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Gamma ray constraints on Decaying Dark Matter

We derive new bounds on decaying Dark Matter from the gamma ray measurements of (i) the isotropic residual (extragalactic) background by Fermi and (ii) the Fornax galaxy cluster by HESS. We find that those from (i) are among the most stringent constraints currently available, for a large range of DM masses and a variety of decay modes, excluding half-lives up to ~10^26 to few 10^27 seconds. In particular, they rule out the interpretation in terms of decaying DM of the e^\pm spectral features in Pamela, Fermi and HESS, unless very conservative choices are adopted. We also discuss future prospects for CTA bounds from Fornax which, contrary to the present HESS constraints of (ii), may allow for an interesting improvement and may become better than those from the current or future extragalactic Fermi data.