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Investigating Active Galactic Nuclei variability with the Cherenkov Telescope Array Observatory

G. Grolleron, J. Biteau, M. Cerruti, R. Grau, L. Gréaux, T. Hovatta, J. -P. Lenain, E. Lindfors, W. Max-Moerbeck, D. Miceli, A. Moralejo, K. Nilsson, E. Prandini, E. Pueschel, S. Kankkunen, J. Becerra Gonzalez, J. Finke, M. Joshi, P. Morris, M. Petropoulou, A. Sarkar, P. Romano, S. Vercellone, M. Zacharias

TL;DR

The paper argues that current gamma-ray instruments limit our understanding of very-high-energy AGN variability and PSD breaks. It presents a modeling-and-simulation framework for CTAO that combines long-term AGN behavior with fast flares using log-normal flux distributions, harder-when-brighter trends, and SSC physics, all fed through a realistic observing pipeline. Simulated results indicate that CTAO can reconstruct long-term light curves and PSDs with higher accuracy and recover flare light curves and spectral variability, including hardness-ratio hysteresis patterns. These findings support CTAO's potential to constrain jet physics, particle acceleration, and emission mechanisms in blazars across a broad range of timescales.

Abstract

Blazars, a type of active galactic nuclei (AGN) with relativistic jets pointed at the observer, exhibit flux variability across the electromagnetic spectrum due to particle acceleration in their jets. Power spectral density (PSD) studies show breaks at specific frequencies, particularly in X-rays, linked to the accretion regime and black hole mass. However, very-high-energy gamma-ray PSD breaks remain unexplored due to current instrument limitations. The Cherenkov Telescope Array Observatory (CTAO), with up to ten times greater sensitivity compared to current generation instruments, will allow precise PSD reconstruction and unprecedented study of blazar flares. These flares reveal key insights into particle acceleration, photon production, and jet properties. The AGN monitoring and flare programs in CTAO's Key Science Project aim to deepen our understanding of blazar emissions.

Investigating Active Galactic Nuclei variability with the Cherenkov Telescope Array Observatory

TL;DR

The paper argues that current gamma-ray instruments limit our understanding of very-high-energy AGN variability and PSD breaks. It presents a modeling-and-simulation framework for CTAO that combines long-term AGN behavior with fast flares using log-normal flux distributions, harder-when-brighter trends, and SSC physics, all fed through a realistic observing pipeline. Simulated results indicate that CTAO can reconstruct long-term light curves and PSDs with higher accuracy and recover flare light curves and spectral variability, including hardness-ratio hysteresis patterns. These findings support CTAO's potential to constrain jet physics, particle acceleration, and emission mechanisms in blazars across a broad range of timescales.

Abstract

Blazars, a type of active galactic nuclei (AGN) with relativistic jets pointed at the observer, exhibit flux variability across the electromagnetic spectrum due to particle acceleration in their jets. Power spectral density (PSD) studies show breaks at specific frequencies, particularly in X-rays, linked to the accretion regime and black hole mass. However, very-high-energy gamma-ray PSD breaks remain unexplored due to current instrument limitations. The Cherenkov Telescope Array Observatory (CTAO), with up to ten times greater sensitivity compared to current generation instruments, will allow precise PSD reconstruction and unprecedented study of blazar flares. These flares reveal key insights into particle acceleration, photon production, and jet properties. The AGN monitoring and flare programs in CTAO's Key Science Project aim to deepen our understanding of blazar emissions.
Paper Structure (9 sections, 1 equation, 6 figures)

This paper contains 9 sections, 1 equation, 6 figures.

Table of Contents

  1. Introduction
  2. AGN modelling
  3. Modelling of the long term AGN behavior
  4. Modelling of the fast variability of AGN
  5. Simulations and reconstruction of AGN observations with CTAO
  6. Results
  7. Long-term lightcurve and PSD reconstruction
  8. Reconstruction of AGN flares
  9. Conclusions

Figures (6)

  • Figure 1: The generated spectra for BL Lac. Colors displaying the time evolution.
  • Figure 2: The time evolution of Mrk 421 spectrum during the flare. Colors displaying the time evolution.
  • Figure 3: Reconstructed LC above 50 GeV and residuals computed between the simulated and reconstructed data for BL Lac for the simulation of 20 years. Gray points are the injected values and red points are the reconstructed ones.
  • Figure 4: PSDs estimate (blue points) of the LC computed from simulated data for BL Lac between 50 and 300 GeV. The red line shows the injection PSD (with a floor level at high frequencies) used to simulate the input data.
  • Figure 5: Reconstructed LC above 30 GeV and residuals computed between the simulated and reconstructed data for the Mrk 421 flare. Gray points are the injected values and red points are the reconstructed ones.
  • ...and 1 more figures