They detected many photons, but I read this as meaning that they had focused their attention on one specific photon that was detected by their instruments: > A

They detected many photons, but I read this as meaning that they had focused their attention on one specific photon that was detected by their instruments: > Among those detections was a suspected high-energy photon at 18 teraelectron volts (TeV)—four times higher than anything seen from a gamma-ray burst before and more energetic than the highest energies achievable by the Large Hadron Collider.