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22,671
result(s) for
"Bursts"
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Heavy-element production in a compact object merger observed by JWST
The mergers of binary compact objects such as neutron stars and black holes are of central interest to several areas of astrophysics, including as the progenitors of gamma-ray bursts (GRBs)
1
, sources of high-frequency gravitational waves (GWs)
2
and likely production sites for heavy-element nucleosynthesis by means of rapid neutron capture (the
r
-process)
3
. Here we present observations of the exceptionally bright GRB 230307A. We show that GRB 230307A belongs to the class of long-duration GRBs associated with compact object mergers
4
–
6
and contains a kilonova similar to AT2017gfo, associated with the GW merger GW170817 (refs.
7
–
12
). We obtained James Webb Space Telescope (JWST) mid-infrared imaging and spectroscopy 29 and 61 days after the burst. The spectroscopy shows an emission line at 2.15 microns, which we interpret as tellurium (atomic mass
A
= 130) and a very red source, emitting most of its light in the mid-infrared owing to the production of lanthanides. These observations demonstrate that nucleosynthesis in GRBs can create
r
-process elements across a broad atomic mass range and play a central role in heavy-element nucleosynthesis across the Universe.
Observations from the JWST of the second brightest GRB ever detected, GRB 230307A, indicate that it belongs to the class of long-duration GRBs resulting from compact object mergers, with the decay of lanthanides powering the longlasting optical and infrared emission.
Journal Article
A Short History of the First 50 Years: From the GRB Prompt Emission and Afterglow Discoveries to the Multimessenger Era
More than fifty years have elapsed from the first discovery of gamma-ray bursts (GRBs) with American Vela satellites, and more than twenty-five years from the discovery with the BeppoSAX satellite of the first X-ray afterglow of a GRB. Thanks to the afterglow discovery and to the possibility given to the optical and radio astronomers to discover the GRB optical counterparts, the long-time mystery about the origin of these events has been solved. Now we know that GRBs are huge explosions, mainly ultra relativistic jets, in galaxies at cosmological distances. Starting from the first GRB detection with the Vela satellites, I will review the story of these discoveries, those obtained with BeppoSAX, the contribution to GRBs by other satellites and ground experiments, among them being Venera, Compton Gamma Ray Observatory, HETE-2, Swift, Fermi, AGILE, MAGIC, H.E.S.S., which were, and some of them are still, very important for the study of GRB properties. Then, I will review the main results obtained thus far and the still open problems and prospects of GRB astronomy.
Journal Article
Decameter Type III Bursts with Changing Frequency Drift-Rate Signs
We discuss properties of type III bursts that change the sign of their drift rate from negative to positive and
vice versa
. Moreover, these bursts may change the sign of their drift rates more than once. These particular type III bursts were observed simultaneously by the radio telescopes UTR-2 (
Ukrainian T-shaped Radio telescope
, Kharkov, Ukraine), URAN-2 (
Ukrainian Radio telescope of the Academy of Sciences
, Poltava, Ukraine), and by the NDA (
Nançay Decametric Array
, Nancay, France) in the frequency range 8 – 41 MHz. The negative drift rates of these bursts are similar to those of previously reported decameter type III bursts and vary from −0.7 MHz s
−1
to −1.7 MHz s
−1
, but their positive drift rates vary in a wider range from 0.44 MHz s
−1
to 6 MHz s
−1
. Unlike inverted U-bursts, the tracks of these type III bursts have C- or inverted C-shapes.
Our basic explanation of the positive drift rate of these type III bursts differs from the common assumption that positive drift rates of type III bursts are connected with electron beam propagation toward the Sun. We propose that, even if electron beams move outward from the Sun, they can generate type III bursts with positive drift rates if in some regions of the solar corona the group velocities of type III radio emissions are lower than the velocities of the electron beams.
Journal Article
Methods and Applications for Amplified Bursts of Picosecond-Spaced Ultrashort Pulses
Generating packages of picosecond-spaced ultrashort pulses yields various advantages in their application in nonlinear spectroscopy, micromachining, and plasma generation. We outline methods of burst amplification, with a focus on recent advancements in the generation and application of amplified pulse bursts.
Journal Article
The physical mechanisms of fast radio bursts
Fast radio bursts are mysterious millisecond-duration transients prevalent in the radio sky. Rapid accumulation of data in recent years has facilitated an understanding of the underlying physical mechanisms of these events. Knowledge gained from the neighbouring fields of gamma-ray bursts and radio pulsars has also offered insights. Here I review developments in this fast-moving field. Two generic categories of radiation model invoking either magnetospheres of compact objects (neutron stars or black holes) or relativistic shocks launched from such objects have been much debated. The recent detection of a Galactic fast radio burst in association with a soft gamma-ray repeater suggests that magnetar engines can produce at least some, and probably all, fast radio bursts. Other engines that could produce fast radio bursts are not required, but are also not impossible.
The mechanisms and origins of fast radio bursts are reviewed in connection with data and insights from the neighbouring fields of gamma-ray bursts and radio pulsars.
Journal Article
Fermi Observations of High-Energy Gamma-Ray Emission from GRB 080916C
Gamma-ray bursts (GRBs) are highly energetic explosions signaling the death of massive stars in distant galaxies. The Gamma-ray Burst Monitor and Large Area Telescope onboard the Fermi Observatory together record GRBs over a broad energy range spanning about 7 decades of gamma-ray energy. In September 2008, Fermi observed the exceptionally luminous GRB 080916C, with the largest apparent energy release yet measured. The high-energy gamma rays are observed to start later and persist longer than the lower energy photons. A simple spectral form fits the entire GRB spectrum, providing strong constraints on emission models. The known distance of the burst enables placing lower limits on the bulk Lorentz factor of the outflow and on the quantum gravity mass.
Journal Article
The extreme El Niño of 2015–2016: the role of westerly and easterly wind bursts, and preconditioning by the failed 2014 event
At the beginning of 2015, as one year earlier in 2014, the scientific community anticipated that El Niño conditions could develop in the tropical Pacific by year-end. Such projections were related to the occurrence of westerly wind bursts during winter–spring of each year that generated strong downwelling Kelvin waves indicative of an emerging El Niño. However, the event’s progression quickly stalled in 2014, but actively continued in 2015, leading to an extreme warm event (comparable to 1997 or 1982). Here, we compare climate evolution during these two years using satellite observations and numerical simulations. We show that during 2014, El Niño development was interrupted mid-year by an exceptionally strong easterly wind burst, whereas during the second year it continued through the summer. Further, we show that the failed 2014 event created favorable conditions for El Niño development during the next year, as it kept ocean heat content recharged and the western Pacific warm pool extended eastward. Subsequently, the winter–spring westerly wind bursts in 2015 were followed by a series of state-dependent westerly bursts as part of a strong positive Bjerknes feedback. Analogue simulations with a coupled GCM wherein we superimpose the observed sequences of westerly and easterly wind bursts support these conclusions, stressing the role of the failed 2014 event in preconditioning the ocean–atmosphere system for the development of an extreme El Niño. In our simulations the probability of an extreme event following early-year westerly wind bursts increases from 14% to nearly 60% due to this preconditioning. Thus, the interplay between westerly and easterly wind bursts shapes El Niño development and diversity.
Journal Article
Review on Experimental and Theoretical Investigations of Ultra-Short Pulsed Laser Ablation of Metals with Burst Pulses
Laser processing with ultra-short double pulses has gained attraction since the beginning of the 2000s. In the last decade, pulse bursts consisting of multiple pulses with a delay of several 10 ns and less found their way into the area of micromachining of metals, opening up completely new process regimes and allowing an increase in the structuring rates and surface quality of machined samples. Several physical effects such as shielding or re-deposition of material have led to a new understanding of the related machining strategies and processing regimes. Results of both experimental and numerical investigations are placed into context for different time scales during laser processing. This review is dedicated to the fundamental physical phenomena taking place during burst processing and their respective effects on machining results of metals in the ultra-short pulse regime for delays ranging from several 100 fs to several microseconds. Furthermore, technical applications based on these effects are reviewed.
Journal Article
A fast radio burst source at a complex magnetized site in a barred galaxy
Fast radio bursts (FRBs) are highly dispersed, millisecond-duration radio bursts
1
–
3
. Recent observations of a Galactic FRB
4
–
8
suggest that at least some FRBs originate from magnetars, but the origin of cosmological FRBs is still not settled. Here we report the detection of 1,863 bursts in 82 h over 54 days from the repeating source FRB 20201124A (ref.
9
). These observations show irregular short-time variation of the Faraday rotation measure (RM), which scrutinizes the density-weighted line-of-sight magnetic field strength, of individual bursts during the first 36 days, followed by a constant RM. We detected circular polarization in more than half of the burst sample, including one burst reaching a high fractional circular polarization of 75%. Oscillations in fractional linear and circular polarizations, as well as polarization angle as a function of wavelength, were detected. All of these features provide evidence for a complicated, dynamically evolving, magnetized immediate environment within about an astronomical unit (
au
; Earth–Sun distance) of the source. Our optical observations of its Milky-Way-sized, metal-rich host galaxy
10
–
12
show a barred spiral, with the FRB source residing in a low-stellar-density interarm region at an intermediate galactocentric distance. This environment is inconsistent with a young magnetar engine formed during an extreme explosion of a massive star that resulted in a long gamma-ray burst or superluminous supernova.
Analysis of a set of 1,863 bursts from the repeating source FRB 20201124A provides evidence of a complicated magnetized site within about an astronomical unit from the source in a barred galaxy.
Journal Article