With a launch expected in 2018, the TARANIS microsatellite is dedicated to the study of transient phenomena observed in
association with thunderstorms. On board the spacecraft, XGRE and IDEE are two instruments dedicated to studying terrestrial
gamma-ray flashes (TGFs) and associated terrestrial electron beams (TEBs). XGRE can detect electrons (energy range: 1 to 10
Monte Carlo simulations of the TARANIS instruments, using a preliminary model of the spacecraft, allow sensitive area estimates
for both instruments. This leads to an averaged effective area of 425
Combining this data with the help of the MC-PEPTITA Monte Carlo simulations of TGF propagation in the atmosphere, we build
a self-consistent model of the TGF and TEB detection rates of RHESSI, AGILE and Fermi. It can then be used to estimate that
TARANIS should detect about 200 TGFs
Terrestrial gamma-ray flashes (TGFs) are short (
A careful analysis of BATSE, RHESSI and Fermi-GBM data permitted the
identification of some longer events with durations more than 1
In the near future, two missions are planned with the primary objective of
TGF detection: ASIM and TARANIS. The Atmosphere-Space Interaction Monitor (ASIM)
is an European Space Agency (ESA) project with scientific leadership
from the Technical University of Denmark (DTU)
These two instruments will be presented in Sect. 2. In Sect. 3 we will make a comparison of the performances of XGRE and IDEE with those of RHESSI, Fermi-GBM and AGILE-MCAL in the context of TGFs. Finally in Sect. 4 we build a self-consistent picture to account for the detection rates of TGF and TEB seen by the satellites flying today in order to estimate the future detection rates of TARANIS.
XGRE can detect photons in the
In general, the energy of an incident electron is difficult to estimate
properly. Using several layers of detectors greatly helps but there remain
uncertainties due to the detector's environment. Positrons will behave very
similarly to electrons, with the addition that they will always annihilate
into two 511
The XGRE instrument is presented in Fig. 1. Figure 1a shows its
position on the TARANIS satellite (highlighted in red). XGRE is composed of
three sensors that are tilted by
The plastic scintillators have a low effective atomic number (
The effective area of XGRE for detecting gamma rays could be determined using
the GEANT4 full mass model of the instrument and satellite. GEANT4 is
a toolkit developed by a international collaboration led by CERN to
simulate the propagation of particles though matter
Two side views of the GEANT4 mass model of XGRE are presented in Fig. 1a. This mass model will be refined in the coming years, using results of calibration campaigns.
To determine the response of the detector to X-rays and gamma rays, we drawn 150
mono-energetic beams of
Any particle that deposits energy above the electronic trigger is
considered to be detected, i.e. above 300
Figure 2a shows the computed effective area of XGRE for gamma rays, using
In Appendix A, we describe how we can calculate an average effective area
to obtain a unique value associated to a detector for detecting TGF or TEB. For
the average effective area of XGRE, the calculation gives
To determine the response of the instrument to electrons (and positrons), we
launch 150 mono-energetic beams of
The simulation requires an initial particle to make a deposit of at least
300
The effective area of XGRE in comparison to electrons is shown by the black curve of
Fig. 2b. There is threshold energy
To determine the effective area averaged over a TEB spectrum,
Summary of the TGF-spectrum averaged (
The IDEE instrument is made of two electron detectors from 80
The spectroscopy is possible up to 4.4
The two IDEE detection units are pointing 60
The effective area vs. energy of IDEE for detecting electrons was estimated
with the GEANT4 mass model of the full TARANIS spacecraft using the same
methodology as for XGRE. An electron is detected if it deposits at least
80
The value of
The effective area averaged over a TEB spectrum,
In this section we present a comparison of the performances of XGRE and IDEE
with those of RHESSI, Fermi-GBM and AGILE-MCAL in the context of TGFs,
without including CGRO-BATSE. CGRO-BATSE detected 79 TGFs
between the years 1991 and 2000, some of which are clearly identified as
TEBs
The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is a NASA
spacecraft designed for the study of high-energy radiation from the sun. It
uses an array of nine high-purity germanium detectors cooled down to liquid
nitrogen temperature. A detailed description of the detector is presented in
The Astro-Rivelatore Gamma a Immagini Leggero (AGILE) is a satellite from the
Italian Space Agency dedicated to the study of high-energy gamma rays
(typically above 50
The Gamma-Ray Burst Monitor (GBM) on board the Fermi spacecraft is presented
into details in
As presented in
Below 30
RHESSI, Fermi and AGILE suffered from issues related to the fact that their
design is not perfectly suited to detect very bright and short events such as
TGFs. Concerning AGILE, this issue was likely solved after the deactivation
of its anti-coincidence shield
For Fermi GBM detectors, the nominal dead time lasts 2.6
XGRE uses lanthanum bromide crystal scintillators coupled with fast
electronics, resulting in a dead time of 350
The dead time of IDEE is less than 4
The TGF detection methods used by RHESSI, Fermi-GBM and AGILE-MCAL are
described respectively in
The IDEE instrument uses a dynamical algorithm which evaluates a floating
background (in preselected energy range and Si
RHESSI, Fermi-GBM and AGILE-MCAL were not designed to detect electrons or positrons, therefore no response matrix is provided for these particles. Nevertheless, we could proceed to Monte Carlo simulations of these detectors to get a basic idea of their performances for detecting TEBs.
The RHESSI detectors are surrounded by several millimetres of aluminum
The effective area of RHESSI against electrons is displayed in Fig. 2b. It
is
Regarding Fermi-GBM, GEANT4 detailed models of single BGO and NaI detectors
are available as GDML files as part of the GRESS software
These single detector models are not enough to estimate the response of
Fermi-GBM to electrons, because they do not take into account their
accommodation on the spacecraft, nor the entire spacecraft (e.g. platform,
subsystems and LAT detector). We could not have access to the full mass
model of the Fermi satellite, but we could build a very simplified version,
by looking to several Fermi-GBM documents; in particular
The response of GBM to mono-energetic electron beams is presented in Fig. 2b.
We followed the same procedure as for RHESSI (the particles are drawn
randomly and uniformly over all directions around the spacecraft). The
effective areas show threshold energies (
Regarding AGILE, the full mass model was provided by the AGILE team (M. Marisaldi, personal communication, 2016). The MCAL detector on the AGILE
spacecraft is surrounded by several elements (e.g. the MITA spacecraft Bus,
the GRID, the Super-AGILE, the anticoincidence system or the carbon fibre
structure surrounding the CsI bars) that will absorb a significant amount of
energy of the electrons before they can reach the CsI crystals
For all these detectors, dead times and pile-up effects are not a big
issue concerning TEB detection. Indeed, the flux
(
The AGILE TGFs of the second catalogue are given between 23 March 2015 and 23 June 2015, and contains 279 TGFs
Concerning terrestrial electrons beams (TEBs), they were detected by RHESSI
and Fermi. RHESSI clearly detected only two TEB events and one of them was
presented
No TEB event was reported by AGILE, and we speculate that this is because the
effective area for detecting TEB is not high enough (
Using the MC-PEPTITA Monte Carlo model
Concerning the time distribution of the source, there are currently two
different results. On one hand, by comparing simulated TGFs with AGILE data,
From Fermi data,
Results of MC-PEPTITA simulations.
The flux profiles resulting from the simulations are presented in Fig. 3a.
The fluxes are presented as a function of the radial distance
(
Below
Concerning electrons, the fluxes are close at the three considered altitudes,
so we only represented the flux at 550
An approximative map of TGFs that can be detected by satellites was built,
based on the TRMM-LISS and OTD global lightning density map
Estimated global detectable TGF density map, and ground tracks of the orbits of TARANIS (planned), RHESSI, Fermi and AGILE. The grey area denotes an approximative South Atlantic anomaly assumed for the simulations, and where TGF can occur but no detection by satellites is possible due to high background.
Altitudes, detection count thresholds, limit radii, detection efficiencies and number of TGFs per year (observed and estimated) for the considered satellites.
Count thresholds, limit radii, detection efficiencies and number of TEBs per year (observed and estimated) for the considered satellites.
Each detector has a minimal threshold of counts
The ratio between this threshold value
Knowing
This detection efficiency is computed using the following algorithm:
We consider a step of time Each time step corresponds to a position of the satellite At each position, the TGF densities from the map ( If
The ratio
One last parameter to be taken into account is the diurnal cycle of
lightning. Lightning activity was found to be non-uniform with local time and
is maximum around 17
The catalogue of Fermi GBM TEBs presents 24 events between 8 July 2008 and
2 February 2015, giving
To determine the TEB detection efficiency, the algorithm presented for the
TGF case has to be modified. If the satellite is located at given
coordinates, the considered density is not the density at this point, but the
sum of the two densities located at the two magnetic footprints of the field
line. These coordinates are determined from MC-PEPTITA runs that can track
the electrons in the geomagnetic field. In these simulations, the electrons
are drawn at 100
From all this information, we can calculate detection efficiencies between
TARANIS and Fermi
The TARANIS spacecraft will have two important instruments with which to study TGFs and TEBs: XGRE and IDEE. XGRE will detect both electrons and X-rays and gamma rays, with the ability to discriminate one type of particle from the other. The IDEE instrument is focused on electrons, with the ability to estimate their pitch angle. The instruments will be able to trigger one another.
Using Monte Carlo simulations, mass models and a standard TGF spectrum, we
can estimate that XGRE will have an effective area of about 425
Using Monte Carlo simulations of the TARANIS, RHESSI AGILE and Fermi
spacecrafts, we could estimate the response of their detectors to electrons
and positrons and provide a quantitative comparison between them. By
combining this knowledge with an approximative world map of detectable TGF
density and with MC-PEPTITA Monte Carlo simulations of TGF propagation in the
atmosphere, we could build an accurate model of the TGF detection rates of
RHESSI, AGILE and Fermi. It could be used to estimate that TARANIS should
detect about 200 TGFs
The GEANT4 mass model, TARANIS satellite, with XGRE and IDEE instruments is still under development and is not publicly available. However, simulations in specific configurations can be requested from the corresponding author: contact David Sarria (david.sarria.89@gmail.com).
The GEANT3 mass model of the RHESSI detector and spacecraft can be requested from David Smith (dsmith@scipp.ucsc.edu)
The GEANT3 mass model of the AGILE detectors and spacecraft can be requested from Martino Marsaldi (martino.marisaldi@uib.no), Marcello Galli (marcello.galli@enea.it) and Francesco Longo (franzlongo1969@gmail.com).
The GEANT4 GDML mass model of the Fermi-GBM BGO and NaI detection units are
publicly available as part of the GRESS software
MC-PEPTITA simulations can be requested from David Sarria (david.sarria.89@gmail.com). The MC-PEPTITA programme was developed under a contract of Centre National d'Etudes Spatiales (CNES) and Direction Generale de l'Armement (DGA), whose permissions are required in order to get access to the source code.
The data generated for this work can be requested from the corresponding author: contact David Sarria (david.sarria.89@gmail.com).
The response matrices of Fermi GBM detectors are publicly available using the
The
We use a custom method to determine the average effective area of an
instrument for detecting TGFs (or TEBs). Using a simulation of a given
instrument, we can launch mono-energetic beams of particles of energy
RHESSI, Fermi-GBM and AGILE-MCAL models have been made for X- and gamma-ray
detection, and such models are usually accurate at about 5
For TARANIS, using calibration measurement at detection unit level, the model
was tested to be about 5
Using the model presented in Sect. 4.4, it is possible to calculate the sensitivity of a X percent inaccuracy of the estimated TARANIS effective areas on the final TGF and TEB detection rate estimation. The results are presented in Table B1.
A count threshold value of
Effect of an overestimated effective area
Effect of an underestimated count threshold
David Sarria prepared most of the manuscript. David Sarria, Remi Chipaux, Jean-Pierre Baronick contributed to the GEANT4 model of the XGRE instruments and TARANIS satellite. David Sarria performed all GEANT4 simulations (TARANIS XGRE, IDEE with satellite and Fermi-GBM). Francois Lebrun, Pierre-Louis Blelly and Philippe Laurent provided a detailed review of the manuscript, important feedback on the XGRE instrument, and the instrument comparison. Remi Chipaux provided a review of the manuscript. Damien Pailot and Miles Lindsey-Clark provided important data used to validate the GEANT4 model of the XGRE instrument, as well as important feedback on the instrument description (Sect. 2.1). Jean-Andre Sauvaud and Pierre Devoto provided the GEANT4 model of IDEE as well as important data for validation. Jean-Andre Sauvaud, Pierre Devoto and Lubomir Prech contributed to the IDEE instrument part of the manuscript (Sect. 2.2). Lubomir Prech provided an important review of the IDEE instrument description. Philippe Laurent performed a GEANT3 simulation on the RHESSI and AGILE mass models, which were provided by David Smith (RHESSI), Martino Marsaldi, Marcello Galli and Francesco Longo (AGILE).
The authors declare that they have no conflict of interest.
We thanks David M. Smith for providing the mass model, the RHESSI spacecraft, and discussion about its response to electrons. We thank Micheal S. Briggs for his help in estimating of the Fermi-GBM response to electrons. We thank Martino Marisaldi, Francesco Longo and Marcello Galli for providing the mass model of the AGILE spacecraft, and their help in discussing the response of MCAL to electrons. This work was granted access to the HPC resources of CALMIP supercomputing centre under the allocation 2015-p1505. We thank the CNES (Centre National d'Etudes Spatiales) for its financial support. The work of Lubomir Prech was supported by the Czech Science Foundation contract 17-06065S. We would like to thank the two anonymous referees for their valuable comments and suggestions that helped to improve the quality of this work. Edited by: Antti Makela Reviewed by: two anonymous referees