LMC N132D: A mature supernova remnant with a power-law gamma-ray spectrum extending beyond 8 TeV
Authors:   H.E.S.S. Collaboration, Abdalla H. , Aharonian F. , Ait Benkhali F. , Angüner E. O. , Arcaro C. , Armand C. , Armstrong T. , Ashkar H. , Backes M. , Baghmanyan V. , Barbosa Martins V. , Barnacka A. , Barnard M. , Batzofin R. , Becherini Y. , Berge D. , Bernlöhr K. , Bi B. , Böttcher M. , Boisson C. , Bolmont J. , de Bony de Lavergne M. , Breuhaus M. , Brose R. , Brun F. , Bulik T. , Bylund T. , Cangemi F. , Caroff S. , Casanova S. , Catalano J. , Chambery P. , Chand T. , Chen A. , Cotter G. , Curyło M. , Damascene Mbarubucyeye J. , Davids I. D. , Davies J. , Devin J. , Djannati-Ataï A. , Dmytriiev A. , Donath A. , Doroshenko V. , Dreyer L. , Du Plessis L. , Duffy C. , Egberts K. , Einecke S. , Ernenwein J.-P. , Fegan S. , Feijen K. , Fiasson A. , Fichet de Clairfontaine G. , Fontaine G. , Lott F. , Füßling M. , Funk S. , Gabici S. , Gallant Y. A. , Giavitto G. , Giunti L. , Glawion D. , Glicenstein J. F. , Grondin M.-H. , Hattingh S. , Haupt M. , Hermann G. , Hinton J. A. , Hofmann W. , Hoischen C. , Holch T. L. , Holler M. , Hörbe M. , Horns D. , Huang Zhiqiu , Huber D. , Jamrozy M. , Jankowsky F. , Joshi V. , Jung-Richardt I. , Kasai E. , Katarzyński K. , Katz U. , Khangulyan D. , Khélifi B. , Klepser S. , Kluźniak W. , Komin Nu. , Konno R. , Kosack K. , Kostunin D. , Kreter M. , Kukec Mezek G. , Kundu A. , Lamanna G. , Le Stum S. , Lemière A. , Lemoine-Goumard M. , Lenain J.-P. , Leuschner F. , Levy C. , Lohse T. , Luashvili A. , Lypova I. , Mackey J. , Majumdar J. , Malyshev D. , Malyshev D. , Marandon V. , Marchegiani P. , Marcowith A. , Mares A. , Martí-Devesa G. , Marx R. , Maurin G. , Meintjes P. J. , Meyer M. , Mitchell A. , Moderski R. , Mohrmann L. , Montanari A. , Moore C. , Moulin E. , Muller J. , Murach T. , Nakashima K. , de Naurois M. , Nayerhoda A. , Ndiyavala H. , Niemiec J. , Priyana Noel A. , O’Brien P. , Oberholzer L. , Odaka H. , Ohm S. , Olivera-Nieto L. , de Ona Wilhelmi E. , Ostrowski M. , Panny S. , Panter M. , Parsons R. D. , Peron G. , Pita S. , Poireau V. , Prokhorov D. A. , Prokoph H. , Pühlhofer G. , Punch M. , Quirrenbach A. , Reichherzer P. , Reimer A. , Reimer O. , Remy Q. , Renaud M. , Reville B. , Rieger F. , Romoli C. , Rowell G. , Rudak B. , Rueda Ricarte H. , Ruiz-Velasco E. , Sahakian V. , Sailer S. , Salzmann H. , Sanchez D. A. , Santangelo A. , Sasaki M. , Schäfer J. , Schüssler F. , Schutte H. M. , Schwanke U. , Senniappan M. , Seyffert A. S. , Shapopi J. N. S. , Shiningayamwe K. , Simoni R. , Sinha A. , Sol H. , Specovius A. , Spencer S. , Spir-Jacob M. , Stawarz Ł. , Steenkamp R. , Stegmann C. , Steinmassl S. , Steppa C. , Sun L. , Takahashi T. , Tanaka T. , Tavernier T. , Taylor A. M. , Terrier R. , Thiersen J. H. E. , Thorpe-Morgan C. , Tluczykont M. , Tomankova L. , Tsirou M. , Tsuji N. , Tuffs R. , Uchiyama Y. , van der Walt D. J. , van Eldik C. , van Rensburg C. , van Soelen B. , Vasileiadis G. , Veh J. , Venter C. , Vincent P. , Vink J. , Völk H. J. , Wagner S. J. , Watson J. , Werner F. , White R. , Wierzcholska A. , Wong Yu Wun , Yassin H. , Yusafzai A. , Zacharias M. , Zanin R. , Zargaryan D. , Zdziarski A. A. , Zech A. , Zhu S. J. , Zmija A. , Zouari S. , Żywucka N. 
Published: August 2021

Context. Supernova remnants (SNRs) are commonly thought to be the dominant sources of Galactic cosmic rays up to the knee of the cosmic-ray spectrum at a few PeV. Imaging Atmospheric Cherenkov Telescopes have revealed young SNRs as very-high-energy (VHE, >100 GeV) gamma-ray sources, but for only a few SNRs the hadronic cosmic-ray origin of their gamma-ray emission is indisputably established. In all these cases, the gamma-ray spectra exhibit a spectral cutoff at energies much below 100 TeV and thus do not reach the PeVatron regime.

Aims. The aim of this work was to achieve a firm detection for the oxygen-rich SNR LMC N132D in the VHE gamma-ray domain with an extended set of data, and to clarify the spectral characteristics and the localization of the gamma-ray emission from this exceptionally powerful gamma-ray-emitting SNR.

Methods. We analyzed 252 h of High Energy Stereoscopic System (H.E.S.S.) observations towards SNR N132D that were accumulated between December 2004 and March 2016 during a deep survey of the Large Magellanic Cloud, adding 104 h of observations to the previously published data set to ensure a > 5σ detection. To broaden the gamma-ray spectral coverage required for modeling the spectral energy distribution, an analysis of Fermi-LAT Pass 8 data was also included.

Results. We unambiguously detect N132D at VHE with a significance of 5.7σ. We report the results of a detailed analysis of its spectrum and localization based on the extended H.E.S.S. data set. The joint analysis of the extended H.E.S.S and Fermi-LAT data results in a spectral energy distribution in the energy range from 1.7 GeV to 14.8 TeV, which suggests a high luminosity of N132D at GeV and TeV energies. We set a lower limit on a gamma-ray cutoff energy of 8 TeV with a confidence level of 95%. The new gamma-ray spectrum as well as multiwavelength observations of N132D when compared to physical models suggests a hadronic origin of the VHE gamma-ray emission.

Conclusions. SNR N132D is a VHE gamma-ray source that shows a spectrum extending to the VHE domain without a spectral cutoff at a few TeV, unlike the younger oxygen-rich SNR Cassiopeia A. The gamma-ray emission is best explained by a dominant hadronic component formed by diffusive shock acceleration. The gamma-ray properties of N132D may be affected by an interaction with a nearby molecular cloud that partially lies inside the 95% confidence region of the source position.