The 3-D position sensitive CZT detector for high-energy astrophysics developed at DTU has been investigated with a digitizer readout system. The 3-D CZT detector is based on the CZT drift-strip ...detector principle and was fabricated using a REDLEN CZT crystal (20 mm × 20 mm × 5 mm). The detector contains 12 drift cells, each comprising one collecting anode strip with four drift strips, biased such that the electrons are focused and collected by the anode strips. Three-dimensional position determination is achieved using the anode strip signals, the drift-strip signals, and the signals from ten cathode strips. For the characterization work, we used a DAQ system with a 16 channels 250-MHz 14-b digitizer, SIS3316. It allowed us to analyze the pulse shapes of the signals from four detector cells at a time. The 3-D CZT setup was characterized with a finely collimated radioactive source of 137Cs at 662 keV. The analysis required development of novel position determination algorithms which are the subject of this paper. Using the digitizer readout, we demonstrate improved position determination compared to the previous read out system based on analog electronics. Position resolutions of 0.4-mm full width at half maximum (FWHM) in the x-, y-, and z-directions were achieved and the energy resolution was 7.2-keV FWHM at 662 keV. The timing information allows identification of multiple interaction events within one detector cell, e.g., Compton scattering followed by photoelectric absorption. These characteristics are very important for a high-energy spectral-imager suitable for use in advanced Compton telescopes, or as focal detector for new hard X-ray and soft γ-ray focusing telescopes or in polarimeter instrumentation. CZT detectors are attractive for these applications since they offer relatively high-quantum efficiency. From a technical point of view it is advantageous that their cooling requirements are modest.
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 ∝E−1exp−E/ϵ, 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.
Plain Language Summary
Terrestrial Gamma ray Flashes (TGF), originating from thunderstorms, are the highest energy natural particle acceleration phenomena occurring on Earth. The production mechanism of TGFs is not well understood. When interacting with the atmosphere, TGFs produce secondary electrons and positrons, and a part gets bounded to Earth's magnetic field lines, and travels large distances in space. They can be detected by instruments on‐board satellites located at the right place (in a window of about 40 km) at the right time (in a window of a few milliseconds). This phenomenon is called a Terrestrial Electron Beam (TEB). By detecting the TEB, we can retrieve information about the TGF that produced it. In this article, we present the first TEB originating from a tropical cyclone and with the lowest energies ever recorded (down to 50 keV). We also provide a method to infer properties of the energy distribution of the source TGF (producing the TEB) based on the energy spectrum of the TEB. Applied to this event, it shows that only TGF energy spectra among the most energetic that were proposed are compatible, and we cannot exclude even more energetic events.
Key Points
Observation of a Terrestrial Electron Beam (TEB) with a spectrum resolved down to 50 keV
A method to constrain the energy spectrum of the source Terrestrial Gamma ray Flash (TGF) based on the detection of the associated TEB is presented
Only TGFs originating from fully developed Relativistic Runaway Electron Avalanche models can explain the observation
First 10 Months of TGF Observations by ASIM Østgaard, N.; Neubert, T.; Reglero, V. ...
Journal of geophysical research. Atmospheres,
27 December 2019, Letnik:
124, Številka:
24
Journal Article
Recenzirano
Odprti dostop
The Atmosphere‐Space Interactions Monitor (ASIM) was launched to the International Space Station on 2 April 2018. The ASIM payload consists of two main instruments, the Modular X‐ray and Gamma‐ray ...Sensor (MXGS) for imaging and spectral analysis of Terrestrial Gamma‐ray Flashes (TGFs) and the Modular Multi‐spectral Imaging Array for detection, imaging, and spectral analysis of Transient Luminous Events and lightning. ASIM is the first space mission designed for simultaneous observations of Transient Luminous Events, TGFs, and optical lightning. During the first 10 months of operation (2 June 2018 to 1 April 2019) the MXGS has observed 217 TGFs. In this paper we report several unprecedented measurements and new scientific results obtained by ASIM during this period: (1) simultaneous TGF observations by Fermi Gamma‐ray Burst Monitor and ASIM MXGS revealing the very good detection capability of ASIM MXGS and showing substructures in the TGF, (2) TGFs and Elves produced during the same lightning flash and even simultaneously have been observed, (3) first imaging of TGFs giving a unique source location, (4) strong statistical support for TGFs being produced during the upward propagation of a leader just before a large current pulse heats up the channel and emits a strong optical pulse, and (5) the t50 duration of TGFs observed from space is shorter than previously reported.
Key Points
Simultaneous measurements of TGF by two spacecraft are presented
Simultaneous measurements of TGF and Elve are not rare coincidence
Imaging of TGF is presented
The sequence of TGF and main optical lightning pulse is resolved
TGFs observed from space have shorter duration than previously reported
We report the first Terrestrial Electron Beam detected by the Atmosphere‐Space Interactions Monitor. It happened on 16 September 2018. The Atmosphere‐Space Interactions Monitor Modular X and Gamma ...ray Sensor recorded a 2 ms long event, with a softer spectrum than typically recorded for Terrestrial Gamma ray Flashes (TGFs). The lightning discharge associated to this event was found in the World Wide Lightning Location Network data, close to the northern footpoint of the magnetic field line that intercepts the International Space Station location. Imaging from a GOES‐R geostationary satellite shows that the source TGF was produced close to an overshooting top of a thunderstorm. Monte‐Carlo simulations were performed to reproduce the observed light curve and energy spectrum. The event can be explained by the secondary electrons and positrons produced by the TGF (i.e., the Terrestrial Electron Beam), even if about 3.5% to 10% of the detected counts may be due to direct TGF photons. A source TGF with a Gaussian angular distribution with standard deviation between 20.6° and 29.8° was found to reproduce the measurement. Assuming an isotropic angular distribution within a cone, compatible half angles are between 30.6° and 41.9°, in agreement with previous studies. The number of required photons for the source TGF could be estimated for various assumption of the source (altitude of production and angular distribution) and is estimated between 1017.2 and 1018.9 photons, that is, compatible with the current consensus.
Plain Language Summary
Terrestrial Gamma Ray Flashes (TGFs) are the highest energy natural particle acceleration phenomena occurring on Earth. They are burst of energetic photons associated with thunderstorms and have a poorly understood production mechanism. When interacting with the atmosphere, TGFs produce secondary electrons and positrons of high energy. A fraction of them can reach space and forms a beam under the effect of Earth's magnetic field, so called Terrestrial Electron Beam (TEB). They can be detected over geographical location with no lightning activity. In the past, most of the TEBs have been detected by the Fermi space telescope and the Compton Gamma ray Observatory. In this article, we report the first detection of a TEB by the Atmosphere‐Space Interactions Monitor, docked on the International Space Station since April 2018. During this event, no lightning activity was detected below the instrument. The TEB's source lightning was actually found to be located 650 km away from detector, very close to an overshooting top of a thundercloud. The comparison of the observation with simulated data made it possible to constrain the geometry of the parent TGF. Our results point toward a relatively wide angular distribution and an intensity of 1017.2 to 1018.9 photons, in agreement with previous studies.
Key Points
Flying over an area with no nearby lightning activity, the ASIM‐MXGS instrument detected a 4 ms long event with a soft spectrum
Observations coupled with simulations suggest that more than 90% of the counts come from a TEB and the rest from the associated TGF
A source TGF with a broad angular distribution and 1017 to 1019 photons can explain the observation
One of the least documented and understood aspects of gamma-ray bursts (GRBs) is the rise phase of the optical light curve. The Ultra-Fast Flash Observatory (UFFO) is an effort to address this ...question through extraordinary opportunities presented by a series of space missions including a small spacecraft observatory. The UFFO is equipped with a fast-response Slewing Mirror Telescope (SMT) that uses a rapidly moving mirror or mirror array to redirect the optical beam rather than slewing the entire spacecraft to aim the optical instrument at the GRB position. The UFFO will probe the early optical rise of GRBs with sub-second response, for the first time, opening a completely new frontier in GRBs and transient studies. Its fast response measurements of the optical emission of dozens of GRBs each year will provide unique probes of the burst mechanism and test the prospect of GRBs as a new standard candle, potentially opening up the z > 10 universe. For the first time we employ a motorized slewing stage in SMT that can point to the event within 1 s after the x-ray trigger provided by the UFFO Burst Alert and Trigger Telescope. These two scientific instruments comprise the UFFO-pathfinder payload, which will be placed onboard the Lomonosov satellite and launched in 2013. The UFFO-pathfinder is the first step of our long-term program of space instruments for rapid-response GRB observations. We describe early photon science, our soon-to-be-launched UFFO-pathfinder hardware and mission, and our next planned mission, the UFFO-100.
Magnetars are strongly magnetized, isolated neutron stars
with magnetic fields up to around 10
gauss, luminosities of approximately 10
-10
ergs per second and rotation periods of about 0.3-12.0 s. ...Very energetic giant flares from galactic magnetars (peak luminosities of 10
-10
ergs per second, lasting approximately 0.1 s) have been detected in hard X-rays and soft γ-rays
, and only one has been detected from outside our galaxy
. During such giant flares, quasi-periodic oscillations (QPOs) with low (less than 150 hertz) and high (greater than 500 hertz) frequencies have been observed
, but their statistical significance has been questioned
. High-frequency QPOs have been seen only during the tail phase of the flare
. Here we report the observation of two broad QPOs at approximately 2,132 hertz and 4,250 hertz in the main peak of a giant γ-ray flare
in the direction of the NGC 253 galaxy
, disappearing after 3.5 milliseconds. The flare was detected on 15 April 2020 by the Atmosphere-Space Interactions Monitor instrument
aboard the International Space Station, which was the only instrument that recorded the main burst phase (0.8-3.2 milliseconds) in the full energy range (50 × 10
to 40 × 10
electronvolts) without suffering from saturation effects such as deadtime and pile-up. Along with sudden spectral variations, these extremely high-frequency oscillations in the burst peak are a crucial component that will aid our understanding of magnetar giant flares.
CZT drift strip detectors for high energy astrophysics Kuvvetli, I.; Budtz-Jørgensen, C.; Caroli, E. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2010, Letnik:
624, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Requirements for X- and gamma ray detectors for future High Energy Astrophysics missions include high detection efficiency and good energy resolution as well as fine position sensitivity even in ...three dimensions.
We report on experimental investigations on the CZT drift detector developed DTU Space. It is operated in the planar transverse field (PTF) mode, with the purpose of demonstrating that the good energy resolution of the CZT drift detector can be combined with the high efficiency of the PTF configuration. Furthermore, we demonstrated and characterized the 3D sensing capabilities of this detector configuration.
The CZT drift strip detector (10
mm×10
mm×2.5
mm) was characterized in both standard illumination geometry, Photon Parallel Field (PPF) configuration and in PTF configuration. The detection efficiency and energy resolution are compared for both configurations . The PTF configuration provided a higher efficiency in agreement with calculations. The detector energy resolution was found to be the same (3
keV FWHM at 122
keV) in both in PPF and PTF .
The depth sensing capabilities offered by drift strip detectors was investigated by illuminating the detector using a collimated photon beam of
57Co radiation in PTF configuration. The width (
300
μ
m
FWHM at 122
keV) of the measured depth distributions was almost equal to the finite beam size. However, the data indicate that the best achievable depth resolution for the CZT drift detector is
90
μ
m
FWHM at 122
keV and that it is determined by the electronic noise from the setup.
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