Gamma-ray Novae: Rare or Nearby?

Journal article

Classical Novae were revealed as a surprise source of γ-rays in Fermi LAT observations. During the first 8 years since the LAT was launched, 6 novae in total have been detected to >5σ in γ-rays, in contrast to the 69 discovered optically in the same period. We attempt to resolve this discrepancy by assuming all novae are γ-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 kpc20 kpc radius and elliptical bulge with semi major axis 3 kpc3 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 rd=5 kpcrd=5 kpc and zd=0.2 kpczd=0.2 kpc, and demonstrate that even such a rudimentary model can easily reproduce the observed fraction of γ-ray novae, implying that these apparently rare sources are in fact nearby and not intrinsically rare. We conclude that classical novae with mR ≤ 12 and within ≈8 kpc≈8 kpc are likely to be discovered in γ-rays using the Fermi LAT.

Authors: Morris, P; Cotter, G; Chadwick, P; Brown, A

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 465
• Pages: 1218-1226
• Publication date: 2016-10-27
• Acceptance date: 2016-10-24
• DOI: 10.1093/mnras/stw2776
• EISSN: 1365-2966
• ISSN: 0035-8711
• Keywords: cataclysmic variables; gamma-rays; novae; M31; extinction