On-ground calibration of the X-ray, gamma-ray, and relativistic electron detector onboard TARANIS

Introduction to the show: ident: Astrophysics. The day in astrophysics: observations, models and what the data forces.

Vera: I'm Vera.

Jocelyn: And I'm Jocelyn, here with Subrahmanyan.

Vera: We're looking at the paper: "On-ground calibration of the X-ray, gamma-ray, and relativistic electron detector onboard TARANIS".

Jocelyn: Here's the gist of the paper. On-ground calibration of the X-ray, gamma-ray, and relativistic electron detector onboard TARANIS provides validation and calibration tests for its performance.

Vera: The results from these tests were used to validate a simulation model of XGRE and TARANIS.

Jocelyn: Detector Composition and Design XGRE consisted of three sensors, each having one layer of LaBr3 crystals for X-ray/gamma-ray detections, and two layers of plastic scintillators for electron and charged-particle discrimination.

Vera: Each detection unit contained an 84×90×8.7 mm3 LaBr3 scintillation crystal (manufactured by Saint-Gobain) sandwiched between two 84×90×5 mm3 plastic scintillators.

Title and authors: Vera: This paper, "On-ground calibration of the X-ray, gamma-ray, and relativistic electron detector onboard TARANIS", focuses on taking this XGRE detector and testing it in a controlled environment to get those solid numbers we need. Jocelyn It's interesting that they brought together a team from Osaka University, CEA Saclay, and the University of Paris for this calibration work.

Subrahmanyan: The authors are clearly spanning the necessary expertise here; you have the engineers building the hardware and the astrophysicists who understand what those measurements actually constrain in terms of cosmic structure formation. Vera Right, so they're essentially bridging that gap between a complex detector system and its performance on a satellite mission.

Jocelyn: They are testing XGRE by looking at its composition—three sensors with LaBr3 crystals and plastic scintillators—and then doing thermal cycle tests using flight models from April to May two thousand eighteen. Subrahmanyan The key thing they're looking for in those tests is how the gain of the detector changes with temperature, because that directly affects how well you measure energy.

Vera: They found a negative correlation on the high-temperature side, meaning as it got hotter, the detector's gain actually decreased. Jocelyn That tells us something important about the thermal stability we have to account for when we plan operations on orbit.

The paper's summary: Vera: The summary of this paper explains that they performed three steps for validation: with the detection units, with the sensors themselves, and then finally with the actual satellite. Jocelyn That stepwise approach is standard in space instrumentation; you check each component before putting it all together.

Subrahmanyan: They detailed how they determined the energy range of those LaBr3 crystals for XGRE1, XGRE2, and XGRE3, finding ranges like zero point zero four to eleven point six MeV for the first sensor and so on. Vera And they gave us specific energy resolution numbers too, such as twenty point five percent, twenty-five point nine percent, and twenty-eight point six percent at zero point six six two MeV for each sensor respectively; those are concrete performance metrics we need to keep in mind when interpreting data later on.

Jocelyn: They also derived an energy calibration function, like E equals zero point plus a factor times the channel number in MeV, which is how they correct the raw counts to get real energy values. Subrahmanyan This calibration function is what allows us to reconstruct the actual X-ray or gamma-ray energy from what the detector actually measured.

Vera: The paper also used Monte Carlo simulations with Geant4 version four point one zero.three hundred thirty and CADMesh version one point one.thirty-three to compare their measurements against the simulation results obtained during the satellite calibration test for XGRE, which helps confirm their model accuracy <ref:2405.04836#pg1>.

The paper's improvements: Jocelyn: Now let's talk about what they suggest improving in the way they use these tests, because that’s where it gets really useful for future work. Vera They propose several key improvements, starting with better event classification for electrons and gamma rays. Subrahmanyan Specifically, they suggest using pulse duration to distinguish between terrestrial gamma-ray flashes and terrestrial electron beams; events longer than one millisecond are interpreted as electron beams rather than TGFs, based on data from BATSE/CGRO <ref:2405.04836#pg1>.

Vera: That’s a significant distinction because it helps us separate the physics of lightning discharges into two different categories. Jocelyn They also suggest using the difference in count rates between the XGRE sensors due to their varying mounting angles to estimate where a TGF is actually originating from, which helps with source localization.

Subrahmanyan: That spatial estimation based on angle differences sounds like a useful way to map out where the high-energy radiation is coming from in a lightning discharge event, which feeds into our models of atmospheric physics. Vera They also offer an improved method for reconstructing energy spectra by applying those derived calibration functions directly to the raw detector counts.

Jocelyn: And they suggest an AI approach to calculate the effective area of XGRE across different elevation and azimuth angles using verified Monte Carlo simulations, which gives us a tool to estimate detection efficiency from various directions. Subrahmanyan This calculation is vital because the effective area itself changes depending on where the incoming radiation is coming from, so knowing that helps us plan our observations better.

Conclusion: Vera: So to wrap up, this paper on "On-ground calibration of the X-ray, gamma-ray, and relativistic electron detector onboard TARANIS" confirms that the hardware works as expected under thermal cycling and provides specific energy ranges for each sensor. Jocelyn The improvements they propose are all about getting more precise information out of the data, specifically better ways to classify particle events and estimate their source location on the ground.

Subrahmanyan: From a cosmological viewpoint, being able to accurately characterize these high-energy atmospheric signals helps us refine our models of how energy is deposited and how those particles interact with the Earth's magnetic field. Vera And that means when we look at the TARANIS data later, we can trust the energy spectra and spatial information more than ever before.

Jocelyn: It sets a clear path for future missions by showing exactly what kind of calibration tests are necessary to get reliable results from instruments designed to study lightning phenomena. Subrahmanyan And those specific calibration procedures will be key when we try to link these atmospheric events back to the larger picture of cosmic particle acceleration.

Vera: We've seen how they've validated the simulation model using Geant4 and comparing it against the actual measurements from the satellite test, which gives a strong foundation for trusting their derived effective areas. Jocelyn So, this paper is about making sure that when we look at TGFs and TEBs, we have the best possible tools to understand what's happening in the atmosphere.

Subrahmanyan: That's it for this paper on "On-ground calibration of the X-ray, gamma-ray, and relativistic electron detector onboard TARANIS".