Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-07-18
Astronomy and Astrophysics
Astrophysics
11 pages including 1 figure. Accepted to PASJ after minor revisions. A discussion on the chance probability of witnessing Sgr
Scientific paper
There are several lines of evidence that the super-massive black hole at the Galactic center had higher activities in the past than directly observed at present. Here I show that these lines of evidence can quantitatively and consistently be explained if the mean accretion rate during the past ~10^7 yrs has been ~10^{3-4} times higher than the current rate, by the picture of radiatively inefficient accretion flow (RIAF) and associated outflow that has been successfully applied to Sgr A*. I argue that this increased rate and its duration are theoretically reasonable in the Galactic center environment, while the accretion rate suddenly dropped about 300 years ago most likely because of the shell passage of the supernova remnant Sgr A East. The chance probability of witnessing Sgr A* in such a low state is not extremely small (~0.5%). The outflow energetics is sufficient to keep the hot (~8 keV) diffuse gas observed in the Galactic center region. Then, I show that a significant amount of positrons should have been created around the event horizon during the higher activity phase, and injected into interstellar medium by the outflow. The predicted positron production rate and propagation distance are close to those required to explain the observed 511 keV annihilation line emission from the Galactic bulge, giving a natural explanation for the large bulge-to-disk ratio of the emission. The expected injection energy into interstellar medium is about 1 MeV, which is also favorable as an explanation of the 511 keV line emission.
No associations
LandOfFree
A RIAF Interpretation for the Past Higher Activity of the Galactic Center Black Hole and the 511 keV Annihilation Emission does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with A RIAF Interpretation for the Past Higher Activity of the Galactic Center Black Hole and the 511 keV Annihilation Emission, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A RIAF Interpretation for the Past Higher Activity of the Galactic Center Black Hole and the 511 keV Annihilation Emission will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-122615