Optical Flashes from Beam-Driven Light Sails with the Roman, Rubin and Euclid Observatories

@misc{guillochon2026optical,
  title = {{Optical Flashes from Beam-Driven Light Sails with the Roman, Rubin and Euclid Observatories}},
  author = {James Guillochon and Abraham Loeb},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.07574},
  eprint = {2609.07574},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.07574},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Optical Flashes from Beam-Driven Light Sails with the Roman, Rubin and Euclid Observatories
AU  - James Guillochon
AU  - Abraham Loeb
PY  - 2026
DA  - 2026/09/07
PB  - arXiv
DO  - 10.48550/arxiv.2609.07574
UR  - https://arxiv.org/abs/2609.07574
AB  - The primary challenge of rocket propulsion is the burden of accelerating the spacecraft's own fuel. Light sails leave the propellant at home, with the achievable speed set by the sail area, the thermal tolerance of its material, and the power of the driving array. In GL15 we showed that leakage from a microwave array driving such a sail between habitable worlds produces Jansky-level radio transients lasting tens of seconds at $100$~pc. We take that leak to optical and near-infrared, where Fresnel matching would shrink the aperture to ∼ 20--$100$~m at 1 μm, but the intensity on that aperture is 2×10^8 W m^−2, five orders above published directed-energy loadings. Spreading $1.5$~TW at ∼20 kW m^−2 is a ∼10~km phased array, pushing the emitters; Lubin's 10^3 W m^−2 loading is a $40$~km array, comfortable but more expensive. A tenth-wave delay on $40$~m tiles sized so one tile still covers the sail leaks $0.054$ of the power ($80$~GW) into a halo. The typical Galactic detection is a single ∼30~s peak at m_AB≃19.4 in F146 at $8$~kpc; a pair $87$~s apart, about one in five, is the confirmation test. \emph{Roman}'s Galactic Bulge Time Domain Survey reaches $109$~kpc at 8σ on a faint host, so a pointed flash of that halo is visible from anywhere in the Galaxy if the beam points at us. For $10−−40$~km optical beamers held to ∼λ/10 at v_max≳250 km s^−1, N_det=1 wants Γ_6h≃16 and a null search limits Γ_6h≲49, a factor-of-three window in launch rate. The real threshold is set by PSF-coincident stellar and instrumental transients. If intensity-limited optical beamers are commonly employed in our galaxy, this activity could be revealed by Roman, Rubin and Euclid at no additional observing cost.
ER  -