If X-ray flashes are due to the forward-jet emissions from gamma-ray bursts (GRBs) observed at large viewing angles, we show that a prompt emission from a counterjet should be observed as a " delayed flash " in the UV or optical band several hours to a day after the X-ray flash. The Ultraviolet and Optical Telescope on Swift can observe the delayed flashes within ～13 Mpc, so that (double-sided) jets of GRBs can be directly confirmed. Since the event rate of delayed flashes detected by Swift may be as small as ～6 x 10~(-5) events yr~(-1), we require more sensitive detectors in future experiments.
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机译：如果X射线闪光是由于在大视角下观察到的伽玛射线暴（GRB）引起的前向喷射发射，则表明应将对立喷射的迅速发射视为紫外或光学中的“延迟闪光”在X射线闪烁后几小时到一天。 Swift上的紫外线和光学望远镜可以观测到约13 Mpc的延迟闪光，因此可以直接确认GRB的（双面）射流。由于Swift侦测到的延迟闪烁事件发生率可能小到〜6 x 10〜（-5）个事件yr〜（-1），因此在未来的实验中我们需要更灵敏的检测器。
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