Mapping the extended TeV source HESS J1857+026 down to Fermi-LAT energies with the MAGIC telescopes

TL;DR

This paper reports the detection and detailed spectral analysis of the extended TeV gamma-ray source HESS J1857+026 using MAGIC telescopes, providing insights into its nature and energy extension.

Contribution

First detailed spectral and morphological analysis of HESS J1857+026 at energies from 100 GeV to 10 TeV with MAGIC.

Findings

Detected the source with high significance in 29 hours of data.

Measured an intrinsic extension of 0.22 degrees in the 200-1000 GeV range.

Spectrum shows no inverse Compton turnover up to 10 TeV.

Abstract

HESS J1857+026 is an extended TeV gamma-ray source discovered by H.E.S.S. very close to the Galactic plane. Located in the vicinity of the pulsar PSR J1856+0245, the source represents a pulsar wind nebula (PWN) candidate. In Fermi-LAT data, 7 photons above 100GeV were associated to it as VHE J1857+0252 by Neronov and Semikoz (2010), while in the previous MeV-GeV catalogs no associated source was reported yet. MAGIC was upgraded to a stereoscopic Cherenkov telescope system in 2009, which substantially improved its performance with respect to extended objects. We observed HESS J1857+026 in 2010 and analysed 29 hours of good quality stereoscopic data, yielding a highly significant detection. We present an energy spectrum from 100GeV to 10TeV and skymaps for two different energy regimes. The spectrum does not show any indication for an inverse Compton turnover, while we find an intrinsic extension of 0.22 \pm 0.02stat \pm 0.02sys in the energy range of 200 - 1000 GeV. We discuss the possible PWN nature of the source and the performance of MAGIC with respect to extended sources.