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The Atmosphere-Space Interactions Monitor (ASIM) is a mission of the European Space Agency launched in April 2018 and hosted onboard the International Space Station (ISS). ASIM is dedicated to study the physics of Transient Luminous Events (TLEs) and Terrestrial Gamma-ray Flashes (TGFs) and their relation to lightning. TGFs are X- and Gamma-ray flashes associated to lightning discharges, with average duration of few tens of microseconds and energies up to 40 MeV. ASIM detects TGFs by means of the Modular X- and Gamma-ray Sensor (MXGS). So far, the MXGS performance (efficiency, effective area) have been evaluated by Monte Carlo simulations only, while energy calibration is monitored using built-in radioactive sources and background lines. TGFs are local events, very rarely observed by more then one spacecraft simultaneously, therefore it is difficult to use them to validate the MXGS performance. Goal of this study is to use cosmic Gamma-ray Bursts (GRBs) simultaneously detected by ASIM and other spacecraft as calibration sources to validate the spectral performance of MXGS. GRBs are the brightest explosions in the universe, associated to the collapse of massive stars or the merger of compact objects, involving at least one neutron star, at cosmological distances. During the period from June 2018 to December 2021, 12 GRBs were detected by ASIM and by one or more other spacecraft. Here we use data from the Konus-WIND mission and from the Fermi Gamma Burst Monitor (GBM), both considered as benchmarks in the field of GRB analysis. We cross-correlate the light curves of the three instruments, and we perform simultaneous spectral analysis using the forward-folding approach. In some cases, we find good consistency between the detectors, indicating an overall validation of the MXGS performance. In other cases, we identified discrepancies, possibly due to absorption from structures of the ISS, currently under investigation. In this presentation, we show our data sample, the methodology used and the preliminary joint spectral analysis results. This work is relevant because it will provide an independent assessment of the MXGS performance, with clear implications for ASIM TGF results.

The Airborne Lighting Observatory for FEGS and TGFs (ALOFT) is a field campaign focused on observing Terrestrial Gamma-ray Flashes (TGFs) and gamma-ray glows from thunderclouds. ALOFT will be flown on a NASA ER-2 research aircraft, flying at 20 km altitude, and the payload includes:1) Fly’s Eye GLM Simulator (FEGS), an array of imaging photometers as well as different wavelengths, and electric field change meters.2) Lightning Instrument Package (LIP), giving three component electric field measurements.3) Several gamma-ray detectors covering four orders of magnitude dynamic range in flux as well as the full energy range for TGF/gamma-ray glow detection.ALOFT is scheduled for July 2023, with 50 flight hours based out of Florida. Flying over thunderstorms in Central America and Caribbean, one of the most active TGF regions on the planet during the most optimal season, the ALOFT campaign will help us to answer the questions:1) How and under what conditions are TGFs produced?2) How extended in space and time are the gamma-ray glows?To answer question 1), the ALOFT campaign will be supported by ground based radio measurements from different locations in Central America and Caribbean.To answer question 2), with realtime downlink of data we will know when the ER-2 encounters gamma-ray glowing thunderclouds, and we will instruct the pilot to have the aircraft perform have repeated overflights over this cloud as long as the glow exists, to answer question 2). This will also help us understand whether gamma-ray glows and TGFs are interrelated.The full set of observational goals of ALOFT are:1. Observe TGFs in one of the most TGF-intense regions on the planet.2. Observe gamma-ray glows in thunderstorms and their relation to TGFs.3. Perform International Space Station Lightning Imaging Sensor (ISS LIS) and Global Lightning Monitor (GLM) validation using improved suborbital instrumentation (including upgraded FEGS).4. Evaluate new design concepts for next-generation spaceborne lightning mappers.5. If relevant instrumentation is available, make measurements useful to advance convection science from a suborbital platform.In this presentation we will give the status and plans for the ALOFT mission.

ELVEs are quickly expanding rings of light emissions excited in the lower ionosphere by the electromagnetic pulse of an electric discharge in a thundercloud. They are commonly observed from space platforms and have been reported in conjunction with other atmospheric-electricity events. One motivation to investigate ELVEs is that their signal may provide insight into the discharge that created them. Until now the modeling of ELVES has either relied on strong simplifications or on the Finite-Difference Time-Domain (FDTD) method to directly solve the Maxwell equations. One limitation of the latter is that non-axisymmetrical discharges (with a slanted channel or a non-vertical magnetic field for example) require computationally expensive, fully three-dimensional meshes, which makes parametric studies of the ELVE features slow and cumbersome. We show here that elementary electromagnetic theory allows one to model ELVEs, even non-axisymmetrical ones, with sufficient accuracy at little computational cost. We then apply our methods to the parametric study of ELVE photometric waveforms as recorded by space-based instruments.

We present the largest catalogue compiled to date of TGFs and associated lightning activity, geostationary satellite cloud images and ERA5 reanalysis data. The TGFs are observed from AGILE, ASIM, FERMI and RHESSI, and the lightning activity by the WWLLN and GLD360 networks. The 1582 TGF events identified are analysed and contextualized relative to lightning flashes. In our analysis, we consider the proportion of TGFs and lightning coming from overshooting tops, and the dependencies on Cloud Top Temperature (CTT) and the Convective Available Potential Energy (CAPE). We find that TGFs come from primarily higher cloud tops than lightning flashes, consistent with previous studies. We also find that CAPE is similar for TGF and lightning-producing cells, and that the proportion of TGF and lightning-producing cells in the overshooting phase are similar. We analyse the regional and seasonal differences between TGFs and lightning and see that regional meteorological effects dominate.

In the first two years of ASIM operations from June 2018 till the end of 2019 486 TGFs have been observed, with a TGF rate of 0.84 per day. Their geographical distribution is consistent with the three main lightning chimneys Central America, Central Africa, and South East of Asia. Figure 1 displays the ISS footprint positions when the TGFs were detected.Figure 1: ISS position for the 2018-2019 ASIM TGFs. Red circles marked those within 4 minutes of the previous TGF detected.If the TGF occurrence follows a stochastic process (each TGF is not related to the next one), the time-difference distribution between a TGF detection and the next one should fit an exponential distribution. For a Δt < 4 minutes the number of TGFs following the exponential distribution is 16. Opposite we got 85 in groups of 2-3 TGFs displayed in Figure 1 in red circles. Analyzing the apparent strong discrepancy in the number of detection in less than 4 minutes (Figure 2) and the number derived from the exponential distribution is one of the motivations of this study.We build a grid of variable dimension cell size to keep the same ISS observing time for each cell in a Monte Carlo code to simulate the TGF generation that has into account the frequency and the anisotropy distribution of the TGFs over the earth.To preserve the total number of TGF observed in Δt < 4 minutes we need to add a parameter related to the “Storm Activity” defined as the time in a cell available to generate a TGF. The model fits observations when this parameter is 7%±1%. The good correlation between model/observation is displayed in Figure 2. Figure 2: The predicted distribution of the TGF pairs (Orange) in 15s bins fits the observations (Blue). The scope of this work is to check the adopted “Storm Activity” value using WWLLN sferics database as a good indicator of storm activity.

Elves are produced when electromagnetic pulses from lightning interact with the lower parts of the ionosphere and are observed from space as expanding rings of light in the UV and visible optical bands. Elves are known to be associated with high peak current lightning. Using data from the Modular Multi-spectral Imaging Array (MMIA) instrument of the Atmosphere-Space Interactions Monitor (ASIM) payload, we search for observations of Elves when high peak currents (>70 kA) are detected by the global ground-based lightning detection network GLD360. We identify two types of events; high peak current detections associated with Elves, and high peak current detections not associated with Elves. To understand why some high peak current discharges do not generate observable Elves, we explore the number of lightning discharges and their peak currents leading up to the events. Preliminary results indicate that for current pulses with peak currents below 100 kA we observe a significant number of Elves, but this quantity depends on the lightning activity within 5 minutes before. Current pulses with peak currents above 120 kA nearly always produce Elves, regardless of the preceding lightning activity.

ALOFT (Airborne Lightning Observatory for FEGS and TGFs) is a flight campaign designed to observe Terrestrial Gamma-ray Flashes (TGF) and gamma-ray glows close to their production source. The campaign consists of 50 flight hours of a NASA ER-2 research aircraft taking off from Florida and is scheduled for July 2023. The ER-2 cruise altitude of 20 km allows flying over active thunderstorms in the Gulf of Mexico and Caribbean region, one of the most TGF-active region on the planet. The main challenge for TGF detection at close distance is the large variability in the expected gamma-ray flux, spanning four orders of magnitude depending on the radial distance from the source. To cope with this challenge, the ALOFT gamma-ray payload consists of several detectors of different size, made of different materials and readout sensors, designed to cover 4 orders of magnitude dynamic range on the typical TGF/gamma-ray glow energy range (~100 keV - ~40 MeV). In addition, the payload includes the Fly’s Eye GLM Simulator (FEGS), an array of imaging photometers sensitive at different wavelengths, and electric field change meters, and the Lightning Instrument Package (LIP), giving three component electric field measurements. The synergy between airborne gamma-ray, optical and electric field measurements, combined with ground-based radio observations, will provide a unique set of observations to constrain the source properties and their physics. This presentation will focus on the ALOFT scientific payload and the system architecture.

TGFs being the bursts of high energy photons shot from Earth’s atmosphere to space, are known to be produced during the initial upward propagation of the +IC lightning leader. VLF and LF radio sferics can often be found in association with the short duration TGFs. The Atmosphere-Space Interactions Monitor (ASIM) instrument provides synchronous X- and gamma-ray measurements with optical recordings in 180-240 nm, 337 nm and 777.4 nm wavelength. This allows for simultaneous detection for TGFs and the lightning processes associated with them.ASIM TGF observations have shown that TGFs within the FOV of the optical instruments are always accompanied by the prominent optical pulse which starts the lightning flash. TGFs have a clear tendency to slightly precede the optical pulse, but the short duration of TGFs together with the optical delay of the lightning light propagating through the cloud do not allow to confidently resolve the true sequence of these events.The same problem is present in radio measurements: radio signature from TGF current is usually mixed with lightning current in the recordings due to temporal proximity of the processes involved.Here we report a remarkable, high fluence and long duration TGF, together with its associated optical recordings. This observation shows clear distinction between the TGF and the associated optical pulse: the optical pulse is subsequent to the TGF, as it starts after the TGF is terminated. This allows to conclude that strong current surges inside the leader channel are not responsible for the TGF generation, and, in turn, the current surge producing the optical pulse can be conditioned by the generated TGF, or even be responsible for TGF termination.

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Gamma-Ray Glows (GRGs) are bursts of high-energy radiation that are emitted by thunderclouds and have a duration of seconds to minutes. These radiation sources are extended over several to tens of square kilometers. GRGs have been observed from detectors on the ground, in aircraft, and on balloons. In this paper, we present a Monte-Carlo model that can be used to study the production and propagation of GRGs. We compare our model to one developed by Zhou et al. (2016) and find small differences between the two. We have also created a library of simulations that is available to the community. Using this library, we were able to reproduce five previous GRG observations from five airborne campaigns: balloons from Eack et al. (1996) and Eack et al. (2000), and aircraft from the ADELE (Kelley et al. 2015), ILDAS (Kochking et al. 2016), and ALOFT campaigns (Østgaard et al. 2019).Our simulation results confirm that the flux of cosmic-ray secondary particles at a given altitude can be enhanced by several percent or even several orders of magnitude due to the effect of thunderstorms' electric fields. These results explain the five observations we studied and will be useful for the upcoming ALOFT-2023 campaign. While some GRGs can be explained solely by the MOS process, the strongest GRGs observed require electric fields significantly larger than the RREA threshold value (E_th). Some of the observations also came with in-situ electric field measurements that were always lower than E_th, but these measurements may not have been taken from the regions where the glows were produced. This study supports the idea that some thunderstorms must have electric fields with magnitudes of at least E_th on a kilometer scale. References :-Effect of near-earth thunderstorms electric field on the intensity of ground cosmic ray positrons/electrons in tibet. Zhou et al. (2016). https://doi.org/10.1016/j.astropartphys.2016.08.004-Balloon-borne x-ray spectrometer for detection of x-rays produced by thunderstorms. Eack et al. 1996. https://doi.org/10.1063/1.1146959-Gamma-ray emissions observed in a thunderstorm anvil. Eack et al. 2000. https://doi.org/10.1029/1999GL010849-Relativistic electron avalanches as a thunderstorm discharge competing with lightning. Kelley et al. 2015. https://doi.org/10.1038/ncomms8845-In-Flight Observation of Gamma Ray Glows by ILDAS. Kochkin et al. 2017. https://doi.org/10.1002/2017JD027405 -Gamma Ray Glow Observations at 20-km Altitude. Østgaard et al. 2019. https://doi.org/10.1029/2019JD030312

Terrestrial Gamma-ray Flashes (TGFs) are short flashes of high-energy photons produced by thunderstorms. They are intense phenomena that may have high photon fluxes with energies up to 40 MeV when observed from detectors in orbit. All instruments in space have suffered instrumental saturation during bright events, including CGRO-BATSE, RHESSI, Fermi-GBM, AGILE-MCAL and ASIM-MXGS. The effects include dead-time and pulse pile-up, which lead to an underestimation of the TGF fluences and, in some cases, incorrect photon energies. A key asset of ASIM is that it has two detectors on the same platform: the High Energy Detector (HED, 300 keV to ~40 MeV) and the Low Energy Detector (LED, 50 keV to 400 keV). LED is only weakly affected, which makes it possible to estimate corrections to the HED measurements for even the brightest TGFs. With the method we propose, we estimate the loss of photons by combining the LED and HED measurements with GEANT4 Monte-Carlo simulations of the detector responses. We applied the method to three TGF events. The first, TGF-200728, has about 0.15 counts per microsecond per unit, and is not expected to experience saturation and is used as a sanity check for the method. The other events, TGF-181102 (1.5 counts per microsecond per unit) and TGF-181025 (2.8 counts per microsecond per unit), indicate that the HED misses at least 50% of the photon counts for the brightest TGF events.

ASIM TGF catalog presents more than one thousand TGF from June 2018 till the end of 2021. Using this dataset, the detection rate of TGF by ASIM was about one TGF per day. The TGF detection is a stochastic process (each TGF is not related with the next) assuming this, the time-difference distribution between one detection and the next should fit an exponential distribution. This time between TGF events distribution fits the exponential with a significant deviation. We see an excess in the number of TGF separated by less than 5 min. From the expected value of less than 1% of the events, we have an 8% of the events in this range. We call that TGF population with a time separation of fewer than 5 minutes “Brother TGF”. Large storm areas could explain this deviation, because of the storm size or also the propagation effects of the TGF inside the storm as an effective mechanism to increase the TGF production in this region. This work we present is a detailed study of the most relevant “Brothers” in the ASIM TGF imaging list. With this, we can locate where these Brothers TGF are located, and add some clues about this Brother TGF production mechanism.

Terrestrial gamma-ray flashes (TGFs) are short and highly energetic bursts of photons, produced in association with lightning in thunderstorms. Elves are rapidly expanding rings of optical emissions, with radii of several hundred kilometers, produced when electromagnetic pulses from lightning hit the base of the ionosphere. The Atmosphere-Space Interactions Monitor (ASIM) detects both TGFs and Elves, sometimes simultaneously. Here, we present a study of observations where TGFs are accompanied by Elves. The optical signatures from Elves are identified from measurements by the ASIM UV photometer. Using ground-based lightning location networks, we find associated sferic detections to these events, placing them mainly over oceans and in coastal regions. Using sferic detections by GLD360, we compare the peak currents of the lightning associated with the TGF-Elve pairs to peak currents associated with other TGFs detected by ASIM, as well as with lightning in general. We show that the TGFs accompanied by Elves are among the shorter TGFs detected by ASIM, and they are associated with very high peak currents of typically several hundred kA.

Atmosphere Space Interaction Monitor (ASIM) has now observed more than 1000 Terrestrila Gamma-ray falshes (TGFs) since the launch in 2018. ASIM has two payloads, the Modular X- and Gamma-ray Sensor (MXGS) and the Modular Multi-Spectral Imaging Assembly (MMIA). MXGS consists of two detector layers, one pixelated detector in the low energy range (50 keV to 400 keV) and another in the high energy range (300 keV to >30 MeV), with temporal resolution of 1µs and 28 ns, respectively. MMIA has three photometers (337 nm, 180-230 nm, 777 nm) and two cameras (337 nm and 777 nm). During nighttime we observe both the TGFs and the lightning that produced them. Multiple and double TGFs separated by 1-2 ms have frequently been observed by ASIM. In this paper we present three events of double TGFs. All of them are associated with optical pulses from a hot leader (777 nm), and the first and second pulses come from the same location, indicating that the double TGFs are produced by the same leader as it propagates upward.

The Atmosphere-Space Interactions Monitor (ASIM) was designed to monitor Terrestrial Gamma-ray Flashes (TGFs) and Transient Luminous Events (TLEs) from space, enabling the study of how these phenomena are related. In this paper, we present observations of 17 TGFs with accompanying Elves. TGFs are short and highly energetic bursts of gamma photons associated with lightning discharges, whereas Elves are TLEs that are observed as concentric rings of ultraviolet (UV) and visible light at ionospheric altitudes, produced by the excitation of N2 molecules when an electromagnetic pulse (EMP) hits the base of the ionosphere. Elves were identified when optical detections in the UV band could be clearly distinguished from other optical signals from lightning strokes. The TGFs they accompanied had short durations and were associated with particularly high peak current lightning. Lightning sferics associated with these events were detected by the global lightning network GLD360 and the World Wide Lightning Location Network (WWLLN), and they were, with the exception of one event, observed over ocean or coastal regions. It is likely that these events were associated with Energetic In-cloud Pulses (EIPs). We show that short duration TGFs tend to be associated with higher peak currents than long duration TGFs.

Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray (2022), Montreal, Jul 17-22, 2022.--Proceedings of SPIE - The International Society for Optical Engineering vol. 12181 Article number 1218126.-- Full list of authors: Amati, Lorenzo; Labanti, Claudio; Mereghetti, Sandro; Frontera, Filippo; Campana, Riccardo; Auricchio, Natalia; Baldazzi, Giuseppe; Bellutti, Pierluigi; Bertuccio, Giuseppe; Branchesi, Marica; Butler, Reginald C.; Caballero-Garcia, Maria D.; Camisasca, Anna E.; Castro-Tirado, Alberto J.; Cavazzini, Leo; Ciolfi, Riccardo; De Rosa, Adriano; Evangelisti, Federico; Farinelli, Ruben; Ferro, Lisa; Ficorella, Francesco; Fiorini, Mauro; Fuschino, Fabio; Gasent-Blesa, Jose L.; Ghirlanda, Giancarlo; Grassi, Marco; Guidorzi, Cristiano; Hedderman, Paul; Kuvvetli, Irfan; La Rosa, Giovanni; Lorenzi, Paolo; Malcovati, Piero; Marchesini, Ezequiel; Marisaldi, Martino; Melchiorri, Michele; Mele, Filippo; Mikhalska, Malgorzata; Orlandini, Mauro; Orleanski, Piotr; Pedersen, Soren M.; Pizzolla, Raffaele; Rachevski, Alexandre; Rashevskaya, Irina; Rosati, Piero; Reglero, Victor; Ronchini, Samuele; Santangelo, Andrea; Salvaterra, Ruben; Sarra, Paolo; Sortino, Francesca; Sottile, Giuseppe; Stratta, Giulia; Squerzanti, Stefano; Stephen, John B.; Tenzer, Chris; Terenzi, Luca; Trois, Alessio; Vacchi, Andrea; Virgilli, Enrico; Volpe, Angela; Winkler, Marek; Zampa, Gianluigi; Zampa, Nicola; Zdziarski, Andrzej, We describe the science case, design and expected performances of the X/Gamma-ray Imaging Spectrometer (XGIS), a GRB and transients monitor developed and studied for the THESEUS mission project, capable of covering an exceptionally wide energy band (2 keV – 10 MeV), with imaging capabilities and location accuracy, With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709

In this article, we report the first investigation over time of the atmospheric conditions around terrestrial gamma-ray flash (TGF) occurrences, using GPS sensors in combination with geostationary satellite observations and ERA5 reanalysis data. The goal is to understand which characteristics are favorable to the development of these events and to investigate if any precursor signals can be expected. A total of 9 TGFs, occurring at a distance lower than 45 km from a GPS sensor, were analyzed and two of them are shown here as an example analysis. Moreover, the lightning activity, collected by the World Wide Lightning Location Network (WWLLN), was used in order to identify any links and correlations with TGF occurrence and precipitable water vapor (PWV) trends. The combined use of GPS and the stroke rate trends identified, for all cases, a recurring pattern in which an increase in PWV is observed on a timescale of about two hours before the TGF occurrence that can be placed within the lightning peak. The temporal relation between the PWV trend and TGF occurrence is strictly related to the position of GPS sensors in relation to TGF coordinates. The life cycle of these storms observed by geostationary sensors described TGF-producing clouds as intense with a wide range of extensions and, in all cases, the TGF is located at the edge of the convective cell. Furthermore, the satellite data provide an added value in associating the GPS water vapor trend to the convective cell generating the TGF. The investigation with ERA5 reanalysis data showed that TGFs mainly occur in convective environments with unexceptional values with respect to the monthly average value of parameters measured at the same location. Moreover, the analysis showed the strong potential of the use of GPS data for the troposphere characterization in areas with complex territorial morphologies. This study provides indications on the dynamics of con-vective systems linked to TGFs and will certainly help refine our understanding of their production, as well as highlighting a potential approach through the use of GPS data to explore the lightning activity trend and TGF occurrences. publishedVersion

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., On February 8, 2019, the Atmosphere-Space Interaction Monitor observed a terrestrial gamma-ray flash (TGF) and an Elve from a positive intracloud (+IC) lightning during the initial breakdown stage of a lightning flash north east of Puerto Rico. A second Elve produced by the return stroke (RS) of a negative cloud-to-ground (−CG) lightning was observed 456 ms later about 300 km south of the first one. Radio measurements show that a short (30 μs) and large (280 kA km) energetic in-cloud pulse (EIP) produced the electromagnetic (EM) wave for the first Elve while the RS of the −CG was the EM source for the second Elve. Assuming that the EIP and the RS were the sources of the 777 nm emissions, both the delay relative to the ultra-violet pulse and the shape and duration of the 777 nm emissions can be explained by scattering and absorption inside the clouds. The TGF produced by the +IC lightning had the same duration as the EIP (∼30 μs). Due to the ±80 μs timing uncertainty of the TGF, we can only state that TGF was produced just before or most likely simultaneously with the EIP. The large 777 nm pulse indicates that a large part of the EIP was produced by a current flowing in a hot channel, but it is likely that the TGF current also contributed significantly to the EIP. © 2021. The Authors., This study was supported by the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no. 320839 and the Research Council of Norway under contracts 223252/F50 (CoE). This study has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skodowska-Curie grant agreement SAINT 722337. A.L. acknowledges support by the European Research Council (ERC) under the European Union H2020 program/ERC grant agreement 681257. This work was supported by the National Science Foundation Dynamic and Physical Meteorology program through grant AGS/1565606. The authors thank the International Space Science Institute, Bern, Switzerland, for providing financial support and meeting facilities in the frame of the International Team no. 471: Understanding the Properties of the Terrestrial Gamma-Ray Flash Population., With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.

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.

The Atmospheric Space Interactions Monitor (ASIM) was launched in 2018, and has since then observed Terrestrial Gamma-ray Flashes (TGFs) and Transient Luminous Events (TLEs). ASIM consists of the Modular X- and Gamma-ray Sensor (MXGS) and the Modular Multispectral Imaging Array (MMIA). Using data from both MXGS and MMIA, we investigate observations of TGFs (detected by MXGS) with accompanying elves (detected by MMIA). We study the optical signatures of the elves detected by a photometer of MMIA operating in the 180-230 nm band. Lightning sferics associated with these events have been detected by WWLLN and GLD360. Several TGFs have associated lightning sferics outside the field of view of MMIA, but due to the expanding rings of the elves we can still observe optical signatures from accompanying elves. Using GLD360 data we also study properties of the lightning strokes.

ASIM has now observed several hundreds of TGFs since the launch in 2018. Highlights and new science from the first ten months of observations were presented in Østgaard et al. (2019) paper. In this presentation we will present observational highlights from the last 1.5 year, when the relative timing accuracy between the TGF observations and the optical measurements is +/- 5 us (compared to +/- 80 us before march 2019). This includes many more simultaneous TGF and Elve observations, high flux TGFs, double TGFs simultaneous with double optical pulses and many TGFs with good radio measurements. ASIM has also observed several Gamma Ray Bursts.

Terrestrial Gamma-ray Flashes (TGFs) are sub-millisecond bursts of high-energy photons associated with lightning flashes in thunderstorms. The Atmosphere-Space Interactions Monitor (ASIM), launched in April 2018, is the first space mission specifically designed to detect TGFs. We will mainly focus on data from the High Energy Detector (HED) which is sensitive to photons with energies from 300 keV to > 30 MeV, and include data from the Low Energy Detector (LED) sensitive in 50 keV to 370 keV energy range. Both HED and LED are part of the Modular X- and Gamma-ray Sensor (MXGS) of ASIM.The energy spectrum of TGFs, together with Monte Carlo simulations, can provide information on the production altitude and beaming geometry of TGFs. Constraints have already been set on the production altitude and beaming geometry using other spacecraft and radio measurements. Some of these studies are based on cumulative spectra of a large number of TGFs (e.g. [1]), which smooth out individual variability. The spectral analysis of individual TGFs has been carried out up to now for Fermi TGFs only, showing spectral diversity [2]. Crucial key factors for individual TGF spectral analysis are a large number of counts, an energy range extended to several tens of MeV, a good energy calibration as well as knowledge and control of any instrumental effects affecting the measurements.Thanks to ASIM’s large effective area and low orbital altitude, single TGFs detected by ASIM have much more count statistics than observations from other spacecraft capable of detecting TGFs. By comparing Monte Carlo simulations to the energy spectrum from single ASIM TGFs we will aim to put stricter constraints on the production altitude and beaming geometry of TGFs. We will present the dataset, method, and some results of the spectral analysis of individual TGFs.References:1. Dwyer, J. R., and D. M. Smith (2005), A comparison between Monte Carlo simulations of runaway breakdown and terrestrial gamma-ray flash observations, Geophys. Res. Lett., 32, L22804, doi:10.1029/2005GL023848.2. Mailyan et al. (2016), The spectroscopy of individual terrestrial gamma-ray flashes: Constraining the source properties, J. Geophys. Res. Space Physics, 121, 11,346–11,363, doi:10.1002/2016JA022702.

We present a sample of Terrestrial Gamma-ray Flashes (TGFs) observed at mid latitudes by the Atmosphere Space Interaction Monitor (ASIM). The events were detected over the period June 2018 - August 2020 in the latitude bands between 35° and 51° and between -35° and -51°; the sample includes the first observations above ±38°. The characteristics of these mid-latitude events are consistent with the global population concerning the number of counts, but durations are significantly shorter. We also analyze the meteorological context and the general evolution of the parent storms and we show that the storms are not extreme in terms of total duration and extension. Finally, we present an estimation of the TGF occurrence rate at mid latitudes, based on ASIM's exposure, the local flash rate and tropopause altitude, and we show that it is outside but very close to two standard deviation from the rate of production at tropical latitudes, corrected by the higher atmospheric absorption of higher latitudes. This means that atmospheric absorption plays a major role in the detection of TGFs at mid latitudes, but we cannot rule out other factors.

Terrestrial Gamma-ray Flashes (TGFs) are short flashes of high energy photons, produced by thunderstorms. When interacting with the atmosphere, they produce relativistic electrons and positrons, and a part gets bounded to geomagnetic field lines and travels large distances in space. This phenomenon is called a Terrestrial Electron Beam (TEB). The Atmosphere-Space Interactions Monitor (ASIM) mounted on-board the International Space Station detected a new TEB event on March 24, 2019, originating from a tropical cyclone, Johanina. Using ASIM's low energy detector, the TEB energy spectrum is resolved down to 50 keV. We provide a new method to contrain the TGF source spectrum based on the detected TEB spectrum. Applied to this event, it shows that only fully developed RREA spectrums are compatible with the observation. More specifically, assuming a TGF spectrum proportional to 1/E exp(-E/ε), the compatible models have ε ≥ 6.5 MeV. We could not exclude models with ε of 8 and 10 MeV. This is the first time the source energy spectrum of a TGF is contrained based on the detection of the associated TEB.

Fast radio bursts (FRBs) are short (millisecond) radio pulses originating from enigmatic sources at extragalactic distances so far lacking a detection in other energy bands. Magnetized neutron stars (magnetars) have been considered as the sources powering the FRBs, but the connection is controversial because of differing energetics and the lack of radio and X-ray detections with similar characteristics in the two classes. We report here the detection by the AGILE satellite on April 28, 2020 of an X-ray burst in coincidence with the very bright radio burst from the Galactic magnetar SGR 1935+2154. The burst detected by AGILE in the hard X-ray band (18-60 keV) lasts about 0.5 seconds, it is spectrally cutoff above 80 keV, and implies an isotropically emitted energy ~ $10^{40}$ erg. This event is remarkable in many ways: it shows for the first time that a magnetar can produce X-ray bursts in coincidence with FRB-like radio bursts; it also suggests that FRBs associated with magnetars may emit X-ray bursts of both magnetospheric and radio-pulse types that may be discovered in nearby sources. Guided by this detection, we discuss SGR 1935+2154 in the context of FRBs, and especially focus on the class of repeating-FRBs. Based on energetics, magnetars with fields B ~ $10^{15}$ G may power the majority of repeating-FRBs. Nearby repeating-FRBs offer a unique occasion to consolidate the FRB-magnetar connection, and we present new data on the X-ray monitoring of nearby FRBs. Our detection enlightens and constrains the physical process leading to FRBs: contrary to previous expectations, high-brightness temperature radio emission coexists with spectrally-cutoff X-ray radiation., Submitted to Nature Astronomy, May 18, 2020

Two gamma-ray glows were observed by a high-altitude NASA ER-2 aircraft flying at 20 km altitude over a thunderstorm in Colorado, USA. The flux of the first glow rapidly intensified and then abruptly decreased within a few tens of milliseconds. On a timescale of seconds, the flux decrease occurred simultaneously with a hybrid intra-cloud/cloud-to-ground lightning discharge beneath the aircraft. However, a more detailed analysis of the discharge dynamics indicated that the discharge activity was unusually calm during the actual period of the flux decrease. The lightning was observed with on-board antennas, optical sensor, and ground-based lightning mapping and location networks. Its closest activity was 12 km away from the aircraft, below and slightly ahead the course. The gamma-ray flux reduction happened roughly in the middle of the lightning development process. The glow spectral analysis for the periods of a weak and strong flux enhancement has been done. The spectra were found to be background-like and similar to each other. publishedVersion

The Atmosphere-Space Interactions Monitor (ASIM) is the first instrument in space specifically designed to observe terrestrial gamma-ray flashes (TGFs). TGFs are high energy photons associated with lightning flashes and we perform the spectral analysis of 17 TGFs detected by ASIM. The TGF sample is carefully selected by rigorous selection criteria to keep a clean sample suitable for spectral analysis, that is, suitable count statistics, low instrumental effects, and reliable source location. Monte Carlo modeling of individual TGFs has been compared to the observed energy spectra to study the possible source altitudes and beaming geometries. A careful model of the instrumental effects has been developed and validated. Several combinations of source altitudes and beaming geometries are accepted by the statistical tests for all the TGFs in the sample resulting in a large uncertainty in the estimate of the intrinsic source luminosity. The analyzed TGFs show significant variations in observed fluence independent of the distance between source and ASIM. A lower limit on the maximum photon energy produced by TGFs is estimated to be 24 MeV for the analyzed TGFs. The intrinsic limitations of TGF spectral analysis from space are also investigated and it is found that the ability to constrain the source altitude and beaming geometries of TGFs strongly depends on the distance between source and satellite. With the current generation of instruments with effective areas in the range of few hundreds cm2, it is very difficult to constrain reliably the source properties without the help of simultaneous measurements in the radio band. publishedVersion

We present a sample of Terrestrial Gamma-ray Flashes (TGFs) observed at mid latitudes by the Atmosphere Space Interaction Monitor (ASIM). The events were detected between June 2018 and August 2020 in the latitude bands between 35° and 51° in both hemispheres, which we hereafter refer to as “mid latitudes.” The sample includes the first observations above urn:x-wiley:2169897X:media:jgrd57293:jgrd57293-math-0001 and consists of 14 events clustered in four geographical regions: north-west Atlantic and eastern USA; Mediterranean Sea; the ocean around South Africa; and north-eastern China and Siberia. We examine the characteristics of each event, both standalone and in the context of the global ASIM TGF data set, and we find that our sample is consistent with the global population concerning the number of counts, but shows significantly shorter durations. We analyze the meteorological context and the general evolution of the parent storms and we show that the storms are not extreme in terms of total duration and extension. Whenever possible, we also include the radio sferics and the peak current of the parent stroke. Finally, we present an estimation of the TGF occurrence rate at mid latitudes, based on ASIM's exposure, the local flash rate and tropopause altitude, and we show that it is outside but very close to two standard deviation from the rate of production at tropical latitudes, corrected by the higher atmospheric absorption of higher latitudes. This means that atmospheric absorption plays a major role in the detection of TGFs at mid latitudes, but we cannot rule out other factors. publishedVersion

Terrestrial Gamma ray Flashes (TGFs) are short flashes of high energy photons, produced by thunderstorms. When interacting with the atmosphere, they produce relativistic electrons and positrons, and a part gets bounded to geomagnetic field lines and travels large distances in space. This phenomenon is called a Terrestrial Electron Beam (TEB). The Atmosphere-Space Interactions Monitor (ASIM) mounted on-board the International Space Station detected a new TEB event on March 24, 2019, originating from the tropical cyclone Johanina. Using ASIM's low energy detector, the TEB energy spectrum is resolved down to 50 keV. We provide a method to constrain the TGF source spectrum based on the detected TEB spectrum. Applied to this event, it shows that only fully developed Relativistic Runaway Electron Avalanche spectra are compatible with the observation. More specifically, assuming a TGF spectrum urn:x-wiley:00948276:media:grl62333:grl62333-math-0001, the compatible models have ϵ ≥ 6.5 MeV (E is the photon energy and ϵ is the cut-off energy). We could not exclude models with ϵ of 8 and 10 MeV. publishedVersion

In this article we report the first investigation over time of the atmospheric conditions around TGFs occurrence, using GPS sensors in combination with geostationary satellite observations and ERA5 reanalyses data. The goal is to understand which characteristics are favourable to the development of these events and to investigate if any precursor signals can be expected. A total of 9 TGFs, occurred at a distance lower than 45 km from a GPS sensor, were analysed and two of them are shown here as an example analysis. Moreover, the lightning activity, collected by the World Wide Lightning Location Network (WWLLN) was used in order to identify any links and correlations with TGF occurrence and PWV trends. The combined use of GPS and the stroke rate trends identified, for all cases, a recurred pattern in which an increase of PWV is observed on a timescale of about two hours before the TGF occurrence that can be placed within the lightning peak. The temporal relation between the PWV trend and TGF occurrence is strictly related to the position of GPS sensors in relation to TGF coordinates. The life cycle of these storms observed by geostationary sensors, described TGFs producing clouds as intense with a wide range of extensions and, in all cases, the TGF is located at the edge of the convective cell. Furthermore, the satellite data give an added value in associating the GPS water vapor trend to the convective cell generating the TGF. The investigation with ERA5 reanalyses data showed that TGFs mainly occur in convective environment with not exceptional values with respect to the monthly average value of parameters measured in the same location. Moreover the analysis showed the strong potential of the use of GPS data for the troposphere characterization in areas with complex territorial morphology. This study provided indications on the dynamics of convective systems linked to TGFs and will certainly help refine our understanding on their production highlights a potential approach through the use of GPS data to explore the lightning activity trend and the TGFs occurrence.

Despite the recognition from their discovery that terrestrial gamma ray flashes (TGFs) originate from thunderstorms, little is known about the TGF-producing storms. The characteristics of such thunderstorms are investigated here using meteorological data, with the aim to set up a framework of analysis to be propagated to more complete TGF archives. In this work, we present the preliminary results. As first analysis, we considered 72 events detected by the Astrorivelatore Gamma ad Immagini Leggero (AGILE) from March 2015 to June 2015, estimating their electric activity in terms of flash production. To this end, we examined World Wide Lightning Location Network lightning data in the spatial and temporal proximity of each AGILE TGFs, searching for relationship between flash rate peak and distribution and the TGF occurrence. Moreover, we analyzed the low-Earth orbiting (LEO) satellite observation of the TGF-producing storms to define, through the capabilities of microwave sensors (both active and passive), the structure of the convective storms correlated with TGF events. In particular, we focused on the Global Precipitation Measurement (GPM) observations and show here a case study observed by the dual-frequency precipitation radar (DPR). Preliminary results indicate that the TGF often occur during the most active lightning phase of the storm, while the intensity of the storm is not a key ingredient for the production of a TGF. The multisensory capability of LEO satellites provide a picture of the storm structure, that, despite the poor coverage, is an unprecedented tool to study such cloud system over remote areas and open ocean. This study framework is meant to be applied to other TGF database, such as the ones collected by other space missions (e.g., FERMI, RHESSI).

On February 8, 2019 the Atmosphere-Space Interaction Monitor (ASIM) passed a thunderstorm system north east of Puerto Rico and observed a TGF and an Elve from the same lightning stroke at the very beginning of a lightning flash. A second Elve was observed 456 ms later but without any signature of a TGF about 300 km south-east of the first Elve. The strokes associated with the two Elve events were detected by WWLLN and Vaisala, which allows for an absolute timing accuracy of the ASIM measurements of at least 100 us. Images of the lighting strokes support the source locations for the Elves and TGF. Both the rise time of the UV pulse by ASIM MMIA photometer and radio measurements from Puerto Rico indicate that the first stroke was an intracloud positive while the latter was a cloud-to-ground stroke. The UV emissions from the Elves preceded the optical emissions in 777 nm by50 us and 90 us, respectively. This can partly be explained by the scattering of 777 nm within the cloud. Current moments derived from radio measurements at Puerto Rico and Duke University indicate a fast (30 us) and large (200 kA) current pulse emitting an electromagnetic wave that produces an Elve and a slow (1-2 ms) current producing the optical signals.

Launched and installed at the International Space Station in April 2018, the Atmosphere-Space Interactions Monitor (ASIM) provides science data since June 2018. Suite of onboard instruments contains optical and high energy detectors payloads. Modular Multi-spectral Imaging Array (MMIA) includes three photometers (180-240 nm, 337 nm and 777.4 nm) sampling at 100 kHz, and two cameras (337 nm and 777.4 nm) sampling at 12 Hz. It allows for lightning and transient luminous events (TLEs) observations during the orbital eclipses. The Modular X- and Gamma-ray Sensor (MXGS) detects X- and Gamma-ray photons, and is dedicated to detection of Terrestrial Gamma-ray Flashes (TGFs). The mutual relative timing accuracy between MXGS and MMIA is as good as +/- 5 µs. TGFs are known to be associated with the +IC lightning discharges. ASIM provides a unique possibility for simultaneous observations of TGFs together with the underlying optical activity inside the thundercloud. In this contribution we summarize the almost two years of ASIM observations to make an overview of the various optical contexts accompanying the TGF production.

One year after the starting of ASIM operational phase, we have succeeded to perform accurate Imaging of 54 TGF. Among them, some have been analysed at extreme imaging conditions in terms of TGF position at the MXGS partially coded field of view. 20 TGF events have angular distances larger than 40º respect to the MXGS FOV centre. Extreme cases at angular distances larger than 50º are presented. Validation of TGF position by WLN data is included in the discussion.The canonical value of 32 LED cnts as the minimum fluency for TGF imaging defined during MXGS development was checked using low luminosity TGF. At the present, we have succeeded to obtain imaging solution for 7 TGF with less than 20 cnts. A sample is presented with indication of position accuracy and S/N ratios. Last part of the presentation is the discussion of a TGF with a very large and asymmetric probability distribution at the MXGS FOV that suggest the TGF as an extended source. Imaging data projected to the Earth surface is compared with GOES data, showing that the TGF is at the edge of a large convective cell, close to the TGF imaging data map. Therefore, we can conclude that for some bright TGF it is possible to estimate the TGF fireball dimensions generated by the iteration of TGF photons with local atmospheric asymmetric matter distributions. The presence of a large CZT tail is coherent with the size of the convective cell.

Terrestrial Gamma-Ray Flashes (TGFs) observed from space appear to be generated after a few milliseconds of optical activity and before the onset of a main optical pulse. The pre-activity is thought to be from a propagating leader and the main optical pulse the emissions from the ensuing stroke. Scattering of photons in the cloud increases the rise time and durations of the pulses and thus allows for estimates of their optical path from their sources.In this presentation we estimate the depth inside thunderclouds of pulses associated with more than 100 TGFs observed by the Atmosphere-Space Interactions Monitor (ASIM) on the International Space Station (ISS). The observations are in narrow bands at 337 nm, to include the strongest line of N22P and 777.4 nm of OI, considered a strong lightning emission line. With the assumption that the sources are instantaneous and at single points within a cloud, we find optical paths for the events by using typical cloud properties. Combined with cloud top heights from a recent study on TGF producing thunderstorms, this gives an estimate at which altitude the optical detections are produced.Data from VAISALA’s lightning location network GLD360 and NASA’s Lightning Imaging Sensor on the ISS (ISS-LIS) will be used to assess the results from the optical analysis. This includes investigations of the correlations between TGF durations, detected peak lightning current and optical path in the cloud.

Terrestrial Gamma-ray Flashes (TGFs) are short (~20 us to ~2 ms) flashes of high energy (< 40 MeV) photons, produced by thunderstorms When interacting with the atmosphere, the TGF’s photons produce relativistic electrons and positrons at higher altitudes, and a fraction is able to escape the atmosphere [1,2,3]. The electrons/positrons are then bounded to Earth's magnetic field lines and can travel large distances inside the ionosphere and the magnetosphere. This phenomenon is called a Terrestrial Electron Beam (TEB).The Atmosphere-Space Interactions Monitor (ASIM), dedicated to the study of TGF and associated events, started to operate in June 2018. ASIM contains an optical instrument (MMIA) made of micro-cameras and photometers, as well the Modular X and Gamma-ray Sensor (MXGS) for high energy radiation. MXGS is composed of the low energy detector (LED, 50 keV to 400 keV) and the High Energy detector (HED, 300 keV to 40 MeV). This presentation is focused on a new event which was detected on March 24, 2019. The TEB originated from rainbands produced by the tropical cyclone Joaninha, in the Indian Ocean, close to Madagascar. This observation shows, for the first time to our knowledge: (1) the low energy part (>50 keV) of the TEB spectrum, using the LED, (2) an estimate of the incoming direction (to ISS) of the electron Beam from recorded data.References:[1] J. R., Dwyer, B. W., Grefenstette and D. M. Smith. High-energy electron beams launched into space by thunderstorms. DOI: 10.1029/2007GL032430. Geophysical Research Letters, 2008.[2] B. E. Carlson T. Gjesteland N. Østgaard. Terrestrial gamma-ray flash electron beam geometry, fluence, and detection frequency. DOI: 10.1029/2011JA016812. Journal of Geophysical Research (Space Physics), 2011.[3] D. Sarria, P. Kochkin, N. Østgaard et al. The First Terrestrial Electron Beam Observed by the Atmosphere-Space Interactions Monitor. DOI: 10.1029/2019JA027071. Journal of Geophysical Research (Space Physics), 2019.

Terrestrial Gamma-ray Flashes (TGFs) are sub milliseconds bursts of high energy photons associated with lightning flashes in thunderstorms. The Atmosphere-Space Interactions Monitor (ASIM), launched in April 2018, is the first space mission specifically designed to detect TGFs. We will mainly focus on data from the High Energy Detector (HED) which is sensitive to photons with energies from 300 keV to > 30 MeV, and include data from the Low Energy Detector (LED) sensitive in 50 keV to 370 keV energy range. Both HED and LED are part of the Modular X- and Gamma-ray Sensor (MXGS) of ASIM.The energy spectrum of TGFs, together with Monte Carlo simulations, can provide information on the production altitude and beaming geometry of TGFs. Constraints have already been set on the production altitude and beaming geometry using other spacecraft and radio measurements. Some of these studies are based on cumulative spectra of a large number of TGFs (e.g. [1]), which smooth out individual variability. The spectral analysis of individual TGFs has been carried out up to now for Fermi TGFs only, showing spectral diversity [2]. Crucial key factors for individual TGF spectral analysis are a large number of counts, an energy range extended to several tens of MeV, a good energy calibration as well as knowledge and control of any instrumental effects affecting the measurements.We strive to put stricter constraints on the production altitude and beaming geometry, by comparing Monte Carlo simulations to energy spectra from single ASIM TGFs. We will present the dataset and method, including the correction for instrumental effects, and preliminary results on individual TGFs.Thanks to ASIM’s large effective area and low orbital altitude, single TGFs detected by ASIM have much more count statistics than observations from other spacecrafts capable of detecting TGFs. ASIM has detected over 550 TGFs up to date (January 2020), and ~115 have more than 100 counts. This allows for a large sample for individual spectral analysis.References:Dwyer, J. R., and D. M. Smith (2005), A comparison between Monte Carlo simulations of runaway breakdown and terrestrial gamma-ray flash observations, Geophys. Res. Lett., 32, L22804, doi:10.1029/2005GL023848. Mailyan et al. (2016), The spectroscopy of individual terrestrial gamma-ray flashes: Constraining the source properties, J. Geophys. Res. Space Physics, 121, 11,346–11,363, doi:10.1002/2016JA022702.

Terrestrial Gamma-ray Flashes (TGFs) are short bursts of gamma radiation originating from thunderclouds; they propagate upwards and are then detected by satellites such as AGILE, Fermi and ASIM. ASIM is the first mission specifically designed for the study of thunderstorm-related phenomena (Neubert et al., 2019); being placed on the ISS, it can for the first time detect TGF events up to more than 51 degrees in latitude.Among the previous missions, RHESSI was the one reaching the highest latitude: 38 degrees. We then consider “high-latitude” for ASIM the band between 35 and 51 degrees of latitude. 9 events have already been observed in this band, inside four distinct geographical regions. At such latitudes, TGFs are expected to experience greater absorption in the troposphere, which makes them more difficult to detect. Moreover, we expect an intrinsically lower production rate due to the lower lightning activity (Smith et al., 2010, Williams et al., 2006).In this work we present the characteristics of those events, in the context of the global ASIM sample collected so far. We also examine whether the observed number of events is statistically compatible with the atmospheric absorption, taking into account the local flash activity and ASIM’s exposure at high latitude.

In 2018, the Atmospheric Space Interactions Monitor (ASIM) was launched and mounted onboard the Columbus module of the International Space Station (ISS). Using data from the Modular X- and Gamma-Ray Sensor (MXGS) and the Modular Multispectral Imaging Array (MMIA), we investigate the time sequence of the TGFs detected by MXGS and the optical pulses detected by the MMIA. The optical pulses are observed in the 337 nm and 777.4 nm, and the X- and gamma-rays are detected by the High Energy Detector of MXGS, which is sensitive to energies from 300 keV to more than 30 MeV. We will also look into the TGF duration and any correlation with the time between the TGFs and the main optical signals. The data used is from June 2018 (shortly after mounting on the Columbus module) until the end of March 2019, when the relative timing uncertainty between the two instruments was +/- 80 us. The data after this is presented in Skeie et al.

The Atmosphere Space Interaction Monitor (ASIM) mission onboard the International Space Station is the first mission specifically dedicated to the observation of Terrestrial Gamma-ray Flashes (TGF) and Transient Luminous Events (TLE). ASIM, together with the Fermi and AGILE satellites, are the only three currently operating missions capable to detect TGFs from space. Depending on orbital parameters, pairs of these missions periodically get closer than few hundreds kilometers, observing the same region on the Earth surface for up to several tens of seconds. This offers the unique chance to observe the same TGF from two different viewing angles. Such observations allow to probe the TGF production geometry and possibly put constraints on production models and electric field geometry at the source.Here we present four TGFs detected by ASIM and simultaneously detected by Fermi (three events) or AGILE (one event) in the period June 2018 - November 2019. We present location data, light curves, and possible constraints to emission geometry based on coupled observations and Monte Carlo simulations.

Using the Modular X- and Gamma-ray Sensor (MXGS) and the Modular Multi-spectral Imaging Array (MMIA) of the Atmosphere-Space Interactions Monitor (ASIM), we investigate the time sequence of the Terrestrial gamma-ray flashes and the optical emissions from the associated lighting. A common observation in the ASIM data is that the TGFs are observed before or during a weak increase in the optical signals in 337 nm and 777.4 nm, and prior to- or at the onset of the main optical pulse. Using data from the MXGS and MMIA instruments for the period from April 2019, we assess the time sequence and the relationship between the observed TGF duration and the time between the onset of the TGF and the onset of the main optical pulse, with a relative timeing uncertainty of +/- 5 µs. The data prior to April 2019 is presented in Bjørge-Engeland et al.

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. publishedVersion

The accuracy of Monte Carlo simulations in reproducing the scientific performance of space telescopes (e.g. angular resolution) is mandatory for a correct design of the mission. A brand-new Monte Carlo simulator of the Astrorivelatore Gamma ad Immagini LEggero (AGILE)/Gamma-Ray Imaging Detector (GRID) space telescope, AGILESim, is built using the customizable Bologna Geant4 Multi-Mission Simulator (BoGEMMS) architecture and the latest Geant4 library to reproduce the instrument performance of the AGILE/GRID instrument. The Monte Carlo simulation output is digitized in the BoGEMMS postprocessing pipeline, according to the instrument electronic read-out logic, then converted into the onboard data handling format, and finally analyzed by the standard mission on-ground reconstruction pipeline, including the Kalman filter, as a real observation in space. In this paper we focus on the scientific validation of AGILESim, performed by reproducing (i) the conversion efficiency of the tracker planes, (ii) the tracker charge readout distribution measured by the on-ground assembly, integration, and verification activity, and (iii) the point-spread function of in-flight observations of the Vela pulsar in the 100 MeV - 1 GeV energy range. We measure an in-flight angular resolution (FWHM) for Vela-like point sources of $2.0^{+0.2}_{-0.3}$ and $0.8^{+0.1}_{-0.1}$ degrees in the 100 - 300 and 300 - 1000 MeV energy bands, respectively. The successful cross-comparison of the simulation results with the AGILE on-ground and in-space performance validates the BoGEMMS framework for its application to future gamma-ray trackers (e.g. e-ASTROGAM and AMEGO).

We focus on two repeating fast radio bursts (FRBs) recently detected by the CHIME/FRB experiment in 2018--2019 (Source 1: 180916.J0158+65, and Source 2: 181030.J1054+73). These sources have low excess dispersion measures (DMs) ($ < 100 \rm \, pc \, cm^{-3}$ and $ < 20 \rm \, pc \, cm^{-3}$, respectively), implying relatively small maximal distances. They were repeatedly observed by AGILE in the MeV--GeV energy range. We do not detect prompt emission simultaneously with these repeating events. This search is particularly significant for the submillisecond and millisecond integrations obtainable by AGILE. The sources are constrained to emit a MeV-fluence in the millisecond range below $F'_{MeV} = 10^{-8} \, \rm erg \, cm^{-2}$ corresponding to an isotropic energy near $E_{MeV,UL} \simeq 2 \times 10^{46}\,$erg for a distance of 150 Mpc (applicable to Source 1). We also searched for $\gamma$-ray emission for time intervals up to 100 days, obtaining 3$\,\sigma$ upper limits (ULs) for the average isotropic luminosity above 50 MeV, $L_{\gamma,UL} \simeq \,$(5-10)$\,\times 10^{43} \rm \, erg \, s^{-1}$. For a source distance near 100 kpc (possibly applicable to Source 2), our ULs imply $E_{MeV,UL}\simeq10^{40} \rm erg$, and $L_{\gamma,UL} \simeq \,$2$\,\times 10^{37} \rm \, erg \, s^{-1}$. Our results are significant in constraining the high-energy emission of underlying sources such as magnetars, or other phenomena related to extragalactic compact objects, and show the prompt emission to be lower than the peak of the 2004 magnetar outburst of SGR 1806-20 for source distances less than about 100 Mpc., Comment: to be published in ApJL

An Airbus A340 aircraft flew over Northern Australia with the In‐Flight Lightning Damage Assessment System (ILDAS) installed onboard. A long‐duration gamma ray emission was detected. The most intense emission was observed at 12 km altitude and lasted for 20 s. Its intensity was 20 times the background counts, and it was abruptly terminated by a distant lightning flash. In this work we reconstruct the aircraft path and event timeline. The glow‐terminating flash triggered a discharge from the aircraft wing that was recorded by a video camera operating onboard. Another count rate increase was observed 6 min later and lasted for 30 s. The lightning activity as reported by ground networks in this region was analyzed. The measured spectra characteristics of the emission were estimated., Key Points Two gamma ray glows were observed at 12 km altitude over Northern AustraliaThe observation was conducted by the In‐flight Lightning Damage Assessment System (ILDAS)Gamma ray glow was terminated by a distant lightning flash

FLARES is an innovative project in the field of rare events searches, such as the search for the neutrinoless double beta decay. It aims at demonstrating the high potential of a technique that combines ultra-pure scintillating crystals with arrays of high performance silicon drift detectors, operated at about 120 K, to reach a 1% level energy resolution. The proposed technique will combine in a single device all the demanding features needed by an ideal experiment looking for rare events. The performance of a first production of matrices of silicon drift detectors as well as first measurements of the low temperature light yield of a selection of high purity scintillating crystals will be presented and discussed. © 2016 Elsevier B.V.