50 research outputs found
A survey of nulling pulsars using the Giant Meterwave Radio Telescope
Several pulsars show sudden cessation of pulsed emission, which is known as
pulsar nulling. In this paper, the nulling behaviour of 15 pulsars is
presented. The nulling fractions of these pulsars, along with the degree of
reduction in the pulse energy during the null phase, are reported for these
pulsars. A quasi-periodic null-burst pattern is reported for PSR J1738-2330.
The distributions of lengths of the null and the burst phases as well as the
typical nulling time scales are estimated for eight strong pulsars. The nulling
pattern of four pulsars with similar nulling fraction are found to be different
from each other, suggesting that the fraction of null pulses does not quantify
the nulling behaviour of a pulsar in full detail. Analysis of these
distributions also indicate that while the null and the burst pulses occur in
groups, the underlying distribution of the interval between a transition from
the null to the burst phase and vice verse appears to be similar to that of a
stochastic Poisson point process.Comment: 10 pages, 7 figures, accepted for publication in MNRA
Fast Radio Burst 121102 Pulse Detection and Periodicity: A Machine Learning Approach
We report the detection of 72 new pulses from the repeating fast radio burst
FRB 121102 in Breakthrough Listen C-band (4-8 GHz) observations at the Green
Bank Telescope. The new pulses were found with a convolutional neural network
in data taken on August 26, 2017, where 21 bursts have been previously
detected. Our technique combines neural network detection with dedispersion
verification. For the current application we demonstrate its advantage over a
traditional brute-force dedis- persion algorithm in terms of higher
sensitivity, lower false positive rates, and faster computational speed.
Together with the 21 previously reported pulses, this observa- tion marks the
highest number of FRB 121102 pulses from a single observation, total- ing 93
pulses in five hours, including 45 pulses within the first 30 minutes. The
number of data points reveal trends in pulse fluence, pulse detection rate, and
pulse frequency structure. We introduce a new periodicity search technique,
based on the Rayleigh test, to analyze the time of arrivals, with which we
exclude with 99% confidence pe- riodicity in time of arrivals with periods
larger than 5.1 times the model-dependent time-stamp uncertainty. In
particular, we rule out constant periods >10 ms in the barycentric arrival
times, though intrinsic periodicity in the time of emission remains plausible.Comment: 32 pages, 10 figure
On Detecting Interstellar Scintillation in Narrowband Radio SETI
To date, the search for radio technosignatures has focused on sky location as
a primary discriminant between technosignature candidates and anthropogenic
radio frequency interference (RFI). In this work, we investigate the
possibility of searching for technosignatures by identifying the presence and
nature of intensity scintillations arising from the turbulent, ionized plasma
of the interstellar medium (ISM). Past works have detailed how interstellar
scattering can both enhance and diminish the detectability of narrowband radio
signals. We use the NE2001 Galactic free electron density model to estimate
scintillation timescales to which narrowband signal searches would be
sensitive, and discuss ways in which we might practically detect strong
intensity scintillations in detected signals. We further analyze the RFI
environment of the Robert C. Byrd Green Bank Telescope (GBT) with the proposed
methodology and comment on the feasibility of using scintillation as a filter
for technosignature candidates.Comment: 17 pages, 8 figures, published by Ap
The Breakthrough Listen Search for Intelligent Life: A 3.95-8.00 GHz Search for Radio Technosignatures in the Restricted Earth Transit Zone
We report on a search for artificial narrowband signals of 20 stars within
the restricted Earth Transit Zone as a part of the ten-year Breakthrough Listen
(BL) search for extraterrestrial intelligence. The restricted Earth Transit
Zone is the region of the sky from which an observer would see the Earth
transit the Sun with an impact parameter of less than 0.5. This region of the
sky is geometrically unique, providing a potential way for an extraterrestrial
intelligence to discover the Solar System. The targets were nearby (7-143 pc)
and the search covered an electromagnetic frequency range of 3.95-8.00 GHz. We
used the Robert C. Byrd Green Bank Telescope to perform these observations with
the standard BL data recorder. We searched these data for artificial narrowband
(Hz) signals with Doppler drift rates of Hz s. We found
one set of potential candidate signals on the target HIP 109656 which was then
found to be consistent with known properties of anthropogenic radio frequency
interference. We find no evidence for radio technosignatures from
extraterrestrial intelligence in our observations. The observing campaign
achieved a minimum detectable flux which would have allowed detections of
emissions that were to times as powerful as the signaling
capability of the Arecibo radar transmitter, for the nearest and furthest stars
respectively. We conclude that at least of the systems in the restricted
Earth Transit Zone within 150 pc do not possess the type of transmitters
searched in this survey. To our knowledge, this is the first targeted search
for extraterrestrial intelligence of the restricted Earth Transit Zone. All
data used in this paper are publicly available via the Breakthrough Listen
Public Data Archive (http://seti.berkeley.edu/bldr2).Comment: 17 pages, 8 figures, submitted to Ap