X-ray emission from Westerlund 2 detected by SRG/ART-XC and Chandra: search for radiation of TeV leptons

Abstract

ABSTRACT We present the results of current observations of the young compact cluster of massive stars Westerlund 2 (Wd2) with the Mikhail Pavlinsky ART-XC telescope aboard the Spectrum-Roentgen-Gamma (SRG) observatory which we analysed together with the archival Chandra data. In general, Wd2 was detected over the whole electromagnetic spectrum including high-energy gamma rays, which revealed a cosmic ray acceleration in this object to the energies up to tens of TeV. The detection of Wd2 with ART-XC allowed us to perform a joint spectral analysis together with the high resolution Chandra observations of the diffuse emission from a few selected regions in the vicinity of the Wd2 core in the 0.4–20 keV range. To fit the Wd2 X-ray spectrum above a few keV one needs either a non-thermal power-law emission component, or a hot plasma with temperatures ∼ 5 keV. Our magnetohydrodynamic modelling of the plasma flows in Wd2 shows substantially lower electron temperatures in the system and thus the presence of the non-thermal component is certainly preferable. A kinetic model of the particle acceleration demonstrated that the non-thermal component may originate from the synchrotron radiation of multi-TeV electrons and positrons produced in Wd2 in accordance with the TeV photons detection from the source.