Details

Autor(en) / Beteiligte

• Aharonian, F.
• Akhperjanian, A. G.
• Behera, B.
• Beilicke, M.
• Benbow, W.
• Berge, D.
• Boisson, C.
• Borrel, V.
• Braun, I.
• Brion, E.
• Brown, A. M.
• Bulik, T.
• Coignet, G.
• Degrange, B.
• Dickinson, H. J.
• Djannati-Ataï, A.
• Domainko, W.
• Drury, L. O'C.
• Dubus, G.
• Egberts, K.
• Emmanoulopoulos, D.
• Espigat, P.
• Feinstein, F.
• Fiasson, A.
• Fontaine, G.
• Fukui, Y.
• Funk, Seb
• Füßling, M.
• Gallant, Y. A.
• Giebels, B.
• Glicenstein, J. F.
• Goret, P.
• Hadjichristidis, C.
• Hauser, D.
• Hauser, M.
• Heinzelmann, G.
• Henri, G.
• Hermann, G.
• Hinton, J. A.
• Hoffmann, A.
• Hofmann, W.
• Hoppe, S.
• Horns, D.
• Jacholkowska, A.
• de Jager, O. C.
• Kerschhaggl, M.
• Komin, Nu
• Lamanna, G.
• Latham, I. J.
• Le Gallou, R.
• Lenain, J.-P.
• Lohse, T.
• Martin, J. M.
• Martineau-Huynh, O.
• Marcowith, A.
• McComb, T. J. L.
• Moderski, R.
• Moriguchi, Y.
• de Naurois, M.
• Nedbal, D.
• Nolan, S. J.
• Orford, K. J.
• Panter, M.
• Pedaletti, G.
• Pelletier, G.
• Pühlhofer, G.
• Punch, M.
• Ranchon, S.
• Raubenheimer, B. C.
• Raue, M.
• Rayner, S. M.
• Reimer, O.
• Renaud, M.
• Ripken, J.
• Rob, L.
• Rolland, L.
• Rowell, G.
• Ruppel, J.
• Sahakian, V.
• Santangelo, A.
• Schlenker, S.
• Schröder, R.
• Schwarzburg, S.
• Schwemmer, S.
• Shalchi, A.
• Stawarz, Ł.
• Steenkamp, R.
• Stegmann, C.
• Takeuchi, T.
• Tam, P. H.
• Terrier, R.
• van Eldik, C.
• Vasileiadis, G.
• Venter, C.
• Vialle, J. P.
• Vincent, P.
• Vivier, M.
• Völk, H. J.
• Wagner, S. J.
• Ward, M.

Titel

Discovery of very high energy gamma-ray emission coincident with molecular clouds in the W 28 (G6.4-0.1) field

Ist Teil von

• Astronomy and astrophysics (Berlin), 2008-04, Vol.481 (2), p.401-410

Ort / Verlag

Les Ulis: EDP Sciences

Erscheinungsjahr

2008

Link zum Volltext

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• Aims. Observations of shell-type supernova remnants (SNRs) in the GeV to multi-TeV γ-ray band, coupled with those at millimetre radio wavelengths, are motivated by the search for cosmic-ray accelerators in our Galaxy. The old-age mixed-morphology SNR W 28 (distance ~2 kpc) is a prime target due to its interaction with molecular clouds along its northeastern boundary and other clouds situated nearby. Methods. We observed the W 28 field (for ~40 h) at very high energy (VHE) γ-ray energies ($E > 0.1$ TeV) with the HESS. Cherenkov telescopes. A reanalysis of EGRET $E > 100$ MeV data was also undertaken. Results from the NANTEN 4 m telescope Galactic plane survey and other CO observations were used to study molecular clouds. Results. We have discovered VHE γ-ray emission (HESS J1801-233) coincident with the northeastern boundary of W 28 and a complex of sources (HESS J1800-240A, B and C) ~0.5° south of W 28 in the Galactic disc. The EGRET source (GRO J1801-2320) is centred on HESS J1801-233 but may also be related to HESS J1800-240 given the large EGRET point spread function. The VHE differential photon spectra are well fit by pure power laws with indices Γ ~2.3 to 2.7. The spectral indices of HESS J1800-240A, B, and C are consistent within statistical errors. All VHE sources are ~10′ in intrinsic radius except for HESS J1800-240C, which appears pointlike. The NANTEN 12CO($J = 1{-}0$) data reveal molecular clouds positionally associating with the VHE emission, spanning a ~15 km s-1 range in local standard of rest velocity. Conclusions. The VHE/molecular cloud association could indicate a hadronic origin for HESS J1801-233 and HESS J1800-240, and several cloud components in projection may contribute to the VHE emission. The clouds have components covering a broad velocity range encompassing the distance estimates for W 28 (~2 kpc) and extending up to ~4 kpc. Assuming hadronic origin and distances of 2 and 4 kpc for cloud components, the required cosmic-ray density enhancement factors (with respect to the solar value) are in the range ~10 to ~30. If situated at 2 kpc distance, such cosmic-ray densities may be supplied by SNRs like W 28. Additionally and/or alternatively, particle acceleration may come from several catalogued SNRs and SNR candidates, the energetic ultra compact HII region W 28A2, and the HII regions M 8 and M 20, along with their associated open clusters. Further sub-mm observations would be recommended to probe in detail the dynamics of the molecular clouds at velocites > 10 km s-1 and their possible connection to W 28.