The X-ray emission of the supernova remnant W49B: indications of a jet-like explosion

We report on an XMM-Newton EPIC observation of the galactic supernova remnant W49B, which, on the basis of previous Chandra observations, has been supposed to be the first remnant of a gamma-ray burst discovered in our galaxy. We performed a spatially resolved spectral analysis, which revealed oversolar abundances of Si, S, Ar, Ca, and Fe. Moreover, a high overabundance of Ni is required in the bright central elongated region. Our results support a scenario where the remnant was generated by an asymmetric bipolar explosion where the eastern jet is hotter and more Fe-rich than the western one. An alternative interpretation which associates the X-ray emission with spherically symmetric ejecta interacting with a dense belt of ambient inhomogeneous material can also explain the X-ray emission morphology. We perform estimates of the mass and energy of the remnant and we compare the observed abundances with the yields produced in hypernovae and supernovae nucleosynthesis models. Our results support the aspherical explosion scenario, but the claim for an association of W49B with an hypernova (and a gamma-ray burst) is not directly supported by any observational evidence.