EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Westerlund 1 and 2 Open Clusters Survey

Guarcello, M. G.; Flaccomio, E.; Albacete-Colombo, J. F.; Almendros-Abad, V.; Anastasopoulou, K.; Andersen, M.; Argiroffi, C.; Bayo, A.; Bartlett, E. S.; Bastian, N.; De Becker, M.; Best, W.; Bonito, R.; Borghese, A.; Calzetti, D; Castellanos, R.; Cecchi-Pestellini, C.; Clark, J. Simon; Clarke, C. J.; Zelati, F. Coti; Damiani, F.; Drake, J. J.; Gennaro, M.; Ginsburg, A.; Grebel, E. K.; Hora, J. L.; Israel, G. L.; Lawrence, G.; Locci, D.; Mapelli, M.; Martinez-Galarza, J. R.; Micela, G.; Miceli, M.; Moraux, E.; Muzic, K.; Najarro, F.; Negueruela, I.; Nota, A.; Pallanca, C.; Prisinzano, L.; Ritchie, B.; Robberto, M.; Rom, T.; Sabbi, E.; Scholz, A.; Sciortino, S.; Trigilio, C.; Umana, G.; Winter, A.; Wright, N. J. and Zeidler, P. (2024). EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Westerlund 1 and 2 Open Clusters Survey. Astronomy & Astrophysics, 682, article no. A49.

DOI: https://doi.org/10.1051/0004-6361/202347778


Context. With a mass exceeding several 104M⊙ and a rich and dense population of massive stars, supermassive young star clusters represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions among stars.

Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars. The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.

Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically, the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec. Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation were carried out using the ACIS-Extract software.

Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a photon flux threshold of approximately 2 × 10−8 photons cm−2s−1. The X-ray sources exhibit a highly concentrated spatial distribution, with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.

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