The LTT3780 system hosts two known exoplanets-LTT3780b, a rocky super-Earth, and LTT3780c, a temperate sub-Neptune-orbiting a nearby M dwarf on opposite sides of the radius valley. LTT3780c has been proposed as a candidate Hycean world, making the system an important target for astrobiological investigation, particularly in light of recent JWST atmospheric observations. Although biosignature and technosignature searches both seek evidence of life beyond Earth, these approaches have historically been pursued independently. Well-characterized exoplanet systems provide an opportunity to combine these complementary search strategies. In this work, we conducted radio technosignature observations of the LTT3780 system using both the Allen Telescope Array (ATA) and the Karl G. Jansky Very Large Array (VLA). The two facilities provide complementary observational capabilities, with the ATA optimized for wide-band multi-beam post-processing analyses and the VLA enabling high-sensitivity real-time interferometric searches. Across approx 30 hr of total observing time, we searched for narrowband Doppler-drifting signals in the frequency range approx 1–10 GHz. After applying comprehensive radio-frequency interference mitigation and multi-beam consistency tests, no candidate signals consistent with astrophysical or technosignature origins were identified. We place minimum detectable effective isotropic radiated power limits of 4.7 X 10^12–3.6 X 10^13W across the observed bands and facilities. Although no technosignatures were detected, this work demonstrates how complementary observation and analysis strategies can be applied to exoplanets of astrobiological interest and serves as a pathfinder for future combined biosignature and technosignature investigations.

K2-18 b, a sub-Neptune exoplanet located in the habitable zone of its host star, has emerged as an important target for atmospheric characterization, and assessments of potential habitability. Motivated by recent interpretations of JWST observations suggesting a hydrogen-rich atmosphere consistent with Hycean-world scenarios, we conducted a coordinated, multiepoch search for narrowband radio technosignatures using the Karl G. Jansky Very Large Array equipped with the COSMIC backend and the MeerKAT telescope with the BLUSE backend. Our observations span frequencies from 544 MHz to 9.8 GHz and include multiple epochs that cover at least one full orbital period of the planet. In this work we outline, create, and apply a comprehensive postprocessing framework that incorporates observatory-informed radio frequency interference masking, drift-rate filtering based on the expected dynamics of the K2-18 system, multibeam spatial discrimination, primary and secondary transit filtering (when applicable), and signal-to-noise-ratio-based excision of weak and strong spurious signals. Across all bands and epochs, no signals consistent with an astrophysical or artificial origin were identified at a limit of 1012-1013 W. These nondetections allow us to place upper limits on the presence of persistent, isotropic narrowband transmitters within the K2-18 system, providing the first interferometric technosignature constraints for a Hycean-planet candidate. Our results demonstrate the efficacy of coordinated multiepoch interferometric searches and establish a methodological framework for future technosignature studies of nearby potentially habitable exoplanets.

In 2025 July, the third-ever interstellar object, 3I/ATLAS, was discovered on its ingress into the solar system. Similar to the NASA Voyager missions sent in 1977, science probes by extraterrestrial life ("artifact technosignatures") could be sent to explore other stellar systems like our own. In this campaign, we used the SETI Institute's Allen Telescope Array to observe 3I/ATLAS from 1-9 GHz. We detected nearly 74 million narrowband hits in 7.25 hr of data using the newly developed search pipeline bliss. We then blanked hits by frequency and drift rate to mitigate radio frequency interference in our dataset, narrowing the dataset down to similar to 2 million hits. These hits were further filtered by the localization code NBeamAnalysis, and the remaining 211 hits were visually inspected in the time-frequency domain. We did not find any signals worthy of additional follow-up. Accounting for the Doppler drift correction and given the nondetection, we are able to set an effective isotropic radiated power upper limit of 10-110 W on radio technosignatures from 3I/ATLAS across the frequency and drift rate ranges covered by our survey.

We present a high-frequency, wideband observing campaign of the hyperactive repeating fast radio burst FRB 20240114A with the Allen Telescope Array. Between 27 January and 29 October 2024, we obtained 1167 hr of on-source observations across 1344 MHz of simultaneous bandwidth covering frequencies from approximately 900 MHz to 7620 MHz. We detected 97 bursts between 900 MHz and 5 GHz, including a strong S-band activity episode, while no bursts were detected in the highest-frequency tunings above 5 GHz despite substantial exposure. This campaign provides one of the very few extended samples of repeating-FRB activity above 3 GHz, a regime that remains sparsely sampled. We find that the burst rate varies strongly with both observing frequency and epoch, confirming that the emission from FRB 20240114A is highly chromatic and band-limited. We measure the spectro-temporal properties of the bursts and their sub-components, confirming that fractional bandwidth remains approximately scale-invariant. Sub-burst durations decrease toward higher frequencies, and the magnitude of the downward drift rate increases with frequency. The cumulative spectral-energy-density distribution above our completeness threshold is well described by a shallow power law, indicating that high-energy bursts contribute substantially to the observed energy output. We also compare our detections with recently proposed long-timescale frequency-modulation models and find that the ATA high-frequency burst storm is not consistent with a strictly phase-coherent modulation inferred from other datasets. Our results demonstrate that incomplete time-frequency coverage can bias interpretations of burst activity and highlight the need for sustained, simultaneous wideband monitoring of hyperactive repeaters.

The search for technosignatures (also known as the Search for Extraterrestrial Intelligence or SETI) depends critically on our ability to distinguish artificial signals from the rich complexity of natural astrophysical phenomena and radio frequency interference from anthropogenic emissions. As the search for technosignatures increasingly aligns with mainstream astrophysics, complementing the search for biosignatures, it demands not only sophisticated statistical and computational approaches, but also deep domain knowledge across the electromagnetic spectrum. The SKA will play a pivotal role in the next-generation of technosignature searches, providing an unprecedented combination of sensitivity, field of view, and spatial resolution over its wavelength range. Integrating wide-field, high-resolution observations with machine learning and multi-wavelength diagnostics will represent key steps forward. The SKA's singular capabilities will render it an indispensable instrument for the rapid identification and follow-up characterisation of promising technosignature candidates. In this chapter, we discuss the request for high temporal and spectral resolution data products with a main focus on frequency-domain SETI. Nevertheless, multiple SKA observing modes have the potential to substantially advance technosignature research.

The field of Search for Extraterrestrial Intelligence (SETI) searches for “technosignatures” could provide the first detection of life beyond Earth through the technology that an extraterrestrial intelligence may have created. Any given SETI survey, if no technosignatures are detected, should set upper limits based on the kinds of technosignatures it should have been able to detect; the sensitivity of many SETI searches requires that their target sources (e.g., Dyson spheres or Kardashev II/III level radio transmitters) emit with power far exceeding the kinds of technology humans have developed. In this paper, we instead turn our gaze Earthward, minimizing the axis of extrapolation by only considering transmission and detection methods commensurate with an Earth 2024 level. We evaluate the maximum distance of detectability for various present-day Earth technosignatures—radio transmissions, atmospheric technosignatures, optical and infrared signatures, and objects in space or on planetary surfaces—using only present-day Earth instruments, providing one of the first fully cross-wavelength comparisons of the growing toolbox of SETI techniques. In this framework, we find that Earth’s space-detectable signatures span 13 orders of magnitude in detectability, with intermittent, celestially targeted radio transmission (i.e., planetary radar) beating out its nearest nonradio competitor by a factor of 10 ^3 in detection distance. This work highlights the growing range of ways that exoplanet technosignatures may be expressed, the growing complexity and visibility of the human impact upon our planet, and the continued importance of the radio frequencies in SETI.

With the discovery of the third confirmed interstellar object (ISO), 3I/ATLAS, we have entered a new phase in the exploration of these long-predicted objects. Though confirmed discovery of ISOs is quite recent, their utility as targets in the search for technosignatures (historically known as the Search for Extraterrestrial Intelligence – SETI) has been discussed for many decades. With the upcoming NSF-DOE Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), the discovery and tracking of such objects is expected to become routine, and thus so must our examination of these objects for possible technosignatures. Here we review the literature surrounding ISOs as targets for technosignatures, which provides a well-developed motivation for such exploration. We outline four broad classes of technosignatures that are well suited for ISO follow-up, including the type of data needed and the best timing for study. Given the limitations in the current understanding of ISOs, we show that care must be taken in identifying technosignatures based primarily on comparison to objects in the Solar System. We therefore provide a roadmap for careful and consistent study of the population of ISOs in the hope of identifying technosignatures.

We present X-ray (0.3-79 keV) and radio (0.25-203 GHz) observations of the most luminous fast blue optical transient (LFBOT) AT 2024wpp at z = 0.0868, spanning 2-280 days after first light. AT 2024wpp shows luminous (LX approximate to 1.5 x 1043 erg s-1), variable X-ray emission with a Compton hump peaking at delta t approximate to 50 days. The X-ray spectrum evolves from a soft (F nu proportional to nu-0.6) to an extremely hard state (F nu proportional to nu 1.26) accompanied by a rebrightening at delta t approximate to 50 days. The X-ray emission properties favor an embedded high-energy source shining through asymmetric expanding ejecta. We detect radio emission peaking at L9 GHz approximate to 1.7 x 1029 erg s-1 Hz-1 at delta t approximate to 73 days. The spectral evolution is unprecedented: the early millimeter fluxes rise nearly an order of magnitude during delta t approximate to 17-32 days, followed by a decline in spectral peak fluxes. We model the radio emission as synchrotron radiation from an expanding blast wave interacting with a dense environment ( M similar to 10-3M circle dot yr-1 for vw = 1000 km s-1). The inferred outflow velocities increase from Gamma beta c approximate to 0.07c to 0.42c during delta t approximate to 32-73 days, indicating an accelerating blast wave. We interpret these observations as a shock propagating through a dense shell of radius approximate to 1016 cm and then accelerating into a steep density profile rho CSM(r) proportional to r-3.1. All radio-bright LFBOTs exhibit similar circumstellar medium (CSM) density profiles (rho CSM proportional to r-3), suggesting similar progenitor processes. The X-ray and radio properties favor a progenitor involving super-Eddington accretion onto a compact object launching mildly relativistic disk wind outflows.

The potential discovery of life beyond Earth presents unique communication challenges for astrobiology. These include ambiguous data, public misconceptions, and the dynamics of social media platforms. Building on National Aeronautics and Space Administration's 2021 Standards of Evidence (SoE) workshop, a diverse group of experts-scientists, science journalists, content creators, and scholars-were convened during February and March of 2024 for the Communicating Discoveries in the Search for Life in the Universe workshop. This report summarizes structured discussions focused on how to responsibly share findings with different public audiences. Key themes that emerged from the workshop included the following: communicating uncertainty, reaching consensus, and building trust between the scientific community and the public. Such efforts will involve navigating the rapidly evolving landscapes of social media and academic (peer-reviewed) journal publishing. Workshop participants emphasized the need for proactive communication, early-career training in science communication, and interdisciplinary partnerships, all of which can foster sound public understandings of astrobiology research and its myriad of practices, mitigate misinformation, and sustain ongoing support for the search for life. In brief, this report includes the workshop rationale and structure, insights gleaned from past case studies and hypothetical future scenarios, common themes that emerged from the breakout groups, a discussion of the relationship of workshop outcomes to SoE, and guidance for individuals, agencies, and institutions. Key Words: Astrobiology-Science communication-Biosignature detection. Astrobiology 25, 743-758.

Changes in a pulsar’s scintillation characteristics over time can be a useful way to probe the properties of the interstellar medium. Monitoring the scintillation bandwidth can be useful for correcting for scattering delay in pulse arrival time, which could be a significant source of error for precision pulsar timing projects. To better understand the magnitude and trend of scintillation bandwidth changes over long timescales (months–years), we performed long-term monitoring of PSR J0332+5434 with the Allen Telescope Array at radio frequencies ranging from 900 to 1956 MHz. In total, we collected more than 300 observations of PSR J0332+5434 over the course of 10 months, with observations taken daily to weekly. We find a mean scintillation bandwidth of 2.6 MHz (scattering delay of 0.06 μ s) with a standard deviation of 1.3 MHz (0.03 μ s) at 1140 MHz and a mean of 14.7 MHz (0.011 μ s) with a standard deviation of 9.1 MHz (0.006 μ s) at 1668 MHz. We see significant change over time on a timescale of ∼200 days, suggesting that, for pulsars that are timed with submicrosecond precision, correcting for similar changes over time will be vital. We find no evidence for periodicity in the scattering delays. We describe a novel method for measuring the scaling index and compare it to established methods. We find the mean scintillation bandwidth frequency scaling goes as ν ^3.1 ± 1.0 .

We present the first multi-epoch broadband radio and millimeter monitoring of an off-nuclear TDE using the VLA, ALMA, ATA, AMI-LA, and the SMA. The off-nuclear TDE 2024tvd exhibits double-peaked radio light curves and the fastest evolving radio emission observed from a TDE to date. With respect to the optical discovery date, the first radio flare rises faster than F_ ν∼ t^9 at Δt = 88-131 days, and then decays as fast as F_ ν∼ t^-6. The emergence of a second radio flare is observed at Δt ≈ 194 days with an initial fast rise of F_ ν∼ t^18, and an optically thin decline of F_ ν∼ t ^-12. We interpret these observations in the context of a self-absorbed and free-free absorbed synchrotron spectrum, while accounting for both synchrotron and external inverse-Compton cooling. We find that a single prompt outflow cannot easily explain these observations and it is likely that either there is only one outflow that was launched at Δt ∼ 80 days, or two distinct outflows, with the second launched at Δt ∼ 170-190 days. The nature of these outflows, whether sub-, mildly-, or ultra-relativistic, is still unclear, and we explore these different scenarios. Finally, we find a temporal coincidence between the launch time of the first radio-emitting outflow and the onset of a power-law component in the X-ray spectrum, attributed to inverse-Compton scattering of thermal photons.

Developing algorithms to search through data efficiently is a challenging part of searching for signs of technology beyond our solar system. We have built a digital signal processing system and computer cluster on the backend of the Karl G. Jansky Very Large Array (VLA) in New Mexico in order to search for signals throughout the Galaxy consistent with our understanding of artificial radio emissions. In our first paper, we described the system design and software pipelines. In this paper, we describe a postprocessing pipeline to identify persistent sources of interference, filter out false positives, and search for signals not immediately identifiable as anthropogenic radio frequency interference during the VLA Sky Survey. As of 01 September 2024, the Commensal Open-source Multi-mode Interferometric Cluster had observed more than 950,000 unique pointings. This paper presents the strategy we employ when commensally observing during the VLA Sky Survey and a postprocessing strategy for the data collected during the survey. To test this postprocessing pipeline, we searched toward 511 stars from the $Gaia$ catalog with coherent beams. This represents about 30 minutes of observation during VLASS, where we typically observe about 2000 sources per hour in the coherent beamforming mode. We did not detect any unidentifiable signals, setting isotropic power limits ranging from 10$^{11}$ to 10$^{16}$W.

We present the first multiepoch broadband radio and millimeter monitoring of an off-nuclear tidal disruption event (TDE) using the Very Large Array, the Atacama Large Millimeter/submillimeter Array, the Allen Telescope Array, the Arcminute Microkelvin Imager Large Array, and the Submillimeter Array. The off-nuclear TDE AT 2024tvd exhibits double-peaked radio light curves and the fastest-evolving radio emission observed from a TDE to date. With respect to the optical discovery date, the first radio flare rises faster than F _ν ∼ t ^9 at Δ t = 88–131 days and then decays as fast as F _ν ∼ t ^−6 . The emergence of a second radio flare is observed at Δ t ≈ 194 days with an initial fast rise of F _ν ∼ t ^18 and an optically thin decline of F _ν ∼ t ^−12 . We interpret these observations in the context of a self-absorbed and free–free absorbed synchrotron spectrum, while accounting for both synchrotron and inverse Compton cooling. We find that a single prompt outflow cannot easily explain these observations and that it is likely that either there is only one outflow that was launched at Δ t ∼ 80 days or there are two distinct outflows, with the second launched at Δ t ∼ 170–190 days. The nature of these outflows, whether sub-, mildly, or ultrarelativistic, is still unclear, and we explore these different scenarios. Finally, we find a temporal coincidence between the launch time of the first radio-emitting outflow and the onset of a power-law component in the X-ray spectrum, attributed to inverse Compton scattering of thermal photons.

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 10 26 W, corresponding to the theoretical power consumption of Kardashev Type II civilizations.

The SETI Ellipsoid is a strategy for technosignature candidate selection that assumes that extraterrestrial civilizations who have observed a galactic-scale event-such as supernova 1987A-may use it as a Schelling point to broadcast synchronized signals indicating their presence. Continuous wide-field surveys of the sky offer a powerful new opportunity to look for these signals, compensating for the uncertainty in their estimated time of arrival. We explore sources in the TESS continuous viewing zone, which corresponds to 5% of all TESS data, observed during the first 3 yr of the mission. Using improved 3D locations for stars from Gaia Early Data Release 3, we identified 32 SN 1987A SETI Ellipsoid targets in the TESS continuous viewing zone with uncertainties better than 0.5 lt-yr. We examined the TESS light curves of these stars during the Ellipsoid crossing event and found no anomalous signatures. We discuss ways to expand this methodology to other surveys, more targets, and different potential signal types.

The search for extraterrestrial intelligence at radio frequencies has focused on spatial filtering as a primary discriminant from terrestrial interference. Individual search campaigns further choose targets or frequencies based on criteria that theoretically maximize the likelihood of detection, serving as high-level filters for interesting targets. Most filters for technosignatures do not rely on intrinsic signal properties, as the radio-frequency interference (RFI) environment is difficult to characterize. In B. Brzycki et al. (2023), we proposed that the effects of interstellar medium (ISM) scintillation on narrowband technosignatures may be detectable under certain conditions. In this work, we perform a dedicated survey for scintillated technosignatures toward the Galactic center and Galactic plane at the C band (3.95-8.0 GHz) using the Robert C. Byrd Green Bank Telescope (GBT) as part of the Breakthrough Listen program. We conduct a Doppler drift search and directional filter to identify potential candidates and analyze results for evidence of scintillation. We characterize the C-band RFI environment at the GBT across multiple observing sessions spread over months and detect RFI signals with confounding scintillation-like intensity modulation. We do not find evidence of putative narrowband transmitters with drift rates between +/- 10 Hz s-1 toward the Galactic center, ISM-scintillated or otherwise, above an equivalent isotropic radiated power of 1.9 x 1017 W up to 8.5 kpc.

A pulsar's scintillation bandwidth is inversely proportional to the scattering delay, making accurate measurements of scintillation bandwidth critical to characterize unmitigated delays in efforts to measure low-frequency gravitational waves with pulsar timing arrays. In this pilot work, we searched for a subset of known pulsars within similar to 97% of the data taken with the Puerto Rico Ultimate Pulsar Processing Instrument for the AO327 survey with the Arecibo telescope, attempting to measure the scintillation bandwidths in the data set by fitting to the 2D autocorrelation function of their dynamic spectra. We successfully measured 38 bandwidths from 23 pulsars (six without prior literature values), finding that: almost all of the measurements are larger than the predictions from NE2001 and YMW16 (two popular galactic models); NE2001 is more consistent with our measurements than YMW16; Gaussian fits to the bandwidth are more consistent with both electron density models than Lorentzian ones; and for the 17 pulsars with prior literature values, the measurements between various sources often vary by a few factors. The success of Gaussian fits may be due to the use of Gaussian fits to train models in previous work. The variance of literature values over time could relate to the scaling factor used to compare measurements, but also seems consistent with time-varying interstellar medium parameters. This work can be extended to the rest of AO327 to further investigate these trends, highlighting the continuing importance of large archival data sets for projects beyond their initial conception.

FRB 20220912A is a repeating Fast Radio Burst (FRB) that was discovered in Fall 2022 and remained highly active for several months. We report the detection of 35 FRBs from 541 hours of follow-up observations of this source using the recently refurbished Allen Telescope Array, covering 1344 MHz of bandwidth primarily centered at 1572 MHz. All 35 FRBs were detected in the lower half of the band with non-detections in the upper half and covered fluences from 4-431 Jy-ms (median$=$48.27 Jy-ms). We find consistency with previous repeater studies for a range of spectrotemporal features including: bursts with downward frequency drifting over time; a positive correlation between bandwidth and center frequency; and a decrease in sub-burst duration over time. We report an apparent decrease in the center frequency of observed bursts over the 2 months of the observing campaign (corresponding to a drop of $6.21\pm 0.76$ MHz per day). We predict a cut-off fluence for FRB 20220912A of $F_\textrm{max}\lesssim 10^4$ Jy-ms, for this source to be consistent with the all-sky rate, and find that FRB 20220912A significantly contributed to the all-sky FRB rate at a level of a few percent for fluences of $\sim$100 Jy-ms. Finally, we investigate characteristic timescales and sub-burst periodicities and find a) a median inter-subburst timescale of 5.82$\pm$1.16 ms in the multi-component bursts and b) no evidence of strict periodicity even in the most evenly-spaced multi-component burst in the sample. Our results demonstrate the importance of wideband observations of FRBs, and provide an important set of observational parameters against which to compare FRB progenitor and emission mechanism models.

Abstract We describe archival observations and analysis of the HD 110067 planetary system using the Green Bank Telescope (GBT) as part of the Breakthrough Listen search for technosignatures. The star hosts six sub-Neptune planets in resonant orbits, and we tune the drift rate range of our search to match the properties of the system derived by Luque et al. Our observations cover frequencies from 1 to 11.2 GHz, using the GBT’s L, S, C, and X-band receivers, to an equivalent isotropic radiated power limit of ∼3 × 1012 W. No technosignatures were found, but this unusual system remains an interesting target for future technosignature searches.

Planet-planet occultations (PPOs) occur when one exoplanet occults another exoplanet in the same system, as seen from the Earth's vantage point. PPOs may provide a unique opportunity to observe radio "spillover" from extraterrestrial intelligences' radio transmissions or radar being transmitted from the farther exoplanet toward the nearer one for the purposes of communication or scientific exploration. Planetary systems with many tightly packed, low-inclination planets, such as TRAPPIST-1, are predicted to have frequent PPOs. Here, the narrowband technosignature search code turboSETI was used in combination with the newly developed NbeamAnalysis filtering pipeline to analyze 28 hr of beamformed data taken with the Allen Telescope Array during 2022 late October and early November, from 0.9 to 9.3 GHz, targeting TRAPPIST-1. During this observing window, seven possible PPO events were predicted using the NbodyGradient code. The filtering pipeline reduced the original list of 25 million candidate signals down to 6 million by rejecting signals that were not sky-localized and, from these, identified a final list of 11,127 candidate signals above a power-law cutoff designed to segregate signals by their attenuation and morphological similarity between beams. All signals were plotted for visual inspection, 2264 of which were found to occur during PPO windows. We report no detections of signals of nonhuman origin, with upper limits calculated for each PPO event exceeding equivalent isotropic radiated powers of 2.17-13.3 TW for minimally drifting signals and 40.8-421 TW in the maximally drifting case. This work constitutes the longest single-target radio search for extraterrestrial intelligence of TRAPPIST-1 to date.