English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We report on variability and correlation studies using multiwavelengthobservations of the blazar Mrk 421 during the month of February, 2010 when anextraordinary flare reaching a level of $\sim$27~Crab Units above 1~TeV wasmeasured in very-high-energy (VHE) $\gamma$-rays with the VERITAS observatory.This is the highest flux state for Mrk 421 ever observed in VHE $\gamma$-rays.Data are analyzed from a coordinated campaign across multiple instrumentsincluding VHE $\gamma$-ray (VERITAS, MAGIC), high-energy (HE) $\gamma$-ray(Fermi-LAT), X-ray (Swift}, RXTE, MAXI), optical (including the GASP-WEBTcollaboration and polarization data) and radio (Mets\"ahovi, OVRO, UMRAO).Light curves are produced spanning multiple days before and after the peak ofthe VHE flare, including over several flare `decline' epochs. The main flarestatistics allow 2-minute time bins to be constructed in both the VHE andoptical bands enabling a cross-correlation analysis that shows evidence for anoptical lag of $\sim$25-55 minutes, the first time-lagged correlation betweenthese bands reported on such short timescales. Limits on the Doppler factor($\delta \gtrsim 33$) and the size of the emission region ($ \delta^{-1}R_B\lesssim 3.8\times 10^{13}\,\,\mbox{cm}$) are obtained from the fastvariability observed by VERITAS during the main flare. Analysis of10-minute-binned VHE and X-ray data over the decline epochs shows anextraordinary range of behavior in the flux-flux relationship: from linear toquadratic to lack of correlation to anti-correlation. Taken together, thesedetailed observations of an unprecedented flare seen in Mrk 421 are difficultto explain by the classic single-zone synchrotron self-Compton model.

The Great Markarian 421 Flare of February 2010: Multiwavelength variability and correlation studies