arXiv subjects

J. C. Tarter

Publications and source records attributed to J. C. Tarter.

5 recordsLinked to original sources

arXiv2019

Radio SETI Observations of the Interstellar Object 'Oumuamua

Note: This is a revised version of the paper that _corrects_a_calculation_error in translating observed Jansky units to EIRP in Watts. Mistakes are labeled below. Motivated by the hypothesis that Oumuamua could conceivably be an interstellar probe, we used the Allen Telescope Array to search for radio transmissions that would indicate a non-natural origin for this object. Observations were made at radio frequencies between 1 and 10 GHz using the Array's correlator receiver with a channel bandwidth of 100 kHz. In frequency regions not corrupted by man-made interference, we find no signal flux with frequency-dependent lower limits of 0.01 Jy at 1 GHz and 0.1 Jy at 7 GHz. For a putative isotropic object, these limits correspond to transmitter powers of (was mistakenly 30 mW) 10 W and (was mistakenly 300 mW) 100 W, respectively. In frequency ranges that are heavily utilized for satellite communications, our sensitivity to weak signals is badly impinged, but we can still place an upper limit of (was mistakenly 10 W) 3 kW for a transmitter on the asteroid. For comparison and validation should a transmitter be discovered, contemporaneous measurements were made on the solar system asteroids 2017 UZ and 2017 WC with comparable sensitivities. Because they are closer to Earth, we place upper limits on transmitter power to be 0.1 and 0.001 times the limits for Oumuamua, respectively.

astro-ph.EP↗

arXiv2018

The Application of Autocorrelation SETI Search Techniques in an ATA Survey

We report a novel radio autocorrelation (AC) search for extraterrestrial intelligence (SETI). For selected frequencies across the terrestrial microwave window (1-10 GHz) observations were conducted at the Allen Telescope Array to identify artificial non-sinusoidal periodic signals with radio bandwidths greater than 4 Hz, which are capable of carrying substantial messages with symbol-rates from 4-1000000 Hz. Out of 243 observations, about half (101) were directed toward sources with known continuum flux > ~1 Jy over the sampled bandwidth (quasars, pulsars, supernova remnants, and masers), based on the hypothesis that they might harbor heretofore undiscovered natural or artificial, repetitive, phase or frequency modulation. The rest of the targets were mostly toward exoplanet stars with no previously discovered continuum flux. No signals attributable to extraterrestrial technology were found in this study. We conclude that the maximum probability that future observations like the ones described here will reveal repetitively modulated emissions is less than 1% for continuum sources and exoplanets, alike. The paper concludes by describing a new approach to expanding this survey to many more targets and much greater sensitivity using archived data from interferometers all over the world.

astro-ph.IM↗

arXiv2016

Radio SETI Observations of the Anomalous Star KIC 8462852

We report on a search for the presence of signals from extraterrestrial intelligence in the direction of the star system KIC 8462852. Observations were made at radio frequencies between 1-10 GHz using the Allen Telescope Array. No narrowband radio signals were found at a level of 180-300 Jy in a 1 Hz channel, or medium band signals above 10 Jy in a 100 kHz channel.

astro-ph.EP↗

arXiv2014

A new class of SETI beacons that contain information (22-aug-2010)

In the cm-wavelength range, an extraterrestrial electromagnetic narrow band (sine wave) beacon is an excellent choice to get alien attention across interstellar distances because 1) it is not strongly affected by interstellar / interplanetary dispersion or scattering, and 2) searching for narrowband signals is computationally efficient (scales as Ns log(Ns) where Ns = number of voltage samples). Here we consider a special case wideband signal where two or more delayed copies of the same signal are transmitted over the same frequency and bandwidth, with the result that ISM dispersion and scattering cancel out during the detection stage. Such a signal is both a good beacon (easy to find) and carries arbitrarily large information rate (limited only by the atmospheric transparency to about 10 GHz). The discovery process uses an autocorrelation algorithm, and we outline a compute scheme where the beacon discovery search can be accomplished with only 2x the processing of a conventional sine wave search, and discuss signal to background response for sighting the beacon. Once the beacon is discovered, the focus turns to information extraction. Information extraction requires similar processing as for generic wideband signal searches, but since we have already identified the beacon, the efficiency of information extraction is negligible.

astro-ph.IM↗

arXiv2012

Primary Beam and Dish Surface Characterization at the Allen Telescope Array by Radio Holography

The Allen Telescope Array (ATA) is a cm-wave interferometer in California, comprising 42 antenna elements with 6-m diameter dishes. We characterize the antenna optical accuracy using two-antenna interferometry and radio holography. The distortion of each telescope relative to the average is small, with RMS differences of 1 percent of beam peak value. Holography provides images of dish illumination pattern, allowing characterization of as-built mirror surfaces. The ATA dishes can experience mm-scale distortions across -2 meter lengths due to mounting stresses or solar radiation. Experimental RMS errors are 0.7 mm at night and 3 mm under worst case solar illumination. For frequencies 4, 10, and 15 GHz, the nighttime values indicate sensitivity losses of 1, 10 and 20 percent, respectively. The ATA.s exceptional wide-bandwidth permits observations over a continuous range 0.5 to 11.2 GHz, and future retrofits may increase this range to 15 GHz. Beam patterns show a slowly varying focus frequency dependence. We probe the antenna optical gain and beam pattern stability as a function of focus and observation frequency, concluding that ATA can produce high fidelity images over a decade of simultaneous observation frequencies. In the day, the antenna sensitivity and pointing accuracy are affected. We find that at frequencies greater than 5 GHz, daytime observations greater than 5 GHz will suffer some sensitivity loss and it may be necessary to make antenna pointing corrections on a 1 to 2 hourly basis.

astro-ph.IM↗