HESS J0632 Research Articles

Explaining the extended GeV gamma-ray emission adjacent to HESS J1825-137

ABSTRACT HESS J1825-137 is one of the most powerful and luminous TeV gamma-ray pulsar wind nebulae (PWN). To the south of HESS J1825-137, Fermi-LAT observation revealed a new region of GeV gamma-ray emission with three apparent peaks (termed here, GeV-ABC). This study presents interstellar medium (ISM) data and spectral energy distribution (SED) modelling towards the GeV emission to understand the underlying particle acceleration. We considered several particle accelerator scenarios – the PWN associated with HESS J1825-137, the progenitor SNR also associated with HESS J1825-137, plus the gamma-ray binary system LS 5039. It was found that the progenitor SNR of HESS J1825-137 has insufficient energetics to account for all GeV emission. GeV-ABC may be a reflection of an earlier epoch in the history of the PWN associated with HESS 1825-137, assuming fast diffusion perhaps including advection. LS 5039 cannot meet the required energetics to be the source of particle acceleration. A combination of HESS J1825-137 and LS 5039 could be plausible sources.

TeV Cosmic-Ray Nucleus Acceleration in Shell-type Supernova Remnants with Hard γ-Ray Spectra

Abstract The emission mechanism for hard γ-ray spectra from supernova remnants (SNRs) is still a matter of debate. Recent multiwavelength observations of the TeV source HESS J1912+101 show that it is associated with an SNR with an age of ∼100 kyr, making it unlikely produce the TeV γ-ray emission via leptonic processes. We analyzed Fermi observations of it and found an extended source with a hard spectrum. HESS J1912+101 may represent a peculiar stage of SNR evolution that dominates the acceleration of TeV cosmic rays. By fitting the multiwavelength spectra of 13 SNRs with hard GeV γ-ray spectra with simple emission models with a density ratio of GeV electrons to protons of ∼10−2, we obtain reasonable mean densities and magnetic fields with a total energy of ∼1050 erg for relativistic ions in each SNR. Among these sources, only two of them, namely SN 1006 and RCW 86, favor a leptonic origin for the γ-ray emission. The magnetic field energy is found to be comparable to that of accelerated relativistic ions and their ratio has a tendency to increase with the age of SNRs. These results suggest that TeV cosmic rays mainly originate from SNRs with hard γ-ray spectra.

HESS J1858+020: A GeV-TeV source possibly powered by cosmic rays from SNR G35.6-0.4

Context. The supernova remnant (SNR) G35.6−0.4 shows a non-thermal radio shell, however, no γ-ray or X-ray counterparts have been found for it thus far. One TeV source, HESS J1858+020, was found near the SNR and this source is spatially associated with some clouds at 3.6 kpc. Aims. To attain a better understanding of the origin of HESS J1858+020, we further investigate the association between SNR cosmic rays (CRs) and the clouds through the Fermi-LAT analysis and hadronic modeling. Methods. We performed the Fermi-LAT analysis to explore the GeV emission in and around the SNR. We explored the SNR physics with previously observed multi-wavelength data. We built a hadronic model using runaway CRs of the SNR to explain the GeV-TeV observation. Results. We found a hard GeV source (SrcX2) that is spatially coincident with both HESS J1858+020 and a molecular cloud complex at 3.6 kpc. In addition, a soft GeV source (SrcX1) was found at the northern edge of the SNR. The GeV spectrum of SrcX2 connects well with the TeV spectrum of HESS J1858+020. The entire γ-ray spectrum ranges from several GeV up to tens of TeV and it follows a power-law with an index of ~2.15. We discuss several pieces of observational evidence to support the middle-aged SNR argument. Using runaway CRs from the SNR, our hadronic model explains the GeV-TeV emission at HESS J1858+020, with a diffusion coefficient that is much lower than the Galactic value.

Chandra Monitoring of the J1809–1917 Pulsar Wind Nebula and Its Field

Abstract PSR J1809–1917 is a young (τ = 51 kyr) and energetic ( erg s−1) radio pulsar powering an X-ray pulsar wind nebula (PWN) that exhibits morphological variability. We report on the results of a new monitoring campaign by the Chandra X-ray Observatory (Chandra), carried out across six epochs with a ∼7 week cadence. The compact nebula can be interpreted as a jet-dominated outflow along the pulsar’s spin axis. Its variability can be the result of Doppler boosting in the kinked jet, whose shape changes with time (akin to the Vela pulsar jet). The deep X-ray image, composed of 405 ks of new and 131 ks of archival Chandra data, reveals an arcminute-scale extended nebula (EN) whose axis of symmetry aligns with both the axis of the compact nebula and the direction toward the peak of the nearby TeV source HESS J1809–193. The EN’s morphology and extent suggest that the pulsar is likely moving through the ambient medium at a transonic velocity. We also resolved a faint 7′ long nonthermal collimated structure protruding from the PWN. It is possibly another instance of a “misaligned outflow” (also known as a “kinetic jet”) produced by high-energy particles escaping the PWN’s confinement and tracing the interstellar magnetic field lines. Finally, taking advantage of the 536 ks exposure, we analyzed the point sources in the J1809 field and classified them using multiwavelength data. None of the classified sources in the field can reasonably be expected to produce the extended TeV flux in the region, suggesting that PSR J1809–1917 is indeed the counterpart to HESS/eHWC J1809–193.

Energy dependent morphology of the pulsar wind nebula HESS J1825-137 withFermi-LAT

Aims.Taking advantage of more than 11 years ofFermi-LAT data, we perform a new and deep analysis of the pulsar wind nebula (PWN) HESS J1825-137. Combining this analysis with recent H.E.S.S. results we investigate and constrain the particle transport mechanisms at work inside the source as well as the system evolution.Methods.The PWN is studied using 11.6 years ofFermi-LAT data between 1 GeV and 1 TeV. In particular, we present the results of the spectral analysis and the first energy-resolved morphological study of the PWN HESS J1825-137 at GeV energies, which provide new insights into theγ-ray characteristics of the nebula.Results.An optimised analysis of the source returns an extended emission region larger than 2°, corresponding to an intrinsic size of about 150 pc, making HESS J1825-137 the most extendedγ-ray PWN currently known. The nebula presents a strong energy dependent morphology within the GeV range, moving from a radius of ∼1.4° below 10 GeV to a radius of ∼0.8° above 100 GeV, with a shift in the centroid location.Conclusions.Thanks to the large extension and peculiar energy-dependent morphology, it is possible to constrain the particle transport mechanisms inside the PWN HESS J1825-137. Using the variation of the source extension and position, as well as the constraints on the particle transport mechanisms, we present a scheme for the possible evolution of the system. Finally, we provide an estimate of the electron energy density and we discuss its nature in the PWN and TeV halo-like scenario.

A Multiwavelength Study of the γ-Ray Binary Candidate HESS J1832–093

Abstract We investigate the nature of the unidentified very-high-energy γ-ray object, HESS J1832–093, in a multiwavelength context. Based on X-ray variability and spectral index ( ), and its broadband spectrum, which was remarkably similar to that of HESS J0632+057—a confirmed γ-ray binary—HESS J1832–093 has been considered a strong γ-ray binary candidate in previous works. In this work, we provide further evidence for this scenario. We obtained a spectrum of its IR counterpart using Gemini/Flamingo, finding absorption lines that are usually seen in massive stars, in particular O stars. We also obtained a rather steep ATCA spectrum ( ), which is consistent with a γ-ray binary. Based on spatial-spectral analysis and variability search, we found that 4FGL J1832.9-0913 is possibly associated with SNR G22.7-0.2 rather than with HESS J1832–093 only.

X-ray andγ-ray orbital variability from theγ-ray binary HESS J1832−093

Context.γ-ray binaries are systems composed of a massive star and a compact object whose interaction leads to particle acceleration up to relativistic energies. In the last fifteen years, a few binaries have been found to emit at high energies, but their number is still low. The TeV source HESS J1832−093 has been proposed as a binary candidate, although its nature is unclear. Neither a GeV counterpart nor a period was detected.Aims.The purpose of this work is to search for a GeV counterpart to understand the origin of the TeV signal detected by H.E.S.S. For an unambiguous identification of its binary nature, finding an orbital modulation is crucial.Methods.We analysed data spanning more than 10 years from theFermiLarge Area Telescope (Fermi-LAT), together withSwiftarchival observations taken between 2015 and 2018, using both the X-Ray Telescope and UV/Optical Telescope. We searched for periodicities in both X-ray and GeV bands.Results.We find a periodic modulation of ∼ 86 days in the X-ray source candidate counterpart XMMU J183245−0921539, together with indications ofγ-ray modulation with a compatible period in the GeV candidate counterpart 4FGL J1832.9−0913. Neither an optical nor a UV counterpart is found at the X-ray source location. The overall spectral energy distribution strongly resembles the knownγ-ray binary HESS J0632+057.Conclusions.Both the spectral energy distribution and the discovery of an orbital period allow the identification of the TeV source HESS J1832−093 as a new member of theγ-ray binary class.

Diffuse γ-ray emission from the vicinity of young massive star cluster RSGC 1

ABSTRACT We report the Fermi Large Area Telescope (Fermi-LAT) detection of the γ-ray emission towards the young massive star cluster RSGC 1. Using the latest source catalogue and diffuse background models, we found that the diffuse γ-ray emission in this region can be resolved into three different components. The GeV γ-ray emission from the region HESS J1837-069 has a photon index of 1.83 ± 0.08. Combining with the HESS and MAGIC data, we argue that the γ-ray emission in this region likely originates from a pulsar wind nebula. The γ-ray emission from the north-west part (region A) can be modelled by an ellipse with the semimajor and semiminor axes of 0.5° and 0.25°, respectively. The GeV emission has a hard spectrum with a photon index of about −2 and partially coincides with the TeV source MAGIC J1835-069. The possible origin of the γ-ray emission in this region is the interaction of the cosmic rays (CRs) accelerated by SNR G24.7+0.6 or/and the OB cluster G25.18+0.26 with the surrounding gas clouds. The GeV γ-ray emission from the south-east region (region B) can be modelled as an ellipse with the semimajor and semiminor axes of 0.9° and 0.5°, respectively, and also reveals a hard γ-ray spectrum. We argue that the most probable origin is the interaction of the accelerated protons in the young massive star cluster RSGC 1 with ambient gas clouds, and the total CR proton energy is estimated to be as high as ${\sim}1\times 10^{50}\ \rm erg$.

Molecular environments of the supernova remnant G359.1−0.5

ABSTRACT We report new CO observations and a detailed molecular-line study of the mixed morphology supernova remnant G359.1−0.5, which contains six OH (1720 MHz) masers along the radio shell, indicative of shock-cloud interaction. Observations of 12CO and 13CO J:1–0 lines were performed in a ∼38 × 38 arcmin area with the on-the-fly technique using the Kit Peak 12 Meter telescope. The molecular study has revealed the existence of a few clumps with densities ∼103 cm−3 compatible in velocity and position with the OH (1720 MHz) masers. These clumps, in turn, appear to be part of a larger, elongated molecular structure ∼34 arcmin long extending between −12.48 and +1.83 km s−1, adjacent to the western edge of the radio shell. According to the densities and relative position with respect to the masers, we conclude that the CO clouds depict unshocked gas, as observed in other remnants with OH (1720 MHz) masers. In addition, we investigated the distribution of the molecular gas towards the adjacent γ-ray source HESS J1745-303 (Aharonian et al. 2006) but could not find any morphological correlation between the γ-rays and the CO emission at any velocity in this region.

Cosmic-ray acceleration and escape from post-adiabatic supernova remnants

Context. Supernova remnants are known to accelerate cosmic rays on account of their nonthermal emission of radio waves, X-rays, and gamma rays. Although there are many models for the acceleration of cosmic rays in supernova remnants, the escape of cosmic rays from these sources has not yet been adequately studied. Aims. We aim to use our time-dependent acceleration code RATPaC to study the acceleration of cosmic rays and their escape in post-adiabatic supernova remnants and calculate the subsequent gamma-ray emission from inverse-Compton scattering and Pion decay. Methods. We performed spherically symmetric 1D simulations in which we simultaneously solved the transport equations for cosmic rays, magnetic turbulence, and the hydrodynamical flow of the thermal plasma in a volume large enough to keep all cosmic rays in the simulation. The transport equations for cosmic rays and magnetic turbulence were coupled via the cosmic-ray gradient and the spatial diffusion coefficient of the cosmic rays, while the cosmic-ray feedback onto the shock structure can be ignored. Our simulations span 100 000 years, thus covering the free-expansion, the Sedov–Taylor, and the beginning of the post-adiabatic phase of the remnant’s evolution. Results. At later stages of the evolution, cosmic rays over a wide range of energy can reside outside of the remnant, creating spectra that are softer than predicted by standard diffusive shock acceleration, and feature breaks in the 10 − 100 GeV-range. The total spectrum of cosmic rays released into the interstellar medium has a spectral index of s ≈ 2.4 above roughly 10 GeV which is close to that required by Galactic propagation models. We further find the gamma-ray luminosity to peak around an age of 4000 years for inverse-Compton-dominated high-energy emission. Remnants expanding in low-density media generally emit more inverse-Compton radiation, matching the fact that the brightest known supernova remnants – RCW86, Vela Jr., HESS J1731−347 and RX J1713.7−3946 – are all expanding in low density environments.

Discovery of a Spatially Extended GeV Source in the Vicinity of the TeV Halo Candidate 2HWC J1912+099: a TeV Halo or Supernova Remnant?

Abstract Observations by the High-Altitude Water Cherenkov Observatory (HAWC) and Milagro have detected spatially extended TeV sources surrounding middle-aged (t ∼ 100–400 kyr) pulsars like Geminga and PSR B0656+14, which have been named “TeV halos,” representing very extended TeV pulsar wind nebulae (PWNe) powered by relatively old pulsars. A few more HAWC-detected sources have been suggested to be TeV halo candidates. In this paper, we search for possible GeV counterparts of three TeV halo candidates with Fermi Large Area Telescopes. We detect a new spatially extended GeV source in the vicinity of the TeV halo candidate 2HWC J1912+099, which is also detected by the High Energy Stereoscopic System (H.E.S.S.) (HESS J1912+101). We find that the size of the GeV source is significantly larger than that of the TeV emission measured by H.E.S.S., and a spatial template characteristic of a PWN can fit the GeV data. We suggest that the GeV source is an extended PWN powered by the central middle-aged pulsar PSR J1913+1011. This discovery favors the TeV halo scenario for the TeV source 2HWC J1912+099 (HESS J1912+101), although the possible shell-like morphology measured by H.E.S.S. challenges this interpretation. Alternatively, the TeV emission could be dominated by a supernova remnant via the hadronic process. Future multi-wavelength observations of the source and more precise measurements of the spatial profile of the TeV emission will be useful to distinguish between the two scenarios.

Probing the Properties of the Pulsar Wind in the Gamma-Ray Binary HESS J0632+057 with NuSTAR and VERITAS Observations

Abstract HESS J0632+057 is a gamma-ray binary composed of a compact object orbiting a Be star with a period of about 315 days. Extensive X-ray and TeV gamma-ray observations have revealed a peculiar light curve containing two peaks, separated by a dip. We present the results of simultaneous observations in hard X-rays with NuSTAR and in TeV gamma-rays with VERITAS, performed in 2017 November and December. These observations correspond to the orbital phases ϕ ≈ 0.22 and 0.3, where the fluxes are rising toward the first light-curve peak. A significant variation of the spectral index from 1.77 ± 0.05 to 1.56 ± 0.05 is observed in the X-ray data. The multiwavelength spectral energy distributions (SED) derived from the observations are interpreted in terms of a leptonic model, in which the compact object is assumed to be a pulsar and nonthermal radiation is emitted by high-energy electrons accelerated at the shock formed by the collision between the stellar and pulsar wind. The results of the SED fitting show that our data can be consistently described within this scenario, and allow us to estimate the magnetization of the pulsar wind at the location of the shock formation. The constraints on the pulsar wind magnetization provided by our results are shown to be consistent with those obtained from other systems.

Is the SNR HESS J1731-347 Colliding with Molecular Clouds?

Abstract The supernova remnant HESS J1731-347 is a young supernova remnant (SNR) that displays a nonthermal X-ray and TeV shell structure. A molecular cloud at a distance of ∼3.2 kpc is spatially coincident with the western part of the SNR, and it was likely hit by the SNR. The X-ray emission from this part of the shell is much lower than from the rest of the SNR. Moreover, a compact GeV emission region coincident with the cloud has been detected with a soft spectrum. These observations seem to imply a shock-cloud collision scenario at this area, where the stalled shock can no longer accelerate super-TeV electrons or maintain strong magnetic turbulence downstream, while the GeV cosmic rays (CRs) are released through this stalled shock. To test this hypothesis, we have performed a detailed Fermi-LAT reanalysis of the HESS J1731-347 region with over nine years of data. Two distinct GeV components are found, one displaying a soft spectrum is from the compact GeV emission region, the other one displaying a hard spectrum is from the rest of the SNR (excluding the cloud region). A hadronic model involving a shock-cloud collision scenario is built to explain the γ-ray emission from this area. It consists of three CR sources: run-away super-TeV CRs that have escaped from the fast shock, leaked GeV CRs from the stalled shock, and the local CR sea. The X-ray and γ-ray emission of the SNR excluding the shock-cloud interaction region is explained in a one-zone leptonic model. Our shock-cloud collision model explains the GeV–TeV observations from the clouds around HESS J1731-347, i.e., a cloud in contact with the SNR and a distant cloud in spatial coincidence to the TeV source HESS J1729-345. We find however that the leaked GeV CRs from the shock-cloud collision do not necessarily dominate the GeV emission from the clouds, due to a comparable contribution from the local CR sea.

VERITAS Detection of LS 5039 and HESS J1825-137

With 8 h of observations, VERITAS confirms the detection of two very high energy gamma-ray sources. The gamma-ray binary LS 5039 is detected with a statistical significance of 8.8σ. The measured flux above 1 TeV is (2.5±0.4)×10−12cm−2s−1 near inferior conjunction and (7.8±2.8)×10−13cm−2s−1 near superior conjunction. The pulsar wind nebula HESS J1825-137 is detected with a statistical significance of 6.7σ and a measured flux above 1 TeV of (3.9±0.8)×10−12cm−2s−1.

Constraints on axions from neutron star in HESS J1731-347

To constrain the allowed range for the axion decay constant fa or, equivalently, for the axion mass ma, we consider the cooling of a neutron star with strong proton superfluidity and normal (non-superfluid) neutrons inside its core and without strong magnetic field, by analogy with the observed supernova remnant in HESS J1731-347. For this specific case, we demonstrate that after the thermal relaxation is over, the hydrostatic structure of the neutron star can be well described with the aid of solution of Einstein field equations, applied to a sphere of fluid in hydrostatic equilibrium, derived by Tolman. The internal temperature of the neutron star is calculated assuming that the cooling occurs dominantly due to production of neutrino pairs and axions in the nn-bremsstrahlung. To impose a constraint to the axion decay constant the fact is used that the currently observed neutron star surface temperature does not deviate from the neutrino cooling scenario. For the KSVZ-axion model we find that fa>1. 9× 108 GeV, while for the DFSZ-axion model we obtain fa>4. 7× 109 GeV.

Modelling multiwavelength emissions from PSR B1259–63/LS 2883: Effects of the stellar disc on shock radiations

PSR B1259–63/LS 2883 is an elliptical pulsar/Be star binary that emits broadband emissions from radio to TeVγ-rays. The massive star possesses an equatorial disc that is inclined with the orbital plane of the pulsar. Non-thermal emission from the system is believed to be produced by pulsar wind shock and double-peak profiles in the X-ray, and TeVγ-ray light curves are related to the phases of the pulsar passing through the disc region of the star. In this paper, we investigate the interactions between the pulsar wind and stellar outflows, especially with the presence of the disc, and present a multiwavelength modelling of the emission from this system. We show that the double-peak profiles of X-ray and TeVγ-ray light curves are caused by the enhancements of the magnetic field and soft photons at the shock during the disc passages. As the pulsar is passing through the equatorial disc, the additional pressure of the disc pushes the shock surface closer to the pulsar, which causes the enhancement of magnetic field in the shock, and thus increases the synchrotron luminosity. The TeVγ-rays due to the inverse-Compton (IC) scattering of shocked electrons with seed photons from the star are expected to peak around periastron, which is inconsistent with observations. However, the shock heating of the stellar disc could provide additional seed photons for IC scattering during the disc passages, and thus produces the double-peak profiles as observed in the TeVγ-ray light curve. Our model can possibly be examined and applied to other similar gamma-ray binaries, such as PSR J2032+4127/MT91 213, HESS J0632+057, and LS I+61°303.

Decade‐long X‐ray observations of HESS J0632+057

AbstractWe present the results of a decade of X‐ray observations of the gamma ray loud binary HESS J0632+057 and interpret the available broadband data in view of the system geometry and emission mechanisms. We have performed an analysis of all X‐ray data available to date from Swift, XMM‐Newton, Chandra, NuSTAR, and Suzaku. We refine the orbital period of the system to be days (95% c.l.), consistent with previous studies but measured with significantly better accuracy. We report on a hydrogen column density and spectral slope variation along the orbit. We argue that the observed variability can be explained within an “inclined disk” model in which the orbit of the compact object is inclined to the disk of the Be star. We show that the observed X‐ray to TeV emissions can originate from a broken cut‐off power‐law population of electrons and describe a way in which future X‐ray/TeV observations can distinguish between the proposed model and the alternative flip‐flop emission scenario of this system.

Very-high-energy Emission from Magnetic Reconnection in the Radiative-inefficient Accretion Flow of SgrA*

Abstract The cosmic-ray (CR) accelerator at the Galactic center (GC) is not yet established by current observations. Here we investigate the radiative-inefficient accretion flow (RIAF) of Sagittarius A* (SgrA*) as a CR accelerator assuming acceleration by turbulent magnetic reconnection, and derive possible emission fluxes of CRs interacting within the RIAF (the central ∼1013 cm). The target environment of the RIAF is modeled with numerical, general relativistic magnetohydrodynamics together with leptonic radiative transfer simulations. The acceleration of the CRs is not computed here. Instead, we inject CRs constrained by the magnetic reconnection power of the accretion flow and compute the emission/absorption of γ-rays due to these CRs interacting with the RIAF, through Monte Carlo simulations employing the CRPropa 3 code. The resulting very-high-energy (VHE) fluxes are not expected to reproduce the point source HESS J1745-290 as the emission of this source is most likely produced at parsec scales. The emission profiles derived here intend to trace the VHE signatures of the RIAF as a CR accelerator and provide predictions for observations of the GC with improved angular resolution and differential flux sensitivity as those of the forthcoming Cerenkov Telescope Array (CTA). Within the scenario presented here, we find that for mass accretion rates ≳10−7 M ⊙yr−1, the RIAF of SgrA* produces VHE fluxes that are consistent with the High Energy Stereoscopic System (H.E.S.S.) upper limits for the GC and potentially observable by the future CTA. The associated neutrino fluxes are negligible compared with the diffuse neutrino emission measured by the IceCube.

Possible Evidence for Cosmic-Ray Acceleration in the Type Ia SNR RCW 86: Spatial Correlation between TeV Gamma-Rays and Interstellar Atomic Protons

Abstract We present a detailed morphological study of TeV gamma-rays, synchrotron radiation, and interstellar gas in the young Type Ia supernova remnant (SNR) RCW 86. We find that the interstellar atomic gas shows good spatial correlation with the gamma-rays, indicating that the TeV gamma-rays from RCW 86 are likely predominantly of hadronic origin. In contrast, the spatial correlation between the interstellar molecular cloud and the TeV gamma-rays is poor in the southeastern shell of the SNR. We argue that this poor correlation can be attributed to the low-energy cosmic rays (∼1 TeV) not penetrating into the dense molecular cloud due to an enhancement of the turbulent magnetic field around the dense cloud of ∼10–100 μG. We also find that the southwestern shell, which is bright in both synchrotron X-ray and radio continuum radiation, shows a significant gamma-ray excess compared with the interstellar proton column density, suggesting that leptonic gamma-rays via inverse Compton scattering possibly contribute alongside the hadronic gamma-rays. The total cosmic-ray energies of the young TeV gamma-ray SNRs—RX J1713.7−3946, Vela Jr, HESS J1731−347, and RCW 86—are roughly similar, which indicates that cosmic rays can be accelerated in both the core-collapse and Type Ia supernovae. The total energy of cosmic rays derived using the gas density, ∼1048–1049 erg, gives a safe lower limit due mainly to the low filling factor of interstellar gas within the shell.

Polarised radio emission associated with HESS J1912+101

The shell-type TeV source HESS J1912+101 was tentatively identified as an old supernova remnant, but is missing counterparts at radio and other frequencies. We analysed the Sino-German Urumqi λ6 cm survey and the Effelsberg λ11 cm and λ21 cm surveys to identify radio emission from HESS J1912+101 to clarify the question of a supernova origin. We find a partial shell of excessive polarisation at λ6 cm at the periphery of HESS J1912+101. At λ11 cm, its polarised emission is faint and suffers from depolarisation, while at λ21 cm, no related polarisation is seen. We could not separate the shell’s total intensity signal from the confusing intense diffuse emission from the inner Galactic plane. However, a high percentage of polarisation in the shell’s synchrotron emission is indicated. Our results support earlier suggestions that HESS J1912+101 is an old supernova remnant. The synchrotron emission is highly polarised, which is typical for evolved supernova remnants with low surface brightness.