Constraints on the non-thermal emission from η Carinae’s blast wave of 1843

¹ Max-Planck-Institut für Kernphysik, PO Box 103980, 69029 Heidelberg, Germany
e-mail: joanna.skilton@mpi-hd.mpg.de
² X-ray and Observational Astronomy Group, Department of Physics and Astronomy, University of Leicester, LE1 7RH, UK
³ School of Physics and Astronomy, University of Leeds, LS2 9JP, UK
⁴ CSIRO Astronomy and Space Science, PO Box 76, Epping, NSW 1710, Australia

Received: 10 November 2011
Accepted: 3 January 2012

Abstract

Non-thermal hard X-ray and high-energy (HE; 1 MeV < E < 100 GeV) γ-ray emission in the direction of η Carinae has been recently detected using the INTEGRAL, AGILE and Fermi satellites. This emission has been interpreted either in the framework of particle acceleration in the colliding wind region between the two massive stars or in the very fast moving blast wave which originates in the historical 1843 “great eruption”. Archival Chandra data has been reanalysed to search for signatures of particle acceleration in η Carinae’s blast wave. No shell-like structure could be detected in hard X-rays and a limit has been placed on the non-thermal X-ray emission from the shell. The time dependence of the target radiation field of the Homunculus is used to develop a single zone model for the blast wave. Attempting to reconcile the X-ray limit with the HE γ-ray emission using this model leads to a very hard electron injection spectrum dN/dE ∝ E ^− Γ with Γ < 1.8, harder than the canonical value expected from diffusive shock acceleration.