Speaker
Mr
Paul Morris
(University of Oxford)
Description
Classical Novae were revealed as a surprise source of $\gamma$-rays in *Fermi* LAT observations. During the first 8 years since the LAT was launched, 6 novae in total have been detected to $ > 5\sigma$ in $\gamma$-rays, in contrast to the $69$ discovered optically in the same period. We attempt to resolve this discrepancy by assuming all novae are $\gamma$-ray emitters, and assigning peak one-day fluxes based on a flat distribution of the known emitters to a simulated population. To determine optical parameters, the spatial distribution and magnitudes of bulge and disc novae in M31 are scaled to the Milky Way, which we approximate as a disc with a $20~\rm{kpc}$ radius and elliptical bulge with semi major axis $3~\rm{kpc}$ and axis ratios 2:1 in the xy plane. We approximate Galactic reddening using a double exponential disc with vertical and radial scale heights of $r_{d} = 5~\rm{kpc}$ and $z_{d} = 0.2~\rm{kpc}$, and demonstrate that even such a rudimentary model can easily reproduce the observed fraction of $\gamma$-ray novae, implying that these apparently rare sources are in fact nearby and not intrinsically rare. We conclude that classical novae with $m_{R} \leq 12$ and within $\approx 8~\rm{kpc}$ are likely to be discovered in $\gamma$-rays using the *Fermi* LAT.
Primary author
Mr
Paul Morris
(University of Oxford)
