What made Markarian 501 emit that unexpected gamma-ray spike?

Blazar Markarian 501 produced an unexpected narrow spike in TeV gamma rays during July 2014, simultaneous with enhanced X-rays. Using two-zone models where magnetic reconnection drives particle acceleration in the jet, researchers show how a small upstream region can generate the spike while a larger downstream zone produces steady emission. The scenario matches observations and aligns with magnetically striped jet models.