Fermi Gamma-ray Space Telescope

The massive star-forming region W49A as a high-energy gamma-ray emitter : detection with the Fermi-LAT

Francois Brun
(Marianne Lemoine-Goumard)


Cosmic ray acceleration is expected to occur in massive star forming regions (SFR) at the termination shock of the strong stellar winds, through collective wind scenarios or via diffusive shock acceleration at supernova remnants shockwaves. Cosmic rays can interact with the abundant molecular material and produce high-energy (HE) gamma-rays. However, since SFRs are usually expected to be extended and can contain standard HE gamma-ray emitters such as SNRs or PWNs, both the detection and the identification of this type of object are challenging. W49A is a giant molecular cloud that hosts several active sites of massive star formation. It is one of the most luminous giant radio HII regions in our Galaxy and is considered one of the best analogue to starburst phenomenon seen in other galaxies. This source, located ~11 kpc away from the sun, has a small angular size and doesn't contain any known SNR or PWN. In addition, the vicinity of the supernova remnant W49B makes the whole W49 complex particularly interesting to comparatively study the particle acceleration efficiency of these two types of astrophysical objects. In this contribution we will present the detection of HE gamma-rays towards W49A with the Fermi-LAT and we will discuss the origin of this emission.