Fermi Gamma-ray Space Telescope

Feb 23, 2015

CTTE Data Temporarily Disabled

The GBM team has temporarily disabled the production of continuous Time-Tagged Event (CTTE) data and will produce TTE data only when in triggered mode. A TTE bandwidth limit is overcome during a brief interval around the time of a trigger, allowing the collection of higher count-rate data than is possible with CTTE data. The reason for the change is the detection of an outburst from SGR 1935+2154 by Swift and Fermi (GCN #17485 and #17496). SGR bursts are short enough to be contained in the high-bandwidth data interval (which ends 0.22 s post-trigger) and this operational change will potentially increase the quality of data for a very bright burst. To mitigate the loss in sensitivity of GBM to weaker, untriggered SGR bursts during this period without CTTE data, the team has also increased the time resolution of continuous CTIME data from 256 ms to its finest resolution of 64 ms. We will monitor the SGR outburst activity and resume CTTE data production and nominal CTIME data resolution when the probability of further bright bursts becomes small. This return to nominal operating mode will be announced as a fermi-news item.