While ESA's satellite INTEGRAL was observing the sky, it spotted a burst of gamma-rays -- high-energy photons -- coming from the nearby galaxy M82. Only a few hours later, ESA's XMM-Newton X-ray space telescope searched for an afterglow from the explosion but found none. An international team realized that the burst must have been an extra-galactic flare from a magnetar, a young neutron star with an exceptionally strong magnetic field.
