Probing an X-Ray Flare Pattern in Mrk 421 Induced by Multiple Stationary Shocks: A Solution to the Bulk Lorentz Factor Crisis

Olivier Hervet, David A. Williams, Abraham D. Falcone, Amanpreet Kaur

Research output: Contribution to journalArticle

Abstract

The common observations of multiple radio VLBI stationary knots in high-frequency-peaked BL Lacs (HBLs) can be interpreted as multiple recollimation shocks accelerating particles along jets. This approach can resolve the so-called "bulk Lorentz factor crisis" of sources with a high Lorentz factor deduced from maximum γ-γ opacity and fast variability and apparently inconsistent slow/stationary radio knots. It also suggests that a unique pattern of the nonthermal emission variability should appear after each strong flare. Taking advantage of the 13 yr of observation of the HBL Mrk 421 by the X-ray Telescope on the Neil Gehrels Swift Observatory (Swift-XRT), we probe for such an intrinsic variability pattern. Its significance is then statistically estimated via comparisons with numerous similar simulated light curves. A suggested variability pattern is identified, consistent with a main flare emission zone located in the most upstream 15.3 GHz radio knot at 0.38 mas from the core. Subsequent flux excesses in the light curve are consistent with a perturbation crossing all of the downstream radio knots with a constant apparent speed of 45c. The significance of the observed variability pattern not arising from stochastic processes is found above three standard deviations, opening a promising path for further investigations in other blazars and with other energy bands. In addition to highlighting the role of stationary radio knots as high-energy particle accelerators in jets, the developed method allows estimates of the apparent speed and size of a jet perturbation without the need to directly observe any motion in jets.

Original languageEnglish (US)
Article number26
JournalAstrophysical Journal
Volume877
Issue number1
DOIs
StatePublished - May 20 2019

Fingerprint

flares
shock
radio
x rays
light curve
Swift observatory
perturbation
nonthermal radiation
blazars
particle accelerators
very long base interferometry
stochastic processes
very long baseline interferometry
stochasticity
opacity
upstream
energy bands
energy
standard deviation
observatory

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

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title = "Probing an X-Ray Flare Pattern in Mrk 421 Induced by Multiple Stationary Shocks: A Solution to the Bulk Lorentz Factor Crisis",
abstract = "The common observations of multiple radio VLBI stationary knots in high-frequency-peaked BL Lacs (HBLs) can be interpreted as multiple recollimation shocks accelerating particles along jets. This approach can resolve the so-called {"}bulk Lorentz factor crisis{"} of sources with a high Lorentz factor deduced from maximum γ-γ opacity and fast variability and apparently inconsistent slow/stationary radio knots. It also suggests that a unique pattern of the nonthermal emission variability should appear after each strong flare. Taking advantage of the 13 yr of observation of the HBL Mrk 421 by the X-ray Telescope on the Neil Gehrels Swift Observatory (Swift-XRT), we probe for such an intrinsic variability pattern. Its significance is then statistically estimated via comparisons with numerous similar simulated light curves. A suggested variability pattern is identified, consistent with a main flare emission zone located in the most upstream 15.3 GHz radio knot at 0.38 mas from the core. Subsequent flux excesses in the light curve are consistent with a perturbation crossing all of the downstream radio knots with a constant apparent speed of 45c. The significance of the observed variability pattern not arising from stochastic processes is found above three standard deviations, opening a promising path for further investigations in other blazars and with other energy bands. In addition to highlighting the role of stationary radio knots as high-energy particle accelerators in jets, the developed method allows estimates of the apparent speed and size of a jet perturbation without the need to directly observe any motion in jets.",
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Probing an X-Ray Flare Pattern in Mrk 421 Induced by Multiple Stationary Shocks : A Solution to the Bulk Lorentz Factor Crisis. / Hervet, Olivier; Williams, David A.; Falcone, Abraham D.; Kaur, Amanpreet.

In: Astrophysical Journal, Vol. 877, No. 1, 26, 20.05.2019.

Research output: Contribution to journalArticle

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