PoS(ICRC2021)789 International th 12–23 July 2021 July 12–23 37 SICS CONFERENCE SICS CONFERENCE Berlin | Germany Berlin Berlin | Germany Cosmic Ray Conference Ray Cosmic rays 휸 ICRC 2021 THE ASTROPARTICLE PHY ICRC 2021 THEASTROPARTICLE PHY and 푐 ONLINE Stefan Ohm 푏 Romed Rauth, 푎 on behalf of the H.E.S.S. Collaboration 푎 Andreas Specovius, -ray emission around Westerlund 1, a massive young stellar cluster in the 훾 ∗ 푎, [email protected] International Cosmic Ray Conference (ICRC 2021) Presenter -ray emission will be discussed in light of multi-wavelength observations. ∗ th 훾 Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen Centre for Astroparticle Physics, Erwin-Rommel-Str. 1, 91058 Erlangen, Germany University of Innsbruck, Institute for Astro-Technikerstr. and 25 Particle / Physics, 8th Floor, 6020 Innsbruck,DESY, Austria Platanenallee 6, 15738 Zeuthen, Germany E-mail: Massive stellar clusters have recentlyhadronic been cosmic rays hypothesised up as toabout candidates PeV very for energies. extended the Previously, acceleration the of H.E.S.S. Collaboration has reported Milky Way. In thistechnique contribution and is we based present on a anand much updated larger the data analysis energy set, that spectrum allowing us employs oflikelihood to a analysis, the constrain which new is better emission. especially the analysis well morphology suited The for largely analysis extended technique sources. used The origin is of a the three-dimensional Copyright owned by the author(s) under the terms of the Creative Commons 푐 푎 푏 © Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). https://pos.sissa.it/ as seen with H.E.S.S. Christopher van Eldik Lars Mohrmann, (a complete list of authors can be found at the end of the proceedings) 37 July 12th – 23rd, 2021 Online – Berlin, Germany The young massive stellar cluster Westerlund 1 in PoS(ICRC2021)789 465 rays − 훾 -ray sources, 훾 Lars Mohrmann mirror diameter, 28 m 458, has previously been reported by the 463 [14]. These circumstances render stan- − − 2 -ray emission with a spectrum extending to energies 훾 , respectively [1,2]. However, all of these estimates have -diameter mirrors, were taken in operation in 2004 and are [12]) and due to the presence of other nearby ◦ 9 kpc . 12 m 2 3 side length. A fifth telescope (CT5), with ∼ ∼ 465 [13] and HESS J1641 120 m , and −

-ray candidate events using the algorithm introduced in [17] and perform the 훾 M 5 463, the pointing directions of the observations are not distributed symmetrically 10 − ∼ , 458 (diameter of rays from the Cygnus Cocoon by LHAASO] [11 supports this scenario. Regarding from its vicinity, labelled HESS J1646 − 훾 5 Myr − 20 TeV The analysis of the region surrounding Westerlund 1 is very challenging for imaging at- H.E.S.S. is an array of five IACTs located in the Khomas Highland in Namibia. The first The Westerlund 1 data set comprises a total of 362 observations of (up to) 28 minutes each, taken Stellar clusters and star forming regions have recently been established as sources of Westerlund 1 is a young, massive stellar cluster hosting rich populations of Wolf Rayet stars, 5 . ∼ 3 100 TeV -ray observations in the TeV energy band. We note that, for example, the recent measurement of > 훾 mospheric Cherenkov telescopesHESS (IACTs) J1646 like H.E.S.S., both because of the large extent of at GeV energies [5–8].been Moreover, hypothesised massive as stellar sources clusters of (and PeV in cosmic particular rays Westerlund [9, 1)10]. have The hypothesis can be tested through of High Energy Stereoscopic System (H.E.S.S.) Collaborationupdated [12]. H.E.S.S. Here, analysis of we a present much results34 larger from data hours an set in with the about previous 164 publication). hours of live time (compared to in particular HESS J1640 and HESS J1641 around Westerlund 1, further adding to thedirection complexity and of energy the of analysis. We reconstruct therejection incoming of hadronic background events with the method detailed in [18]. For each observation, we four telescopes (CT1-4), featuring in particular Westerlund 1, the detection of dard analysis techniques, in whichsource-free regions the in residual the field hadronic of view, backgroundperform close is to a unapplicable. typically likelihood In analysis estimated order that from tobackground employs address in this a each challenge, 3-dimensional we observation. (3D) While modelits this for application approach the is to residual still the hadronic relatively analysis newthe of in analysis H.E.S.S. using IACT the data data Gammapy analysis, has software package beenpossibility [16] explored to (version 0.17), and perform which likelihood verified naturally analyses [15]. provides based the on We 3D carry background out models. 2. H.E.S.S. data set and analyis arranged in a square with between May 2004 and October 2017, adding upthat to a part total of live time the of observations 164.2 were hours. primarily Owing targeted to at the the fact neighbouring sources HESS J1640 was added in the centre of thehere array in was 2012. recorded Because prior a to considerable thethis portion of installation contribution. the of data CT5, set data analysed from this telescope have not been used for been disputed and are subject of ongoing debate (see e.g. [3,4] and references therein). OB supergiants and Yellow Hypergiants [1].to Its age, total mass, and distance have been estimated The young massive stellar cluster Westerlund 1 as seen with H.E.S.S. 1. Introduction

PoS(ICRC2021)789

− − − −

cm [10 ] sr s F

9 1 1 2 465 4611 − 15 10 5 0 35 30 25 20 − 458. − m 40 -ray emission in Lars Mohrmann 훾 m 44 H.E.S.S. preliminary (b) m . The position of the stellar 48 Right Ascension m 37 TeV . 52 h 0 16 0 0 0 0 0 0 -LAT 4FGL catalogue [19] are marked with 30 00 30 00 30 00 in all directions. The algorithm converges ◦ ◦ ◦ ◦ ◦ 44 45 46 47 − − − − 3

. Declination Fermi 0

3

infiac [ Significance ] σ 5 . 0 5 0 . . . 2 0 5 0 5 . . . . 5 2 0 − 15 12 10 7 . The grey, dashed line displays the boundary of the exclusion map. 휎 m . The blue and orange diamond mark the position of HESS J1640 1 40 − sr 1 − s m 2 45 − (a) H.E.S.S. preliminary cm 9 and enlarging these regions by − m Right Ascension 50 -ray emission. We obtain the exclusion map through an iterative procedure, where 10 휎 463, respectively, whereas the green and red triangle show the location of PSR J1648 of the pointing direction and from outside an exclusion map that covers regions 훾 4601, respectively. Sources from the 4 − − ◦ ) × 2 m 5 . 55 h Sky maps of the Westerlund 1 region, for energies above in order to ensure that all parts of the observed region of interest have sufficient exposure 27 16 / ◦ ◦ ◦ 20 / 46 47 45 Using the adjusted background model, we derive sky maps that display the As a first step in the analysis, we determine a lower energy threshold for each observation,

5 − − −

. Declination 37 TeV . 12 ( and PSR J1650 the region around Westerlund 1, see.1 Fig. Following [ 12], we convolve the measured and predicted with significant we first adjust the backgroundgenerate model a new using map the by identifying current regionsof map with greater an (beginning than excess with of events an corresponding empty to one), a significance and circles. Note that both color scales are saturated at the maximum observed value for HESS J1646 down to this energy.background To model to improve the the observed data description for eachslope of observation above the by the fitting residual its energy normalisation threshold background, and of wefrom spectral the then within observation. adjust For the this adjustment, we consider only events after 5 iterations and we find a very gooddata agreement outside between the the background final model and exclusion the map. observed 3. Results requiring both that the energy bias is tolerable (belowabove 10%) this and that threshold the (see background model [15] is reliable for0 details). We furthermore enforce a minimal energy threshold of cluster is marked bymap, the with contour black lines star, atBox the 4 regions green / used 8 dashed for / the line 12 extraction denotes of the spectra Galacticand are HESS plane. J1641 indicated as well. (a) Significance (b) Flux map, with contour lines at construct a model for the residual hadronic background,and depending reconstructed on energy, two following field-of-view the coordinates procedure describedcarry in out [15]. the We subsequent then high-level employ analysis. Gammapy to Figure 1: The young massive stellar cluster Westerlund 1 as seen with H.E.S.S. PoS(ICRC2021)789 ) 2 . Γ 1 − 465 -ray 퐸 9 TeV − 훾 . 4 ∝ 0 . 1 퐸 < E < d 9 TeV . / 4 10 TeV 푁 2 TeV 8 . . d 1 E > E > 0 for each region, Lars Mohrmann Γ H.E.S.S. preliminary 6 . 0 458, is largely extended − 65 TeV 2 TeV . . 0 1 4 . 0 < E < < E < 37 TeV . Radial distance to Westerlund 1 [deg] 0 2 . 0 37 TeV 65 TeV . . E > 0 0 Radial profiles of the observed excess events In a next step, we aim to study the energy . 0 . 3 0 . 00 75 50 25 00 75 50 25 2 ......

1 0 0 0 0 1 1 1 to the resulting counts spectra.show In Fig. the3(a), best-fit we valuesas of a function ofcentre the of said angular region separation from the of positionerlund the of 1. West- We find that practically all values are spectrum of the observed emission, both forentire the source region andthis for end, sub-regions. we extract eventsdicted To (observed by and the pre- background model) fromthe 16 each square of regions indicated infit Fig. a1(a) power-lawand spectral model ( − omlsdecs [a.u.] excess Normalised Figure 2: in different energy bands. The profilescorrected are acceptance- and normalised, so thatcompared. their shapes can be 4 and dof tests, 푁 − − / 2 2 휒 radius before computing the maps, in order to smooth small- 5.43 / 6 4.86 / 6 4.30 / 6 3.88 / 6 휒 -ray emission from the region surrounding Westerlund 1 with 9 TeV . ◦ 훾 4 22 -ray signal associated with the nearby sources HESS J1640 . 훾 > 0 463, we observe 2 3804 659 4852 4448 . − . . 1 9 1065 0 4 37 14 169 . test (cf.2, Fig. see text for details). . 10 350 − 4 − − 2 0 ) such that a comparable number ) and exhibits various peaks (or “hot spots”). Notably, there is no peak at the position of 휒 > 2 > ◦ 65 . > as additional bands.1 Table lists all Energy bands considered in the analysis. 37 . 1 . 1 0 0 ∼ 9 TeV . Besides detecting a strong An important question concerns the ob- We observe no difference in shape between 4 Energy range [TeV] Excess 10 TeV > Table 1: The second column listsevents, the the third column total denotes the number resultcomparison of of the shape excess and HESS J1641 a very complex morphology. The emission region, denoted HESS J1646 served morphology asAs a a function test of forprofiles energy. of this, the observed we emission, showgies for above in all the threshold ener- 2 Fig. as wellradial energy as for bands. separate ergy We bands define (with boundaries the at first 0.37,and 0.65, three 1.2, en- of excess events above background is observed in each and consider energies energy bands along with theof observed excess number events within theregions displayed total in of Fig. 1(a). 16 square the profiles at differentquantify energies. this finding, In order we to carry out The young massive stellar cluster Westerlund 1 as seen with H.E.S.S. counts with a top-hat kernel of scale fluctuations. Overlaid onfinal the exclusion significance map as map well (Fig. following as1(a)), to the extract we energy location display spectra. of theemission 16 We boundary follows compute square a of the power-law regions, spectrum the flux labelled with map index a–p, (Fig. that1(b) ) we assuming use that the in the (radius the stellar cluster itself, rather, Westerlund 1to seems its to immediate lie surroundings. within a region with lower flux, compared comparing the radial profileoutside this for band each (such energycolumn that of band1, the Table indicate with two that the are one radial statistically profiles that are independent). consistent is with each The computed other results, across from all listed energies. all in the events last PoS(ICRC2021)789 06 (1) . 100 0 ± 33 we find . 2 , however, we = 푝 1 TeV Lars Mohrmann from the average Γ H.E.S.S. preliminary > 10 휎 100 TeV 4 푝 -decay model (red line). 퐸 [TeV] 458 extends to at least 0 and adopt as distance to E 휋 − 3 − . (b) erg 2 10 cm ) to fit a primary proton spectrum 1 = model 1 0 푛 Sum of box regions Combined flux points π 9 kpc . 3 / 푑

11 12 13

of all sub-regions, as a function of the angular − − −

× )(

10 10 10

Γ − −

] s cm [TeV d d 3 E N/ E

2 1 2 − 5 2 . 10 cm 1 ] / -ray emission is caused by the interaction of cosmic-ray 푛 deg 훾 ( 0 . 49 1 ) to the combined flux points; the red line in Fig. 3(b) denotes 10 ) × 푝 cut 8 . 5 퐸 0 / ∼ 푝 푝 퐸 6 . , respectively. For the total energy in protons with 푊 0 (− (a) . The best-fit spectral index and cut-off energy are given by TeV exp ) · 4 . 0 푝 130 250 9 kpc Γ . + − 푝 − 3 -ray spectrum. We assume a target gas density of 퐸 2 = 훾 . 400 0 ∝ ( 푑 Spectrum results. (a) Best-fit spectral index 푝 Angular separation from Westerlund 1 position [ = H.E.S.S. preliminary 퐸 d 0 푝 cut . / 0 Motivated by the similarity of the energy spectra obtained for the sub-regions, we derive The combined flux points show that the emission from HESS J1646 6 4 2 0 8

퐸 . . . . . 푝

More specifically, we make use of Gammapy’s wrapper class for naima models.

2 2 2 3 2 oe a pcrlindex spectral law Power Γ 1 푁 d Figure 3: several tens of While TeV. the highest-energy pointspower-law tend extrapolation, we to do lie not below find the a clear expectation indication fromto of a study a simple cut-off the to possibility the spectrum that either. the In observed order ( and separation from the stellaruncertainty, cluster respectively. (b) position. Combined flux points The (black) red and result line of and fitting a band denote the weighted average and its protons with ambient gas, we employ the naima packagethe resulting [20] combined flux points for the entireThese emission combined region flux by points adding are up displayed theerror in flux bars Fig. points contain3(b). of a all In systematic sub-regions. addition uncertaintyat to low related the energies to statistical – uncertainty, the the that background we modelobserved determine data – by in contributing comparing source-free mostly regions the positioned rate outside of the events exclusion predicted map. by the model to the The young massive stellar cluster Westerlund 1 as seen with H.E.S.S. The best-fit power-law spectra ofindicating all a sub-regions smaller are angular displayed separationby by of the the the dashed blue region solid line. from blue For thenote lines visualisation Westerlund that purposes (with 1 the we darker position); observed plot shades their excess all is power-law sum spectra not up is significant to denoted up to this energy for anycompatible of the with individual sub-regions. the averagepossible index exception is of region “d”, all for which regions,of the spectral shown all index other deviates by regions. by the about We red note,perfectly, and however, that line that the the in deviation true may the spectrum thereforeof does be plot. the not less power-law indices. need significant We than to The conclude suggested follow that by a only theacross the energy power the spectrum comparison law emission does region. not vary in shape significantly the source

PoS(ICRC2021)789

HI − ] s m [K ∆ v

T ), 1 1 − 2 0 8 6 4 2 0 -ray ...... 0 0 0 1 1 0 0 훾 erg s 35 m 10 40 × Lars Mohrmann 2 m 44 ¤ 퐸 > 4601 may be contributing m − H.E.S.S. preliminary 48 Right Ascension m . The blue lines denote significance 1 52 -ray emission measured with H.E.S.S. − h , which approximately corresponds 455216, albeit with a lower energy- 훾 1 16 − Hydrogen gas maps. The map in − km s ) km s 0 0 0 0 0 0 50 ) 30 00 30 00 30 00 − -ray emission is challenging to accomodate. ◦ ◦ ◦ ◦ , 훾 44 45 46 47 50

-ray emission is produced as a by-product of

− − − − 60 − Declination 훾 , (− contours of the Figure 4: the background showswhereas the H purple contour lines I display(from CO emission emission [22]), both (from integrated [21]) in the velocity interval (same as in Fig. 1(a)).tion The of Westerlund black 1. star marks the posi- 6 60 4611 and/or PSR J1650 − (− -ray emission in a hadronic scenario requires the existence 훾 4601], [23 are potential sources of high-energy electrons. In − )[24]. However, taking into account the complex structure of , that is, the (supposed) distance of Westerlund 1 [2]. 1 − 9 kpc . -ray emission as mea- erg s 3 훾 33 ∼ -ray emission. 458 is a largely extended 10 훾 − × 3 458 and in particular the lack of energy-dependent morphology (or, equivalently, the 4611 and PSR J1650 − ¤ − 퐸 < -ray emission is produced through in- 훾 As the explanation of the observed Turning to hadronic scenarios, in which the With our updated analysis, we confirm We consider first the possibility that (part 4 Figure shows both the H I and CO emis- -ray source exhibiting a very complex mor- -ray emission around Westerlund 1 may be interpreted as supporting evidence for this, and could 훾 훾 to a (near) distance of of target material for interactions ofvicinity of the Westerlund cosmic 1 rays, from we radio infersurvey observations. the [21]) and, presence We as consider of a both hydrogen tracer H gasintegrate of I in the dense emission emission the clouds in (from of the the velocity molecular SGPS interval hydrogen, CO emission (from [22]). We Notwithstanding this, in particular PSR J1648 The young massive stellar cluster Westerlund 1 as seen with H.E.S.S. PSR J1648 addition, Westerlund 1 harbours a magnetar, CXOU J164710.2 loss rate ( HESS J1646 uniformity of the energy spectrum acrossof the these source objects is region), responsible a for scenario the in entire which observed any combination to the emission in theiremission immediate in surroundings, between and the we two pulsars. note that we observe a peak in the many of the findings[12]: previously HESS presented J1646 in of) the sured by H.E.S.S. (thiswhile work). the H We I note measurementsence that, indicate of the hydrogen gas pres- in the relevantlocations region, of the the dense gas cloudsdo traced not by coincide CO very well withplaying the the highest regions dis- 4. Discussion phology. Its spectrum extends to several tensTeV of and is uniform across the emission region. verse Compton (IC) scatteringelectrons of (“leptonic” scenario). cosmic-ray Two pulsars with high energy-loss rates ( interactions of cosmic-ray nuclei, we notecosmic-ray that source candidate no – supernova has remnant been (SNR)the found – in stellar often the cluster favoured vicinity as of is a Westerlund 1 apast to supernova plausible date. (SN) source Nonetheless, activity of (up cosmicor to in rays, 150 which SNe interacting may could winds have of be occurred massive accelerated during stars either the [10], due cluster or life to time a [25]) combination of both. The observed enhanced sion, compared with the PoS(ICRC2021)789 Inferring the -ray emission Lars Mohrmann 훾 (2015) 113. (2020) 2497. (2020) A80. 453 Diffuse 492 639 -ray emission observed with 훾 The Age of Westerland 1 (2005) 949. (2020) 3405. Ultrahard spectra of PeV neutrinos On the massive stellar population 434 494 -ray emission from the vicinity of young rays requires the presence of target material Massive stars as major factories of Galactic 훾 훾 Astron. Astrophys. , (2007) 993. 7 Mon. Not. R. Astron. Soc. Mon. Not. R. Astron. Soc. , , 468 Diffuse -ray emission near the young massive cluster NGC Astron. Astrophys. 훾 , (2019) 561. The distance and neutral environment of the massive stellar 3 Diffuse Mon. Not. R. Astron. Soc. (2017) A107. (2020) A60. , (2021) 16. -ray signal may indicate that Westerlund 1 is located at another 훾 The diffuse gamma-ray emission toward the Galactic mini starburst 600 640 912 Astron. Astrophys. , with the Nature Astronomy , 9 kpc . Astrophys. J. 3 , ∼ Astron. Astrophys. , a community-developed core Python package for TeV gamma-ray astronomy [16]. Astron. Astrophys. 2 , , cosmic rays W43 toward the massive star-forming region, W40 from supernovae in compact star clusters massive star cluster RSGC 1 parallax of Westerlund 1 from Gaia DR2 Revisited 3603 cluster Westerlund 1 of the super star cluster Westerlund 1 Full acknowledgements for H.E.S.S. can be found at https://www.mpi-hd.mpg.de/hfm/HESS/ https://gammapy.org 2 [6] R.-Z. Yang and Y. Wang, [7] X.-N. Sun, R.-Z. Yang and X.-Y. Wang, [8] X.-N. Sun, R.-Z. Yang, Y.-F. Liang, F.-K. Peng, H.-M. Zhang et al., [9] A.M. Bykov, D.C. Ellison, P.E. Gladilin and S.M. Osipov, [3] M. Aghakhanloo, J.W. Murphy, N. Smith, J. Parejko, M. Diaz-Rodriguez et al., [5] R.-Z. Yang and F. Aharonian, [2] R. Kothes and S.M. Dougherty, [4] E.R. Beasor, B. Davies, N. Smith, R.D. Gehrz and D.F. Figer, [1] J.S. Clark, I. Negueruela, P. Crowther and S.P. Goodwin, [10] F. Aharonian, R. Yang and E. de Oña Wilhelmi, The young massive stellar cluster Westerlund 1 as seen with H.E.S.S. indicate that a cavity – surroundedmedium by by a the shell cluster. of swept-up However, gas the – production has of been blown into the interstellar .pages/publications/auxiliary/HESS-Acknowledgements-2021.html ThisGammapy research made use of References for interactions. That we doemission not at find an obviousdistance correlation (see of e.g. dense [3]), gas or cloudse.g. that as [26]). the traced region by harbours A CO gas moreH.E.S.S. that detailed will is be study not presented of well in possible a traced forthcoming by explanations publication. CO for emission the (see Acknowledgments PoS(ICRC2021)789 , 158 716 The Astron. , -ray 훾 (2006) 203. -ray Galactic Lars Mohrmann 훾 650 -ray supernova A Neutron Star Astrophys. J. 훾 , Astrophys. J. Suppl. , Validation of (2009) 383. Proc. 35th Int. Cosmic (2012) A114. -ray astronomy Diffuse, Nonthermal 31 Astrophys. J. Suppl. 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Ashkar 13 , D. Berge 8 , H. Yassin , R. Tuffs , J.A. Hinton , A. Dmytriiev , M. Ostrowski , A.M. Taylor , G. Lamanna 3 , A. Montanari , H. Ndiyavala , S. Klepser 14 , Y.A. Gallant 19 31 9 6 , J.N.S. Shapopi 21 11 , Ł. Stawarz 19 10 6 21 21 , M. Jamrozy , G. Pühlhofer , A. Mares 21 8 , R. Brose 11 26 , D.A. Sanchez , C. Venter 3 , F. Rieger , S. Zouari , A. Chen 3 15 19 6 19 , A. Luashvili , N. Tsuji 3 33 , A. Kundu , S. Gabici , T. Armstrong , G. Hermann , B. Khélifi 7 , J.-P. Ernenwein , Y. Becherini 14 , T. Tavernier 19 , J. Veh 11 31 , M. Hörbe , A.S. Seyffert 24 13 31 , A. Nayerhoda 26 , Yu Wun Wong , L. Mohrmann 27 14 , B. Reville , T. Chand , A. Zmija , H. Prokoph 25 , A. Djannati-Ataï 10 , M. Spir-Jacob 32 26 20 11 35 8 , A. Marcowith , M. Breuhaus 20 7 , T. Lohse , H. Salzmann 13 , E. de Ona Wilhelmi , S. Funk 3 , M. Tsirou 17 3 11 , M. Haupt 19 , C. Armand 6 6 , T. Tanaka , D. Huber , S. Einecke , R. Batzofin 3 , S.J. Zhu 31 6 23 , J. Devin , M. Renaud , D. Khangulyan 16 8 , G. Vasileiadis 3 , C. Levy , S. Spencer , G. Kukec Mezek , M. Senniappan , R. Moderski 19 , P. Chambery , S. Sailer 34 6 9 3 15 , M. de Naurois 19 19 36 9 19 , M. Füßling , A. Wierzcholska , C. Arcaro , D.A. Prokhorov 1 3 5 , P. Marchegiani , S. Hattingh 7 3 , A. Zech 20 , L. Olivera-Nieto , L. Tomankova , J. Davies , Q. Remy , U. Katz 32 , K. Egberts 1 11 , M. Barnard 28 , T. Takahashi 27 30 , Zhiqiu Huang 22 , M. Kreter 12 35 , F. Lott , F. Schüssler 28 , A. Mitchell 11 , J. Catalano , F. Leuschner 25 33 , B. van Soelen , M. de Bony de Lavergne , R. White 19 , A. Specovius 10 , V. Sahakian 1 17 3 8 3 17 , V. Poireau , K. Nakashima , S. Ohm 21 , E.O. Angüner 6 11 , L. Sun , V. Marandon 3 , O. Reimer , C. Duffy , I.D. Davids 23 19 6 , M.-H. Grondin 27 11 9 , D. Horns , A.A. Zdziarski 4 27 , A. Barnacka , , M. Tluczykont , K. Katarzyński , G. Fontaine , M. Meyer 2 , D. Kostunin , S. Pita 11 1 , F. Werner , U. Schwanke 9 15 3 , J.-P. Lenain , S. Casanova 16 34 8 6 , J. Bolmont 20 17 16 , T. Murach , H. Spackman , C. van Rensburg , C. Steppa 25 16 , A. Reimer 3 , E. Ruiz-Velasco , L. Oberholzer 9 19 9 , D. Malyshev , F. Ait Benkhali 22 , M. Holler , L. Du Plessis , E. Kasai 4 15 , 6 , G. Peron 11 3 19 , J.F. Glicenstein , , K. Kosack , J. Watson , S. Caroff , D. Zargaryan 33 2 19 , H. Sol 3 11 29 17 , H.M. Schutte , P.J. Meintjes , J. Muller 26 7 , C. Boisson 19 9 6 , P. O’Brien , C. van Eldik , V. Barbosa Martins , C. Thorpe-Morgan , S. Steinmassl , P. Reichherzer 6 , L. Dreyer 6 12 10 11 29 , R. Zanin 15 , , D. Malyshev , T. L. Holch , J. Damascene Mbarubucyeye , R. Konno , M. Lemoine-Goumard 16 23 , D. Glawion 11 1 23 , A. Sinha , F. Aharonian , F. Cangemi , H. Rueda Ricarte , J. Schäfer , G. Fichet de Clairfontaine 9 13 21 , R.D. Parsons , , S.J. Wagner 1 , G. Maurin 7 , E. Moulin 35 3 , I. Jung-Richardt 3 14 32 19 8 21 29 19 , M. Böttcher 15 Instytut Fizyki PAN, ul. Ja¸drowej Radzikowskiego 152, 31-342DESY, D-15738 Kraków, Poland Zeuthen, Germany Obserwatorium Astronomiczne, Uniwersytet Jagielloński, ul. OrlaSchool 171, of 30-244 Physics, University Kraków, of Poland theDepartment Witwatersrand, 1 of Jan Physics and Smuts Electrical Avenue, Braamfontein, Engineering,Institut Johannesburg, Linnaeus für 2050 University, Astronomie South 351 und Africa 95 Astrophysik, Växjö, Universität Sweden Laboratoire Tübingen, Sand Univers et 1, Théories, D 72076 Observatoire de Tübingen,Sorbonne Germany Paris, Université, Université Université PSL, Paris CNRS, Diderot, Université de Sorbonne Paris, Paris 92190 Cité, Meudon, CNRS/IN2P3, France LaboratoireAstronomical de Observatory, The Physique Nucléaire University of et Warsaw, Al. deFriedrich-Alexander-Universität Hautes Erlangen-Nürnberg, Ujazdowskie 4, Erlangen 00-478 Warsaw, Centre Poland for Astroparticle Physics, Erwin-Rommel-Str.Université Bordeaux, CNRS/IN2P3, 1, Centre d’Études D NucléairesUniversité de 91058 de Bordeaux Paris, Gradignan, CNRS, 33175 Astroparticule Gradignan, etDepartment France Cosmologie, of F-75013 Physics Paris, and France Astronomy, TheInstitut University für of Physik Leicester, und University Road, Astronomie, Leicester, Universität LE1School Potsdam, 7RH, of Karl-Liebknecht-Strasse 24/25, United Physical Sciences, Kingdom D University 14476 of Potsdam,Laboratoire Adelaide, Germany Leprince-Ringuet, Adelaide 5005, École Australia Polytechnique, CNRS, InstitutLaboratoire Polytechnique de Univers Paris, et F-91128 Particules Palaiseau, France de Montpellier, Université Montpellier, CNRS/IN2P3,Institut für CC Astro- 72, und Place Teilchenphysik, Leopold-Franzens-Universität Innsbruck, EugèneUniversität A-6020 Hamburg, Bataillon, Innsbruck, Institut Austria für F-34095 Experimentalphysik, Luruper Chaussee 149, D 22761 Hamburg, Germany University of Namibia, Department of Physics,Dublin Private Institute Bag for 13301, Advanced Windhoek Studies, 10005, 31 Namibia Max-Planck-Institut Fitzwilliam für Place, Kernphysik, Dublin P.O. 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Fiasson The young massive stellar cluster Westerlund 1 as seen with H.E.S.S. Full Authors List: H.E.S.S. Collaboration H. Abdalla T. Bylund H. Dalgleish V. Doroshenko V. Baghmanyan B. Bi PoS(ICRC2021)789 Lars Mohrmann 10 Landessternwarte, Universität Heidelberg, Königstuhl, D 69117Institute Heidelberg, Germany of Astronomy, Faculty of Physics, Astronomy andDepartment Informatics, of Nicolaus Physics, Rikkyo Copernicus University, 3-34-1 University, Nishi-Ikebukuro,Nicolaus Grudziadzka Toshima-ku, Copernicus Tokyo Astronomical 171-8501, 5, Center, Japan 87-100 Polish AcademyInstitut of für Sciences, Physik, ul. Humboldt-Universität zu Bartycka Berlin, 18,Department Newtonstr. 00-716 of 15, Warsaw, Poland Physics, D University 12489 of Berlin, the Germany GRAPPA, Free Anton Pannekoek State, Institute PO for Box Astronomy, University 339, of Bloemfontein Amsterdam, 9300, Science South Park 904, Africa 1098 XHYerevan Amsterdam, Physics The Institute, Nether- 2 Alikhanian Brothers St., 375036 Yerevan, Armenia The young massive stellar cluster Westerlund 1 as seen with H.E.S.S. 29 30 Torun, Poland 31 32 33 34 35 lands 36