GRB 180325 A在z=2.25处的光学余辉光谱中的2175 nm消光特性
The 2175 Å extinction feature in the optical afterglow spectrum of GRB 180325A at z=2.25
摘要：
在2175 ° C的紫外线消光特征在银河系中随处可见，但在高红移时很少被发现。在这里，我们报告的光谱检测的视线上的2175隆起的γ射线暴（GRB）余辉GRB 180325 A在z=2.2486，唯一明确的检测在过去十年的GRB后续行动，在四个不同的时期与北欧光学望远镜（NOT）和甚大望远镜（VLT）/X-射手。附加的余辉光度观测是用伽马射线暴光学和近红外探测器（GROND）获得的。我们构建了近红外X射线光谱能量分布（SED）在四个光谱时期。SEDs可以用一个单一的幂律和一个消光律很好地描述，其R_V~4.4，A_V~1.5，消光特性为2175 μ m。撞击强度和消光曲线比银河系的平均消光曲线要浅。我们从VLT/X-射手光谱确定了[Zn/H]>-0.98的金属丰度。我们探测到与伽玛暴相关的强中性碳，其等效宽度为Wr（λ1656）= 0.85+/-0.05。我们还探测到来自宿主星系的光学发射线。根据Hα发射线通量，计算出该星系的恒星形成速率为46+/-4Msun/yr，恒星质量为log M*/Msun ~9.3+/-0.4，表明该星系属于主序星星系。
英文摘要：
The UV extinction feature at 2175 Å is ubiquitously observed in the Galaxy but is rarely detected at high redshifts. Here we report the spectroscopic detection of the 2175 Å bump on the sightline to the γ-ray burst (GRB) afterglow GRB 180325A at z=2.2486, the only unambiguous detection over the past ten years of GRB follow-up, at four different epochs with the Nordic Optical Telescope (NOT) and the Very Large Telescope (VLT)/X-shooter. Additional photometric observations of the afterglow are obtained with the Gamma-Ray burst Optical and Near-Infrared Detector (GROND). We construct the near-infrared to X-ray spectral energy distributions (SEDs) at four spectroscopic epochs. The SEDs are well-described by a single power-law and an extinction law with R_V~4.4, A_V~1.5, and the 2175 Å extinction feature. The bump strength and extinction curve are shallower than the average Galactic extinction curve. We determine a metallicity of [Zn/H]>-0.98 from the VLT/X-shooter spectrum. We detect strong neutral carbon associated with the GRB with an equivalent width of Wr(λ1656) = 0.85+/-0.05. We also detect optical emission lines from the host galaxy. Based on the Hαemission line flux, the derived dust-corrected star-formation rate is ~46+/-4 M_sun/yr and the predicted stellar mass is log M*/M_sun~9.3+/-0.4, suggesting the host galaxy is amongst the main-sequence star-forming galaxies.
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