Time-Tagged Event (TTE) data, with 2 microsecond time resolution and 128 energy channels, is the most informative data for Gamma-Ray Burst Monitor (GBM) on-board the Fermi space telescope. Limited by the downlink bandwidth, the standard continuous data are binned in either 0.256 s or 4.096 s, and TTE data is enabled only for 330 s when GBM is triggered. The onboard trigger time scale (≥ 16 ms) makes GBM relatively insensitive to short transient sources with duration less than tens of ms, like Terrestrial Gamma-ray Flashes (TGF) and weaker Short Gamma-Ray Bursts (sGRBs), and makes finding short-period pulsars in continuous data difficult.
To further extend the scientific output of GBM, thanks to improvements in flight software, in the data processing pipeline, and extra downlinks, we have begun operating in a new mode where TTE data is collected for the whole orbit. With such continuous TTE data, a ground search can be implemented on time scales finer than 16 ms, which will result in finding more TGFs and sGRBs. The TGF detection rate is estimated to be 900/year, an order of magnitude improvement in sensitivity over the onboard trigger rate. The ability to discover weaker sGRBs will increase the number of gamma-ray counterparts GBM can provide for gravitational wave detections by Advanced LIGO/Virgo after 2015.