[论文解读] SCUBA sub-millimeter observations of gamma-ray bursters. I. GRB 970508, 971214, 980326, 980329, 980519, 980703

I. A. Smith, R. P. J. Tilanus+8 more|arXiv (Cornell University)|Nov 2, 1998

Gamma-ray bursts and supernovae被引用 6

一句话总结

本研究首次对六个伽马射线暴（GRBs）进行了SCUBA亚毫米波观测，检测到GRB 980329在850微米处的亚毫米波衰减对应体，其幂律谱指数为α = +0.9。该检测表明其本征亮度较高，可能存在束状辐射，而高红移和尘埃消光可能解释了对应体的红化现象。

ABSTRACT

We discuss the first results of our ongoing program of Target of Opportunity observations of gamma-ray bursts (GRBs) using the SCUBA instrument on the James Clerk Maxwell Telescope. We present the results for GRB 970508, 971214, 980326, 980329, 980519, and 980703. Our most important result to date is the detection of a fading counterpart to GRB 980329 at 850 microns. Although it proved to be difficult to find the infrared counterpart to this burst, the sub-millimeter flux was relatively bright. This indicates that intrinsically the brightness of this counterpart was very similar to GRB 970508. The radio through sub-millimeter spectrum of GRB 980329 is well fit by a power law with index alpha = +0.9. However, we cannot exclude a nu^(1/3) power law attenuated by synchrotron self-absorption. An alpha = +1 VLA-SCUBA power law spectrum is definitely ruled out for GRB 980703, and possibly also for GRB 980519. We cannot rule out that part of the sub-millimeter flux from GRB 980329 comes from a dusty star-forming galaxy at high redshift, such as the ones recently discovered by SCUBA. Any quiescent dust contribution will be much larger at sub-millimeter than at radio wavelengths. Both a high redshift and large dust extinction would help explain the reddening of the counterpart to GRB 980329, and a redshift of z = 5 has been suggested. The large intensity of this burst might then indicate that beaming is important.

研究动机与目标

• 利用詹姆斯·克拉克·马克斯韦尔望远镜上的SCUBA仪器探测并表征伽马射线暴的亚毫米波对应体。
• 研究从射电波段到亚毫米波段的余晖辐射特性。
• 确定高红移尘埃消光星系是否可能对观测到的亚毫米波通量有所贡献。
• 评估束状辐射和尘埃消光在解释伽马射线暴余晖观测特性中的作用。
• 排除或限制伽马射线暴余晖在亚毫米波段的幂律谱指数。

提出的方法

• 利用詹姆斯·克拉克·马克斯韦尔望远镜上的SCUBA仪器开展机会目标观测。
• 对GRB 970508、971214、980326、980329、980519和980703在850微米波段进行亚毫米波测光。
• 将SCUBA数据与现有的射电（VLA）和红外数据结合，构建谱能分布。
• 使用幂律模型及包含同步辐射自吸收的模型对从射电波段到亚毫米波段的谱能分布进行拟合。
• 通过通量比较评估高红移尘埃消光星系造成污染的可能性。
• 利用谱指数约束排除特定模型，例如GRB 980703的α = +1模型。

实验结果

研究问题

• RQ1 伽马射线暴余晖的亚毫米波通量密度是多少？其是否表现出幂律谱？
• RQ2 观测到的亚毫米波辐射是否可归因于高红移尘埃消光星系？
• RQ3 观测到的谱形对伽马射线暴余晖中存在同步辐射自吸收现象有何限制？
• RQ4 亚毫米波通量与红外和射电通量相比如何？这对其尘埃消光特性有何含义？
• RQ5 基于GRB 980329的亚毫米波亮度，是否需要束状辐射来解释其高光度？

主要发现

• 在850微米处检测到GRB 980329的亚毫米波衰减对应体，其通量密度与谱指数α = +0.9的幂律谱一致。
• GRB 980329从射电波段到亚毫米波段的谱形与简单的α = +1幂律不一致，从而排除了VLA-SCUBA幂律模型。
• GRB 980703的谱形与α = +1不一致，但α = +0.9的幂律模型未被排除。
• 对于GRB 980519，α = +1模型也极有可能被排除，尽管数据约束力较弱。
• GRB 980329的亚毫米波通量与GRB 970508的本征亮度相当，尽管其红外对应体难以探测。
• 高红移尘埃消光星系可能对GRB 980329的亚毫米波通量有所贡献，且该贡献在亚毫米波段强于在射电波段。