Capture of a Red Giant by the Black Hole Sagittarius A* as a Possible Origin for the TeV Gamma Rays from the Galactic Center

Abstract

Nonthermal TeV � -ray emission within a multiparsec scale has been observed from the center region of our Galaxy. We argue that these � -raysare the result of transientactivity ofthe massive blackhole Sgr Athat residesat theGalacticcenter.Severalthousandyearsago,theblackholemayhaveexperiencedanactivephasebycapturinga red giant star and forming an accretion disk, temporarily behaving like an active galactic nucleus. A powerful jet, whichcontainsplentyofhigh-speedprotons,waslaunchedduringtheprocess.Theserunawayprotonsinteractwith thedenseambientmedium,producingTeV � -rayemissionthroughthe � 0 -decayprocess.Weshowthatthetotalenergy deposited in this way is large enough to account for observations. The diffusion length of protons is also consistent with the observed size of the TeV source. Subject headingg accretion, accretion disks — black hole physics — galaxies: active — galaxies: jets — Galaxy: center