SETI at X-ray Energies - Parasitic Searches from Astrophysical Observations

TL;DR

The paper investigates the prospect of SETI in the X-ray regime by leveraging parasitic searches within astrophysical observations of X-ray binaries and isolated neutron stars. It outlines plausible beacon creation mechanisms, defines a three-tier signal taxonomy (look-at-me, carrier, and high-information) and discusses the detectability of such signals given current and upcoming high time and high spectral resolution X-ray instruments. The analysis highlights the advantages of X-ray channels—extreme luminosities, low ISM absorption, and dispersion-free propagation—alongside practical challenges like photon-limited data rates and telemetry constraints, arguing that onboard processing and all-sky monitors mitigate these issues. The work argues for incorporating X-ray sources into multiwavelength SETI strategies and emphasizes exploiting new detectors and archival data to systematically search for artificial modulations across time and energy scales, potentially guiding cross-band follow-ups.

Abstract

If a sufficiently advanced civilization can either modulate the emission from an X-ray binary, or make use of the natural high luminosity to power an artificial transmitter, these can serve as good beacons for interstellar communication without involving excessive energy costs to the broadcasting civilization. In addition, the small number of X-ray binaries in the Galaxy considerably reduces the number of targets that must be investigated compared to searches in other energy bands. Low mass X-ray binaries containing neutron stars in particular are considered as prime potential natural and artificial beacons and high time resolution (better than 1ms) observations are encouraged. All sky monitors provide the capability of detecting brief powerful artificial signals from isolated neutron stars. New capabilities of X-ray astronomy satellites developed for astrophysical purposes are enabling SETI in new parameter regimes. For example, the X-ray Timing Explorer satellite provides the capability of exploring the sub-millisecond region. Other planned X-ray astronomy satellites should provide significantly improved spectral resolution. While SETI at X-ray energies is highly speculative (and rather unfashionable) by using a parasitic approach little additional cost is involved. The inclusion of X-ray binaries in target lists for SETI at radio and other wavebands is also advocated.