Fermi LAT and GBM detection of the X6.9 Solar Flare of August 9 2011

ATel #3552; Nicola Omodei (Stanford U.), Giacomo Vianello (SLAC), Melissa Pesce-Rollins (INFN Pisa), Alice Allafort (KIPAC), David Gruber (MPE), on behalf of the Fermi LAT and GBM collaborations
on 12 Aug 2011; 19:38 UT
Credential Certification: Gino Tosti (tosti@pg.infn.it)

Tweet

Using a non standard analysis technique developed to maximize the efficiency of detecting low energy gamma-rays (20 MeV - 1 GeV) from rapid transient sources, the Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, detected an increasing gamma-ray flux in temporal coincidence with the bright X6.9 Solar Flare of August 9 2011. The excess is in spatial coincidence with the position of the Sun at the time of the flare. Gamma-ray emission has been detected with a post-trial significance of 11.5 sigma above background. The main emission episode is approximately between 08:01:40 and 08:05:00 UT, and possibly a tail visible until around 08:08:20 UT. The peak of the emission is observed around 08:03:20.0 UT (Fermi Mission Elapsed Time (MET)=334569802).

Due to pile up of hard X-rays in the Anti-Coincidence Detector in coincidence with the bright Solar Flare, standard gamma-ray event data from MET=334569555 to MET=334571070 should not be used to evaluate the spectrum.

Using standard P7SOURCE event class, excluding the aforementioned time interval and selecting only events with a reconstructed energy above 100 MeV, the Sun was not detected in any time intervals where it was in the field of view. After the prompt flare, the Sun was observed for 19 minutes starting at 09:20 UT and the flux upper limit (95% C.L, >100 MeV) is 9.1x10^-7 ph cm^-2 s^-1.

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of the Sun will continue. For this detection, the Fermi LAT contact person is Nicola Omodei (nicola.omodei@gmail.com)

This Solar Flare was also independently detected by the Gamma-Ray Burst Monitor (GBM). GBM is composed of 12 thallium-activated sodium iodide (NaI) scintillation detectors (8 keV to 1 MeV) and two bismuth germanate scintillation (BGO) detectors (150 keV - 40 MeV). The GBM trigger occurred at 08:01:01.2 UT (Fermi MET= 334569663) and gamma-ray emission is detected up to ~ 08:13 UT in the 50 keV - 300 keV energy range. The most energetic emission episode (> 500 keV) started at ~ 08:02:05 UT and lasted until ~ 08:03:43 UT with gamma-ray energies detected up to about 5 MeV in the BGO. The peak of the emission is observed at 08:02:11 UT. In addition, GBM detected a second, softer and fainter, solar flare emission episode starting only 16 minutes after the first trigger.

The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.