Gamma-ray astronomy

Abstract:

Fermi LAT data revealed classical novae as unexpected gamma-ray sources, yet only 6 of 69 of those optically detected in the first 8 years of Fermi LAT observations were confirmed as > 5? gamma-ray sources. These proceedings outline Monte Carlo simulations in which a population of Galactic novae were simulated based on spatial distributions and R-band magnitudes based on their M31 counterparts. Interstellar extinction was added using a double exponential disc model, and gamma-ray properties were defined based on those of the original 6 gamma-ray novae. We demonstrate that observations are consistent will all classical novae being gamma-ray sources, and that the gamma-ray sky background is the largest inhibitor when discovering these sources. Furthermore, we predict that all classical novae occurring within ? 8 kpc and with m R ? 12 will be detected using the Fermi LAT.

Abstract:

Observations of binary stars containing an accreting black hole or neutron star often show x-ray emission extending to high energies (>10 kilo--electron volts), which is ascribed to an accretion disk corona of energetic particles akin to those seen in the solar corona. Despite their ubiquity, the physical conditions in accretion disk coronae remain poorly constrained. Using simultaneous infrared, optical, x-ray, and radio observations of the Galactic black hole system V404 Cygni, showing a rapid synchrotron cooling event in its 2015 outburst, we present a precise 461 ± 12 gauss magnetic field measurement in the corona. This measurement is substantially lower than previous estimates for such systems, providing constraints on physical models of accretion physics in black hole and neutron star binary systems.