X-ray Flux and Spectral Variability of Six TeV Blazars with \textit{NuSTAR}

TL;DR

This study presents timing and spectral analysis of six TeV blazars observed with NuSTAR, revealing intraday variability in two sources, estimating physical parameters, and characterizing their spectral shapes.

Contribution

First detailed NuSTAR timing and spectral analysis of six TeV blazars, identifying intraday variability and modeling their spectra with power-law and log-parabola fits.

Findings

Intraday variability detected in 1ES 1101-232 and 1ES 1218+304.

Estimated magnetic field B ~ 0.03 G and emission region size ~1.19 x 10^{16} cm.

Spectral shapes characterized by power-law and log-parabola models.

Abstract

We report the first results of timing and spectral studies of \textit{Nuclear Spectroscopic Telescope Array (NuSTAR)} observations of six TeV emitting high-frequency peaked blazars: 1ES 0347$-$121, 1ES 0414$+$009, RGB J0710$+$591, 1ES 1101$-$232, 1ES 1218$+$304 and H 2356-309. Two out of these six TeV blazars, 1ES 1101$-$232 and 1ES 1218$+$304, showed strong evidence of intraday variations in the 3--79 keV energy range during those observations. We also found a hint of an intraday variability timescale of 23.5 ks in the light curve of 1ES 1218$+$304 using an autocorrelation function analysis. We obtained magnetic field $B \sim 0.03$ G, electron Lorentz factor $\gamma \sim 2.16 \times 10^6 $ and emission region size $R \sim 1.19 \times 10^{16} $ cm for 1ES 1218$+$304 using that variability timescale. The other blazars' light curves do not show any variability timescales shorter than their observation lengths; however, we note that the data were both noisier and sparser for them. We also investigated the spectral shape of these TeV blazars and found that the spectrum of 1ES 0414$+$009 is well described by a single power-law with photon index $\Gamma \sim 2.77$. The spectra of the other five HBLs are somewhat better represented by log-parabola models with local photon indices (at 10 keV) $\alpha \sim 2.23-2.67$ and curvature parameters, $\beta \sim 0.27-0.43$.