Prompt Jet Launching and Delayed Thermal Disk in Tidal Disruption Event for Prolonged Activity GRB 220706A

Abstract

GRB 220706A exhibits X-ray flaring activity extending to ~51 days after the trigger, along with a luminous optical thermal component emerging on a timescale of ~10^6 s. Such prolonged central-engine activity could be powered by a collapsar fed by an extended stellar envelope. However, a relativistic jet may struggle to break out of the extended envelope. These challenges motivate a tidal disruption event (TDE), although explaining both the early relativistic jet and the luminous late optical thermal emission within one TDE framework remains difficult. We investigate a TDE scenario in which shocks between stellar debris streams drive the early inflow of some debris, potentially carrying preexisting fossil magnetic flux toward the black hole (BH) and powering an initial relativistic jet via the Blandford-Znajek mechanism. The remaining debris circularizes into an accretion disk, whose thermal emission accounts for the late optical thermal component. For GRB 220706A, the optical timescale, luminosity, and color temperature are consistent with disruption of a blue supergiant (M_*~50M_{sun}, R_*~20~R_{sun}) by a BH of mass M_{BH}~10^5 M_{sun}, assuming that the accretion disk forms on a timescale comparable to the orbital period of the most tightly bound stellar debris. A magnetic field strength of ~10^5 G is required near the BH before disruption to power a jet capable of producing the inferred gamma-ray luminosity. Continued fallback may sustain central-engine activity beyond the observed X-ray flaring episode, making future X-ray monitoring a test of this scenario.