Metal-poor massive stars typically end their lives as blue supergiants (BSGs). Gamma-ray bursts (GRBs) from such progenitors could have an ultra-long duration of relativistic jets. For example, Population III (Pop III) GRBs at z 10-20 might be observable as X-ray-rich events with a typical duration of T 90 104(1 + z) s. The recent GRB111209A at z = 0.677 has an ultra-long duration of T 90 2.5 × 104 s and it has been suggested that its progenitor might have been a metal-poor BSG in the local universe. Here, we suggest that luminous UV/optical/infrared emission is associated with this new class of GRBs from metal-poor BSGs. Before the jet head breaks out of the progenitor envelope, the energy injected by the jet is stored in a hot plasma cocoon, which finally emerges and expands as a baryon-loaded fireball. We show that the photospheric emissions from the cocoon fireball could be intrinsically very bright (L peak 1042-1044 erg s-1) in UV/optical bands (εpeak 10 eV) with a typical duration of 00 days in the rest frame. Such cocoon emissions from Pop III GRBs might be detectable in infrared bands at years after Pop III GRBs at up to z 15 by upcoming facilities such as the James Webb Space Telescope. We also suggest that GRB111209A might have been rebrightening in UV/optical bands up to an AB magnitude of ≲ 26. The cocoon emission from local metal-poor BSGs might have been observed previously as luminous supernovae without GRBs since they can be seen from the off-axis direction of the jet.
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