LST-1/CTAO
I started my journey in this field with the prototype of the Large-Sized Telescope (LST-1) of the Cherenkov Telescope Array Observatory (CTAO), first of the four planned LSTs in the northern site of CTAO, located in Observatorio del Roque de los Muchachos on the Canary island of La Palma, Spain. (The southern site is planned to be in Paranal, Chile.) Acharyya et al. (2019)
The CTAO is a next-generation observatory for gamma-ray astrophysics designed to detect gamma rays in the energy range 20 GeV to 300 TeV (what are these units?). For the best coverage of the full energy range, three categories of IACTs will be deployed: Large-Sized Telescopes (LSTs), Medium-Sized Telescopes (MSTs) and Small-Sized Telescopes (SSTs). The larger the telescope, the fainter the Cherenkov light it can detect. Therefore, the LSTs are designed to measure the low-energy range while the SSTs will be able to detect the highest-energy gamma rays.
Extra-Galactic Astrophysics
The origin of gamma-ray emissions in the jets of AGNs, as well as the location of the emissions along the jets, are important open questions in astrophysics. I’m interested in studying the very high energy (VHE) emissions from extra-Galactic blazars (a kind of AGN whose jets are closely aligned to our line of sight). Their emissions are strongly modified by relativistic effects and can exhibit strong and rapid variabilities. Studying these variabilities on various timescales as well as over a range of energies help us understand the nature of these emissions. In particular, my colleagues and I are analysing data collected by the LST-1 telescope from a blazar called PG 1553+113 to investigate short-term (intra-night) variabilities in its photon flux.
Further reading:
- A. Ruina et al., Search for VHE Short-Timescale Variability in PG1553+113 (2024) Conference poster (proceedings coming soon!)
- H. Luciani, Characterization of PG1553+113 with the LST-1, Master thesis (2023), UniPd archive
- MAGIC Collaboration, The variability patterns of the TeV blazar PG 1553 + 113 from a decade of MAGIC and multiband observations, MNRAS, 529(4), p.3894–3911 (2024) DOI
Cosmic Rays with Direct Cherenkov Light
Primarly designed to detect Cherenkov light from gamma-ray air showers, IACTs have also been used to study cosmic rays using Direct Cherenkov (DC) light, which is the Cherenkov radiation emitted by a highly energetic cosmic-ray particle before producing an air shower. This can be achieved because of the following properties:
- The flux of DC light is directly proportional to the squared particle charge, Z2, whereas that of Cherenkov light of the shower is proportional to Z.
- DC light is generated at a higher altitude, where the air is less dense. As such, it will arrive in a much narrower cone than the the Cherenkov light from the air shower. It will be detected on the cameras of the IACTs slightly shifted in position and slightly delayed in time.
- IACT cameras have a sharp enough angular resolution (approx. 0.1° FOV per pixel) and a time resolution of the order of nanoseconds. Therefore, they can differentiate between the two kinds of Cherenkov signals.
An interesting incentive: The dependance of DC-light on Z2 makes it an optimal technique for measuring cosmic-ray compositions, especially for iron, as it has a high Z and a relatively high abundance. However, there are still significant limiting factors of this technique which make DC light detection quite challenging.
Further reading: