Neighbourhood Astrophysics: Detecting Gamma-ray Flashes above the Earth

Many of our Astro PhD students partake in other projects outside of their area of research. Ahlam Al Qasim (a 2nd year PhD student) and Aisha AlMannaei (a 1st year PhD student) are both working on Cubesat RAAD (Rapid Acquisition Atmospheric Detector), a mission recently funded by the UAE Space Agency through winning the Mini-satellite competition held last year. The competition was seeking out proposals from university students across the UAE for a science mission to be integrated on a Cubesat, with a launch opportunity in 2020. Their mission is aimed at studying the phenomenon of Terrestrial Gamma-Ray Flashes (TGFs), which are highly energetic events emitted via thundercloud activity in Earth’s atmosphere. Ahlam is the student PI of the science case and TGF simulations, and Aisha is the student PI for the detector development. Here, they discuss how the project was initiated and eventually extended to a fully funded mission, and what their current roles are.

Terrestrial Gamma-ray Flashes (TGFs), which are sudden bursts of gamma-ray radiation triggered by lightning or thunderstorm activity, are channeled above the Earth’s atmosphere into outer space. Many scientists believed that these very energetic types of radiation could only be generated near the Sun, or in black holes, large galaxies, or neutron stars, until TGF events were first discovered by the Burst and Transient Source Experiment (BATSE) in 1994 on the Compton Gamma-Ray Observatory (CGRO), which was a NASA spacecraft. This is what makes them very interesting to study, being the sole source of gamma-ray production within our planet.

Studying TGFs can help us address important scientific questions. Cubesat RAAD is focused on addressing two main science goals:
  1. How does lightning work, and what triggers it?
  2. Is there radiation danger to people on commercial airplanes flying above thunderstorms, where TGFs are expected to occur?
Ahlam and Aisha share their insights on how the mission came to life and what inspired them to pursue it further beyond their undergraduate theses.
a
The idea of developing a dedicated mission to study TGFs was first sparked when I did an internship at the Italian Space Agency’s Science Data Center (ASDC) during the summer of my second year as an undergraduate. My internship was under the AGILE satellite’s data center for the study of gamma-ray emission. This experience exposed me to this very peculiar phenomenon that occurs on our planet, and consequently inspired me to design a CubeSat science mission for my undergraduate thesis centered around TGFs. What I inherently realized is that our knowledge about TGF mechanisms comes from gamma-ray satellites partially pointing towards earth, such as AGILE and FERMI, and there are no successful missions (yet) solely designed to study TGFs science. Thus, our knowledge on them is very limited.
 
Hence, I set in mind a goal to explicitly target TGFs producing low energy gamma-rays and in turn collect and analyze data focused on this phenomenon to improve correlation studies with lightning and atmospheric parameters. This can be achieved by developing a gamma-ray detector for the science payload of the mission. My current role is focused on simulating TGF events that we would expect to see from our gamma-ray detector for a Low Earth Orbit (LEO), and in turn understand how that limits our triggering and telemetry requirements for the mission, and see if we can detect spectral features of TGFs that haven’t been observed before by past missions (such as the 511 keV line).
Ahlam Al Qasim
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The 511 keV line observed in the spectra of TGFs.
Once Ahlam established the science case and set the requirements for the TGF detector under the supervision of the NYUAD physics department, I started developing a prototype detector for the planned science payload array, which consists of photomultiplier tubes coupled with scintillation crystals. This has shown to be one of the fastest and most compact detectors designed to detect gamma-rays with a low voltage consumption. 
Through the tests I carried on the prototype, the performance showed that it can withstand extreme temperatures that would be expected in space. These tests helped me develop a protocol for characterizing the entire detector as an extension of Ahlam’s undergraduate thesis. What I’ll be working on next is space-qualifying the instrument for this mission. This will involve testing the detector against various vibration, temperature, and pressure ranges expected in space for our orbit. 

-Aisha AlMannaei

cube1

cube2

Images of the detector prototype.

We look forward to integrating our payload into the cubesat once it’s fully developed and flying it into space once it gets approved for launch! To check for updates on the mission, please follow us on Twitter at @RaadDetector!

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