Probing cosmic-ray distribution around Cygnus OB2

Discussion timeslot (ZOOM-Meeting): 15. July 2021 - 18:00
ZOOM-Meeting URL: https://desy.zoom.us/j/98542982538
ZOOM-Meeting ID: 98542982538
ZOOM-Meeting Passcode: ICRC2021
Corresponding Session: https://icrc2021-venue.desy.de/channel/44-The-Origins-of-Galactic-Cosmic-Rays-GAD-GAI-CRD/125
Live-Stream URL: https://icrc2021-venue.desy.de/livestream/Discussion-04/5

Abstract:
'Massive star clusters (MSCs) have recently received renewed attention as possible cosmic ray (CR) factories. In fact, the conversion of a few % of the cluster kinetic energy into accelerated particles can easily account for the gamma-ray emission observed in coincidence with some MSCs, in a scenario where gamma-rays would result from pions produced in collisions between the relativistic hadrons and the ambient gas. In addition, the gamma-ray spatial profile suggests that CRs are continuously produced during a period compatible with the typical age of a MSC. Cygnus OB2 is one of the most massive star clusters in the Milky Way, located near the Cygnus X star-forming complex. Fermi-LAT observations of the region revealed an extended gamma-ray emission (Cygnus Cocoon) possibly coming from CRs accelerated by Cygnus OB2. Recent studies claim that this extended emission is compatible with a CR distribution of freshly accelerated escaping particles. In this work, we compare the observed gamma-ray emission and its radial profile with the prediction of a theoretical model where particles are accelerated at the termination shock of the cluster wind. In particular, we study the impact that different distribution of gas around the cluster have in shaping the Cocoon morphology. While the total gamma-ray emission is very well reproduced, implying a maximum energy of accelerated protons of ~100 TeV, the predicted radial shape is almost flat, compatible with HAWC data but not with Fermi-LAT ones.'

Authors: Stefano Menchiari
Co-Authors: Elena Amato | Giovanni Morlino | Niccolò Bucciantini
Indico-ID: 621
Proceeding URL: https://pos.sissa.it/395/920