Optical and near-infrared observations of the GRB020405 afterglow ?
Optical and near-infrared observations of the GRB020405 afterglow ?
复制标题
GRB020405 余辉的光学和近红外观测？
DOI：
10.1051/0004-6361:20030491
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发表时间：
2003
影响因子：
4.8
通讯作者：
E. V. Heuvel
中科院分区：
文献类型：
--
作者：
N. Masetti;E. Palazzi;E. Pian;A. Simoncelli;L. Hunt;E. Maiorano;A. Levan;L. Christensen;E. Rol;S. Savaglio;S. Savaglio;R. Falomo;A. Castro;J. Hjorth;A. Delsanti;M. Pannella;V. Mohan;S. Pandey;R. Sagar;L. Amati;I. Burud;J. M. C. Cer'on;F. Frontera;A. Fruchter;J. Fynbo;J. Gorosabel;L. Kaper;S. Klose;C. Kouveliotou;L. Nicastro;H. Pedersen;J. Rhoads;I. Salamanca;N. Tanvir;P. Vreeswijk;R. Wijers;E. V. Heuvel
我们报告GRB 020405的光学和近红外（NIR）余辉的光度，光谱和偏振监测。使用8台不同的望远镜进行的地面光学观测在高能瞬发事件发生后约1天开始，持续时间为2010天;增加了存档的HST数据，将覆盖范围扩大到伽玛射线暴发生后的20150天。我们报告的余辉在近红外波段的第一次检测。在宿主星系的光谱中检测到的巴耳末和氧发射线表明，伽玛暴位于红移z = 0.691。在余辉光谱中，在z = 0.691和z = 0.472处检测到Fe II和Mg II吸收系统。后一个系统很可能是由位于GRB 020405主星系西南方0.22”的星系复合体中的吸收云引起的。因此，第一次，星系负责干预吸收线系统的光谱中的伽玛射线暴余辉光谱确定。余辉的光学和近红外光度测定表明，在伽玛暴发生后1至10天内，所有波段的衰变均符合指数a = 1.54 '0.06的单一幂律。晚历元的VLT J波段和HST光学点位于这个幂律的外推之上，因此在GRB后10-20天的VRIJ光变曲线中出现了一个平台（或“凸起”）。在伽玛暴后的第120天以后，光变曲线符合指数α' = 1.85 ′ 0.15的幂律衰变。虽然其他作者已经提出了复制与模板的超新星（SN）1998 bw，被认为是原型的“超新星”的凸点，我们建议，它也可以建模与SN具有相同的时间配置文件作为其他建议的超新星SN 2002 ap，但1.3等明亮的峰值，并位于GRB红移。另外，一个冲击反射可能是导致再亮的原因。R波段单偏振测量表明余辉是偏振的，P = 1.5 ′ 0.4%，偏振角θ = 172° ′8°。宽带光学近红外光谱通量分布显示，在第一天后的伽玛暴，整个J带的斜率的变化，我们解释为由于存在的电子冷却频率VC。对标准火球模型中多波长光谱的分析表明，指数p = 2.7的相对论性电子群通过同步辐射产生光学近红外辐射，在爆炸性膨胀的爆炸波中，可以忽略不计的宿主星系灭绝，以及通过逆康普顿散射较低频率的余辉光子产生X射线。
We report on photometric, spectroscopic and polarimetric monitoring of the optical and near-infrared (NIR) afterglow of GRB020405. Ground-based optical observations, performed with 8 different telescopes, started about 1 day after the high-energy prompt event and spanned a period of ∼10 days; the addition of archival HST data extended the coverage up to ∼150 days after the GRB. We report the first detection of the afterglow in NIR bands. The detection of Balmer and oxygen emission lines in the optical spectrum of the host galaxy indicates that the GRB is located at redshift z = 0.691. Fe II and Mg II absorption systems are detected at z = 0.691 and at z = 0.472 in the afterglow optical spectrum. The latter system is likely caused by absorbing clouds in the galaxy complex located ∼2" southwest of the GRB020405 host. Hence, for the first time, the galaxy responsible for an intervening absorption line system in the spectrum of a GRB afterglow is spectroscopically identified. Optical and NIR photometry of the afterglow indicates that, between 1 and 10 days after the GRB, the decay in all bands is consistent with a single power law of index a = 1.54 ′0.06. The late-epoch VLT J-band and HST optical points lie above the extrapolation of this power law, so that a plateau (or "bump") is apparent in the VRIJ light curves at 10-20 days after the GRB. The light curves at epochs later than day ∼20 after the GRB are consistent with a power-law decay with index α' = 1.85 ′ 0.15. While other authors have proposed to reproduce the bump with the template of the supernova (SN) 1998bw, considered the prototypical "hypernova", we suggest that it can also be modeled with a SN having the same temporal profile as the other proposed hypernova SN2002ap, but 1.3 mag brighter at peak, and located at the GRB redshift. Alternatively, a shock re-energization may be responsible for the rebrightening. A single polarimetric R-band measurement shows that the afterglow is polarized, with P = 1.5 ′ 0.4% and polarization angle 0 = 172° ′8°. Broad-band optical-NIR spectral flux distributions show, in the first days after the GRB, a change of slope across the J band which we interpret as due to the presence of the electron cooling frequency v c . The analysis of the multiwavelength spectrum within the standard fireball model suggests that a population of relativistic electrons with index p ∼ 2.7 produces the optical-NIR emission via synchrotron radiation in an adiabatically expanding blastwave, with negligible host galaxy extinction, and the X-rays via Inverse Compton scattering off lower-frequency afterglow photons.