Please use this identifier to cite or link to this item:
https://hdl.handle.net/2440/50811
Citations | ||
Scopus | Web of Science® | Altmetric |
---|---|---|
?
|
?
|
Type: | Journal article |
Title: | Discovery of very high energy gamma-ray emission coincident with molecular clouds in the W 28 (G6.4-0.1) field |
Author: | Aharonian, F. Akhperjanian, A. Bazer-Bachi, A. Behera, B. Beilicke, M. Benbow, W. Berge, D. Bernlohr, K. Boisson, C. Bolz, O. Borrel, V. Braun, I. Brion, E. Brown, A. Buhler, R. Bulik, T. Busching, I. Boutelier, T. Carrigan, S. Chadwick, P. et al. |
Citation: | Astronomy and Astrophysics: a European journal, 2008; 481(2):401-410 |
Publisher: | EDP Sciences |
Issue Date: | 2008 |
ISSN: | 0004-6361 1432-0746 |
Statement of Responsibility: | F. Aharonian ... G. Rowell ... et al. |
Abstract: | 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. |
Keywords: | gamma rays: observations |
Rights: | © ESO 2008. Article published by EDP Sciences |
DOI: | 10.1051/0004-6361:20077765 |
Published version: | http://dx.doi.org/10.1051/0004-6361:20077765 |
Appears in Collections: | Aurora harvest 5 Chemistry and Physics publications |
Files in This Item:
File | Description | Size | Format | |
---|---|---|---|---|
hdl_50811.pdf | Published version | 1.12 MB | Adobe PDF | View/Open |
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.