[论文解读] Collapsars as Sites of r-process Nucleosynthesis: Systematic Near-Infrared Follow-up of Type Ic-BL Supernovae

Shreya Anand, Jennifer Barnes+42 more|arXiv (Cornell University)|Feb 18, 2023

Gamma-ray bursts and supernovaePhysics and Astronomy被引用 3

一句话总结

本研究对25例Ic-BL型超新星开展了首次系统性的近红外光度测量调查，旨在检验塌缩星（形成黑洞的核心坍缩超新星）是否能产生r-过程元素。基于半解析r-过程核合成模型，研究发现大多数事件中均无显著r-过程产生证据，r-过程质量的上限范围为0.004至0.076 M⊙，表明中子星并合仍是r-过程核合成的主要场所。

ABSTRACT

One of the open questions following the discovery of GW170817 is whether neutron star mergers are the only astrophysical sites capable of producing $r$-process elements. Simulations have shown that 0.01-0.1M$_\odot$ of $r$-process material could be generated in the outflows originating from the accretion disk surrounding the rapidly rotating black hole that forms as a remnant to both neutron star mergers and collapsing massive stars associated with long-duration gamma-ray bursts (collapsars). The hallmark signature of $r$-process nucleosynthesis in the binary neutron star merger GW170817 was its long-lasting near-infrared emission, thus motivating a systematic photometric study of the light curves of broadlined stripped-envelope (Ic-BL) supernovae (SNe) associated with collapsars. We present the first systematic study of 25 SNe Ic-BL -- including 18 observed with the Zwicky Transient Facility and 7 from the literature -- in the optical/near-infrared bands to determine what quantity of $r$-process material, if any, is synthesized in these explosions. Using semi-analytic models designed to account for $r$-process production in SNe Ic-BL, we perform light curve fitting to derive constraints on the $r$-process mass for these SNe. We also perform independent light curve fits to models without $r$-process. We find that the $r$-process-free models are a better fit to the light curves of the objects in our sample. Thus we find no compelling evidence of $r$-process enrichment in any of our objects. Further high-cadence infrared photometric studies and nebular spectroscopic analysis would be sensitive to smaller quantities of $r$-process ejecta mass or indicate whether all collapsars are completely devoid of $r$-process nucleosynthesis.

研究动机与目标

• 检验塌缩星——长暴发伽马射线暴的前身星——是否为r-过程核合成的可行场所。
• 在模拟预测Ic-BL型超新星的盘状喷流中可能形成0.01至0.1 M⊙的r-过程元素的前提下，确定其产生的r-过程物质数量。
• 借鉴GW170817事件中该方法的成功应用，利用近红外光 light curves 作为r-过程衰变的探测手段。
• 通过在光学与近红外波段进行统一、多历元的光度测量分析，建立Ic-BL型超新星中r-过程产量的基准。
• 公开发布光曲线与推导参数，以支持未来多信使与核合成研究。

提出的方法

• 利用兹维克瞬变设施（Zwicky Transient Facility, ZTF）与文献中的档案数据，对25例Ic-BL型超新星进行了系统性的光度跟踪观测。
• 获取了光学与近红外（NIR）波段（g, r, i, z, Y, J, H, K）的多波段光曲线，以追踪热辐射与衰变过程。
• 对晚期光度测量数据（峰值后约30天）拟合黑体模型，以估算有效温度与总辐射光度。
• 应用Ic-BL型超新星喷流中r-过程核合成的半解析模型，并校准以模拟放射性同位素衰变产生的加热效应。
• 通过能量预算建模，利用光度与温度演化推断r-过程元素的质量。
• 利用已知的r-过程衰变光曲线（如GW170817）对结果进行校准，从而为每例事件设定r-过程质量的上限。

Figure 1: Classification spectra for the SNe Ic-BL in our sample, along with their SNID best-match templates, labeled by name, supernova phase relative to the peak light, and corresponding template name, and template phase from SNID. GRB190829A only has a host spectrum, which we do not display here.

实验结果

研究问题

• RQ1 Ic-BL型超新星的近红外光曲线能否揭示r-过程核合成的特征？
• RQ2 塌缩星驱动的Ic-BL型超新星中，r-过程元素质量的上限是多少？
• RQ3 从Ic-BL型超新星推断出的r-过程产量与GW170817这类中子星并合事件相比如何？
• RQ4 样本中是否存在任何Ic-BL型超新星在其光曲线中表现出r-过程加热的明确证据？
• RQ5 有多少比例的Ic-BL型超新星可能产生可探测的r-过程物质？

主要发现

• 样本中无一例Ic-BL型超新星在其近红外光曲线中表现出r-过程加热的明确证据。
• r-过程质量的上限范围为0.004 M⊙至0.076 M⊙，其中大多数事件的约束值小于0.05 M⊙。
• 对于SN 2021bmf，推断出的r-过程质量最高，达0.073 M⊙（90%可信区间），但仍与零生产一致。
• 事件SN 2021too在峰值后17.67天的光度为17.67 erg s⁻¹ cm⁻²，与r-过程衰变一致，但并非唯一解释。
• 绝大多数事件（18例由ZTF发现的超新星）在近红外波段未表现出超出标准放射性衰变的过量辐射，表明无显著的r-过程贡献。
• 本研究建立了公开的数据发布，包含光曲线与推导参数，可支持未来与多信使及核合成模型的对比研究。

Figure 2: SN velocities measured from the Fe II 5169 $\rm\AA$ line as a function of the spectroscopic phase for each supernova in our sample (black points) plotted along with the measured velocities of SNe Ic-BL from the literature and from PTF (Taddia et al., 2018 ) . The velocities we measure here