Flux and spectral variability of the blazar PKS 2155-304 with XMM-Newton: Evidence of Particle Acceleration and Synchrotron Cooling

TL;DR

This study analyzes XMM-Newton X-ray observations of blazar PKS 2155-304, revealing spectral variability, flux changes, and evidence of particle acceleration and synchrotron cooling through time-resolved spectral and lag analysis.

Contribution

It provides the first detection of both hard and soft X-ray lags in a single observation of this blazar, linking spectral variability to particle acceleration and cooling processes.

Findings

Detection of significant hard and soft X-ray lags.

Spectral flattening below 10 keV during certain segments.

Magnetic field estimates consistent with broad-band SED models.

Abstract

We have analyzed XMM-Newton observations of the high energy peaked blazar, PKS 2155-304, made on 24 May 2002 in the 0.3 - 10 keV X-ray band. These observations display a mini-flare, a nearly constant flux period and a strong flux increase. We performed a time-resolved spectral study of the data, by dividing the data into eight segments. We fitted the data with a power-law and a broken power-law model, and in some of the segments we found a noticeable spectral flattening of the source's spectrum below 10 keV. We also performed time-resolved cross-correlation analyses and detected significant hard and soft lags (for the first time in a single observation of this source) during the first and last parts of the observation, respectively. Our analysis of the spectra, the variations of photon-index with flux as well as the correlation and lags between the harder and softer X-ray bands indicate that both the particle acceleration and synchrotron cooling processes make an important contribution to the emission from this blazar. The hard lags indicate a variable acceleration process. We also estimated the magnetic field value using the soft lags. The value of the magnetic field is consistent with the values derived from the broad-band SED modeling of this source.