  On 2009 June 5, the Gamma-ray Burst Monitor (GBM) onboard the Fermi Gamma-ray
Space Telescope triggered on two short, and relatively dim bursts with spectral
properties similar to Soft Gamma Repeater (SGR) bursts. Independent
localizations of the bursts by triangulation with the Konus-RF and with the
Swift satellite, confirmed their origin from the same, previously unknown,
source. The subsequent discovery of X-ray pulsations with the Rossi X-ray
Timing Explorer (RXTE), confirmed the magnetar nature of the new source, SGR
J0418+5729. We describe here the Fermi/GBM observations, the discovery and the
localization of this new SGR, and our infrared and Chandra X-ray observations.
We also present a detailed temporal and spectral study of the two GBM bursts.
SGR J0418+5729 is the second source discovered in the same region of the sky in
the last year, the other one being SGR J0501+4516. Both sources lie in the
direction of the galactic anti-center and presumably at the nearby distance of
~2 kpc (assuming they reside in the Perseus arm of our galaxy). The
near-threshold GBM detection of bursts from SGR J0418+5729 suggests that there
may be more such dim SGRs throughout our galaxy, possibly exceeding the
population of bright SGRs. Finally, using sample statistics, we conclude that
the implications of the new SGR discovery on the number of observable active
magnetars in our galaxy at any given time is <10, in agreement with our earlier
estimates.
