2022A&A...666A.124A

Query : 2022A&A...666A.124A

2022A&A...666A.124A - Astronomy and Astrophysics, volume 666A124 (2022/10-1)

A deep spectromorphological study of the γ-ray emission surrounding the young massive stellar cluster Westerlund 1.

AHARONIAN F., ASHKAR H., BACKES M., BARBOSA MARTINS V., BECHERINI Y., BERGE D., BI B., BOTTCHER M., DE BONY DE LAVERGNE M., BRADASCIO F., BROSE R., BRUN F., BULIK T., BURGER-SCHEIDLIN C., CANGEMI F., CAROFF S., CASANOVA S., CERRUTI M., CHAND T., CHANDRA S., CHEN A., CHIBUEZE O., CRISTOFARI P., DAMASCENE MBARUBUCYEYE J., DJANNATI-ATAI A., ERNENWEIN J.-P., FEIJEN K., FICHET DE CLAIRFONTAINE G., FONTAINE G., FUNK S., GABICI S., GALLANT Y.A., GHAFOURIZADEH S., GIAVITTO G., GIUNTI L., GLAWION D., GLICENSTEIN J.F., GOSWAMI P., GRONDIN M.-H., HARER L.K., HAUPT M., HINTON J.A., HORBE M., HOFMANN W., HOLCH T.L., HOLLER M., HORNS D., JAMROZY M., JOSHI V., JUNG-RICHARDT I., KASAI E., KATARZYNSKI K., KATZ U., KHELIFI B., KLUZNIAK W., KOMIN N., KOSACK K., KOSTUNIN D., KUKEC MEZEK G., LANG R.G., LE STUM S., LEMIERE A., LEMOINE-GOUMARD M., LENAIN J.-P., LEUSCHNER F., LOHSE T., LUASHVILI A., LYPOVA I., MACKEY J., MAJUMDAR J., MALYSHEV D., MARANDON V., MARCHEGIANI P., MARCOWITH A., MARTI-DEVESA G., MARX R., MAURIN G., MEYER M., MITCHELL A., MODERSKI R., MOHRMANN L., MONTANARI A., MOULIN E., MULLER J., MURACH T., NAKASHIMA K., DE NAUROIS M., NAYERHODA A., NIEMIEC J., OHM S., OLIVERA-NIETO L., DE ONA WILHELMI E., OSTROWSKI M., PANNY S., PANTER M., PARSONS R.D., PERON G., PROKHOROV D.A., PUHLHOFER G., PUNCH M., QUIRRENBACH A., RAUTH R., REICHHERZER P., REIMER A., REIMER O., RENAUD M., REVILLE B., RIEGER F., ROWELL G., RUDAK B., RUIZ-VELASCO E., SAHAKIAN V., SALZMANN H., SANCHEZ D.A., SANTANGELO A., SASAKI M., SCHUSSLER F., SCHUTTE H.M., SCHWANKE U., SHAPOPI J.N.S., SPECOVIUS A., SPENCER S., STAWARZ L., STEENKAMP R., STEINMASSL S., STEPPA C., SUSHCH I., SUZUKI H., TAKAHASHI T., TANAKA T., TERRIER R., THORPE-MORGAN C., TSIROU M., TSUJI N., TUFFS R., UNBEHAUN T., VAN ELDIK C., VAN SOELEN B., VECCHI M., VEH J., VENTER C., VINK J., WAGNER S.J., WHITE R., WIERZCHOLSKA A., WONG Y.W., ZACHARIAS M., ZARGARYAN D., ZDZIARSKI A.A., ZHU S.J., ZOUARI S., ZYWUCKA N., BLACKWELL R., BRAIDING C., BURTON M., CUBUK K., FILIPOVIC M., TOTHILL N. and WONG G.

Abstract (from CDS):


Context. Young massive stellar clusters are extreme environments and potentially provide the means for efficient particle acceleration. Indeed, they are increasingly considered as being responsible for a significant fraction of cosmic rays (CRs) that are accelerated within the Milky Way. Westerlund 1, the most massive known young stellar cluster in our Galaxy, is a prime candidate for studying this hypothesis. While the very-high-energy γ-ray source HESS J1646-458 has been detected in the vicinity of Westerlund 1 in the past, its association could not be firmly identified.
Aims. We aim to identify the physical processes responsible for the γ-ray emission around Westerlund 1 and thus to understand the role of massive stellar clusters in the acceleration of Galactic CRs better.
Methods. Using 164 h of data recorded with the High Energy Stereoscopic System (H.E.S.S.), we carried out a deep spectromorphological study of the γ-ray emission of HESS J1646-458. We furthermore employed H I and CO observations of the region to infer the presence of gas that could serve as target material for interactions of accelerated CRs.
Results. We detected large-scale (∼2° diameter) γ-ray emission with a complex morphology, exhibiting a shell-like structure and showing no significant variation with γ-ray energy. The combined energy spectrum of the emission extends to several tens of TeV, and it is uniform across the entire source region. We did not find a clear correlation of the γ-ray emission with gas clouds as identified through H I and CO observations.
Conclusions. We conclude that, of the known objects within the region, only Westerlund 1 can explain the majority of the γ-ray emission. Several CR acceleration sites and mechanisms are conceivable and discussed in detail. While it seems clear that Westerlund 1 acts as a powerful particle accelerator, no firm conclusions on the contribution of massive stellar clusters to the flux of Galactic CRs in general can be drawn at this point.

Abstract Copyright: © F. Aharonian et al. 2022

Journal keyword(s): acceleration of particles - radiation mechanisms: non-thermal - shock waves - stars: massive - gamma rays: general - galaxies: star clusters: individual: Westerlund 1

Simbad objects: 24

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Number of rows : 24
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 19090 0
2 NAME 30 Dor C Rad 05 36 07.70 -69 11 52.6           ~ 87 1
3 V* V712 Car EB* 10 23 58.0126366512 -57 45 48.937268268 15.466 15.473 13.5 12.6   O3If*/WN6+O3If*/WN6 176 0
4 Cl Westerlund 2 OpC 10 23 58.1 -57 45 49           ~ 400 0
5 GUM 29 HII 10 24 14.6 -57 46 58           ~ 219 0
6 * eta Car s*b 10 45 03.545808 -59 41 03.95124 6.37 7.03 6.48 6.123 4.41 LBV 2543 0
7 SNR G338.3-00.0 SNR 16 40 43.2 -46 31 48           ~ 175 2
8 HESS J1641-463 gam 16 41 01.7 -46 18 11           ~ 27 0
9 HESS J1645-455 gam 16 45 -45.5           ~ 1 0
10 4U 1642-45 LXB 16 45 48.1 -45 36 42           ~ 467 1
11 HESS J1646-458 gam 16 46 00.0 -45 48 00           ~ 14 0
12 HESS J1647-465 gam 16 47 -46.5           ~ 1 0
13 Cl Westerlund 1 OpC 16 47 02.4 -45 51 07           ~ 655 1
14 PSR J1647-4552 Psr 16 47 10.18 -45 52 16.7           ~ 217 1
15 PSR J1648-4611 Psr 16 48 22.02 -46 11 16.0           ~ 73 0
16 HESS J1649-460 gam 16 49 -46.0           ~ 2 0
17 PSR J1650-4601 Psr 16 50 18.62 -46 01 18.6           ~ 13 0
18 HESS J1652-462 gam 16 52 -46.2           ~ 1 0
19 NAME 1806-20 Star Cluster OpC 18 08 39.0 -20 24 39           ~ 35 1
20 PSR J1808-2024 Psr 18 08 39.32 -20 24 40.1           ~ 1316 2
21 [KMN95] Star A s*b 18 08 40.312 -20 24 41.14           LBV 43 3
22 PSR B1823-13 Psr 18 26 13.06 -13 34 48.1           ~ 460 1
23 NAME Cyg X Cld 20 30 04.7973633 +40 51 36.002197           ~ 962 1
24 NAME Cyg Complex reg 20 32 +45.0           ~ 667 0

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