 3C 66A. The new MAGIC stereoscopic system is shown to play an essential role for the separation between 3C 66A and the nearby radio galaxy 3C 66B, which is at a distance of only $6^\prime$. The derived integral flux above $100\eh{GeV}$ is 8.3% of Crab Nebula flux and the energy spectrum is reproduced by a power law of photon index $3.64 \pm 0.39_{\rm stat} \pm 0.25_{\rm sys}$. Within errors, this is compatible with the one derived by VERITAS in 2009. From the spectra corrected for absorption by the extragalactic background light, we only find small differences between the four models that we applied, and constrain the redshift of the blazar to $z < 0.68$.