GRB 250704B/EP250704a a Short Gamma-Ray Burst Powered by a Magnetar

Abstract GRB 250704B/EP250704a, identified as a short gamma-ray burst (sGRB), exhibited prolonged X-ray emission following the prompt phase. The event also showed an unusual optical and infrared (IR) plateau lasting nearly one day, followed by a rapid achromatic decline. This event was extensively monitored by multiple space- and ground-based observatories across the electromagnetic spectrum. We present temporal and spectral analyses of the prompt, extended X-ray, and afterglow emission spanning radio to gamma-ray energies during the first two days after the burst. The observed multi-wavelength properties are consistent with a long-lived accreting millisecond magnetar remnant. In this framework, the extended X-ray emission is interpreted as internal dissipation within a relativistic magnetized outflow powered by the magnetar spin-down luminosity, whereas the optical/IR and radio emission are explained as synchrotron forward-shock radiation with continuous energy injection. The steep late-time decay is explained through temporal evolution of the microphysical parameters during the post-jet-break phase. The X-ray observations can be interpreted as a superposition of internal dissipation and synchrotron forward-shock emission. These results favour the presence of a long-lived magnetar remnant powering the multi-wavelength evolution of GRB 250704B/EP250704a.