arXiv subjects

Steve Croft

Publications and source records attributed to Steve Croft.

At least 55 records · Page 3Linked to original sources

arXiv2021

Absence of bursts between 4-8 GHz from FRB20200120E located in an M81 Globular Cluster

We report the non-detection of dispersed bursts between 4 - 8 GHz from 2.5 hours of observations of FRB20200120E at 6 GHz using the Robert C. Byrd Green Bank Telescope. Our fluence limits are several times lower than the average burst fluences reported at 600 and 1400 MHz. We conclude that these non-detections are either due to high-frequency bursts being weaker and/or scintillation-induced modulated. It is also likely that our observations were non-concurrent with any activity window of FRB20200120E.

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arXiv2021

Strategies for Maximizing Detection Rate in Radio SETI

The Search for Extraterrestrial intelligence (SETI) is a scientific and cultural effort seeking evidence of intelligent life beyond earth. Radio SETI observes the radio spectrum for ''technosignatures" that could be produced by an advanced ET society. This work models radio SETI as an end-to-end system, and focuses on narrow-band intentional transmissions. We look at strategies to maximize the expected number of detections per year (DPY) of search. Assuming that ET civilizations will be associated with star systems, we want to maximize the number of stars that may be observed at one time. Assuming a representative star density, this requires maximizing the search volume in a cone defined by the detection range and field of view (FOV). The parameter trades are modified from the case where one simply maximizes signal-to-noise ratio. Instead, a joint optimization between FOV and sensitivity is needed. Some implications: 1) Instead of focusing on the terrestrial microwave window of 1-10 GHz, frequencies below 1 GHz may be optimal for detection rate due to the larger field of view; 2) Arrays of smaller dishes should be favored compared to a single dish of equivalent area; 3) Aperture arrays are desirable due to their large potential FOV. Many radio telescopes under development will provide both high sensitivity and large FOV, and should offer much improved SETI detection rates. Still higher DPY is needed, however, to achieve results in reasonable time horizons, which should be possible by greatly expanding computation capability to the next-generation wide-FOV antenna arrays.

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arXiv2021

The Breakthrough Listen Search for Intelligent Life: Searching for Technosignatures in Observations of TESS Targets of Interest

Exoplanetary systems are prime targets for the Search for Extraterrestrial Intelligence (SETI). With the recent uptick in the identification of candidate and confirmed exoplanets through the work of missions like the Transiting Exoplanet Survey Satellite (TESS), we are beginning to understand that Earth-like planets are common. In this work, we extend the Breakthrough Listen (BL) search for extraterrestrial intelligence to include targeted searches of stars identified by TESS as potential exoplanet hosts. We report on 113 30-min cadence observations collected for 28 targets selected from the TESS Input Catalog (TIC) from among those identified as containing signatures of transiting planets. The targets were searched for narrowband signals from 1-11 GHz using the turboSETI pipeline architecture modified for compatibility with the Google Cloud environment. Data were searched for drift rates of +/-4 Hz/s above a minimum signal-to-noise threshold of 10, following the parameters of previous searches conducted by Price et al. (2020) and Enriquez et al. (2017). The observations presented in this work establish some of the deepest limits to date over such a wide band (1-11 GHz) for life beyond Earth. We determine that fewer than 12.72% of the observed targets possess transmitters operating at these frequencies with an Equivalent Isotropic Radiated Power (EIRP) greater than our derived threshold of 4.9*10^(14) W.

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arXiv2021

The Breakthrough Listen Search For Intelligent Life Near the Galactic Center I

A line-of-sight towards the Galactic Center (GC) offers the largest number of potentially habitable systems of any direction in the sky. The Breakthrough Listen program is undertaking the most sensitive and deepest targeted SETI surveys towards the GC. Here, we outline our observing strategies with Robert C. Byrd Green Bank Telescope (GBT) and Parkes telescope to conduct 600 hours of deep observations across 0.7--93 GHz. We report preliminary results from our survey for ETI beacons across 1--8 GHz with 7.0 and 11.2 hours of observations with Parkes and GBT, respectively. With our narrowband drifting signal search, we were able to place meaningful constraints on ETI transmitters across 1--4 GHz and 3.9--8 GHz with EIRP limits of $\geq$4$\times$10$^{18}$ W among 60 million stars and $\geq$5$\times$10$^{17}$ W among half a million stars, respectively. For the first time, we were able to constrain the existence of artificially dispersed transient signals across 3.9--8 GHz with EIRP $\geq$1$\times$10$^{14}$ W/Hz with a repetition period $\leq$4.3 hours. We also searched our 11.2 hours of deep observations of the GC and its surrounding region for Fast Radio Burst-like magnetars with the DM up to 5000 pc cm$^{-3}$ with maximum pulse widths up to 90 ms at 6 GHz. We detected several hundred transient bursts from SGR J1745$-$2900, but did not detect any new transient burst with the peak luminosity limit across our observed band of $\geq$10$^{31}$ erg s$^{-1}$ and burst-rate of $\geq$0.23 burst-hr$^{-1}$. These limits are comparable to bright transient emission seen from other Galactic radio-loud magnetars, constraining their presence at the GC.

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arXiv2021

The Breakthrough Listen Search for Intelligent Life: MeerKAT Target Selection

New radio telescope arrays offer unique opportunities for large-scale commensal SETI surveys. Ethernet-based architectures are allowing multiple users to access telescope data simultaneously by means of multicast Ethernet subscriptions. Breakthrough Listen will take advantage of this by conducting a commensal SETI survey on the MeerKAT radio telescope in South Africa. By subscribing to raw voltage data streams, Breakthrough Listen will be able to beamform commensally anywhere within the field of view during primary science observations. The survey will be conducted with unprecedented speed by forming and processing 64 coherent beams simultaneously, allowing the observation of several million objects within a few years. Both coherent and incoherent observing modes are planned. We present the list of desired sources for observation and explain how these sources were selected from the Gaia DR2 catalog. Given observations planned by MeerKAT's primary telescope users, we discuss their effects on the commensal survey and propose a commensal observing strategy in response. Finally, we outline our proposed approach towards observing one million nearby stars and analyse expected observing progress in the coming years.

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arXiv2021

Re-Analysis of Breakthrough Listen Observations of FRB 121102: Polarization Properties of Eight New Spectrally Narrow Bursts

We report polarization properties for eight narrowband bursts from FRB 121102 that have been re-detected in a high-frequency (4-8 GHz) Breakthrough Listen observation with the Green Bank Telescope, originally taken on 2017 August 26. The bursts were found to exhibit nearly 100% linear polarization, Faraday rotation measures (RM) bordering 9.3$\times$10$^4$ rad-m$^{-2}$, and stable polarization position angles (PA), all of which agree with burst properties previously reported for FRB 121102 at the same epoch. We confirm that these detections are indeed physical bursts with limited spectral occupancies and further support the use of sub-banded search techniques in FRB detection.

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arXiv2020

The Breakthrough Listen Search for Intelligent Life: Public Data, Formats, Reduction and Archiving

Breakthrough Listen is the most comprehensive and sensitive search for extraterrestrial intelligence (SETI) to date, employing a collection of international observational facilities including both radio and optical telescopes. During the first three years of the Listen program, thousands of targets have been observed with the Green Bank Telescope (GBT), Parkes Telescope and Automated Planet Finder. At GBT and Parkes, observations have been performed ranging from 700 MHz to 26 GHz, with raw data volumes averaging over 1PB / day. A pseudo-real time software spectroscopy suite is used to produce multi-resolution spectrograms amounting to approximately 400 GB hr^-1 GHz^-1 beam^-1. For certain targets, raw baseband voltage data is also preserved. Observations with the Automated Planet Finder produce both 2-dimensional and 1-dimensional high resolution (R~10^5) echelle spectral data. Although the primary purpose of Listen data acquisition is for SETI, a range of secondary science has also been performed with these data, including studies of fast radio bursts. Other current and potential research topics include spectral line studies, searches for certain kinds of dark matter, probes of interstellar scattering, pulsar searches, radio transient searches and investigations of stellar activity. Listen data are also being used in the development of algorithms, including machine learning approaches to modulation scheme classification and outlier detection, that have wide applicability not just for astronomical research but for a broad range of science and engineering. In this paper, we describe the hardware and software pipeline used for collection, reduction, archival, and public dissemination of Listen data. We describe the data formats and tools, and present Breakthrough Listen Data Release 1.0 (BLDR 1.0), a defined set of publicly-available raw and reduced data totalling 1 PB.

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arXiv2020

Narrow-Band Signal Localization for SETI on Noisy Synthetic Spectrogram Data

As it stands today, the search for extraterrestrial intelligence (SETI) is highly dependent on our ability to detect interesting candidate signals, or technosignatures, in radio telescope observations and distinguish these from human radio frequency interference (RFI). Current signal search pipelines look for signals in spectrograms of intensity as a function of time and frequency (which can be thought of as images), but tend to do poorly in identifying multiple signals in a single data frame. This is especially apparent when there are dim signals in the same frame as bright, high signal-to-noise ratio (SNR) signals. In this work, we approach this problem using convolutional neural networks (CNN) as a computationally efficient method for localizing signals in synthetic observations resembling data collected by Breakthrough Listen using the Green Bank Telescope. We generate two synthetic datasets, the first with exactly one signal at various SNR levels and the second with exactly two signals, one of which represents RFI. We find that a residual CNN with strided convolutions and using multiple image normalizations as input outperforms a more basic CNN with max pooling trained on inputs with only one normalization. Training each model on a smaller subset of the training data at higher SNR levels results in a significant increase in model performance, reducing root mean square errors by at least a factor of 3 at an SNR of 25 dB. Although each model produces outliers with significant error, these results demonstrate that using CNNs to analyze signal location is promising, especially in image frames that are crowded with multiple signals.

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arXiv2020

Breakthrough Listen Search for Technosignatures Towards the Kepler-160 System

We have conducted a search for artificial radio emission associated with the Kepler-160 system following the report of the discovery of the Earth-like planet candidate KOI-456.04 on 2020 June 4 (arXiv:1905.09038v2). Our search targeted both narrowband (2.97 Hz) drifting ($\pm 4$ Hz s$^{-1})$ and wideband pulsed (5 ms at all bandwidths) artificially-dispersed technosignatures using the turboSETI (arXiv:1709.03491v2) and SPANDAK pipelines, respectively, from 1-8 GHz. No candidates were identified above an upper limit Equivalent Isotropic Radiated Power (EIRP) of $5.9 \times 10^{14}$ W for narrowband emission and $7.3 \times 10^{12}$ W for wideband emission. Here we briefly describe our observations and data reduction procedure.

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arXiv2020

Opportunities to Search for Extra-Terrestrial Intelligence with the Five-hundred-meter Aperture Spherical radio Telescope

The discovery of ubiquitous habitable extrasolar planets, combined with revolutionary advances in instrumentation and observational capabilities, has ushered in a renaissance in the search for extra-terrestrial intelligence (SETI). Large scale SETI activities are now underway at numerous international facilities. The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the largest single-aperture radio telescope in the world, well positioned to conduct sensitive searches for radio emission indicative of exo-intelligence. SETI is one of the five key science goals specified in the original FAST project plan. A collaboration with the Breakthrough Listen Initiative has been initiated in 2016 with a joint statement signed both by Dr. Jun Yan, the then director of the National Astronomical Observatories, Chinese Academy of Sciences (NAOC), and Dr. Peter Worden, the Chairman of the Breakthrough Prize Foundation. In this paper, we highlight some of the unique features of FAST that will allow for novel SETI observations. We identify and describe three different signal types indicative of a technological source, namely, narrow-band, wide-band artificially dispersed, and modulated signals. We here propose observations with FAST to achieve sensitivities never before explored.

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arXiv2020

The Breakthrough Listen Search for Intelligent Life: Observations of 1327 Nearby Stars over 1.10-3.45 GHz

Breakthrough Listen (BL) is a ten-year initiative to search for signatures of technologically capable life beyond Earth via radio and optical observations of the local Universe. A core part of the BL program is a comprehensive survey of 1702 nearby stars at radio wavelengths (1-10 GHz). Here, we report on observations with the 64-m CSIRO Parkes radio telescope in New South Wales, Australia, and the 100-m Robert C. Byrd Green Bank radio telescope in West Virginia, USA. Over 2016 January to 2019 March, a sample of 1138 stars was observed at Green Bank using the 1.10-1.90 GHz and 1.80-2.80 GHz receivers, and 189 stars were observed with Parkes over 2.60-3.45 GHz. We searched these data for the presence of engineered signals with Doppler-acceleration drift rates between -4 to 4 Hz/s. Here, we detail our data analysis techniques and provide examples of detected events. After excluding events with characteristics consistent with terrestrial radio interference, we are left with zero candidates. Given the sensitivity of our observations, we can put an upper limit on the power of potential radio transmitters at these frequencies at 2x10^12 W, and 9x10^12 W for GBT and Parkes respectively. These observations constitute the most comprehensive search over 1.10-3.45 GHz for technosignatures to date. All data products, totalling ~219 TB, are available for download as part of the first BL data release (DR1), as described in a companion paper (Lebofsky et. al., 2019)

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arXiv2019

Breakthrough Listen Follow-up of the Random Transiter (EPIC 249706694/HD 139139) with the Green Bank Telescope

The star EPIC 249706694 (HD 139139) was found to exhibit 28 transit-like events over an 87 day period during the Kepler mission's K2 Campaign 15 (Rappaport et al. 2019). These events did not fall into an identifiable pattern and could not be explained by a multitude of transit scenarios explored by the authors. We conduct follow-up observations at C-band frequencies with the Green Bank Telescope as part of the ongoing Breakthrough Listen search for technosignatures. We search for narrow band signals above a signal-to-noise threshold of 10 and with Doppler drift rates within +-5 Hz/s. We detect no evidence of technosignatures from EPIC 249706694 and derive an upper limit for the EIRP (Equivalent Isotropic Radiated Power) of putative transmissions to be 10 TW.

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arXiv2019

The Breakthrough Listen Search for Extraterrestrial Intelligence

The discovery of the ubiquity of habitable extrasolar planets, combined with revolutionary advances in instrumentation and observational capabilities, have ushered in a renaissance in the millenia-old quest to answer our most profound question about the Universe and our place within it - Are we alone? The Breakthrough Listen Initiative, announced in July 2015 as a 10-year 100M USD program, is the most comprehensive effort in history to quantify the distribution of advanced, technologically capable life in the universe. In this white paper, we outline the status of the on-going observing campaign with our primary observing facilities, as well as planned activities with these instruments over the next few years. We also list collaborative facilities which will conduct searches for technosignatures in either primary observing mode, or commensally. We highlight some of the novel analysis techniques we are bringing to bear on multi-petabyte data sets, including machine learning tools we are deploying to search for a broader range of technosignatures than was previously possible.

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arXiv2019

Commensal, Multi-user Observations with an Ethernet-based Jansky Very Large Array

Over the last decade, the continuing decline in the cost of digital computing technology has brought about a dramatic transformation in how digital instrumentation for radio astronomy is developed and operated. In most cases, it is now possible to interface consumer computing hardware, e.g. inexpensive graphics processing units and storage devices, directly to the raw data streams produced by radio telescopes. Such systems bring with them myriad benefits: straightforward upgrade paths, cost savings through leveraging an economy of scale, and a lowered barrier to entry for scientists and engineers seeking to add new instrument capabilities. Additionally, the typical data-interconnect technology used with general-purpose computing hardware -- Ethernet -- naturally permits multiple subscribers to a single raw data stream. This allows multiple science programs to be conducted in parallel. When combined with broad bandwidths and wide primary fields of view, radio telescopes become capable of achieving many science goals simultaneously. Moreover, because many science programs are not strongly dependent on observing cadence and direction (e.g. searches for extraterrestrial intelligence and radio transient surveys), these so-called "commensal" observing programs can dramatically increase the scientific productivity and discovery potential of an observatory. In this whitepaper, we detail a project to add an Ethernet-based commensal observing mode to the Jansky Very Large Array (VLA), and discuss how this mode could be leveraged to conduct a powerful program to constrain the distribution of advanced life in the universe through a search for radio emission indicative of technology. We also discuss other potential science use-cases for the system, and how the system could be used for technology development towards next-generation processing systems for the Next Generation VLA.

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arXiv2019

The Promise of Data Science for the Technosignatures Field

This paper outlines some of the possible advancements for the technosignatures searches using the new methods currently rapidly developing in computer science, such as machine learning and deep learning. It also showcases a couple of case studies of large research programs where such methods have been already successfully implemented with notable results. We consider that the availability of data from all sky, all the time observations paired with the latest developments in computational capabilities and algorithms currently used in artificial intelligence, including automation, will spur an unprecedented development of the technosignatures search efforts.

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arXiv2019

The radio search for technosignatures in the decade 2020-2030

Advancing the scientific frontier in the search for life in the universe requires support of searches for both biosignatures and technosignatures. A modest budgetary increment can expand the search for life in the universe from primitive to complex life and from the solar neighborhood to the entire Galaxy.

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arXiv2019

Self-supervised Anomaly Detection for Narrowband SETI

The Search for Extra-terrestrial Intelligence (SETI) aims to find technological signals of extra-solar origin. Radio frequency SETI is characterized by large unlabeled datasets and complex interference environment. The infinite possibilities of potential signal types require generalizable signal processing techniques with little human supervision. We present a generative model of self-supervised deep learning that can be used for anomaly detection and spatial filtering. We develop and evaluate our approach on spectrograms containing narrowband signals collected by Breakthrough Listen at the Green Bank telescope. The proposed approach is not meant to replace current narrowband searches but to demonstrate the potential to generalize to other signal types.

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arXiv2018

The Breakthrough Listen Search for Intelligent Life: Searching Boyajian's Star for Laser Line Emission

Boyajian' s Star (KIC 8462852) has received significant attention due to its unusual periodic brightness fluctuations detected by the Kepler Spacecraft and subsequent ground based observations. Possible explanations for the dips in the photometric measurements include interstellar or circumstellar dust, and it has been speculated that an artificial megastructure could be responsible. We analyze 177 high-resolution spectra of Boyajian's Star in an effort to detect potential laser signals from extraterrestrial civilizations. The spectra were obtained by the Lick Observatory's Automated Planet Finder telescope as part of the Breakthrough Listen Project, and cover the wavelength range of visible light from 374 to 970 nm. We calculate that the APF would be capable of detecting lasers of power greater than approximately 24 MW at the distance of Boyajian's Star, d = 1470 ly. The top candidates from the analysis can all be explained as either cosmic ray hits, stellar emission lines or atmospheric air glow emission lines.

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