Fast Radio Search Detects 0.714kHz Periodic Signals from Nearby Stars

Scientists are intensifying the search for extraterrestrial intelligence, and a new study presents results from a focused radio search of five nearby stars. Yu Hu, Bo-Lun Huang, and Vishal Gajjar, alongside colleagues including Xiao-Hang Luan and Zhen-Zhao Tao, from the Institute for Frontiers in Astronomy and Astrophysics and Dezhou University, utilised the powerful FAST radio telescope to scan for narrow-band, periodic radio signals. This research, detailing observations at L-band, represents a significant step forward in the Search for Extraterrestrial Intelligence (SETI) by establishing stringent upper limits on the potential power of any artificial beacons emanating from these stellar systems , currently the most sensitive constraints of their kind.

FAST Telescope Searches Nearby Stars for Signals

Scientists have reported a radio Search for Extraterrestrial Intelligence (SETI) focused on identifying periodic, kHz-wide signals emanating from five of the closest stars observable with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Employing the 19-beam L-band receiver, spanning frequencies from 1.05 to 1.45GHz, the team secured 1200-second tracking observations of Groombridge 34A/B, Ross 248, 61 Cygni B, and Ross 128. Dynamic spectra, captured across all beams and both linear polarisations, underwent a channel-by-channel search utilising a fast-folding algorithm, meticulously designed to detect periods ranging from 1.1 to 300 seconds. A sophisticated, multi-layered Radio Frequency Interference (RFI) mitigation pipeline was central to the analysis, leveraging multi-beam occupancy, cross-target bad-channel statistics, XX/YY polarisation coincidence, broad frequency masking, and narrow, site-specific RFI exclusion zones, culminating in clustering within period-frequency space.
This innovative pipeline was rigorously validated using FAST observations of PSR B0329+54, successfully recovering the known 0.714-second spin period and its harmonic structure within the anticipated beam. For the selected stellar sample, successive data reduction steps diminished raw Fast Folding Algorithm (FFA) hit lists, exceeding 10^6 hits per target, to a manageable number of cluster-level candidates. Crucially, all remaining candidates exhibited clear signatures of radio-frequency interference in both phase-time and phase-frequency diagnostics, leading the researchers to report no convincing detections of periodic transmitters within the parameters of their search. The study establishes upper limits of approximately (7-9) x 10^9W on the isotropic-equivalent Effective Isotropic Radiated Power (EIRP) of kHz-wide periodic beacons at these stars, representing some of the most stringent constraints yet placed on periodic radio emission from nearby stellar systems.

Researchers utilised the radiometer equation, coupled with an adopted signal-to-noise detection threshold of 25, and a duty cycle assumption of 0.1, to calculate these upper limits. The work opens new avenues for exploring potential technosignatures by extending FFA-based searches into a regime of enhanced sensitivity and sky coverage, facilitated by FAST’s unique capabilities. FAST’s 300m illuminated aperture and 19-beam L-band receiver deliver system temperatures around 25K, providing a sensitivity exceeding that of previous single-dish facilities at comparable frequencies. The multi-beam architecture further enhances RFI rejection, while the high spectral resolution and stability of the L-band backend enable coherent searches for faint, repeating signals, a crucial advancement in the field of SETI.

The selection of Groombridge 34A/B, Ross 248, 61 Cygni B, and Ross 128 as targets was driven by their proximity, all within 3-4 parsecs, and their status as low-mass M or K dwarfs with long main-sequence lifetimes. These stars also either host confirmed or strongly suspected low-mass planets, making them prime candidates for harbouring potentially habitable environments. Consequently, even transmitters with modest power output, or terrestrial-level radio leakage, would be detectable with FAST, allowing the team to establish exceptionally sensitive upper limits on potential extraterrestrial signals. This research builds upon and extends the BLIPSS framework, adapting it for FAST’s multi-beam L-band data and demonstrating a powerful approach to uncovering subtle periodic technosignatures in the vastness of space.

FAST SETI Search of Nearby Stars began observing

Scientists initiated a radio SETI search targeting periodic, kHz-wide signals from five of the closest stars observable with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Employing the 19-beam L-band receiver (1.05-1.45GHz), the research team secured 1200s tracking observations of Groombridge 34A/B, Ross 248, 61 Cygni B, and Ross 128. Dynamic spectra, captured across all beams and both linear polarisations, underwent channel-by-channel analysis using a fast-folding algorithm, designed to detect periods ranging from 1.1 to 300s. A sophisticated, multi-layer radio-frequency interference (RFI) mitigation pipeline was engineered to enhance signal detection.

This pipeline leverages multi-beam occupancy, cross-target bad-channel statistics, XX/YY polarisation coincidence, broad frequency masking, and narrow, site-specific RFI exclusion zones, culminating in clustering by period and frequency. To validate this complex system, the team analysed FAST observations of PSR B0329+54, successfully recovering the known 0.714s spin period and its harmonic structure within the expected beam. This validation confirmed the pipeline’s efficacy and reliability before applying it to the stellar sample. Successive data reduction cuts diminished raw Fast Folding Algorithm (FFA) hit lists, exceeding 10^6 hits per target, to a manageable number of cluster-level candidates.

However, detailed phase-time and phase-frequency diagnostics revealed that all remaining candidates exhibited characteristics consistent with radio-frequency interference. Consequently, the study reports no convincing detections of periodic transmitters within the searched parameter space. The team harnessed the radiometer equation, adopting a signal-to-noise ratio threshold of 25 and a duty cycle delta of 0.1, to establish upper limits of approximately (7-9) x 10^9W on the isotropic-equivalent EIRP of kHz-wide periodic beacons at these stars, among the most stringent constraints to date. FAST’s L-band multibeam system delivers exceptional sensitivity, boasting a gain of approximately 16 K Jy−1 and a system temperature of around 25 K for the central beam.

The system’s 19-beam receiver provides simultaneous coverage, with each beam exhibiting a half-power beam width of roughly 2. ′9 at 1.25GHz. The backend operated in search mode, utilising the SPEC(F) spectral processor to generate 1,024k frequency channels across a 400MHz bandwidth, achieving a frequency resolution of 476.84Hz per channel. Raw data, recorded in FITS format and converted to filterbank files, were then processed using the BLIPSS software framework, enabling a per-channel FFA search over the specified period range with dual linear polarizations and all 19 beams. This innovative approach builds upon and extends the BLIPSS framework, specifically adapted for FAST’s multi-beam L-band data.

FAST SETI reveals stringent periodic signal limits

Scientists conducting a radio Search for Extraterrestrial Intelligence (SETI) have achieved stringent upper limits on potential periodic signals emanating from five nearby stars. Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), the team obtained 1200-second tracking observations of Groombridge 34A/B, Ross 248, 61 Cygni B, and Ross 128, employing the 19-beam L-band receiver operating between 1.05 and 1.45GHz. Experiments revealed a search for kHz-wide signals with periods ranging from 1.1 to 300 seconds, utilising a fast-folding algorithm and a sophisticated multi-layer Radio Frequency Interference (RFI) mitigation pipeline. The data conditioning pipeline successfully reduced raw Fast Folding Algorithm (FFA) hit lists, exceeding 10^6 hits per target, to a manageable number of cluster-level candidates.

Tests prove that the pipeline, validated against observations of the pulsar PSR B0329+54, accurately recovered the known 0.714-second spin period and its harmonic structure within the expected beam. Measurements confirm the recovery of expected signals, demonstrating the pipeline’s efficacy in distinguishing genuine periodic signals from spurious detections. Results demonstrate no convincing detections of periodic transmitters within the searched parameters. The team measured the system-equivalent flux density at approximately 2 Jy, providing exceptional sensitivity to narrowband or quasi-periodic signals.

The breakthrough delivers upper limits of approximately (7-9) x 10^9W on the isotropic-equivalent Effective Isotropic Radiated Power (EIRP) of kHz-wide periodic beacons at these stars, representing some of the most stringent constraints to date. Scientists recorded a frequency resolution of 476.84Hz per channel, utilising 1,024k frequency channels across a 400MHz bandwidth. The FAST observations leveraged a gain of approximately 16 K Jy−1 and a system temperature of around 25 K, crucial for detecting faint signals. These measurements establish a new benchmark for sensitivity in periodic radio SETI searches, paving the way for future investigations with enhanced capabilities and broader parameter space coverage. This work provides crucial data for assessing the potential for detecting artificial signals from nearby stellar systems.

FAST SETI search yields no signals

Scientists have conducted a radio Search for Extraterrestrial Intelligence (SETI) targeting five nearby stars, Groombridge 34A/B, Ross 248, 61 Cygni B, and Ross 128, using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Observations employed the 19-beam L-band receiver, focusing on periodic signals between 1.1 and 300 seconds in duration. A sophisticated multi-layer Radio Frequency Interference (RFI) mitigation pipeline was developed to enhance signal detection, utilising data from multiple beams and polarisations, alongside frequency masking and site-specific RFI exclusion. The pipeline’s effectiveness was validated through observations of the pulsar PSR B0329+54, successfully recovering its known spin period and harmonic structure.

Despite processing extensive data and reducing initial hit lists from over a million candidates per target, researchers found no convincing evidence of periodic transmitters. The study established upper limits of approximately 7-9x 10^9W on the isotropic-equivalent Effective Isotropic Radiated Power (EIRP) of kHz-wide periodic beacons at these stars, representing some of the most stringent constraints to date on radio emission from nearby stellar systems. The authors acknowledge limitations stemming from the challenge of distinguishing genuine signals from residual RFI, and the assumption of a 0.1 duty cycle for potential beacons. Future research will focus on expanding these surveys with longer observation times and broader frequency coverage, potentially increasing the sensitivity to weaker or differently modulated signals. These findings, while not yielding a detection, significantly advance the field by refining search parameters and establishing robust upper limits on potential extraterrestrial signals.