The relentless variability of Mrk 421 from the TeV to the radio

Abstract

The origin of the gamma-ray emission of the blazar Mrk 421 is still a matter of debate. We used 5.5 years of unbiased observing campaign data, obtained using the FACT telescope and the Fermi LAT detector at TeV and GeV energies, the longest and densest so far, together with contemporaneous multi-wavelength observations, to characterise the variability of Mrk 421 and to constrain the underlying physical mechanisms. We studied and correlated light curves obtained by ten different instruments and found two significant results. The TeV and X-ray light curves are very well correlated with a lag of <0.6 days. The GeV and radio (15 Ghz band) light curves are widely and strongly correlated. Variations of the GeV light curve lead those in the radio. Lepto-hadronic and purely hadronic models in the frame of shock acceleration predict proton acceleration or cooling timescales that are ruled out by the short variability timescales and delays observed in Mrk 421. Instead the observations match the predictions of leptonic models.

10 pages, 8 figures, 1 table

References in corpus (16)

• A hadronic origin for ultra-high-frequency-peaked BL Lac objects
• Multiwavelength Observations of Markarian 421 in March 2001: an Unprecedented View on the X-ray/TeV Correlated Variability
• Observations of Mkn 421 with the MAGIC Telescope
• Time-correlation between the radio and gamma-ray activity in blazars and the production site of the gamma-ray emission
• Unprecedented study of the broadband emission of Mrk 421 during flaring activity in March 2010
• Superorbital variability of X-ray and radio emission of Cyg X-1 - II. Dependence of the orbital modulation and spectral hardness on the superorbital phase
• Multiwavelength observations of Mrk 501 in 2008
• Scenarios for ultrafast gamma-ray variability in AGN
• Calibration and performance of the photon sensor response of FACT -- The First G-APD Cherenkov telescope
• A combined radio and GeV gamma-ray view of the 2012 and 2013 flares of Mrk 421
• Unravelling the complex behavior of Mrk 421 with simultaneous X-ray and VHE observations during an extreme flaring activity in April 2013
• Long-term optical polarization variability and multiwavelength analysis of Blazar Mrk 421
• X-ray Intra-day Variability of the TeV Blazar Mrk 421 with Suzaku
• The high energy spectrum of 3C 273
• Testing one-zone synchrotron-self-Compton models with spectral energy distributions of Mrk 421
• Zenith angle dependence of the cosmic ray rate as measured with Imaging air-Cherenkov Telescopes

Cited by in corpus (9)

• Radio$-\gamma -$ray response in blazars as a signature of adiabatic blob expansion
• Study of correlation between optical flux and polarization variations in BL Lac objects
• Rapid X-ray Variability in Mkn 421 during a Multiwavelength Campaign
• Long-term multi-band photometric monitoring of Mrk 501
• Insights from the first flaring activity of a high-synchrotron-peaked blazar with X-ray polarization and VHE gamma rays
• Flux and spectral variability of Mrk 421 during its moderate activity state using NuSTAR: Possible accretion disc contribution?
• Decade-long periodicity study of 2FHL blazars with historical optical data
• Not so Swift: 20 years of multiwavelength observations of Mrk 421 and Mrk 501
• The January 2010 flare of Mrk421: Insights from a stochastic acceleration model