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Related Experiment Videos

Simultaneous multifrequency observations of Markarian 421.

J Brodie1, S Bowyer, A Tennant

  • 1Space Sciences Laboratory, University of California, Berkeley, USA.

The Astrophysical Journal
|July 1, 1987
PubMed
Summary

Observations of the BL Lacertae object Mrk 421 revealed rapid X-ray flux changes. These X-ray variations were not mirrored in radio or ultraviolet emissions, challenging simple synchrotron models for this active galactic nucleus.

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Area of Science:

  • * Astronomy and Astrophysics
  • * High-Energy Astrophysics
  • * Active Galactic Nuclei (AGN) research

Background:

  • * BL Lacertae objects are known for their high variability across the electromagnetic spectrum.
  • * Previous models struggled to explain the simultaneous multi-wavelength behavior of these objects.

Purpose of the Study:

  • * To investigate the rapid X-ray variability of the BL Lacertae object Mrk 421.
  • * To compare X-ray flux changes with simultaneous radio, optical, and ultraviolet observations.
  • * To test the validity of standard synchrotron and synchrotron self-Compton models.

Main Methods:

  • * Simultaneous multi-wavelength observations of Mrk 421 using radio, optical, ultraviolet, and X-ray (EXOSAT observatory) bands.
  • * Analysis of X-ray flux variations on timescales of days and shorter (approx. 10,000 s).
Keywords:
NASA Discipline ExobiologyNon-NASA Center

Related Experiment Videos

  • * Comparison of observed spectral energy distributions with theoretical models, including power-law and exponential cutoff models.

    • Main Results:

    • * Dramatic X-ray flux changes (factor of 8 in 2-10 keV) occurred on timescales < 1 month, not replicated at longer wavelengths.
    • * Ultraviolet flux changes lagged behind X-ray variations, consistent with longer electron cooling times.
    • * Simple synchrotron models were inadequate; modified models involving relativistic beaming or optical self-absorption breaks were proposed.
    • * A high-energy exponential cutoff improved X-ray spectral fits, yielding a spectral index similar to optical values.

    Conclusions:

    • * The observed multi-wavelength behavior of Mrk 421 challenges simple synchrotron emission models.
    • * Relativistic beaming or specific synchrotron break models may explain the spectral discrepancies.
    • * Short-term X-ray variability might indicate particle injection timescales.
    • * An exponential cutoff in the X-ray spectrum provides a better fit and aligns spectral indices with optical observations.