INTEGRAL observations of the blazar Mrk 421 in outburst (Results of a multi-wavelength campaign)

TL;DR

This paper presents a multi-wavelength observational study of the blazar Mrk 421 during an outburst, analyzing X-ray flares, spectral changes, and estimating physical parameters like emission region size and magnetic field strength.

Contribution

It provides new insights into the timing, spectral behavior, and physical conditions of Mrk 421 during an outburst through coordinated multi-wavelength observations.

Findings

Detected four strong X-ray flares not seen at other wavelengths.

Estimated the emission region size from the fastest X-ray rise.

Derived the magnetic-field strength from observed time lags.

Abstract

We report the results of a multi-wavelength campaign on the blazar Mrk 421 during outburst. We observed four strong flares at X-ray energies that were not seen at other wavelengths (partially because of missing data). From the fastest rise in the X-rays, an upper limit could be derived on the extension of the emission region. A time lag between high-energy and low-energy X-rays was observed, which allowed an estimation of the magnetic-field strength. The spectral analysis of the X-rays revealed a slight spectral hardening of the low-energy (3 - 43 keV) spectral index. The hardness-ratio analysis of the Swift-XRT (0.2 - 10 keV) data indicated a small correlation with the intensity; i. e., a hard-to-soft evolution was observed. At the energies of IBIS/ISGRI (20 - 150 keV), such correlations are less obvious. A multiwavelength spectrum was composed and the X-ray and bolometric luminosities are calculated.