AI 中文总结
本研究通过一年宽带射电监测GRB 250702B，分析其射电辐射特性，约束喷流参数，探讨其前身星可能为恒星质量黑洞并合或中等质量/恒星质量黑洞潮汐瓦解事件，排除超大质量黑洞潮汐瓦解事件的可能性。
AI 中文摘要
我们对独特的河外瞬变源GRB 250702B开展了广泛的射电监测活动，观测覆盖了发现后6至356天（观测者坐标系），频率范围为0.65至233 GHz。射电辐射呈现出平滑演化的峰值同步辐射谱，与绝热激波膨胀到分层环境介质的情况一致（电子数密度n_e∝R^{-k}，k=1.5至2）。我们在低频（≤3 GHz）光变曲线中检测到显著的变化，将其解释为星际闪烁，由此给出激波阵面图像大小的近似约束：1.2×10^16 cm ≤ R⊥ ≤ 5×10^17 cm。流量密度和临界同步辐射频率的时间演化表明，驱动射电辐射的激波可能是半张开角θ_j≥15度、低洛伦兹因子（Γ≤10）的喷流，或是半张开角θ_j≤2度的高度相对论性喷流。对于恒星质量黑洞引擎（如氦星并合），预期会形成窄喷流，此场景下经束流修正的动能与长伽马射线暴的已知分布一致（E_K~10^51 erg）；而宽喷流场景则需要包含长时间吸积的前身星。我们推导并证明，中等质量或恒星质量黑洞的潮汐瓦解事件（TDE）是可行的可能性，此场景下经束流修正的动能处于相对论性超大质量黑洞（SMBH）TDE已知分布的低端（E_K~10^50 erg）。由于与观测时标不兼容，我们不倾向于认为这是SMBH TDE。若在未来一年内检测到喷流关闭，将倾向于支持白矮星-中等质量黑洞（WD-IMBH）TDE，因为其超爱丁顿吸积的理论持续时间比主序星TDE通道更短。
英文摘要
We present an extensive radio monitoring campaign of the unique extragalactic transient GRB 250702B, with observations spanning 0.65-233 GHz from 6-356 d (observer frame) post-discovery. The radio emission shows a smoothly evolving peaked synchrotron spectrum consistent with an adiabatic shock expanding into a stratified ambient medium ($n_e\propto R^{-k}$; $k= 1.5-2$). We detect significant variability in the low frequency ($\leq3$ GHz) light curves which we interpret as interstellar scintillation, placing an approximate bound on the blast wave image size of $1.2\times10^{16}\lesssim R_{\perp} \lesssim 5\times10^{17}$ cm. The temporal evolution of the flux density and critical synchrotron frequencies suggest the shock that powers the radio emission is potentially a wide-angle $θ_j\gtrsim15$ deg, low Lorentz factor ($Γ\lesssim10$) jet, or a narrow $θ_j\lesssim2$ deg highly relativistic jet. A narrow jet is expected for a stellar-mass black hole engine, such as a helium star merger, and the beaming-corrected kinetic energy in this scenario is consistent with the known distribution for long GRBs ($E_K\sim10^{51}$ erg). The wide-angle jet scenario would instead require a progenitor involving prolonged accretion. We derive and show an intermediate or stellar-mass black hole tidal disruption event are viable possibilities. The beaming-corrected kinetic energy in this scenario is on the low end of the known distribution for relativistic SMBH TDEs ($E_K\sim10^{50}$ erg). We disfavour an SMBH TDE due to lack of compatibility with the observed timescales. The detection of a jet shut off within the next year would favour a WD-IMBH TDE due to the shorter theoretical duration of super-Eddington accretion than the main-sequence TDE channels.
Comments29 pages, 15 figures, submitted to MNRAS. All data in Table D1 available in machine readable format upon request. Comments welcome
