The First GECAM Observation Results on Terrestrial Gamma-ray Flashes and Terrestrial Electron Beams

Current space‐based observations of terrestrial gamma ray flashes (TGFs) are capable of identifying only TGFs that exceed a lower brightness threshold. Observationally, dim TGFs that fall below this threshold are consequently difficult to find using photon‐only search algorithms. Such TGFs are a potentially important part of the overall global TGF rate, and information on their occurrence rate would give important insight into TGF generation mechanisms. We describe and implement a lightning‐based search for TGFs that uses the location and time of National Lightning Detection Network reported positive polarity, in‐cloud (+IC) discharges of the type known to be directly associated with TGFs. These events identify a 200 μs search window when any associated TGF photons would have been detected. We show that this approach can detect TGFs without requiring a lower threshold on the detected photon brightness of the event, and thus is capable, in principle, of finding a population of weak TGFs. We find that TGFs occur at a rate between 1 in 40 and 1 in 500 of in‐cloud lightning events that meet our study's criteria. The distribution of gamma ray counts in the search windows exhibits a statistically significant lack of nearby dim TGFs below the GBM search threshold. The data favor a brightness distribution in which nearby observationally dim TGFs are rare.

We present a complete and systematic search for terrestrial gamma‐ray flashes (TGFs), detected by AGILE, that are associated with radio sferics detected by the World Wide Lightning Location Network (WWLLN) in the period February 2009 to September 2018. The search algorithms and characteristics of these new TGFs will be presented and discussed. The number of WWLLN identified (WI) TGFs shows that previous TGF selection criteria needs to be reviewed as they do not identify all the WI TGFs in the data set. In this analysis we confirm with an independent data set that WI TGFs tend to have shorter time duration than TGFs without a WWLLN match. TGFs occurs more often on coastal and ocean regions compared to the distribution of lightning activity. Several multipulse TGFs were identified and their WWLLN match are always associated with the last gamma‐ray pulse. We also present the first Terrestrial Electron Beam detected by AGILE. This data set together with the TGF sample identified by selection criteria (companion paper Maiorana et al., 2020) constitute the 3rd AGILE TGF catalog.

[1] The Gamma-Ray Burst Monitor (GBM) on the Fermi Gamma-Ray Space Telescope (Fermi) detected 50 terrestrial gamma-ray flashes (TGFs) during its first 20 months of operation. The high efficiency and large area of the GBM detectors, combined with their fine timing capabilities and relatively high throughput, allow unprecedented studies of the temporal properties of TGFs. The TGF pulses are observed to have durations as brief as ∼0.05 ms, shorter than previously measured. There is a relatively narrow distribution of pulse durations; the majority of pulses have total durations between 0.10 and 0.40 ms. In some TGF events, risetimes as short as ∼0.01 ms and falltimes as short as ∼0.03 ms are observed. Three of the 50 TGFs presented here have well-separated, double peaks. Perhaps as many as 10 other TGFs show evidence, to varying degrees, of overlapping peaks. Weak emission is seen at the leading or trailing edges of some events. Five of the 50 TGFs are considerably longer than usual; these are believed to be caused by incident electrons transported from a TGF at the geomagnetic conjugate point. TGF temporal properties can be used to discriminate between models of the origin of TGFs and also provide some basic physical properties of the TGF process.

Many details of how thunderstorms generate terrestrial gamma ray flashes (TGFs) and other forms of high‐energy radiation remain uncertain, including the basic question of where they are produced. We exploit the association of distinct low‐frequency radio emissions with generation of terrestrial gamma ray flashes (TGFs) to directly measure for the first time the TGF source altitude. Analysis of two events reveals source altitudes of 11.8 ± 0.4 km and 11.9 ± 0.9 km. This places the source region in the interior of the thunderstorm between the two main charge layers and implies an intrinsic TGF brightness of approximately 1018 runaway electrons. The electric current in this nontraditional lightning process is found to be strong enough to drive nonlinear effects in the ionosphere, and in one case is comparable to the highest peak current lightning processes on the planet.

Unique spaceborne measurements of the three‐dimensional structure of convective clouds producing terrestrial gamma ray flashes (TGFs) were performed using both active and passive microwave sensors on board the Global Precipitation Measurement (GPM)‐Core Observatory satellite, finding coherent features for nine TGF‐producing storms. The delineation of cloud structure using the radar reflectivity factor shows convective cells with significant vertical development and thick layers with high ice content. Compared to other cumulonimbus clouds in the tropics, the TGFs counterparts have higher reflectivity values above 3 and 8 km altitude showing in all cases a cumulonimbus tower and the TGFs locations are very close, or coincident, to these high Z columns, where reflectivity exceeds 50 dBz. Using the GPM Microwave Imager radiometer, most thunderstorms show a very strong depression of polarization corrected temperature (PCT) at channel 89 GHz, indicating a strong scattering signal by ice in the upper cloud layers. At channel 166 GHZ, the difference between vertical and horizontal brightness temperature signal always returns positive values, from 0.2 up to 13.7 K indicating a complex structure with randomly/vertically oriented ice particles. The PCT was used to characterize the analyzed storms in terms of hydrometeor types, confirming in 7/9 cases a high likelihood of hail/graupel presence. To perform analysis on the TGFs parent flashes, radio atmospherics data from the Earth Networks Total Lightning Network lightning network were used. Waveform data indicate that all cases are intra‐cloud events and TGFs typically take place during the peak of flash rate production. Finally, the analysis of the most intense event is shown.

We provide evidence that Terrestrial Gamma‐Ray Flashes (TGFs), in well isolated thunderstorms, tend to occur during periods of low and declining flash rates, and when the flash amplitudes are larger than average. This conclusion comes from examining the results of 371 manually tracked TGF‐producing thunderstorms. Fermi‐GBM identified TGFs are used for this analysis and lightning data come from both World Wide Lightning Location Network and Earth Networks Total Lightning Network. The data from these storms suggest that TGFs are likely to occur in almost every phase of storms that last longer than an hour, but tend to occur later on in shorter storms. We also note that, in short storms, TGFs are more likely to accompany a flash when the flash rates of the storm are lower than average, and they are less likely per flash during the peak flash rate periods of the storms. We find that the tendency for TGFs to occur while the flash rate is falling and when the amplitudes of flashes (the sum of the absolute values of peak currents of all constituent sferics in the flash) are larger than average, does not depend strongly on the duration of the storms. This implies that not just any lightning flash can or even will produce a TGF, but that the electrical conditions of the storm play a crucial role in TGF production.

<p indent="0mm">The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) monitors gamma-ray bursts (GRBs) coincident with gravitational wave events over the whole sky. It also monitors other burst events, such as the high-energy radiation of fast radio bursts, various GRBs, and magnetar bursts. GECAM can measure the energy spectra, light curves, and location of all kinds of bursts. GECAM consists of two small satellites which operate in the same low earth orbit but in opposite geocentric directions. To obtain an all-sky field of view, the two satellites operate in opposite orbital phases. The GECAM payload includes two kinds of detectors: charged particle detector (CPD) and gamma-ray detector (GRD). Each GRD module consists of a LaBr₃:Ce scintillator and a SiPM array, and its gamma-ray detection range is <sc>5 keV–5 MeV.</sc> GECAM retrieves the locations of events such as GRBs through analyzing the data of the multiple GRDs on both satellites. Meanwhile, the CPD consists of a plastic scintillator and a SiPM array that detects charged particles of energies from <sc>300 keV</sc> to <sc>5 MeV.</sc> The GECAM distinguishes the charged particle burst events in space by jointly analyzing the GRD and CPD data. The payload electronic box (EBOX) provides in-flight trigger and burst localization. The trigger and burst location data are transmitted by a BeiDou Short Message system, which allows GECAM to guide other telescopes to do follow-up observations.

We have studied the spectacular 1991 June X-class flares using gamma-ray data from the Charged Particle Detectors (CPDs) of the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO) and 80 GHz millimeter data from Nobeyama, Japan. The CPDs were the only CGRO instrument that did not saturate during the extremely intense 1991 June 4 flare. We have shown that for this flare the CPDs respond to MeV photons, most of which are due to bremsstrahlung produced by relativistic electrons at the Sun. We have further shown that the gamma-ray and millimeter observations agree numerically if the 80 GHz radiation is gyrosynchrotron radiation produced by trapped electrons and the gamma rays are thick-target bremsstrahlung due to electrons precipitating out of the trap. The requirement that the trapping time obtained from the numerical comparison be consistent with the observed time profiles implies a magnetic field between about 200 and 300 G and an electron spectral index between about 3 to 5. By comparing the CPD observations with both the 80 GHz data and nuclear line data from the Energetic Gamma Ray Experiment Telescope (EGRET) and the Oriented Scintillation Spectroscopy Experiment (OSSE) on CGRO for the flares of June 4, 6, 9, and 11, we found that the ratio of the CPD counts to both the millimeter flux densities and the nuclear line fluences decreases with decreasing flare heliocentric angle. All of these flares were produced in the same active region. We interpreted this result in terms of a loop model in which the gyrosynchrotron emission is produced in the coronal portion of the loop where the electrons are kept isotropic by pitch angle scattering due to plasma turbulence, while the bremsstrahlung is produced by precipitating electrons that interact anisotropically. We found that the trapping time in the coronal portion is time dependent, reaching a minimum of about 10 s at the peak of the CPD count rate. We suggested the damping of the turbulence as a possible reason for the variation of the trapping time. turbulence as a possible reason for the variation of the trapping time.

An investigation of the dependence of film density on group and phase velocities in a Love Wave Device shows potential for acoustic‐based charged particle detection (CPD). Exposure of an ion sensitive photoresist to charged particles causes localized changes in density through either scission or cross‐linking. A theoretical model was developed to study ion fluence effects on Love Wave sensitivity based on: ion energy, effective density changes, layer thickness and mode selection. The model is based on a Poly(Methyl Methacralate) (PMMA) film deposited on a Quartz substrate. The effect of Helium ion fluence on the properties of PMMA has previously been studied. These guidelines were used as an initial basis for the prediction of helium ion detection in a PMMA layer. Procedures for experimental characterization of ion effects on the material properties of PMMA are reviewed. Techniques for experimental validation of the predicted velocity shifts are discussed. A Love Wave Device for CPD could potentially prov...

We characterize the evolution of spectral and temporal properties of several Galactic black hole transients during outburst decay using the data from well sampled PCA/\rxte observations close to the transition to the low/hard state. We find several global patterns of evolution for spectral and temporal parameters before, during, and after the transition. We show that the changes in temporal properties (sudden increase or decrease in the rms amplitude of variability) are much sharper than the changes in the spectral properties, and it is much easier to identify a state transition with the temporal properties. The spectral index shows a drop 3-5 days before the transition for some of our sources. The ratio of the power-law flux to the total flux in the 3-25 keV band increases close to the transition, which may mean that the system must be dominated by the coronal emission for the transition to occur. We also show that the power-law flux shows a sharp change along with the temporal properties during the transitions which may indicate a threshold transition volume for the corona. The evolution of the spectral and temporal properties after the transition is consistent with the idea that the inner accretion disk moves away from the black hole. Based on the evolution of spectral and temporal parameters and changes during the transitions, we discuss possible scenarios of how the transition is happening.

Since plastic detectors are easy to fabricate and have good scintillation properties, they have been used as various forms for cosmic-ray detection. Major factors to determine a detector's efficiency are scintillator size, scintillation transfer material, and the photo acceptor equipment. The size of a plastic scintillator and the photo acceptor equipment (photo multiplier tube, photodiode, etc.) can be decided easily in the design process but the scintillation transfer material has to be selected circumspectly. Light guides using Polymethylmethacrylate (PMMA) have a very high transmittance, but are large in size and very expensive, while a wavelength shifter fiber can transfer the scintillation at a decreased transfer efficiency. Therefore, a detector using a wavelength shifter fiber requires a proper optimization for maximum efficiency. In this study, three detectors of 1000×500×10 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> size were fabricated. The wavelength shifter fibers were mounted by optical cement into grooves and the detection efficiency for charged particles was evaluated. The main goal was to measure the detection efficiency for cosmic-ray charged particles detector using a wavelength shifter fiber in order to evaluate the possibility of replacing the expensive PMMA light guides. And, this study was compared with efficiency of ¿ATHLET¿ charged particle detector. We are going to prove that we can fabricate a cosmic-ray charged particle detector with a performance identical to an advanced nation's one.

Materials for radiation detection are critically important and urgently demanded in diverse fields, starting from fundamental scientific research to medical diagnostics, homeland security, and environmental monitoring. Low-dimensional halides (LDHs) exhibiting efficient self-trapped exciton (STE) emission with high photoluminescence quantum yield (PLQY) have recently shown a great potential as scintillators. However, an overlooked issue of exciton-exciton interaction in LDHs under ionizing radiation hinders the broadening of its radiation detection applications. Here, we demonstrate an exceptional enhancement of exciton-harvesting efficiency in zero-dimensional (0D) Cs3Cu2I5:Tl halide single crystals by forming strongly localized Tl-bound excitons. Because of the suppression of non-radiative exciton-exciton interaction, an excellent α/β pulse-shape-discrimination (PSD) figure-of-merit (FoM) factor of 2.64, a superior rejection ratio of 10−9, and a high scintillation yield of 26 000 photons MeV−1 under 5.49 MeV α-ray are achieved in Cs3Cu2I5:Tl single crystals, outperforming the commercial ZnS:Ag/PVT composites for charged particle detection applications. Furthermore, a radiation detector prototype based on Cs3Cu2I5:Tl single crystal demonstrates the capability of identifying radioactive 220Rn gas for environmental radiation monitoring applications. We believe that the exciton-harvesting strategy proposed here can greatly boost the applications of LDHs materials.

The Equivalent Noise Charge (ENC) of Monolithic Active Pixel Sensors has been determined using an analytical approach. The ENC is an important characteristic when these sensors are used for charged particle detection as it determines the Signal to Noise ratio. This paper gives the dominant contributions to the temporal noise as a function of an observation time directly related to the clocking frequency of the pixel array. Measured data made on MIMOSA8 array confirms the validity of the approach. In addition both theoretical computation and experimental data show that the residual ENC is of the order of 10 e- and can be further reduced.

Characterisation of HEPAPS4—A family of CMOS active pixel sensors for charged particle detection

We present the first reported instance of an image-charge detector for charged particles in which detection elements are patterned onto printed circuit boards. In contrast to conventional techniques involving separately machined and positioned segments of metal tubing, this technique is much simpler to assemble, align, and connect to electrical wiring, with no loss in sensitivity. The performance of single-stage and 5-stage charge detectors is demonstrated using electrospray-charged, micrometer-size polystyrene spheres. Both velocity and charge of each particle are measured. Multiple detection stages--which require no extra effort to pattern or setup compared with a single stage--result in an ensemble averaging effect, improving the detection limit over what can be achieved with a single-stage detector. A comparison is made between the printed circuit board detector and a conventional tubular charge detector and found to be statistically equivalent. These results demonstrate and illustrate that devices for detection, analysis, and/or manipulation of charged particles and ions can be made using printed circuit boards rather than using separately fabricated metal electrodes.