The nearby long gamma-ray burst (GRB) 190829A was observed using the Hubble Space Telescope/Wide Field Camera 3/infrared grisms about four weeks to 500 days after the burst. We find the spectral features of its associated supernova, SN 2019oyw, are redshifted by several thousand km s−1 compared to the redshift of the large spiral galaxy on which it is superposed. This velocity offset is seen in several features but most clearly in Ca ii near-infrared triplet λλ8498, 8542, 8662 (CaIR3). We also analyze Very Large Telescope/FOcal Reducer and low dispersion Spectrograph and X-shooter spectra of the supernova (SN) and find strong evolution with time of its P-Cygni features of CaIR3 from the blue to the red. However, comparison with a large sample of Type Ic-BL and Ic SNe shows no other object with the CaIR3 line as red as that of SN 2019oyw were it at the z = 0.0785 redshift of the disk galaxy. This implies that SN 2019oyw is either a highly unusual SN or is moving rapidly with respect to its apparent host. Indeed, using CaIR3 we find the redshift of SN 2019oyw is 0.0944 ≤ z ≤ 0.1156. The GRB-SN is superposed on a particularly dusty region of the massive spiral galaxy; therefore, while we see no sign of a small host galaxy behind the spiral, it could be obscured. Our work provides a surprising result on the origins of GRB 190829A, as well as insights into the time evolution of GRB-SNe spectra and a method for directly determining the redshift of a GRB-SN using the evolution of strong spectral features such as CaIR3.

中文翻译：

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GRB 190829A/SN 2019oyw 的红移：GRB-SN 进化的案例研究


附近的长伽马射线暴 （GRB） 190829A 是在大爆发后大约 4 周至 500 天使用哈勃太空望远镜/宽视场相机 3/红外磁共振观测到的。我们发现，与它叠加的大型螺旋星系的红移相比，其相关超新星 SN 2019oyw 的光谱特征红移了数千公里 s−1。这种速度偏移在几个特征中可见，但在 Ca ii 近红外三重态 λλ8498、8542、8662 （CaIR3） 中最为明显。我们还分析了超新星 （SN） 的甚大望远镜/焦光还原器、低色散光谱仪和 X 射手光谱，发现 CaIR3 的 P-Cygni 特征随时间从蓝色到红色的强烈演变。然而，与Ic-BL型和Ic SNe型的大样本进行比较，在盘星系的z = 0.0785红移处，没有其他天体的CaIR3线像SN 2019oyw那样红。这意味着 SN 2019oyw 要么是一个非常不寻常的 SN，要么相对于其明显的宿主正在快速移动。事实上，使用 CaIR3 我们发现 SN 2019oyw 的红移是 0.0944 ≤ z ≤ 0.1156。GRB-SN 叠加在大质量螺旋星系的一个特别尘埃的区域;因此，虽然我们在漩涡后面没有看到一个小宿主星系的迹象，但它可能被掩盖了。我们的工作为 GRB 190829A 的起源提供了令人惊讶的结果，以及对 GRB-SNe 光谱时间演变的见解，以及一种利用 CaIR3 等强光谱特征的演变直接确定 GRB-SN 红移的方法。