Possible Detection of Gamma-Rays from Epsilon Eridani
Abstract
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, ɛ Eridani, Fomalhaut, and Vega. For three stars (τ Ceti, Fomalhaut, and Vega), we establish upper limits that are consistent with theoretical expectations. For ɛ 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 ɛ Eridani, the >100 MeV gamma-ray luminosity is ∼1027 erg s-1 ≃ 3 × 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 ɛ 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 ɛ Eridani, this would be the first indication of gamma-ray emission from the vicinity of a main-sequence star other than the Sun.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2019
- DOI:
- 10.3847/1538-4357/ab1a3c
- arXiv:
- arXiv:1810.04194
- Bibcode:
- 2019ApJ...878....8R
- Keywords:
-
- gamma rays: stars;
- protoplanetary disks;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 13 pages, 6 figures. Key results are summarized in Table 2 and Figure 5. Accepted to ApJ