Signature of Inverse Compton emission from blazars

TL;DR

This study analyzes X-ray spectral and timing data from 14 blazars to identify the transition from synchrotron to inverse Compton emission, constraining break energies and magnetic fields, and exploring variability patterns.

Contribution

It provides the first detailed spectral and timing analysis of low and intermediate peaked blazars, constraining emission transition energies and magnetic field strengths.

Findings

Transition from synchrotron to inverse Compton emission detected in 7 sources.

Break energies constrained between 0.6 and 10 keV.

Magnetic fields estimated between 0.03 and 0.88 G.

Abstract

Blazars are classified into high, intermediate and low energy peaked sources based on the location of their synchrotron peak. This lies in infra-red/optical to ultra-violet bands for low and intermediate peaked blazars. The transition from synchrotron to inverse Compton emission falls in the X-ray bands for such sources. We present the spectral and timing analysis of 14 low and intermediate energy peaked blazars ob- served with XMMNewton spanning 31 epochs. Parametric fits to X-ray spectra helps constrain the possible location of transition from the high energy end of the syn- chrotron to the low energy end of the inverse Compton emission. In seven sources in our sample, we infer such a transition and constrain the break energy in the range 0.6 10 keV. The Lomb-Scargle periodogram is used to estimate the power spectral density (PSD) shape. It is well described by a power law in a majority of light curves, the index being flatter compared to general expectation from AGN, ranging here between 0.01 and 1.12, possibly due to short observation durations resulting in an absence of long term trends. A toy model involving synchrotron self-Compton (SSC) and exter- nal Compton (EC; disk, broad line region, torus) mechanisms are used to estimate magnetic field strength 6 0.03 - 0.88 G in sources displaying the energy break and infer a prominent EC contribution. The timescale for variability being shorter than synchrotron cooling implies steeper PSD slopes which are inferred in these sources.