X-ray Flux and Spectral Variability of the TeV Blazars Mrk 421 and PKS 2155-304

TL;DR

This paper reviews the X-ray flux and spectral variability of the TeV blazars Mrk 421 and PKS 2155-304, highlighting their diverse timescales and implications for understanding their emission mechanisms and physical properties.

Contribution

It provides a comprehensive review of observed X-ray variability in these blazars, emphasizing the significance of variability studies in constraining physical parameters.

Findings

Variability occurs on timescales from minutes to years.

Flux and spectral changes help estimate black hole mass.

Variability informs emission mechanisms and jet/disk physics.

Abstract

We reviewed X-ray flux and spectral variability properties studied to date by various X-ray satellites for Mrk 421 and PKS 2155-304, which are TeV emitting blazars. Mrk 421 and PKS 2155-304 are the most X-ray luminous blazars in the northern and southern hemispheres, respectively. Blazars show flux and spectral variabilities in the complete electromagnetic spectrum on diverse timescales ranging from a few minutes to hours, days, weeks, months and even several years. The flux and spectral variability on different timescales can be used to constrain the size of the emitting region, estimate the super massive black hole mass, find the dominant emission mechanism in the close vicinity of the super massive black hole, search for quasi-periodic oscillations in time series data and~several other physical parameters of blazars. Flux and spectral variability is also a dominant tool to explain jet as well as disk emission from blazars at different epochs of observations.