We report on the detection of a very rapid TeV gamma-ray flare from BL Lacertae on 2011 June 28 with the Very Energetic Radiation Imaging Telescope Array System ( VERITAS ) .
The flaring activity was observed during a 34.6-minute exposure , when the integral flux above 200Â GeV reached ( 3.4 \pm 0.6 ) \times 10 ^ { -6 } \text { photons } \text { m } ^ { -2 } \text { s } ^ { -1 } , roughly 125 % of the Crab Nebula flux measured by VERITAS .
The light curve indicates that the observations missed the rising phase of the flare but covered a significant portion of the decaying phase .
The exponential decay time was determined to be 13 \pm 4 minutes , making it one of the most rapid gamma-ray flares seen from a TeV blazar .
The gamma-ray spectrum of BL Lacertae during the flare was soft , with a photon index of 3.6 \pm 0.4 , which is in agreement with the measurement made previously by MAGIC in a lower flaring state .
Contemporaneous radio observations of the source with the Very Long Baseline Array ( VLBA ) revealed the emergence of a new , superluminal component from the core around the time of the TeV gamma-ray flare , accompanied by changes in the optical polarization angle .
Changes in flux also appear to have occurred at optical , UV , and GeV gamma-ray wavelengths at the time of the flare , although they are difficult to quantify precisely due to sparse coverage .
A strong flare was seen at radio wavelengths roughly four months later , which might be related to the gamma-ray flaring activities .
We discuss the implications of these multiwavelength results .