Latest results on Galactic sources as seen in VHE gamma-rays

📝 Abstract

As of early 2009, latest results on Galactic sources (mainly shell-type and plerionic supernova remnants), as observed in the very-high-energy gamma-ray domain, are reviewed. A particular attention is given to those obtained with the H.E.S.S experiment during its Galactic Plane Survey which now covers the inner part of the Milky Way. From the well identified gamma-ray sources to those without any obvious counterpart and the putative Galactic diffuse emission, this observational window fully deserves to be celebrated during this International Year of Astronomy, as a new mean to image the Galaxy and reveal sites of particle acceleration, potentially at the origin of Galactic cosmic rays.

💡 Analysis

As of early 2009, latest results on Galactic sources (mainly shell-type and plerionic supernova remnants), as observed in the very-high-energy gamma-ray domain, are reviewed. A particular attention is given to those obtained with the H.E.S.S experiment during its Galactic Plane Survey which now covers the inner part of the Milky Way. From the well identified gamma-ray sources to those without any obvious counterpart and the putative Galactic diffuse emission, this observational window fully deserves to be celebrated during this International Year of Astronomy, as a new mean to image the Galaxy and reveal sites of particle acceleration, potentially at the origin of Galactic cosmic rays.

📄 Content

arXiv:0905.1287v1 [astro-ph.HE] 8 May 2009 Latest results on Galactic sources as seen in VHE gamma-rays M. Renaud Laboratoire APC, CNRS-UMR 7164, Universit´e Paris 7, 10, rue Alice Domon et L´eonie Duquet, 75025 Paris Cedex 13, France As of early 2009, latest results on Galactic sources (mainly shell-type and plerionic supernova remnants), as observed in the very-high-energy γ-ray domain, are reviewed. A particular attention is given to those obtained with the H.E.S.S. experiment during its Galactic Plane Survey which now covers the inner part of the Milky Way. From the well identified γ-ray sources to those without any obvious counterpart and the putative Galactic diffuse emission, this observational window fully deserves to be celebrated during this International Year of Astronomy, as a new mean to image the Galaxy and reveal sites of particle acceleration, potentially at the origin of Galactic cosmic rays. 1 Introduction Current generation of Imaging Atmospheric Cherenkov Telescopes (hereafter, IACTs) have re- cently revealed a new population of Galactic sources emitting in the very-high energy (VHE; E

100 GeV) gamma-ray domain 26. In particular, the H.E.S.S. experiment, through a Galactic Plane Survey performed over the last five years and covering the inner Galaxy (ℓ∈[-90◦,60◦], |b| < 3◦, see Figure 1), has accomplished a major breakthrough by revealing most of these new VHE γ-ray sources, as shown in Figure 2. A variety of source classes, identified (i.e. coincident) with sources known at traditional wavelengths, was found, among them several shell-type super- nova remnants (hereafter, SNRs), isolated or interacting with the surrounding medium, many young and middle-aged offset pulsar wind nebulae (hereafter, PWNe), some young massive star clusters, and a bunch of γ-ray binaries. In regards with SNRs and PWNe, one of the main pending question concerns the nature of the observed VHE γ-ray emission, which relates to the parent population of accelerated particles, or, in other words, the difficulty in disentangling the hadronic and leptonic contributions to the observed emission. This is in turn intimately linked to the more general question of the origin of Galactic cosmic rays (hereafter, CRs). As we shall see in the following, these questions can be efficiently addressed through a detailed investigation of the broadband spectrum of these sources, from radio to VHE γ-ray domains, coupled with the recent theoretical developments of acceleration mechanisms. Figure 1: H.E.S.S. significance image of the inner part of the Galaxy (ℓ∈[-60◦,40◦], |b| < 3◦), as of 2008 (from Chaves et al., H.E.S.S. collaboration, 2008). The color transition from blue to red is set to 5 σ. Besides these sources whose nature is firmly established thanks to the existing multi-wavelength observations, many others fall into the category of the so-called dark sources (i.e. with no clear counterpart at other wavelengths) 44. This can be first explained by the fact that the majority of the VHE γ-ray sources are extended, on scales of the order of tens of arcminutes, with no clear sub-structure. Although current IACTs have reached unprecedented sensitivities and an- gular resolutions, the morphology of most of the faint sources can not be characterised precisely. Moreover, instruments in other domains (radio, infrared, X-rays) usually feature angular resolu- tions at the arcsecond / subarcminute scales, often coupled with relatively small field of views, which (1) does not permit one to perform deep surveys of the whole Galactic Plane, and (2) makes it difficult to reveal large-scale structures coincident with these newly discovered sources. Sep/97 Jun/00 Mar/03 Dec/05 Aug/08 Date 20 40 60 80 Number of VHE Galactic sources Figure 2: A history of VHE Galactic astronomy. The number of VHE Galactic sources is shown against the date, which corresponds to either the date of the publication or the date of the conference where the discovery has been officially announced. The number of Galactic sources has tremendously increased by steps over the last five years, particularly through the Galactic Plane Surveys (GPS, EGPS standing for the extension of the GPS) conducted with H.E.S.S.. HD-Gamma08 corresponds to the 4th International Meeting on High Energy Gamma-Ray Astronomy which was held in Heidelberg, july 2008. The sources marked in red have been revealed in between these steps, mainly thanks to dedicated observations. The extrapolation in time depicted by the dashed line serves as an estimate of the number of new sources which might be revealed in the incoming era of H.E.S.S. II (Southern Hemisphere), MAGIC II and VERITAS (Northern Hemisphere). In this contribution, latest results on VHE Galactic sources are reviewed, with a particular attention to those obtained with H.E.S.S.. The well-identified cases, such as shell-type SNRs and PWNe, are discussed in sections 2 and 3 respectively, together with the implications and new questions related to the accelera

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