Astrophys. J., 878, 8-8 (2019/June-2)
Possible detection of gamma-rays from epsilon Eridani.
RILEY A.H., STRIGARI L.E., PORTER T.A., BLANDFORD R.D., MURGIA S., KERR M. and JOHANNESSON G.
Abstract (from CDS):
We use the Fermi Large Area Telescope gamma-ray observatory to search for gamma-ray emission from four nearby, debris disk-hosting main-sequence stars: τ Ceti, ε Eridani, Fomalhaut, and Vega. For three stars (τ Ceti, Fomalhaut, and Vega), we establish upper limits that are consistent with theoretical expectations. For ε Eridani, we find a possible spatially coincident source with a soft energy spectrum of dN/dE ∼ E–3.6. However, at this stage we are unable to rule out that this emission is due to a more extended feature in the diffuse background. In the interpretation that the emission is due to ε Eridani, the >100 MeV gamma-ray luminosity is ∼1027 erg s–1 ≃ 3 x 10–7 L☉, which is ∼1010 times the gamma-ray luminosity from the disk of the quiet Sun. We find <=2σ evidence of source variability over a ∼7 yr timescale. In the interpretation that the gamma-ray emission is from ε Eridani itself, we consider two possible models: (1) cosmic-ray collisions with solid bodies in the debris disk, which extends out ∼60 au from the host star, and (2) emission from the stellar activity. For the former model, assuming a total disk mass consistent with infrared measurements, we find that the size distribution of bodies is steeper than expected for a collisional cascade state. If confirmed as being associated with ε Eridani, this would be the first indication of gamma-ray emission from the vicinity of a main-sequence star other than the Sun.
© 2019. The American Astronomical Society. All rights reserved.
gamma rays: stars - protoplanetary disks
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