On Detecting Interstellar Scintillation in Narrowband Radio SETI

Brzycki, Bryan; Siemion, Andrew; Pater, Imke de; Cordes, J. M.; Gajjar, Vishal; Lacki, Brian C.; Sheikh, Sofia

doi:10.3847/1538-4357/acdee0

Cited by 5 publications

(3 citation statements)

References 58 publications

(76 reference statements)

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“…This leads to fluctuations that are correlated on long timescales. In fact, even if the broadcast itself is perfectly coherent, scintillation in the interstellar medium introduces observed variability (Cordes et al 1997;Brzycki et al 2023) Both the fully coherent and partially coherent cases can be covered in a single formula with the use of a factor describing the self-interference:…”

Section: Fully and Partially Coherent Radio Broadcastsmentioning

confidence: 99%

Artificial Broadcasts as Galactic Populations. II. Comparing Individualist and Collective Bounds on Broadcast Populations in Single Galaxies

Lacki

2024

ApJ

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The search for extraterrestrial intelligence includes efforts to constrain populations of artificial broadcasts in other galaxies. Previous efforts use individualist methods, searching for single broadcasts with high signal-to-noise ratio. These would be detected as observables with extreme values. This approach is limited to very bright broadcasts and also is subject to confusion, where a large number of broadcasts blend together to form a noise continuum. The mean value of the total emission provides an additional collective bound: the luminosity of the transmitters is no higher than the galaxy’s observed luminosity. Using the framework developed in Paper I, I evaluate how confusion affects individualist searches. I then compare individualist and collective approaches for radio broadcasts from the Milky Way, M31, and three Virgo Cluster elliptical galaxies. For current observations, confusion blurs narrowband radio broadcasts together in the Virgo ellipticals when there is one broadcast per gigahertz per 1000 stars. The collective bound implies fewer than ∼ 10 6 ( ℓ ¯ / 10 13 W ) − 1 L-band broadcasts per star per gigahertz in the Milky Way wideband and is about 10 and 400 times stronger in M31 and M59, respectively. Applying the collective bound to the far-infrared–radio correlation yields constraints on radio broadcast populations in star-forming galaxies throughout the Universe. The collective bound allows us to rule out large regions of broadcast population parameter space even for distant galaxies. It also imposes constraints on gamma-ray, neutrino, and gravitational-wave broadcasts in the nearest galaxies.

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Section: Fully and Partially Coherent Radio Broadcastsmentioning

confidence: 99%

Artificial Broadcasts as Galactic Populations. II. Comparing Individualist and Collective Bounds on Broadcast Populations in Single Galaxies

Lacki

2024

ApJ

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“…Despite this, doubts persist about its reality, because it cannot be established from the available data whether the signal is genuinely extrasolar, nor has it repeated (Gray & Ellingsen 2002). In principle, this is a solvable problem, though; for example, by looking for interstellar scintillation that could verify its extrasolar origin (Brzycki et al 2023).…”

Section: Prmentioning

confidence: 99%

Deconstructing Alien Hunting

Kipping,

Wright

2023

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The search for extraterrestrial (alien) life is one of the greatest scientific quests, yet it raises fundamental questions about just what we should be looking for and how. We approach alien hunting from the perspective of an experimenter engaging in binary classification with some true- and confounding-positive probabilities (TPP and CPP). We derive the Bayes factor in such a framework between two competing hypotheses, which we use to classify experiments as either impotent, imperfect, or ideal. Similarly, the experimenter can be classified as dogmatic, biased, or agnostic. We show how the unbounded explanatory and evasion capability of aliens poses fundamental problems to experiments directly seeking aliens. Instead, we advocate framing the experiments as looking for that outside of known processes, which means the hypotheses we test do not directly concern aliens per se. To connect back to aliens requires a second level of model selection, for which we derive the final odds ratio in a Bayesian framework. This reveals that it is fundamentally impossible to ever establish alien life at some threshold odds ratio,  crit , unless we deem the prior probability that some as-yet-undiscovered natural process could explain the event is less than ( 1 +  crit ) − 1 . This elucidates how alien hunters need to carefully consider the challenging problem of how probable unknown unknowns are, such as new physics or chemistry, and how it is arguably most fruitful to focus on experiments for which our domain knowledge is thought to be asymptotically complete.

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“…Taking observations many characteristic timescales apart can lead to nonrepeatability of signal detections if amplitude modulations are significant enough, but the likelihood of detection for a strongly scattered signal can be increased by taking many repeated observations of the same location, separated by periods of time longer than a characteristic scintillation timescale (Cordes et al 1997). Work is ongoing to better understand the impact of scintillation on narrowband radio SETI surveys and develop strategies for the detection of scintillating signals (Brzycki et al 2023). SETI surveys of the GC have applied the method of repeated observations (Gajjar et al 2021), but the observing overhead and storage requirements for this sample prevented its application to our survey.…”

Section: Limits On Repeatabilitymentioning

confidence: 99%

The Breakthrough Listen Search for Intelligent Life: Technosignature Search of 97 Nearby Galaxies

Choza,

Bautista,

Croft

et al. 2023

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The Breakthrough Listen search for intelligent life is, to date, the most extensive technosignature search of nearby celestial objects. We present a radio technosignature search of the centers of 97 nearby galaxies, observed by Breakthrough Listen at the Robert C. Byrd Green Bank Telescope. We performed a narrowband Doppler drift search using the turboSETI pipeline with a minimum signal-to-noise parameter threshold of 10, across a drift rate range of ±4 Hz s−1, with a spectral resolution of 3 Hz and a time resolution of ∼18.25 s. We removed radio frequency interference (RFI) by using an on-source/off-source cadence pattern of six observations and discarding signals with Doppler drift rates of 0. We assess factors affecting the sensitivity of the Breakthrough Listen data reduction and search pipeline using signal injection and recovery techniques and apply new methods for the investigation of the RFI environment. We present results in four frequency bands covering 1–11 GHz, and place constraints on the presence of transmitters with equivalent isotropic radiated power on the order of 1026 W, corresponding to the theoretical power consumption of Kardashev Type II civilizations.

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On Detecting Interstellar Scintillation in Narrowband Radio SETI

Cited by 5 publications

References 58 publications

Artificial Broadcasts as Galactic Populations. II. Comparing Individualist and Collective Bounds on Broadcast Populations in Single Galaxies

Artificial Broadcasts as Galactic Populations. II. Comparing Individualist and Collective Bounds on Broadcast Populations in Single Galaxies

Deconstructing Alien Hunting

The Breakthrough Listen Search for Intelligent Life: Technosignature Search of 97 Nearby Galaxies

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