X-ray flux variability of Blazar Mrk 501 observed using NuSTAR

Abstract

We present a detailed spectral study of 12 X-ray NuSTAR observations of the BL Lac object Markarian (or Mrk) 501, spanning a period from 2013 to 2022. We extracted source spectra within an 80-arcseconds radius around the source center and background with a radius of 300-arcseconds. The X-ray flux variability of our sample was derived by extracting the Blazar Mrk 501 sample spectra and fitting them with six models in the XSPEC package; these models yielded similar results. The spectral models covered various physical processes, including thermal bremsstrahlung emission. In addition, we investigated the time variations of the model parameters. By comparing the fits from the six models, we found that the zpowerlw model is the best representation of the data in the low state, while the bremsstrahlung-zpowerlaw model best represents the data across all energy ranges. To verify the X-ray variability of our data, we fit their spectra, extracted using the same method from the same instrument, with the same model to estimate their X-ray luminosity and flux. To verify the variability of the estimated fluxes, we fitted them using the bremsstrahlung-zpowerlaw model and found clear variability over the 12 observations. The bremsstrahlung-zpowerlaw model was the best model fitting the data in the 3 – 50 keV band. The highest variability was found in observation 60002024006, with a flux variability of 39.72 × ${10}^{-11}$ (erg cm⁻² s⁻¹). While the lowest variability was found in observation 60466006002, with a flux variability of 1.34 × ${10}^{-11}$ (erg cm⁻² s⁻¹), making the flux variability range 38.38 × ${10}^{-11}$ (erg cm⁻² s⁻¹).