A bright megaelectronvolt emission line in γ\gamma-ray burst GRB 221009A

The highly variable and energetic pulsed emission of a long gamma-ray burst (GRB) is thought to originate from local, rapid dissipation of kinetic or magnetic energy within an ultra-relativistic jet launched by a newborn compact object, formed during the collapse of a massive star. The spectra of GRB pulses are best modelled by power-law segments, indicating the dominance of non-thermal radiation processes. Spectral lines in the X-ray and soft $\gamma$-ray regime for the afterglow have been searched for intensively, but never confirmed. No line features ever been identified in the high energy prompt emission. Here we report the discovery of a highly significant ($> 6 \sigma$) narrow emission feature at around $10$ MeV in the brightest ever GRB 221009A. By modelling its profile with a Gaussian, we find a roughly constant width $\sigma \sim 1$ MeV and temporal evolution both in energy ($\sim 12$ MeV to $\sim 6$ MeV) and luminosity ($\sim 10^{50}$ erg/s to $\sim 2 \times 10^{49}$ erg/s) over 80 seconds. We interpret this feature as a blue-shifted annihilation line of relatively cold ($k_\mathrm{B}T\ll m_\mathrm{e}c^2$) electron-positron pairs, which could have formed within the jet region where the brightest pulses of the GRB were produced. A detailed understanding of the conditions that can give rise to such a feature could shed light on the so far poorly understood GRB jet properties and energy dissipation mechanism.Comment: Submitte

Characterizing radio emission from extensive air showers with the SLAC-T510 experiment, with applications to ANITA

Seckel, DavidNeutrino and cosmic ray astronomy allow scientists to gather information about the highest energy processes in the universe. However, since cosmic rays are charged nuclei moving in astrophysical magnetic fields, it has not been possible to determine their sources by studying their arrival directions. A pointed neutrino flux is expected at such energies, either direct from the sources or due to the GZK process, where high energy cosmic rays interact with cosmic microwave photons as they travel through the universe. Detection methods make use of particle cascades initiated by these high energy primaries. In particular, the electromagnetic radiation in radio frequencies generated by particle cascades is a powerful tool. Particle cascades emit radiation by the Askaryan process, where a charge excess in the cascade emits coherently. In the presence of a magnetic field, a transverse current develops which also emits coherently in the radio regime. Theoretical models describe this radiation and are widely used to reconstruct the energy, geometry, and composition of observed events. Therefore, understanding and validating models describing this radiation is of great importance to neutrino and cosmic ray astronomy. ☐ The SLAC T-510 beam test is the first experiment to produce a particle cascade in a controlled setting in the presence of a magnetic field. Radio-frequency (RF) emission is collected in the region of the Cherenkov cone in two polarizations designed to separately capture Askaryan and magnetically induced radiation. Field intensity, linearity with magnetic field, and spectral content are compared to particle-level simulations. The data provide experimental evidence supporting theoretical models, and show the first laboratory results of the scaling of the radiative strength with the magnetic field. ☐ SLAC T-510 grew out of a need to calibrate the sensitivity of the ANITA (Antarctic Impulsive Transient Antenna) experiment to cosmic ray air showers. ANITA uses radio techniques to detect the highest energy neutrinos and cosmic rays. An array of broadband antennas flies over Antarctica looking for signals from neutrinos interacting in ice and cosmic rays interacting in the atmosphere. The ANITA 3 flight took place in the austral summer of 2014-2015. ☐ In this dissertation I describe the SLAC T-510 experiment and results, as well as preparation and flight from the 2014 ANITA 3 campaign.University of Delaware, Department of Physics and AstronomyPh.D

LOFAR lightning imaging:mapping lightning with nanosecond precision

\u3cp\u3eLightning mapping technology has proven instrumental in understanding lightning. In this work we present a pipeline that can use lightning observed by the LOw-Frequency ARray (LOFAR) radio telescope to construct a 3-D map of the flash. We show that LOFAR has unparalleled precision, on the order of meters, even for lightning flashes that are over 20 km outside the area enclosed by LOFAR antennas (∼3,200 km\u3csup\u3e2\u3c/sup\u3e), and can potentially locate over 10,000 sources per lightning flash. We also show that LOFAR is the first lightning mapping system that is sensitive to the spatial structure of the electrical current during individual lightning leader steps.\u3c/p\u3

Needle-like structures discovered on positively charged lightning branches

\u3cp\u3e Lightning is a dangerous yet poorly understood natural phenomenon. Lightning forms a network of plasma channels propagating away from the initiation point with both positively and negatively charged ends—called positive and negative leaders \u3csup\u3e1\u3c/sup\u3e . Negative leaders propagate in discrete steps, emitting copious radio pulses in the 30–300-megahertz frequency band \u3csup\u3e2–8\u3c/sup\u3e that can be remotely sensed and imaged with high spatial and temporal resolution \u3csup\u3e9–11\u3c/sup\u3e . Positive leaders propagate more continuously and thus emit very little high-frequency radiation \u3csup\u3e12\u3c/sup\u3e . Radio emission from positive leaders has nevertheless been mapped \u3csup\u3e13–15\u3c/sup\u3e , and exhibits a pattern that is different from that of negative leaders \u3csup\u3e11–13,16,17\u3c/sup\u3e . Furthermore, it has been inferred that positive leaders can become transiently disconnected from negative leaders \u3csup\u3e9,12,16,18–20\u3c/sup\u3e , which may lead to current pulses that both reconnect positive leaders to negative leaders \u3csup\u3e11,16,17,20–22\u3c/sup\u3e and cause multiple cloud-to-ground lightning events \u3csup\u3e1\u3c/sup\u3e . The disconnection process is thought to be due to negative differential resistance \u3csup\u3e18\u3c/sup\u3e , but this does not explain why the disconnections form primarily on positive leaders \u3csup\u3e22\u3c/sup\u3e , or why the current in cloud-to-ground lightning never goes to zero \u3csup\u3e23\u3c/sup\u3e . Indeed, it is still not understood how positive leaders emit radio-frequency radiation or why they behave differently from negative leaders. Here we report three-dimensional radio interferometric observations of lightning over the Netherlands with unprecedented spatiotemporal resolution. We find small plasma structures—which we call ‘needles’—that are the dominant source of radio emission from the positive leaders. These structures appear to drain charge from the leader, and are probably the reason why positive leaders disconnect from negative ones, and why cloud-to-ground lightning connects to the ground multiple times. \u3c/p\u3

High-energy and ultra-high-energy neutrinos: A Snowmass white paper

Astrophysical neutrinos are excellent probes of astroparticle physics and high-energy physics. With energies far beyond solar, supernovae, atmospheric, and accelerator neutrinos, high-energy and ultra-high-energy neutrinos probe fundamental physics from the TeV scale to the EeV scale and beyond. They are sensitive to physics both within and beyond the Standard Model through their production mechanisms and in their propagation over cosmological distances. They carry unique information about their extreme non-thermal sources by giving insight into regions that are opaque to electromagnetic radiation. This white paper describes the opportunities astrophysical neutrino observations offer for astrophysics and high-energy physics, today and in coming years

High-Energy and Ultra-High-Energy Neutrinos

Astrophysical neutrinos are excellent probes of astroparticle physics and high-energy physics. With energies far beyond solar, supernovae, atmospheric, and accelerator neutrinos, high-energy and ultra-high-energy neutrinos probe fundamental physics from the TeV scale to the EeV scale and beyond. They are sensitive to physics both within and beyond the Standard Model through their production mechanisms and in their propagation over cosmological distances. They carry unique information about their extreme non-thermal sources by giving insight into regions that are opaque to electromagnetic radiation. This white paper describes the opportunities astrophysical neutrino observations offer for astrophysics and high-energy physics, today and in coming years

High-energy and ultra-high-energy neutrinos:A Snowmass white paper

Astrophysical neutrinos are excellent probes of astroparticle physics and high-energy physics. With energies far beyond solar, supernovae, atmospheric, and accelerator neutrinos, high-energy and ultra-high-energy neutrinos probe fundamental physics from the TeV scale to the EeV scale and beyond. They are sensitive to physics both within and beyond the Standard Model through their production mechanisms and in their propagation over cosmological distances. They carry unique information about their extreme non-thermal sources by giving insight into regions that are opaque to electromagnetic radiation. This white paper describes the opportunities astrophysical neutrino observations offer for astrophysics and high-energy physics, today and in coming years

High-Energy and Ultra-High-Energy Neutrinos

International audienceAstrophysical neutrinos are excellent probes of astroparticle physics and high-energy physics. With energies far beyond solar, supernovae, atmospheric, and accelerator neutrinos, high-energy and ultra-high-energy neutrinos probe fundamental physics from the TeV scale to the EeV scale and beyond. They are sensitive to physics both within and beyond the Standard Model through their production mechanisms and in their propagation over cosmological distances. They carry unique information about their extreme non-thermal sources by giving insight into regions that are opaque to electromagnetic radiation. This white paper describes the opportunities astrophysical neutrino observations offer for astrophysics and high-energy physics, today and in coming years