Search for Gravitational Waves Associated with Gamma-Ray Bursts Detected by Fermi and Swift during the LIGO-Virgo Run O3b

We search for gravitational-wave signals associated with gamma-ray bursts (GRBs) detected by the Fermi and Swift satellites during the second half of the third observing run of Advanced LIGO and Advanced Virgo (2019 November 1 15:00 UTC-2020 March 27 17:00 UTC). We conduct two independent searches: A generic gravitational-wave transients search to analyze 86 GRBs and an analysis to target binary mergers with at least one neutron star as short GRB progenitors for 17 events. We find no significant evidence for gravitational-wave signals associated with any of these GRBs. A weighted binomial test of the combined results finds no evidence for subthreshold gravitational-wave signals associated with this GRB ensemble either. We use several source types and signal morphologies during the searches, resulting in lower bounds on the estimated distance to each GRB. Finally, we constrain the population of low-luminosity short GRBs using results from the first to the third observing runs of Advanced LIGO and Advanced Virgo. The resulting population is in accordance with the local binary neutron star merger rate. © 2022. The Author(s). Published by the American Astronomical Society

Narrowband Searches for Continuous and Long-duration Transient Gravitational Waves from Known Pulsars in the LIGO-Virgo Third Observing Run

Isolated neutron stars that are asymmetric with respect to their spin axis are possible sources of detectable continuous gravitational waves. This paper presents a fully coherent search for such signals from eighteen pulsars in data from LIGO and Virgo's third observing run (O3). For known pulsars, efficient and sensitive matched-filter searches can be carried out if one assumes the gravitational radiation is phase-locked to the electromagnetic emission. In the search presented here, we relax this assumption and allow both the frequency and the time derivative of the frequency of the gravitational waves to vary in a small range around those inferred from electromagnetic observations. We find no evidence for continuous gravitational waves, and set upper limits on the strain amplitude for each target. These limits are more constraining for seven of the targets than the spin-down limit defined by ascribing all rotational energy loss to gravitational radiation. In an additional search, we look in O3 data for long-duration (hours-months) transient gravitational waves in the aftermath of pulsar glitches for six targets with a total of nine glitches. We report two marginal outliers from this search, but find no clear evidence for such emission either. The resulting duration-dependent strain upper limits do not surpass indirect energy constraints for any of these targets. © 2022. The Author(s). Published by the American Astronomical Society

Seasonal fluctuations in rodent seed caching and consumption behaviour in fynbos shrublands: Implications for fire management

AbstractThe consumption and dispersal of seeds by rodents play an important role in the seed bank dynamics of many plant species. Seed dispersal versus consumption patterns may however vary seasonally with food availability. We investigated whether the fate of Leucadendron sessile seeds was seasonally variable, and whether it could be explained by food availability. First we established that the seeds of most non-serotinous, large-seeded plants were released in early summer. Then we monitored seed dispersal and consumption behaviour, primarily by the nocturnal seed caching and dispersing rodent, Acomys subspinosus over one year. To investigate seasonal fluctuations in the diet of A. subspinosus, we conducted regular faecal analyses of this rodent and compared them to those of Rhabdomys pumilio, a diurnal rodent which is known to consume seeds but not cache them. While the diet of R. pumilio does not appear to fluctuate greatly across seasons, the diet of A. subspinosus does. A. subspinosus changes its diet from an insect dominated diet in winter and spring to a diet with a strong seed component in summer and autumn. Corresponding to this dietary shift, A. subspinosus changes its primary foraging behaviour from seed consumption to seed burial. These results suggest that a plentiful bank of seeds in autumn encourages seed caching but that by winter, the seed bank is so depleted that A. subspinosus consumes whatever it finds until summer when the seed bank is replenished. Our results suggest that A. subspinosus seed dispersal and consumptive behaviour fluctuates during the year and this appears to be related to seed availability. This is likely to cause temporal fluctuations in the seed bank, and consequently the timing of fires will have strong effects on seed germination