The Ultraviolet Flash Accompanying Grbs from Neutron-rich Internal Shocks

In the neutron-rich internal shocks model for Gamma-ray Burts (GRBs), the Lorentz factors (LFs) of ions shells are variable, so are the LFs of accompanying neutron shells. For slow neutron shells with a typical LF ∼ tens, the typical β−decay radius reads Rβ,s ∼ several× 10cm, which is much larger than the typical internal shocks radius ∼ 10cm, so their impact on the internal shocks may be unimportant. However, as GRBs last long enough (T90 > 20(1 + z)s), one earlier but slower ejected neutron shell will be swept successively by later ejected ion shells in the range ∼ 10cm − 10cm, where slow neutrons have decayed significantly. We show in this work that ion shells interacting with the β−decay products of slow neutron shells can power a ultraviolet (UV) flash bright to 12th magnitude during the prompt γ−ray emission phase or slightly delayed, which can be detected by the upcoming Satellite SWIFT in the near future. Subject headings: gamma rays:bursts — radiation mechanisms: nonthermal — shock waves