Abstract:
Highly variable Markarian 421 is a bright high–synchrotron energy peaked blazar showing a wide featureless
nonthermal spectrum, making it a good candidate for our study of intraday flux and spectral variations over time.
We analyze its X-ray observations over 17 yr, taken with the EPIC-pn instrument, to probe into the intraday
variability properties, focusing on the photon energy band of 0.3–10.0 keV, and its soft (0.3–2.0 keV) and hard
(2.0–10.0 keV) subbands. To examine the flux variability, fractional variability amplitudes and minimum
variability timescales have been calculated. We also probed into the spectral variability by studying the hardness
ratio for each observation, the correlation between the two energy bands, using the discrete correlation function,
and inspecting the normalized light curves. The parameters obtained from these methods were studied for any
correlations or nonrandom trends. From this work, we speculate on the constraints on the possible particle
acceleration and emission processes in the jet, for a better understanding of the processes involving turbulent
behavior, except for shocks. A positive discrete correlation function between the two subbands indicates the role of
the same electron population in the emission of photons in the two bands. A correlation between the parameter of
flux variability and the parameters of spectral variation and lags in the subenergy bands provides the constraints to
be considered for any modeling of emission processes.
