Testing two-jet models of GRBs with the orphan afterglow

Two-jet models are introduced to explain the complex time profiles and diversities of early afterglows in the Swift era. Testing these afterglow models is important because it relates not only to the afterglow emission mechanism, but also to the activity of the central engines of gamma-ray bursts (GRBs). In this paper, we suggest a new method of testing two-jet models by using orphan afterglows of GRBs. If afterglows are actually composed of two jets, we can observe two peaks in the orphan afterglows in the optical band. Typically, the first peak appears on 10(4) - 10(5)s and the second peak on 10(5) - 10(6)s. Therefore, first we observe the orphan afterglow in the X-ray band, and if we follow up the afterglow in the optical band, we can observe two peaks.