FRB 20201124A 峰值频率约 1 GHz 的窄带频谱：对能量函数和辐射物理的启示
Narrowly-Banded Spectra with Peak Frequency Around 1 GHz of FRB 20201124A: Implications for Energy Function and Radiation Physics
AI总结：
本研究利用FAST望远镜探测的1268个FRB 20201124A暴样本，通过频谱拟合和蒙特卡洛模拟，揭示了其窄带频谱特征、内禀能量函数，并对比了其他重复暴，提出不同等离子体环境导致辐射差异。
摘要：
快速射电暴（FRB）的辐射物理仍是一个未解之谜。当前观测发现，FRB 20201124A 的窄带暴在 0.4-2 GHz 范围内活跃，其频谱峰值频率（$ν^{\rm obs}_{p}$）大多接近 $\sim 1$ GHz。利用 FAST 望远镜探测到的 FRB 20201124A 的 1268 个暴样本，我们表明 71.4% 的事件（带内暴）的 $1σ$ 频谱范围位于 FAST 通带之内。通过用高斯函数拟合频谱轮廓，其内禀暴能量（$E^{\rm obs}_{\rm BWe}$）和频谱宽度（$σ_s^{\rm obs}$）得到了很好的测量。得到的 $E^{\rm obs}_{\rm BWe}$ 和 $σ_s^{\rm obs}$ 分布呈对数正态分布，中心分别位于 $\log E^{\rm obs}_{\rm BWe}/{\rm erg}=37.2~ (σ=0.76)$ 和 $\log σ_s^{\rm obs}/{\rm GHz}=-1.16~ (σ=0.17)$。我们的蒙特卡洛模拟分析推断其内禀 $ν_p$ 分布为以 $ν_{p,c}=1.16$ GHz（$σ=0.22$）为中心的正态函数，其内禀能量函数为 $Φ(E)\propto E^{-0.60}e^{-E/E_c}$，其中 $E_c=9.49 \times 10^{37}$ erg。我们将这些结果与典型重复暴 FRB 20121102A 和 FRB 20190520B 的结果进行比较，后者在多个特定频率的宽频率范围内活跃，并讨论了在事件率和能量函数估计上可能存在的观测偏差。基于这些结果，我们认为 FRB 20201124A 可能发生在经过精细调谐的等离子体中，在窄频率范围内产生脉泽辐射，而 FRB 20121102A 和 FRB 20190520B 可能涉及团块等离子体条件，使得脉泽发射在宽范围内的几个特定频率附近发生。
英文摘要：
The radiation physics of fast radio bursts (FRBs) remains an open question. Current observations have discovered that narrowly-banded bursts of FRB 20201124A are active in 0.4-2 GHz and their spectral peak frequency ($ν^{\rm obs}_{p}$) are mostly toward $\sim 1$ GHz. Utilizing a sample of 1268 bursts of FRB 20201124A detected with the FAST telescope, we show that the $1σ$ spectral regime of 71.4\% events (in-band bursts) is within the FAST bandpass. Their intrinsic burst energies ($E^{\rm obs}_{\rm BWe}$) and spectral widths ($σ_s^{\rm obs}$) are well measured by fitting the spectral profile with a Gaussian function. The derived $E^{\rm obs}_{\rm BWe}$ and $σ_s^{\rm obs}$ distributions are log-normal and centering at $\log E^{\rm obs}_{\rm BWe}/{\rm erg}=37.2~ (σ=0.76)$ and $\log σ_s^{\rm obs}/{\rm GHz}=-1.16~ (σ=0.17)$. Our Monte Carlo simulation analysis infers its intrinsic $ν_p$ distribution as a normal function centered at $ν_{p,c}=1.16$ GHz ($σ=0.22$) and its intrinsic energy function as $Φ(E)\propto E^{-0.60}e^{-E/E_c}$ with $E_c=9.49 \times 10^{37}$ erg. We compare these results with that of typical repeating FRBs 20121102A and 20190520B that are active over a broad frequency range at several specific frequencies and discuss possible observational biases on the estimation of the event rate and energy function. Based on these results, we argue that FRB 20201124A likely occurs in a fine-tuned plasma for maser radiations at a narrow frequency range, while FRB 20121102A and FRB 20190520B could involve clumpy plasma conditions that make maser emission around several specific frequencies in a broad range.
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