Very-High-Energy $\gamma$-Ray Observations of the Blazar 1ES 2344+514 with VERITAS

TL;DR

This paper reports extensive very-high-energy gamma-ray observations of the blazar 1ES 2344+514 by VERITAS, analyzing its variability, spectrum, and stability over multiple years, providing the most comprehensive study to date.

Contribution

It presents the most detailed VHE gamma-ray observational analysis of 1ES 2344+514, including variability, spectral fitting, and source localization, extending the energy spectrum up to at least 8 TeV.

Findings

Detected the source with 20.8σ significance in 47.2 hours.

Observed variability on short and long timescales, rejecting constant flux models.

Spectrum extends to at least 8 TeV and is well fitted by a power-law with index 2.46, with evidence for a possible exponential cutoff.

Abstract

We present very-high-energy $\gamma$-ray observations of the BL Lac object 1ES 2344+514 taken by the Very Energetic Radiation Imaging Telescope Array System (VERITAS) between 2007 and 2015. 1ES 2344+514 is detected with a statistical significance above background of $20.8\sigma$ in $47.2$ hours (livetime) of observations, making this the most comprehensive very-high-energy study of 1ES 2344+514 to date. Using these observations the temporal properties of 1ES 2344+514 are studied on short and long times scales. We fit a constant flux model to nightly- and seasonally-binned light curves and apply a fractional variability test, to determine the stability of the source on different timescales. We reject the constant-flux model for the 2007-2008 and 2014-2015 nightly-binned light curves and for the long-term seasonally-binned light curve at the $> 3\sigma$ level. The spectra of the time-averaged emission before and after correction for attenuation by the extragalactic background light are obtained. The observed time-averaged spectrum above 200 GeV is satisfactorily fitted (${\chi^2/NDF = 7.89/6}$) by a power-law function with index $\Gamma = 2.46 \pm 0.06_{stat} \pm 0.20_{sys} $ and extends to at least 8 TeV. The extragalactic-background-light-deabsorbed spectrum is adequately fit (${\chi^2/NDF = 6.73/6}$) by a power-law function with index $\Gamma = 2.15 \pm 0.06_{stat} \pm 0.20_{sys} $ while an F-test indicates that the power-law with exponential cutoff function provides a marginally-better fit ($\chi^2/NDF $ = $2.56 / 5 $) at the 2.1$\sigma$ level. The source location is found to be consistent with the published radio location and its spatial extent is consistent with a point source.