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Research Result Report
ICRR Inter-University Research Program 2023
Research Subject: Engineering runs of the first Large Size Telescope of CTA andconstruction of LST2-4 in La Palma Canary Islands, Spain
Principal Investigator:

MAZIN, DanielParticipating Researchers: Daniela Hadasch, Koji Noda, Juan Cortina, Carlos Diaz,Thomas Schweizer, Holger Wetteskind, Carlos Delgado, Riccardo Rando, Takayuki
Saito, Armand Fiasson, Ievgen Vovk, Marcel Strzys

Summary of Research Result：
The purpose of the project is to commission thefirst Large Size Telescope (LST, see Figure 1) ofthe CTA project in La Palma, Canary Islands,Spain. In FY2023 the goal was to validate theinterface between the LST telescope and thecentral control system of the CTA observatory
Figure 1: Completed LST1 in La
Palma in October 2018.

called ACADA.
Statusof

thecommissioning:

Severalcommissioning goals have been achieved in

FY2023. In particular, 30% of LST commissioning open items have been closed toincrease the safety and reliability of the telescope, most of them related with thecontrol software. On the hardware side, a snow cover has been installed to protect
sensitive telescope parts, in particular cables, from ice falling from the mirrors inwinter. One of the highlights of FY2023 was anintegration test between the control softwaredeveloped by the CTA ACADA team and thecontrols

softwaredevelopedbytheLST

collaboration, involving in total about 30 people
from the two projects. The integration took placein La Palma in September and October 2023 andwent very well, underlying the robustness of theFigure 2: Data taken since Jan 2020

telescope’s software and hardware.

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Scientific exploitation: LST1 took regular observations in 2023. The amount of datataken (see Fig. 2) amounts to over 2000 hours since January 2020 underlying thatthe telescope is working reliably over the last years. In December 2023, a gamma-ray
signal from a distant Active Galactic Nuclei OP313 (z=0.997) has been discovered
with LST1 (https://www.astronomerstelegram.org/?read=16381) proving that thesensitivity of LST1, even as a stand-alone telescope, is sufficient to produce greatscientific results. A corresponding publication on this discovery is in preparation.
Several other scientific results are in preparation: RS Oph detection, study of theCrab pulsar, limits of the emission from GRB221009A. Already published in FY 2023
are the following papers: LST1 performance (Abe, H., et al,: ApJ, 956:80 (2023)),
LST1-MAGIC performance (Abe, H., et al,: A&A, 680, A66 (2023)), and LHAASO
J2108+5157 (Abe, S., et al. A&A, 673, A75 (2023)). Some 10 more scientificpublications are in preparation.
LST2-4 construction: In parallel with the LST1 operation, the construction of thethree further LSTs in La Palma, LST2-4, is ongoing. In FY2023 the civil works on thethree telescopes have been finalized. In the next step, the azimuth rail has been

Figure 3: Status of the LSTs in La Palma. From left to right: LST1, LST2, LST3 and LST4mounted. After that the mechanical structure has been erected and the mirror dishassembled. The status of the works as of the end of FY2023 can be seen in Figure 3.
One can see that the works are staged: LST4 (on the left) is the most advanced,
followed by LST3 and LST2. The telescope construction works are expected to finish
by FY2026 with first light of LST4 in FY2026 followed by LST3 and LST2.
No.

E04