Search for electromagnetic super- preshowers using gamma-ray - - PowerPoint PPT Presentation

Search for electromagnetic super- preshowers using gamma-ray telescopes

• K. Almeida Cheminant¹ (speaker), D. Góra¹, N. Dhital¹, P. Homola¹,
• P. Poznański² for the CREDO Collaboration*

¹ Institute of Nuclear Physics PAS, Cracow, Poland ² Cracow University of Technology, Cracow, Poland

35th International Cosmic Ray Conference – ICRC 2017 12-20 July, 2017 Bexco, Busan, Korea

* website: credo.science

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Motivations: UHE photons and super-preshowers

➢Severe constraints for exotic scenarios

→ limits apply to single ultra-high energy (UHE) photons, assuming no screening [e.g. Lorentz violation with photon decay (T. Jacobson et al. (2006)]

Niechciol for the Pierre Auger Collab., proc. of ICRC 2017

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(SPS → Super-preshower)

➢What if we assume the possibility of cascading processes for UHE

photons? Can we observe multiple air showers correlated in time? → Unique signature!

Motivations: UHE photons and super-preshowers

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How?

➢

Cosmic Ray Extremely Distributed Observatory: a unifying, global cosmic-ray project (see ICRC 2017 Proceedings – [PL013]) → wide energy distribution in SPSs: the entire cosmic-ray spectrum is concerned.

➢Various types of super-preshowers (SPS) based on time and spatial

spread.

➢Pioneer study: detecting type A SPS and UHE photons with Imaging

Atmospheric Cherenkov Telescopes (IACTs)

THIS TALK

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Example of screening: Preshower effect

➢Cascade of electromagnetic particles generated by interaction with

geomagnetic field.

➢SPS Type A: classical preshower effect

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IACTs and Hillas analysis

➢Air showers generated by

ensembles of photons at the top of the atmosphere → Emission of Cherenkov photons

➢Detection of Cherenkov

photons by IACTs cameras

Hillas parameters

• A. M. Hillas, Proc. of

19th ICRC (1985)

• M. Sharma et al. (2014)

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Simulation chain

PRESHOWER photon primary: E=40 EeV, θ=80°, φ=180° Example with the future Cherenkov Telescope Array (CTA) at La Palma.

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Simulation chain

PRESHOWER photon primary: E=40 EeV, θ=80°, φ=180° CORSIKA (D. Heck, et al. 1998) Air showers (Options: IACT, QSGJETII, CURVED, etc.)

mpi-hd.mpg.de/hfm/HESS

Example with the future Cherenkov Telescope Array (CTA) at La Palma.

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Simulation chain

PRESHOWER photon primary: E=40 EeV, θ=80°, φ=180° CORSIKA (D. Heck, et al. 1998) Air showers (Options: IACT, QSGJETII, CURVED, etc.) Sim_telarray (K. Bernlöhr 2008) Detectors response 4 LSTs 15 MSTs

cta-observatory.org/about/array-locations/la-palma/

mpi-hd.mpg.de/hfm/HESS

Example with the future Cherenkov Telescope Array (CTA) at La Palma.

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Longitudinal profiles of Cherenkov light

➢Maxima of photon-induced showers deeper in the atmosphere than

proton-induced showers (for similar interaction point)

➢SPSs with higher interaction point (multiple photons): air shower

maxima shifted towards proton showers maxima → difficulties in identifying SPSs with current observation modes.

➢Large zenith angles allow the observation of the muon plateau.

→ possible identification of SPSs.

Muons Gammas Electrons/positrons What we see!

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Images on the camera

➢SPSs higher interaction point

and muon poor: →images are dimmer and smaller in size than in the proton case. →less muon rings.

➢Multiple air showers initiated

by SPSs → new class of events are expected.

PROTON SPS

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Hillas parameters: preliminary results

Top: RIMP=1300m ; Bottom: RIMP=4000m SPS PROTON PHOTON

➢Potential for event by event discrimination.

→ cut on multivariate analysis could allow discrimination with low statistics (how many events do we need?).

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Event rate

➢Event rate

with and assuming: 1- SHDM I model: NEXP= 0.002 events/hour 2- Auger limit: NEXP= 0.00002 events/hour

N =φ (E>E0)×A×4 π

A=π Rimp

2

E0=40 EeV

Niechciol for the Pierre Auger Collab., proc. of ICRC 2017

Large time exposure needed!

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Sensitivity

➢First estimation:

Using eq. 7 of Neronov et al. (2016):

• A. Neronov et al., Phys. Rev (2016), astro-ph/1610.01794

Fmin= E0 AΩK T exp

GeV cm-² s-1 sr-1

A=π Rimp

2 ×19

with in extended observation mode

ΩK=0.1: duty cycle

T exp=1 year : exposure time

Fmin=1.33×10

−9 GeV cm-² s-1 sr-1

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Conclusion and outlook

➢Possible discrimination between SPSs and CRs based on a multi-

variate analysis and nearly horizontal observations with IACTs.

➢IACTs sensitivity to photons/SPS at large zenith angles comparable to

Pierre Auger Observatory.

➢Study of SPS type C and D would allow to go lower in energy and reach

better sensitivity.

➢Complete search for super-preshowers: with multi-detector global

approach proposed by CREDO (PL013 this conference), involving gamma-ray telescopes, cosmic-ray

• bservatories,

and neutrino detectors.