86 research outputs found
Probing the extragalactic fast transient sky at minute timescales with DECam
Searches for optical transients are usually performed with a cadence of days
to weeks, optimised for supernova discovery. The optical fast transient sky is
still largely unexplored, with only a few surveys to date having placed
meaningful constraints on the detection of extragalactic transients evolving at
sub-hour timescales. Here, we present the results of deep searches for dim,
minute-timescale extragalactic fast transients using the Dark Energy Camera, a
core facility of our all-wavelength and all-messenger Deeper, Wider, Faster
programme. We used continuous 20s exposures to systematically probe timescales
down to 1.17 minutes at magnitude limits (AB), detecting hundreds of
transient and variable sources. Nine candidates passed our strict criteria on
duration and non-stellarity, all of which could be classified as flare stars
based on deep multi-band imaging. Searches for fast radio burst and gamma-ray
counterparts during simultaneous multi-facility observations yielded no
counterparts to the optical transients. Also, no long-term variability was
detected with pre-imaging and follow-up observations using the SkyMapper
optical telescope. We place upper limits for minute-timescale fast optical
transient rates for a range of depths and timescales. Finally, we demonstrate
that optical -band light curve behaviour alone cannot discriminate between
confirmed extragalactic fast transients such as prompt GRB flashes and Galactic
stellar flares.Comment: Published in MNRA
Detection of a glitch in the pulsar J1709-4429
We report the detection of a glitch event in the pulsar J17094429 (also
known as B170644) during regular monitoring observations with the Molonglo
Observatory Synthesis Telescope (UTMOST). The glitch was found during timing
operations, in which we regularly observe over 400 pulsars with up to daily
cadence, while commensally searching for Rotating Radio Transients, pulsars,
and FRBs. With a fractional size of ,
the glitch reported here is by far the smallest known for this pulsar,
attesting to the efficacy of glitch searches with high cadence using UTMOST.Comment: 3 pages, 1 figur
The UTMOST pulsar timing programme II:Timing noise across the pulsar population
While pulsars possess exceptional rotational stability, large scale timing
studies have revealed at least two distinct types of irregularities in their
rotation: red timing noise and glitches. Using modern Bayesian techniques, we
investigated the timing noise properties of 300 bright southern-sky radio
pulsars that have been observed over 1.0-4.8 years by the upgraded Molonglo
Observatory Synthesis Telescope (MOST). We reanalysed the spin and spin-down
changes associated with nine previously reported pulsar glitches, report the
discovery of three new glitches and four unusual glitch-like events in the
rotational evolution of PSR J18250935. We develop a refined Bayesian
framework for determining how red noise strength scales with pulsar spin
frequency () and spin-down frequency (), which we apply to a
sample of 280 non-recycled pulsars. With this new method and a simple power-law
scaling relation, we show that red noise strength scales across the
non-recycled pulsar population as , where and . This method can be
easily adapted to utilise more complex, astrophysically motivated red noise
models. Lastly, we highlight our timing of the double neutron star PSR
J07373039, and the rediscovery of a bright radio pulsar originally found
during the first Molonglo pulsar surveys with an incorrectly catalogued
position.Comment: Accepted by MNRAS. 28 pages, 8 figures, 8 table
COSMIC: An Ethernet-based Commensal, Multimode Digital Backend on the Karl G. Jansky Very Large Array for the Search for Extraterrestrial Intelligence
The primary goal of the search for extraterrestrial intelligence (SETI) is to
gain an understanding of the prevalence of technologically advanced beings
(organic or inorganic) in the Galaxy. One way to approach this is to look for
technosignatures: remotely detectable indicators of technology, such as
temporal or spectral electromagnetic emissions consistent with an artificial
source. With the new Commensal Open-Source Multimode Interferometer Cluster
(COSMIC) digital backend on the Karl G. Jansky Very Large Array (VLA), we aim
to conduct a search for technosignatures that is significantly more
comprehensive, more sensitive, and more efficient than previously attempted.
The COSMIC system is currently operational on the VLA, recording data, and
designed with the flexibility to provide user-requested modes. This paper
describes the hardware system design, the current software pipeline, and plans
for future development.Comment: 30 pages, 17 figures. Accepted for publication in A
Precise Measurements of Self-absorbed Rising Reverse Shock Emission from Gamma-ray Burst 221009A
The deaths of massive stars are sometimes accompanied by the launch of highly
relativistic and collimated jets. If the jet is pointed towards Earth, we
observe a "prompt" gamma-ray burst due to internal shocks or magnetic
reconnection events within the jet, followed by a long-lived broadband
synchrotron afterglow as the jet interacts with the circum-burst material.
While there is solid observational evidence that emission from multiple shocks
contributes to the afterglow signature, detailed studies of the reverse shock,
which travels back into the explosion ejecta, are hampered by a lack of
early-time observations, particularly in the radio band. We present rapid
follow-up radio observations of the exceptionally bright gamma-ray burst GRB
221009A which reveal an optically thick rising component from the reverse shock
in unprecedented detail both temporally and in frequency space. From this, we
are able to constrain the size, Lorentz factor, and internal energy of the
outflow while providing accurate predictions for the location of the peak
frequency of the reverse shock in the first few hours after the burst.Comment: 11 figures, 4 table
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