First RHESSI terrestrial gamma ray flash catalog

Abstract

We present a summary of data from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) terrestrial gamma ray flash (TGF) catalog. We describe the RHESSI search algorithm and discuss its limitations due to its design emphasis on cleanliness rather than completeness. This search algorithm has identified 820 TGFs between March of 2002 and February of 2008. Radiation damage to the RHESSI detectors has resulted in a decreased sensitivity after early 2006 and a corresponding decrease in the number of identified TGFs in the years 2006–2008. Prior to this, the average rate of occurrence was one TGF every 2.35 days. RHESSI has seen multiple TGFs associated with a single storm system, either in the same orbit or in the subsequent orbit. The X‐ray flux in a 100 ms pedestal region surrounding all of the TGFs is (1.3 ± 1.9) × 10−3 times the average peak flux of a TGF. We show that RHESSI was counting at or near its maximum throughput during the peak 50 μs of many of the TGFs and that we do not yet know the maximum possible brightness of a TGF. On short time scales, some TGFs may be much brighter than could be observed by either RHESSI or BATSE. Finally, we show that there is no detectable change in the spectrum of TGFs when they are grouped by brightness, geographic latitude, geomagnetic latitude, or the local day or night.