A radio technosignature search towards Proxima Centauri resulting in a signal-of-interest
Shane Smith · Danny C. Price · Sofia Z. Sheikh · Daniel J. Czech · Steve Croft · David DeBoer · Vishal Gajjar · Howard Isaacson · Brian C. Lacki · Matt Lebofsky · David H. E. MacMahon · Cherry Ng · Karen I. Perez · Andrew P. V. Siemion · Claire Isabel Webb · Jamie Drew · S. Pete Worden · Andrew Zic
Nature Astronomy · 2021
Breakthrough Listen's most sensitive single-target radio search detected one narrowband signal-of-interest (BLC1 at 982 MHz) toward Proxima Centauri over six days in 2019, ultimately attributing it to anthropogenic intermodulation interference while setting an EIRP detection floor of 1.9 GW.
Brief
Smith et al. (2021) used the Parkes Murriyang UWL receiver (0.704–4.032 GHz) to observe Proxima Centauri for 26 hours 9 minutes across six days in April–May 2019, generating 19.5 TB of data. A Doppler-drift search with TURBO SETI yielded 4,172,702 total hits and 5,160 on-source events; only one, BLC1, at 982.002571 MHz with a drift rate of 0.038 Hz/s, survived all filtering rounds. The companion paper (Sheikh et al. 2021) attributes BLC1 to a complex intermodulation product of multiple local human-generated transmitters. The search sets a minimum detectable EIRP of 1.9 GW, a factor of 3.6 improvement over the prior Proxima Centauri limit and 1.6x better than GBT L/S-band observations of Barnard's Star.
Metadata
- Category
- Search
- Venue
- Nature Astronomy
- Type
- Peer-reviewed
- Year
- 2021
- Authors
- Shane Smith, Danny C. Price, Sofia Z. Sheikh, Daniel J. Czech, Steve Croft, David DeBoer, Vishal Gajjar, Howard Isaacson, Brian C. Lacki, Matt Lebofsky, David H. E. MacMahon, Cherry Ng, Karen I. Perez, Andrew P. V. Siemion, Claire Isabel Webb, Jamie Drew, S. Pete Worden, Andrew Zic
- arXiv
- 2111.08007
- Access
- Open access
- Length
- 2.5 M
- Programs
- Breakthrough Listen, Breakthrough Initiatives, Breakthrough Starshot, Project Phoenix
- Instruments
- Parkes Murriyang UWL receiver, BL Parkes Digital Recorder (BLPDR), ASKAP, HARPS spectrometer
- Data sources
- TURBO SETI, BLIMPY, Australian Radiofrequency Spectrum Plan (ARSP), FCC frequency allocation database, Australian Communications and Media Authority Register of Radiocommunications Licences
- Tags
- SETI, technosignature, radio, narrowband, Doppler drift, RFI mitigation, exoplanet
Key points
- BLC1 detected at 982.002571 MHz with a drift rate of 0.038 Hz/s, persisting for ~2.5 hours exclusively in on-source pointings toward Proxima Centauri.p.2
- Of 4,172,702 total hits and 5,160 on-source events, exactly one candidate survived all three rounds of filtering and visual inspection.p.2
- Minimum detectable EIRP = 1.9 GW, a 3.6x improvement over the prior Proxima Centauri limit of 6.2 GW and 1.6x better than GBT L/S-band observations of Barnard's Star.p.3
- Total data volume: 19.5 TB, approximately 118x more than any single-source Breakthrough Listen observation prior to this campaign.p.6
- Observation cadence used 30-minute on-source dwell times (vs. the standard 5-minute BL cadence), trading sensitivity to short-duration signals for improved detection of persistent weak ones.p.4
- UWL receiver system temperature is 22 K, compared to 35 K for the Parkes 10-cm receiver used in the prior search, directly contributing to the improved sensitivity.p.3
- BLC1 falls within a frequency band allocated to aeronautical radionavigation, but no registered transmitter at that frequency exists within 1,000 km of the observatory.p.3
- Companion paper (Sheikh et al. 2021) concludes BLC1 is a complex intermodulation product of multiple human-generated interference sources, not a technosignature.p.3
Verbatim
“This signal, 'BLC1', has characteristics broadly consistent with hypothesized technosignatures and is one of the most compelling candidates to date.”
p.1“our observations of Proxima Centauri are the most sensitive search for radio technosignatures ever undertaken on a star target.”
p.1“BLC1 was detected at 982.002571 MHz, with a drift rate of 0.038 Hzs − 1 .”
p.2“The final data volume for the six day observation period is 19.5 TB: about 118 × more data than were obtained for any single source in previous BL searches”
p.6“As such, our search of Proxima Centauri is decisively the most sensitive and comprehensive technosignature search done for a stellar target.”
p.3
Most interesting
- BLC1 persisted for over 2 hours in on-source pointings and fell within the aeronautical radionavigation band, yet no licensed transmitter within 1,000 km of Parkes operated at that exact frequency, a combination that initially made it difficult to dismiss.
- The 19.5 TB six-day dataset is 118x larger than any prior single-source Breakthrough Listen observation, captured by running the BL Parkes Digital Recorder in parallel with the primary UWL signal processor 'Medusa' without interrupting the primary science campaign.
- The Doppler drift rate search range was tailored specifically to Proxima b's orbital and rotational parameters (P_Pb = 11.18427 ± 0.00070 days, r_Pb = 0.04864 ± 0.00031 AU), rather than applying a generic sweep.
- Three stellar flare events from Proxima Centauri (AB1, AB2, AB3) were detected during the campaign by ASKAP, including one Type IV burst, the Parkes observations were part of a broader space-weather monitoring campaign, not a dedicated SETI run.
- A negative drift rate bias (~15% of hits vs. 10% positive) was observed across the full dataset, attributed to non-geosynchronous satellites rather than astrophysical drift.
- A parallel archival optical search of HARPS spectra (2004–2019), motivated by the radio observations described here, would have detected laser emission from Proxima Centauri at power levels below 120 kW.