Observation of the PeVatron candidate SNR G106.3-2 with the LST1+MAGIC Cherenkov telescopes

The CTA (Cherenkov Telescope Array) is a worldwide project to construct the next generation ground based very high energy gamma ray instrument [1]-[2]. CTA will use tens of Imaging Air Cherenkov Telescopes (IACT) of three different sizes (mirror diameter of 4 m, 12 m and 23 m) deployed on two sites, one on each hemisphere (La Palma on the Canary Islands and Paranal in Chile). The observatory will detect gamma-rays with energy ranging from 20 GeV up to 300 TeV by imaging the Cherenkov light emitted from the charged particle shower produced by the interaction of the primary gamma ray in the upper atmosphere.

The unconventional capabilities of CTA will address, among others, the intriguing question of the origin of the very high energy galactic cosmic rays by the search for galactic sources capable of accelerating cosmic rays up to the PeV energies, called PeVatrons. Recently, the Supernova Remnant (SNR) G106.3-2.7 has been indicated as a highly promising PeVatron candidate [4]. In fact, G106.3-2.7 emits gamma-rays up to 500 TeV from an extended region ( 0.2o) well separated from the SNR pulsar (J2229+6114) and in spatial correlation with a local molecular cloud.

The CTA observatory completion is foreseen in 2025 but the first Large-Sized Telescope (LST1) is already installed and taking data in La Palma. LST1 is placed very close to the two MAGIC telescopes [3], which are one of the presently active IACT experiments. This configuration permits to perform joint observations of the same source with the three telescopes LST1+MAGIC increasing the effective detection area and improving the energy and angular resolution, thanks to the enhanced quality reconstruction of stereoscopic data. While the LST1+MAGIC telescopes cannot reach enough sensitivity to access energies above 100 TeV, they can provide exclusive and unprecedented data for establishing the spectral morphology of this exciting PeVatron candidate in the 100 GeV-100 TeV energy region. A campaign of joint observations of G106.3-2.7 will start in 2022 and will continue in the following years.

The PhD project will be on the analysis of the data of the coming campaign, its ambitious target will be to contribute in disclosing the hadronic or leptonic nature of this promising PeVatron. In order to maximize the effective area at very high energy, G106.3-2.7 will be observed at large zenith angle (LZA), 62o-70o, which represents a challenging detection condition. The project will start with the development and verification of the joint LST1+MAGIC stereo reconstruction chain [5] at LZA, using Monte Carlo (MC) data. This MC study will aim to optimize the data reconstruction and selection in order to reach a high quality “Instrument Response Function” and sensitivity for this specific source. Real data will be then reconstructed so as to achieve both a morphological and a spectral reconstruction of the source in the 100 GeV-100 TeV energy range. Finally, the high-quality LST1-MAGIC data will be used for a multiwavelength analysis that will compare different emission models and try to disentangle the nature of the source.

The project will include the participation to the LST1+MAGIC observation campaign with stays of four weeks in the Roque de los Muchachos Observatory in La Palma.

The CPPM CTA group works since several years in the building and commissioning of the LST1 telescope and on the preparatory studies for the research of galactic PeVatrons with CTA [6][7].

Candidates should send their CV and motivation letter as well as grades (Licence, M1, M2) to cassol@cppm.in2p3.fr and costant@cppm.in2p3.fr before 10/4/2022. Applications will be selected on the base of qualifications and an oral interview.

References:

[1] Science with the Cherenkov Telescope Array: https://arxiv.org/abs/1709.07997

[2] https://www.cta-observatory.org/

[3] MAGIC Collaboration, Aleksi?, J. et al. Astropart. Phys. 72 (2016) 76–94.

[4] Z. Cao et al. Nature, 594, 33–36 (2021); M. Amenomori et al. Nature Astronomy, 5, 460–464 (2021)

[5] https://github.com/cta-observatory/magic-cta-pipe

[6] O. Angüner et al. “Cherenkov Telescope Array potential in the search for Galactic PeVatrons”, ICRC 2019

[7] G. Verna et al. “HAWC J2227+610: a potential PeVatron candidate for the CTA in the northern hemisphere”, ICRC 2021