HESS J1427-608: an unusual hard unbroken $\gamma -$ray spectrum in a very wide energy range

Abstract

We report the detection of a GeV $\gamma$-ray source which is spatially overlapping and thus very likely associated with the unidentified very-high-energy (VHE) $\gamma$-ray source HESS J1427-608 with the Pass 8 data recorded by the Fermi Large Area Telescope. The photon spectrum of this source is best described by a power-law with an index of $1.85\pm 0.17$ in the energy range of $3-500$ GeV, and the measured flux connects smoothly with that of HESS J1427-608 at a few hundred GeV. This source shows no significant extension and time variation. The broadband GeV-TeV emission over four decades of energies can be well fitted by a single power-law function with an index of 2.0, without obvious indication of spectral cutoff toward high energies. Such a result implies that HESS J1427-608 may be a PeV particle accelerator. We discuss possible nature of HESS J1427-608 according to the multi-wavelength spectral fittings. Given the relatively large errors, either a leptonic or a hadronic model can explain the multi-wavelength data from radio to VHE $\gamma$-rays. The inferred magnetic field strength is a few $\mu$G, which is smaller than typical values of supernova remnants (SNRs), and is consistent with some pulsar wind nebulae (PWNe). On the other hand, the flat $\gamma$-ray spectrum is slightly different from typical PWNe but similar to that of some known SNRs.

arXiv comment8 pages, 8 figures, 2 tables, Accepted for publication in ApJ

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• Detection of GeV $\gamma$-ray emission in the direction of HESS J1731-347 with Fermi-LAT
• HESS J1640-465 -- a Gamma-ray emitting pulsar wind nebula ?
• Search for PeV Gamma-Ray Emission from the Southern Hemisphere with 5 Years of Data from the IceCube Observatory
• Multiwavelength constraints on the unidentified Galactic TeV sources HESS J1427$-$608, HESS J1458$-$608, and new VHE $\gamma$-ray source candidates
• Fermi-LAT detection of GeV $\gamma$-ray emission from Type Ia supernova remnant G272.2-3.2
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