MAXI investigation into the longterm X-ray variability from the very-high-energy gamma-ray blazar Mrk 421

الأصل · EN

The archetypical very-high-energy gamma-ray blazar Mrk 421 was monitored for more than 3 years with the Gas Slit Camera onboard Monitor of All Sky X-ray Image (MAXI), and its longterm X-ray variability was investigated. The MAXI lightcurve in the 3 -- 10 keV range was transformed to the periodogram in the frequency range f = 1 × 10⁻⁸ -- 2 × 10⁻⁶ Hz. The artifacts on the periodogram, resulting from data gaps in the observed lightcurve, were extensively simulated for variations with a power-law like Power Spectrum Density (PSD). By comparing the observed and simulated periodograms, the PSD index was evaluated as α= 1.60 ± 0.25. This index is smaller than that obtained in the higher frequency range (f > 1 × 10⁻⁵ Hz), namely, α= 2.14 ± 0.06 in the 1998 ASCA observation of the object. The MAXI data impose a lower limit on the PSD break at f b = 5 × 10⁻⁶ Hz, consistent with the break of f b = 9.5 × 10⁻⁶ Hz, suggested from the ASCA data. The low frequency PSD index of Mrk 421 derived with MAXI falls well within the range of the typical value among nearby Seyfert galaxies (α= 1 -- 2). The physical implications from these results are briefly discussed.