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arXiv · 2507.04407

Resolving the origin of the unidentified TeV source HESS J1626-490 as a relic of the ancient cosmic-ray factory SNR G335.2+0.1

Tomohiko Oka·Wataru Ishizaki·Masaki Mori·Hidetoshi Sano·Hiromasa Suzuki·Takaaki Tanaka
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Abstract

While decades of observations in the TeV gamma-ray band have revealed more than 200~sources with radio or X-ray counterparts, there remain dozens of unidentified TeV sources, which may provide crucial information of cosmic ray (CR) accelerators. HESS J1626$-$490 is an unidentified TeV gamma-ray source but is expected to originate from CRs that escaped from the nearby supernova remnant (SNR) G335.2+0.1 and are interacting with dense interstellar clouds. To test this scenario, we scrutinize the properties of the SNR and search for non-thermal counterparts by analyzing observational data in the radio, X-ray, and GeV gamma-ray bands. From analysis of the H\,{\sc i} and $^{12}$CO ($J{=}1{-}0$) line data, we identify the cloud associated with the SNR and compare the morphologies of the cloud and the gamma-ray emission. The distance and age of the SNR are estimated to be $3.3 \pm 0.6$~kpc and ${\sim}5$~kyr, respectively. From X-ray and GeV gamma-ray data analyses, we find an extended GeV gamma-ray emission overlapping with the SNR and H.E.S.S. source regions but no X-ray emission. The location of the peak of the extended GeV emission changes from near the SNR at $\lesssim 1$~GeV to the H.E.S.S. source at $>10$~GeV. We find a spectral hardening at ${\sim}50$~GeV, which is consistent with the existence of two components in the gamma-ray emission. We find that a combination of emission from the escaped CRs and the SNR itself can reproduce the observed broadband spectrum, on the assumption that the SNR has accelerated protons to ${\gtrsim}100$~TeV in the past.

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Tomohiko Oka, Wataru Ishizaki, Masaki Mori, Hidetoshi Sano, Hiromasa Suzuki, Takaaki Tanaka. 2025-07-06. Resolving the origin of the unidentified TeV source HESS J1626-490 as a relic of the ancient cosmic-ray factory SNR G335.2+0.1. https://arxiv.org/abs/2507.04407

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