arXiv subjects

G. Dubus

Publications and source records attributed to G. Dubus.

At least 19 recordsLinked to original sources

arXiv2023

Spiral-wave-driven accretion in quiescent dwarf nov{\ae}

In dwarf nov{\ae} and low-mass X-ray binaries, the tidal potential excites spiral waves in the accretion disc. Spiral wave driven accretion may be important in quiescent discs, where the angular momentum transport mechanism has yet to be identified. Previous studies were limited to unrealistically high temperatures for numerical studies or to specific regimes for analytical studies. We perform the first numerical simulation of spiral wave driven accretion in the cold temperature regime appropriate to quiescent discs, which have Mach numbers > 100. We use the new GPU-accelerated finite volume code Idefix to produce global hydrodynamics 2D simulations of the accretion discs of dwarf nov{\ae} systems with a fine-enough spatial resolution to capture the short scale-height of cold, quiescent discs with Mach numbers ranging from 80 to 370. Running the simulations on timescales of tens of binary orbits shows transient angular momentum transport that decays as the disc relaxes from its initial conditions. We find the angular momentum parameter {\alpha} drops to values << 0.01 , too weak to drive accretion in quiescence.

astro-ph.HE↗

arXiv2022

Gamma-ray Eclipses and Orbital Modulation Transitions in the Candidate Redback 4FGL J1702.7-5655

Observations with the Fermi Large Area Telescope (LAT) of the gamma-ray source 4FGL J1702.7-5655, previously classified as a candidate millisecond pulsar, show highly-significant modulation at a period of 0.2438033 days (~ 5.85 hours). Further examination of the folded light curve indicates the presence of narrow eclipses, suggesting this is a redback binary system. An examination of the long-term properties of the modulation over 13 years of LAT observations indicates that the orbital modulation of the gamma-rays changed from a simple eclipse before early 2013, to a broader, more easily detected, quasi-sinusoidal modulation. In addition, the time of the eclipse shifts to ~0.05 later in phase. This change in the orbital modulation properties is, however, not accompanied by a significant overall change in gamma-ray flux or spectrum. The quasi-sinusoidal component peaks ~0.5 out of phase with the eclipse, which would indicate inferior conjunction of the compact object in the system. Swift X-ray Telescope observations reveal a possible X-ray counterpart within the LAT error ellipse. However, radio observations obtained with the Australia Telescope Compact Array do not detect a source in the region. 4FGL J1702.7-5655 appears to have changed its state in 2013, perhaps related to changes in the intrabinary shock in the system. We discuss how the properties of 4FGL J1702.7-5655 compare to other binary millisecond pulsars that have exhibited orbital modulation in gamma rays.

astro-ph.HE↗

arXiv2020

Using radial velocities to reveal black holes in binaries: a test case

Aims. Large radial velocity variations in the LAMOST spectra of giant stars have been used to infer the presence of unseen companions. Some of them have been proposed as possible black hole candidates. We test this selection by investigating the classification of the one candidate having a known X-ray counterpart (UCAC4 721-037069). Methods. We obtained time-resolved spectra from the Liverpool Telescope and a 5ks observation from the Chandra observatory to fully constrain the orbital parameters and the X-ray emission of this system. Results. We find the source to be an eclipsing stellar binary that can be classified as a RS CVn. The giant star fills its Roche Lobe and the binary mass ratio is greater than one. The system may be an example of stable mass transfer from an intermediate-mass star with a convective envelope. Conclusions. Using only radial velocity to identify black hole candidates can lead to many false positives. The presence of an optical orbital modulation, such as observed for all LAMOST candidates, will in most cases indicate that this is a stellar binary.

astro-ph.HE↗

arXiv2020

Thermally-Driven Disc Winds as a Mechanism for X-ray Irradiation Heating in Black Hole X-ray Binaries: The Case Study of GX339-4

X-ray irradiation heating of accretion discs in black hole X-ray binaries (BHXBs) plays a key role in regulating their outburst cycles. However, despite decades of theoretical and observational efforts, the physical mechanism(s) responsible for irradiating these discs remains largely unknown. We have built an observationally-based methodology to estimate the strength of irradiation of BHXB discs by combining multiwavelength X-ray and optical/IR data throughout transient outbursts. We apply this to $\sim15$ yrs of activity in the Galactic BHXB GX339$-$4. Our findings suggest that the irradiation heating required by the optical data is large in this system. Direct illumination of the outer disc does not produce sufficient irradiation, but this should also produce a thermal-radiative wind which adds to the irradiation heating by scattering flux down onto the disc. However, analytic estimates of X-ray illumination from scattering in the wind is still not sufficient to produce the observed heating, even in combination with direct illumination. Either the analytic thermal-radiative wind models are underestimating the effect of the wind, or there are additional scattering mechanisms at work, such as magnetically-driven outflows, acting to increase the optical/IR flux. While wind-driven irradiation is likely a common feature among long-period BHXBs, fully understanding the driving mechanism(s) behind such a wind will require radiation-hydrodynamic simulations.

astro-ph.HE↗

arXiv2019

The impact of thermal winds on the outburst lightcurves of black hole X-ray binaries

The observed signatures of winds from X-ray binaries are broadly consistent with thermal winds, driven by X-ray irradiation of the outer accretion disc. Thermal winds produce mass outflow rates that can exceed the accretion rate in the disc. We study the impact of this mass loss on the stability and lightcurves of X-ray binaries subject to the thermal-viscous instability, which drives their outbursts. Strong mass loss could shut off outbursts early, as proposed for the 2015 outburst of V404 Cyg. We use an analytical model for thermal (Compton) wind mass loss. Scattering in the strong wind expected of long Porb systems enhances the irradiation heating of the outer disc, keeping it stable against the thermal-viscous instability. This accounts very well for the existence of persistently bright systems with large discs such as Cyg X-2, 1E 1740.7-2942, or GRS 1758-258. Wind mass loss shortens the outburst, as expected, but insufficiently to explain the rapid decay timescale of black hole X-ray binary outbursts. However, varying irradiation due to scattering in the wind produces lightcurves with plateaus in long Porb systems like GRO J1655-40. Mass loss is not a major driver for the outburst dynamics up to luminosities 0.1-0.2 L_Edd. Higher luminosities may produce stronger mass loss but their study is complicated since the wind becomes opaque. Magnetic winds seem more promising to explain the fast decay timescales generically seen in black hole X-ray binaries. Thermal winds can play an important role in the outburst dynamics through the varying irradiation heating. This may be evidenced by relating changes in wind properties, X-ray spectra or luminosity, with changes in the optical emission that traces the outer disc. Simulations should enable more accurate estimates of the dependence of the irradiation onto the disc as a function of irradiation spectrum, radius and disc wind properties.

astro-ph.HE↗

arXiv2019

Discovery of the Galactic High-Mass Gamma-ray Binary 4FGL J1405.1-6119

We report the identification from multi-wavelength observations of the Fermi Large Area Telescope (LAT) source 4FGL J1405.1-6119 (= 3FGL J1405.4-6119) as a high-mass gamma-ray binary. Observations with the LAT show that gamma-ray emission from the system is modulated at a period of 13.7135 +/- 0.0019 days, with the presence of two maxima per orbit with different spectral properties. X-ray observations using the Neil Gehrels Swift Observatory X-ray Telescope (XRT) show that X-ray emission is also modulated at this period, but with a single maximum that is closer to the secondary lower-energy gamma-ray maximum. A radio source, coincident with the X-ray source, is also found from Australia Telescope Compact Array (ATCA) observations, and the radio emission is modulated on the gamma-ray period with similar phasing to the X-ray emission. A large degree of interstellar obscuration severely hampers optical observations, but a near-infrared counterpart is found. Near-infrared spectroscopy indicates an O6 III spectral classification. This is the third gamma-ray binary to be discovered with the Fermi LAT from periodic modulation of the gamma-ray emission, the other two sources also have early O star, rather than Be star, counterparts. We consider at what distances we can detect such modulated gamma-ray emission with the LAT, and examine constraints on the gamma-ray binary population of the Milky Way.

astro-ph.HE↗

arXiv2018

The Curious Case of Swift J1753.5-0127: A Black Hole Low-mass X-ray Binary Analogue to Z Cam Type Dwarf Novae

Swift J1753.5-0127 (J1753) is a candidate black hole low-mass X-ray binary (BH-LMXB) that was discovered in outburst in May 2005. It remained in outburst for $\sim12$ years, exhibiting a wide range of variability on various timescales, before entering quiescence after two short-lived, low-luminosity "mini-outbursts" in April 2017. The unusually long outburst duration in such a short-period ($P_{\rm orb}\approx3.24$ hrs) source, and complex variability observed during this outburst period, challenges the predictions of the widely accepted disc-instability model, which has been shown to broadly reproduce the behaviour of LMXB systems well. The long-term behaviour observed in J1753 is reminiscent of the Z Cam class of dwarf novae, whereby variable mass transfer from the companion star drives unusual outbursts, characterized by stalled decays and abrupt changes in luminosity. Using sophisticated modelling of the multi-wavelength light curves and spectra of J1753, during the $\sim12$ years the source was active, we investigate the hypothesis that periods of enhanced mass transfer from the companion star may have driven this unusually long outburst. Our modelling suggests that J1753 is in fact a BH-LMXB analogue to Z Cam systems, where the variable mass transfer from the companion star is driven by the changing irradiation properties of the system, affecting both the disc and companion star.

astro-ph.HE↗

arXiv2018

Understanding X-ray Irradiation in Low-Mass X-ray Binaries directly from their Light-Curves

The X-ray light-curves of the recurring outbursts observed in low-mass X-ray binaries provide strong test beds for constraining (still) poorly understood disc-accretion processes. These light-curves act as a powerful diagnostic to probe the physics behind the mechanisms driving mass inflow and outflow in these binary systems. We have thus developed an innovative methodology, combining a foundation of Bayesian statistics, observed X-ray light-curves, and accretion disc theory. With this methodology, we characterize the angular-momentum (and mass) transport processes in an accretion disc, as well as the properties of the X-ray irradiation-heating that regulates the decay from outburst maximum in low-mass X-ray transients. We recently applied our methodology to the Galactic black-hole low-mass X-ray binary population, deriving from their lightcurves the first-ever quantitative measurements of the $α$-viscosity parameter in these systems \citep{tetarenko2018}. In this paper, we continue the study of these binaries, using Bayesian methods to investigate the X-ray irradiation of their discs during outbursts of strong accretion. We find that the predictions of the disc-instability model, assuming a source of X-ray irradiation proportional to the central accretion rate throughout outburst, do not adequately describe the later stages of BH-LMXB outburst light-curves. We postulate that the complex and varied light-curve morphology observed across the population is evidence for irradiation that varies in time and space within the disc, throughout individual transient outbursts. Lastly, we demonstrate the robustness of our methodology, by accurately reproducing the synthetic model light-curves computed from numerical codes built to simulate accretion flows in binary systems.

astro-ph.HE↗

arXiv2018

H.E.S.S. discovery of very high energy gamma-ray emission from PKS 0625-354

PKS 0625-354 (z=0.055) was observed with the four H.E.S.S. telescopes in 2012 during 5.5 hours. The source was detected above an energy threshold of 200 GeV at a significance level of 6.1$σ$. No significant variability is found in these observations. The source is well described with a power-law spectrum with photon index $Γ =2.84 \pm 0.50_{stat} \pm 0.10_{syst}$ and normalization (at $E_0$=1.0 TeV) $N_0(E_0)=(0.58 \pm 0.22_{stat} \pm 0.12_{syst})\times10^{-12}$ TeV$^{-1}$cm$^{-2}$s$^{-1}$. Multi-wavelength data collected with Fermi-LAT, Swift-XRT, Swift-UVOT, ATOM and WISE are also analysed. Significant variability is observed only in the Fermi-LAT $γ$-ray and Swift-XRT X-ray energy bands. Having a good multi-wavelength coverage from radio to very high energy, we performed a broadband modelling from two types of emission scenarios. The results from a one zone lepto-hadronic, and a multi-zone leptonic models are compared and discussed. On the grounds of energetics, our analysis favours a leptonic multi-zone model. Models associated to the X-ray variability constraint supports previous results suggesting a BL Lac nature of PKS 0625-354, with, however, a large-scale jet structure typical of a radio galaxy.

astro-ph.HE↗

arXiv2018

Strong disc winds traced throughout outbursts in black-hole X-ray binaries

Recurring outbursts associated with matter flowing onto compact stellar remnants (black-holes, neutron stars, white dwarfs) in close binary systems, provide strong test beds for constraining the poorly understood accretion process. The efficiency of angular momentum (and thus mass) transport in accretion discs, which has traditionally been encoded in the $α$-viscosity parameter, shapes the light-curves of these outbursts. Numerical simulations of the magneto-rotational instability that is believed to be the physical mechanism behind this transport find values of $α\sim 0.1-0.2$ as required from observations of accreting white dwarfs. Equivalent $α$-viscosity parameters have never been estimated in discs around neutron stars or black holes. Here we report the results of an analysis of archival X-ray light-curves of twenty-one black hole X-ray binary outbursts. Applying a Bayesian approach for a model of accretion allows us to determine corresponding $α$-viscosity parameters, directly from the light curves, to be $α\sim$0.2--1. This result may be interpreted either as a strong intrinsic rate of angular momentum transport in the disc, which can only be sustained by the magneto-rotational instability if a large-scale magnetic field threads the disc, or as a direct indication that mass is being lost from the disc through substantial mass outflows strongly shaping the X-ray binary outburst. Furthermore, the lack of correlation between our estimates of $α$-viscosity and accretion state implies that such outflows can remove a significant fraction of disc mass in all black hole X-ray binary accretion states, favouring magnetically-driven winds over thermally-driven winds that require specific radiative conditions.

astro-ph.HE↗

arXiv2017

Impact of convection and resistivity on angular momentum transport in dwarf novae

The eruptive cycles of dwarf novae (DN) are thought to be due to a thermal-viscous instability in the accretion disk surrounding the white dwarf (WD). This model has long been known to imply a stress to pressure ratio α~0.1 in outburst compared to α~ 0.01 in quiescence. Such an enhancement in $α$ has recently been observed in simulations of turbulent transport driven by the magneto-rotational instability (MRI) when convection is present, without requiring a net magnetic flux. We independently recover this result by carrying out PLUTO MHD simulations of vertically stratified, radiative, shearing boxes with the thermodynamics and opacities appropriate to DN. The results are robust against the choice of vertical boundary conditions. The thermal equilibrium solutions found by the simulations trace the well-known S-curve in the density-temperature plane. We confirm that the high values of α~ 0.1 occur near the tip of the hot branch of the S-curve, where convection is active. However, we also present thermally-stable simulations at lower temperatures that have standard values of α~ 0.03 despite the presence of vigorous convection. We find no simple relationship between αand the strength of the convection, as measured by the ratio of convective to radiative flux. The cold branch is only very weakly ionized so, in the second part of this work, we studied the impact of non-ideal MHD effects on transport. We include resistivity in the simulations and find that the MRI-driven transport is quenched (α~ 0) below the critical density at which the magnetic Reynolds number R_m \leq 10^4. This is problematic as X-ray emission observed in quiescent systems requires ongoing accretion onto the WD. We verify that these X-rays cannot self-sustain MRI-driven turbulence by photo-ionizing the disk and discuss possible solutions to the issue of accretion in quiescence.

astro-ph.SR↗

arXiv2017

Accretion-ejection morphology of the microquasar SS433 resolved at sub-au scale

We present the first optical observation at sub-milliarcsecond (mas) scale of the microquasar SS 433 obtained with the GRAVITY instrument on the VLT interferometer. The 3.5 hour exposure reveals a rich K-band spectrum dominated by hydrogen Br$γ $ and \ion{He}{i} lines, as well as (red-shifted) emission lines coming from the jets. The K-band continuum emitting region is dominated by a marginally resolved point source ($<$ 1 mas) embedded inside a diffuse background accounting for 10\% of the total flux. The jet line positions agree well with the ones expected from the jet kinematic model, an interpretation also supported by the consistent sign (i.e. negative/positive for the receding/approaching jet component) of the phase shifts observed in the lines. The significant visibility drop across the jet lines, together with the small and nearly identical phases for all baselines, point toward a jet that is offset by less than 0.5 mas from the continuum source and resolved in the direction of propagation, with a typical size of 2 mas. The jet position angle of $\sim$80$^{\circ}$ is consistent with the expected one at the observation date. Jet emission so close to the central binary system would suggest that line locking, if relevant to explain the amplitude and stability of the 0.26c jet velocity, operates on elements heavier than hydrogen. The Br$γ $ profile is broad and double peaked. It is better resolved than the continuum and the change of the phase signal sign across the line on all baselines suggests an East-West oriented geometry alike the jet direction and supporting a (polar) disk wind origin.

astro-ph.HE↗

arXiv2017

The population of TeV pulsar wind nebulae in the H.E.S.S. Galactic Plane Survey

The nine-year H.E.S.S. Galactic Plane Survey (HGPS) yielded the most uniform observation scan of the inner Milky Way in the TeV gamma-ray band to date. The sky maps and source catalogue of the HGPS allow for a systematic study of the population of TeV pulsar wind nebulae found throughout the last decade. To investigate the nature and evolution of pulsar wind nebulae, for the first time we also present several upper limits for regions around pulsars without a detected TeV wind nebula. Our data exhibit a correlation of TeV surface brightness with pulsar spin-down power $\dot{E}$. This seems to be caused both by an increase of extension with decreasing $\dot{E}$, and hence with time, compatible with a power law $R_\mathrm{PWN}(\dot{E}) \sim \dot{E}^{-0.65 \pm 0.20}$, and by a mild decrease of TeV gamma-ray luminosity with decreasing $\dot{E}$, compatible with $L_{1-10\,\mathrm{TeV}} \sim \dot{E}^{0.59 \pm 0.21}$. We also find that the offsets of pulsars with respect to the wind nebula centres with ages around 10 kyr are frequently larger than can be plausibly explained by pulsar proper motion and could be due to an asymmetric environment. In the present data, it seems that a large pulsar offset is correlated with a high apparent TeV efficiency $L_{1-10\,\mathrm{TeV}}/\dot{E}$. In addition to 14 HGPS sources considered as firmly identified pulsar wind nebulae and 5 additional pulsar wind nebulae taken from literature, we find 10 HGPS sources that form likely TeV pulsar wind nebula candidates. Using a model that subsumes the present common understanding of the very high-energy radiative evolution of pulsar wind nebulae, we find that the trends and variations of the TeV observables and limits can be reproduced to a good level, drawing a consistent picture of present-day TeV data and theory.

astro-ph.HE↗

arXiv2016

Gamma-ray blazar spectra with H.E.S.S. II mono analysis: the case of PKS 2155-304 and PG 1553+113

The addition of a 28 m Cherenkov telescope (CT5) to the H.E.S.S. array extended the experiment's sensitivity to lower energies. The lowest energy threshold is obtained using monoscopic analysis of data taken with CT5, providing access to gamma-ray energies below 100 GeV. Such an extension of the instrument's energy range is particularly beneficial for studies of Active Galactic Nuclei with soft spectra, as expected for those at a redshift > 0.5. The high-frequency peaked BL Lac objects PKS 2155-304 (z = 0.116) and PG 1553+113 (0.43 < z < 0.58) are among the brightest objects in the gamma-ray sky, both showing clear signatures of gamma-ray absorption at E > 100 GeV interpreted as being due to interactions with the extragalactic background light (EBL). Multiple observational campaigns of PKS 2155-304 and PG 1553+113 were conducted during 2013 and 2014 using the full H.E.S.S. II instrument. A monoscopic analysis of the data taken with the new CT5 telescope was developed along with an investigation into the systematic uncertainties on the spectral parameters. The energy spectra of PKS 2155-304 and PG 1553+113 were reconstructed down to energies of 80 GeV for PKS 2155-304, which transits near zenith, and 110 GeV for the more northern PG 1553+113. The measured spectra, well fitted in both cases by a log-parabola spectral model (with a 5.0 sigma statistical preference for non-zero curvature for PKS 2155-304 and 4.5 sigma for PG 1553+113), were found consistent with spectra derived from contemporaneous Fermi-LAT data, indicating a sharp break in the observed spectra of both sources at E ~ 100 GeV. When corrected for EBL absorption, the intrinsic H.E.S.S. II mono and Fermi-LAT spectrum of PKS 2155-304 was found to show significant curvature. For PG 1553+113, however, no significant detection of curvature in the intrinsic spectrum could be found within statistical and systematic uncertainties.

astro-ph.HE↗

arXiv2016

Observations of Binary Systems with the H.E.S.S. Telescopes

Observations of binary systems obtained recently with the High Energy Stereoscopic System (H.E.S.S) of Cherenkov telescopes are reported. The outcomes of a detailed observation campaign on PSR B1259-63 during its periastron passage in 2014 will be presented. This system was observed for the first time with H.E.S.S. II, providing spectra and light curves down to 200 GeV, which will be compared with observations conducted during previous periastron passages and with results from an analysis of contemporaneously taken Fermi-LAT data. Also long-term observations of LS 5039 with H.E.S.S in phase I and phase II are reported. This source was monitored at very high energies (VHEs) in a period of time spanning more than ten years. Its spectral energy distribution measured with H.E.S.S. II extends down to 120 GeV. Spectral results from the Fermi-LAT observations are shown as well, and the compatibility with H.E.S.S. results in the overlapping energy range is discussed. The identification of the new gamma-ray binary candidate HESS J1832-093 will also be presented. Furthermore, the search for VHE emission from the microquasars GRS 1915+105, Circinus X-1 and V4641 Sgr based on data from H.E.S.S. observations conducted contemporaneously with the RXTE satellite experiment will be reported. These data provide constraints on the integral gamma-ray flux at different X-ray states of the three sources.

astro-ph.HE↗

arXiv2016

Characterizing the gamma-ray long-term variability of PKS 2155-304 with H.E.S.S. and Fermi-LAT

Studying the temporal variability of BL Lac objects at the highest energies provides unique insights into the extreme physical processes occurring in relativistic jets and in the vicinity of super-massive black holes. To this end, the long-term variability of the BL Lac object PKS 2155-304 is analyzed in the high (HE, 100 MeV < E < 300 GeV) and very high energy (VHE, E > 200 GeV) gamma-ray domain. Over the course of ~9 yr of H.E.S.S observations the VHE light curve in the quiescent state is consistent with a log-normal behavior. The VHE variability in this state is well described by flicker noise (power-spectral-density index ß_VHE = 1.10 +0.10 -0.13) on time scales larger than one day. An analysis of 5.5 yr of HE Fermi LAT data gives consistent results (ß_HE = 1.20 +0.21 -0.23, on time scales larger than 10 days) compatible with the VHE findings. The HE and VHE power spectral densities show a scale invariance across the probed time ranges. A direct linear correlation between the VHE and HE fluxes could neither be excluded nor firmly established. These long-term-variability properties are discussed and compared to the red noise behavior (ß ~ 2) seen on shorter time scales during VHE-flaring states. The difference in power spectral noise behavior at VHE energies during quiescent and flaring states provides evidence that these states are influenced by different physical processes, while the compatibility of the HE and VHE long-term results is suggestive of a common physical link as it might be introduced by an underlying jet-disk connection.

astro-ph.HE↗

arXiv2016

H.E.S.S. limits on line-like dark matter signatures in the 100 GeV to 2 TeV energy range close to the Galactic Centre

A search for dark matter line-like signals was performed in the vicinity of the Galactic Centre by the H.E.S.S. experiment on observational data taken in 2014. An unbinned likelihood analysis was developed to improve the sensitivity to line-like signals. The upgraded analysis along with newer data extend the energy coverage of the previous measurement down to 100 GeV. The 18 h of data collected with the H.E.S.S. array allow one to rule out at 95% CL the presence of a 130 GeV line (at $l = -1.5^{\circ}, b = 0^{\circ}$ and for a dark matter profile centered at this location) previously reported in Fermi-LAT data. This new analysis overlaps significantly in energy with previous Fermi-LAT and H.E.S.S. results. No significant excess associated with dark matter annihilations was found in the energy range 100 GeV to 2 TeV and upper limits on the gamma-ray flux and the velocity weighted annihilation cross-section are derived adopting an Einasto dark matter halo profile. Expected limits for present and future large statistics H.E.S.S. observations are also given.

astro-ph.HE↗

arXiv2016

The supernova remnant W49B as seen with H.E.S.S. and Fermi-LAT

The supernova remnant (SNR) W49B originated from a core-collapse supernova that occurred between one and four thousand years ago, and subsequently evolved into a mixed-morphology remnant, which is interacting with molecular clouds (MC). $γ$-ray observations of SNR/MC associations are a powerful tool to constrain the origin of Galactic cosmic-rays, as they can probe the acceleration of hadrons through their interaction with the surrounding medium and subsequent emission of non-thermal photons. The detection of a $γ$-ray source coincident with W49B at very high energies (VHE; E > 100 GeV) with the H.E.S.S. Cherenkov telescopes is reported together with a study of the source with 5 years of Fermi-LAT high energy $γ$-ray (0.06 - 300 GeV) data. The smoothly-connected combined source spectrum, measured from 60 MeV to multi-TeV energies, shows two significant spectral breaks at $304\pm20$ MeV and $8.4_{-2.5}^{+2.2}$ GeV, the latter being constrained by the joint fit from the two instruments. The detected spectral features are similar to those observed in several other SNR/MC associations and are found to be indicative of $γ$-ray emission produced through neutral-pion decay.

astro-ph.HE↗