Magnetar outbursts: an observational review
  Transient outbursts from magnetars have shown to be a key property of their
emission, and one of the main way to discover new sources of this class. From
the discovery of the first transient event around 2003, we now count about a
dozen of outbursts, which increased the number of these strongly magnetic
neutron stars by a third in six years. Magnetar outbursts might involve their
multi-band emission resulting in an increased activity from radio to hard
X-ray, usually with a soft X-ray flux increasing by a factor of 10-1000 with
respect to the quiescent level. A connected X-ray spectral evolution is also
often observed, with a spectral softening during the outburst decay. The flux
decay times vary a lot from source to source, ranging from a few weeks to
several years, as also the decay law which can be exponential-like, a power-law
or even multiple power-laws can be required to model the flux decrease. We
review here on the latest observational results on the multi-band emission of
magnetars, and summarize one by one all the transient events which could be
studied to date from these sources.
