M. Renaud

Detection of TeV emission from the intriguing composite SNR G327.1-1.1

The shock wave of supernova remnants (SNRs) and the wind termination shock in pulsar wind nebula (PWNe) are considered as prime candidates to accelerate the bulk of Galactic cosmic ray (CR) ions and electrons. The SNRs hosting a PWN (known as composite SNRs) provide excellent laboratories to test these hypotheses. The SNR G327.1- 1.1 belongs to this category and exhibits a shell and a bright central PWN, both seen in radio and X-rays. Interestingly, the radio observations of the PWN show an extended blob of emission and a curious narrow finger structure pointing towards the offset compact X-ray source indicating a possible fast moving pulsar in the SNR and/or an asymmetric passage of the reverse shock. We report here on the observations, for a total of 45 hours, of the SNR G327.1-1.1 with the H.E.S.S. telescope array which resulted in the detection of TeV -ray emission in spatial coincidence with the PWN.

Pulsar Wind Nebula candidates recently discovered by H.E.S.S.

H.E.S.S. is currently the most sensitive instrument in the very‐high‐energy (VHE; E>100 GeV) gamma‐ray domain and has revealed many new sources along the Galactic Plane, a significant fraction of which seems to be associated with energetic pulsars. HESS J1825‐137 and Vela X are considered to be the prototypes of such sources, where the large VHE nebula results from the whole history of the pulsar wind and the supernova remnant host, both evolving in a complex interstellar medium. These nebulae have been shown to be offset from the pulsar position and, in the first case, a spectral steepening at increasing distance from the pulsar has been measured. In this context, we present the updated results on two previously published sources, namely HESS J1809‐193 and HESS J1912+101, and the preliminary results on the newly discovered HESS J1356‐645. These extended VHE sources are thought to be associated with the energetic pulsars PSR J1809‐1917, PSR J1913+1011 and PSR J1357‐6429, respectively. We shall discuss the...

Discovery of new TeV supernova remnant shells in the Galactic plane with H.E.S.S.

Supernova remnants (SNRs) are prime candidates for efficient particle acceleration up to the knee in the cosmic ray particle spectrum. In this work we present a new method for a systematic search for new TeV-emitting SNR shells in 2864 hours of H.E.S.S. phase I data used for the H.E.S.S. Galactic Plane Survey. This new method, which correctly identifies the known shell morphologies of the TeV SNRs covered by the survey, HESS J1731-347, RX 1713.7-3946, RCW 86, and Vela Junior, reveals also the existence of three new SNR candidates. All three candidates were extensively studied regarding their morphological, spectral, and multi-wavelength (MWL) properties. HESS J1534-571 was associated with the radio SNR candidate G323.7-1.0, and thus is classified as an SNR. HESS J1912+101 and HESS J1614-518, on the other hand, do not have radio or X-ray counterparts that would permit to identify them firmly as SNRs, and therefore they remain SNR candidates, discovered first at TeV energies as such. Further MWL follow up o...

HESS J1848‐018: Discovery Of VHE γ‐ray Emission From The Direction Of W 43

The extended H.E.S.S. Galactic Plane Survey has resulted in the discovery of numerous very‐high‐energy (VHE; E>100 GeV) γ‐ray emitting sources. One of the most recent discoveries is HESS J1848‐018, which is detected with a post‐trial significance of over 5 σ. HESS J1848‐018 is found to be significantly extended with respect to the H.E.S.S. point spread function (∼0.1°) and has a complex morphology. An extensive search for multi‐wavelength counterparts (from radio to X‐ray) has found it to be in the direction of, but slightly offset from, the star‐forming region W 43, which hosts a giant HII region (G30.8‐0.2), a giant molecular cloud, and the Wolf‐Rayet star WR 121a in the main stellar cluster. If HESS J1848‐018 is indeed associated with W 43, it would be only the second known case, after Westerlund 2, of VHE γ‐ray emission associated with a star‐forming region. We report on the details of this new detection, including a comprehensive analysis of the multi‐wave length data currently available.

Discovery of a pulsar wind nebula associated with IGR J18490‐0000

The IBIS/ISGRI camera on board the INTEGRAL observatory has performed a full survey of the Galactic disk in the hard X‐ray regime from 20 keV up to several hundred of keV with an unprecedented sensitivity and angular resolution in this energy range. Among a large number of compact binary systems, this survey has revealed a number of unidentified objects. Using X‐ray observations of one of these sources, IGR J18490‐0000, we discovered a rather bright non‐thermal pointlike object surrounded by an extended diffuse nebula compatible with the Integral position. The morphology and spectral behaviour of both pointlike and extended X‐ray emissions are reminiscent of a young pulsar wind nebula of a few thousands years. The H.E.S.S. Array has observed the region and we present the TeV detection of the object. We compare this object to other PWNe visible in the hard X‐ray and TeV regime.

Very-high-energy gamma radiation from supernova remnants as seen with H.E.S.S

Very-high-energy (VHE, E > 100 GeV) gamma radiation has already been detected from several supernova remnants (SNRs). These objects, which are well-studied in radio, optical and X-ray wavelengths, constitute one of the most intriguing source classes in VHE astronomy. H.E.S.S., an array of four imaging atmospheric Cherenkov telescopes in Namibia, has recorded an extensive dataset of VHE gamma-ray observations covering the central region of the Milky Way, both from pointed observations as well as from the Galactic Plane Survey conducted in the inner region of the Galaxy. From radio observations, several hundred SNRs are known in the Milky Way, but until now only few of them have been identified as VHE gamma-ray emitters. Using the H.E.S.S. dataset and a large ensemble of radio SNRs localized in the inner region of the Galaxy, the standard framework that links the origin of cosmic rays to the gamma-ray visibility of SNRs can now be tested. Here we present the ensemble of investigated SNRs and discuss constraints on the parameter space used within a theoretical model of hadronic VHE gamma-ray production.

On the nature of HESS J1503‐582 revealed by the H.E.S.S. experiment: Coincidence with a FVW?

The H.E.S.S. survey of the inner Galaxy in the very‐high‐energy (VHE; E>100 GeV) gamma‐ray domain has led to the discovery of many extended sources, some of which do not appear to be associated with any obvious counterpart at traditional wavelengths (radio, infrared and X‐ray). We present the preliminary H.E.S.S. observations on one of these so‐called “dark” sources, namely HESS J1503‐582. After discussing its preliminary properties, we show the results of our search for counterparts in several astronomical windows. We then discuss its possible association with a “Forbidden‐Velocity‐Wing,” a characteristic 21 cm HI line structure that appears as a deviation from the canonical Galactic rotation curve.

Constraints on cosmic-ray efficiency in the supernova remnant RCW 86

Several young supernova remnants (SNRs) have recently been detected in the high-and very-high energy gamma-ray domains, and the nature of this emission is still hotly debated. We have studied the broadband nonthermal emission from one of these SNRs, namely RCW 86, by analyzing ∼40 months of Fermi/LAT data in the high-energy domain, and the archival X-ray data from several instruments. The derived Fermi/LAT upper limits, together with the H.E.S.S. measurements, are incompatible with a standard E−2p hadronic emission arising from p-p interactions, and can only be accommodated by a particle spectrum harder than E−1.8p. In such hadronic scenario, the total energy in hadrons ηCR = ECR/ESN is ∼ 0.07 d2.52/n¯cm−3 (with d2.5≡d/2.5kpc and n¯cm−3≡n¯/1cm−3), and the average magnetic field B must be larger than 50 μG in order to significantly suppress any leptonic contribution. On the other hand, the interpretation of the gamma-ray emission by inverse Compton scattering reproduces the multi-wavelength data using a re...

H.E.S.S. Observations of the Young Composite SNR Kes 75

The composite supernova remnant (SNR) kes 75 harbors a bright pulsar wind nebula (PWN) powered by a young and energetic high magnetic field pulsar, which has recently been the subject of magnetar‐like bursts. Besides, intense thermal X‐ray emission from the remnant shell indicates that high density ambient matter is currently swept‐up by the supernova shock. Observations of Kes 75 in the TeV range is therefore important because it probes the young PWN physics as well as cosmic ray acceleration in SNR shells because of the large target density for pion production and decay. H.E.S.S. has detected very high energy emission (VHE) from this object. We present an updated analysis of this object and discuss the actual origin of the VHE emission and the physical implications of this detection for the PWN and cosmic‐ray (CR) acceleration by the SNR shell.

Probing Efficient Cosmic-Ray Acceleration in Young Supernovae

The formation of a core collapse supernovae (SNe) results in a fast (but non- or mildly-relativistic) shock wave expanding outwards into the surrounding medium. The medium itself is likely modified due to the stellar mass-loss from the massive star progenitor, which may be Wolf-Rayet stars (for Type Ib/c SNe), red supergiant stars (for type IIP and perhaps IIb and IIL SNe), or some other stellar type. The wind mass-loss parameters determine the density structure of the surrounding medium. Combined with the velocity of the SN shock wave, this regulates the shock acceleration process. In this article we discuss the essential parameters that control the particle acceleration and gamma-ray emission in SNe, with particular reference to the Type IIb SN 1993J. The shock wave expanding into the high density medium leads to fast particle acceleration, giving rise to rapidly-growing plasma instabilities driven by the acceleration process itself. The instabilities grow over intraday timescales. This growth, combined with the interplay of non-linear processes, results in the amplification of the magnetic field at the shock front, which can adequately account for the magnetic field strengths deduced from radio monitoring of the source. The maximum particle energy can reach, and perhaps exceed, 1 PeV, depending on the dominant instability. The gamma-ray signal is found to be heavily absorbed by pair production process during the first week after the outburst. We derive the time dependent particle spectra and associated hadronic signatures of secondary particles (gamma-ray, leptons and neutrinos) arising from proton proton interactions. We find that the Cherenkov Telescope Array (CTA) should be able to detect objects like SN 1993J above 1 TeV. We predict a low neutrino flux above 10 TeV, implying a detectability horizon with current or planned neutrino telescopes of 1 Mpc.