X-Ray Spectral Variability of the TeV HBL Blazar PG 1553+113 with XMM-Newton

TL;DR

This study analyzes X-ray spectral variability of the TeV blazar PG 1553+113 over multiple observations, revealing spectral model preferences, potential inverse Compton signatures, and synchrotron peak shifts, indicating jet particle dynamics.

Contribution

It provides a comprehensive spectral variability analysis of PG 1553+113 using XMM-Newton data, highlighting model fits, spectral features, and jet emission properties.

Findings

14 spectra fit well with Log-Parabola models

Two observations show inverse Compton signatures

Synchrotron peaks vary between 4.59 and 48.61 eV

Abstract

We present an extensive X-ray spectral variability study of the TeV photon-emitting high-energy-peaked BL Lacertae object PG 1553+113, using the data from EPIC-PN camera of XMM-Newton, which observed the source during its operational period from Sep 2001 to Nov 2024. X-ray spectra in this energy range, $0.6-7.0$ keV, were fitted with absorbed Power-law (PL) and absorbed Log-Parabola (LP) models. We found with 99$\%$ confidence that 14 of them were fit well by LP models having parameters in the range $\alpha\simeq2.13-2.80$, and $\beta\simeq0.04-0.18$, one spectrum favours a LP model with $\beta<0$, while simple PL models with $\Gamma\simeq2.53-2.69$ were sufficient to describe the X-ray spectra of the remaining 15. Two of these 30 observations showed strong signatures of an additional inverse Compton component, while one showed weaker indications. On fitting joint Optical Monitor and EPIC-PN data with LP models, we found synchrotron peaks in the energy range of $\nu_s\simeq4.59-48.61$ eV. This indicates that the spectral evolution is probably caused by variations in particle acceleration or cooling conditions within the jet.