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Geminga is a nearby (250 pc) middle-aged (spin-down time scale ~12,000 years)pulsar associated with a supernova remnant. Geminga has been a prime candidatefor the origin of the unexpectedly high flux of cosmic-ray positrons above 10GeV detected at Earth. Extended TeV gamma-ray emission from a 2-degree regionaround the Geminga pulsar was detected by the HAWC observatory, thus suggestingefficient, high-energy leptonic acceleration. Fermi-LAT observations show thatthe density of GeV leptons in the TeV nebula is lower than predicted by singlezone and two zone diffusion models constrained with the HAWC measurements.However, the energy gap between Fermi-LAT and HAWC (~500 GeV to ~1 TeV) remainsunder-examined. The VERITAS gamma-ray observatory is sensitive in the energyrange from 100 GeV to greater than 30 TeV, filling the gap between Fermi-LATand HAWC. Therefore, VERITAS measurements potentially provide missinginformation. VERITAS has observed Geminga for 93 hours since 2009 including 28hours in the 2018/2019 season. However, the standard VERITAS data analysistechniques have insufficient sensitivity to sources extended at the scale ofthe HAWC detection, due to difficulties with background estimation. Wedeveloped the Matched Runs Method (MRM) for VERITAS analysis of spatiallyextended sources. MRM has been demonstrated to be an effective technique byapplying it to archival VERITAS data, and we are currently applying it to theGeminga observations. Here we present the summary of the MRM.

Search for Very-High-Energy (E $>$ 100 GeV) Emission from Geminga Supernova by VERITAS