标题： 导致在BOAT GRB221009A中检测到电子对湮灭线的物理条件 显示英文标题

标题： Physical conditions that lead to the detection of the pair annihilation line in the BOAT GRB221009A

摘要： 所有时间中最明亮的GRB221009A显示出一个狭窄且随时间变化的MeV辐射线的证据。 在这里，我们表明这条线可以解释为瞬时辐射区域中的电子对湮灭所致，并且其时间演化自然地解释为瞬时辐射结束后高纬度辐射（从视线方向更高角度发出的辐射）。 我们考虑了电子对产生机制的高光学深度和低光学深度两种情况，并找到了可接受的解，其中GRB的洛伦兹因子$\Gamma \approx 600$和辐射半径$r \gtrsim 10^{16.5}$~cm。 我们讨论了这种线出现的条件，并表明需要高光度和洛伦兹因子的独特组合，且该组合处于相当狭窄的范围内才能检测到该线。 这解释了为什么这种湮灭线在GRB中很少被观测到。 显示英文摘要

摘要： The brightest of all time (BOAT) GRB221009A show evidence for a narrow, evolving MeV emission line. Here, we show that this line can be explained as due to pair annihilation in the prompt emission region, and that its temporal evolution is naturally explained as the high-latitude emission (emission from higher angles from the line of sight) after prompt emission is over. We consider both the high and low optical depth for pair production regimes, and find acceptable solutions, with the GRB Lorentz factor $\Gamma \approx 600$ and the emission radius $r \gtrsim 10^{16.5}$~cm. We discuss the conditions for the appearance of such a line, and show that a unique combination of high luminosity and Lorentz factor that is in a fairly narrow range are required for the line detection. This explains why such an annihilation line is rarely observed in GRBs.