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arXiv 0710.5740astro-ph
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PG 1553+113的HESS观测和VLT光谱

HESS Observations and VLT Spectroscopy of PG 1553+113

HESS Collaboration, F. Aharonian

备注：
9 pages, 12 Figures; Accepted for publication in Astronomy & Astrophysics; (Revision has simple typo in table 1 MJD column corrected.)
发表信息：
Astrophys.J.661:236-249,2007
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摘要：

目的：研究BL Lac PG 1553+113的甚高能（VHE; E>100 GeV）γ射线发射特性。试图测量这个物体目前未知的红移。方法：于2005年和2006年使用高能立体视系统（HESS）对PG 1553+113进行VHE观察。PG 1553+113的H+K（1.45-2.45微米）光谱是在2006年3月用智利ESO甚大望远镜（VLT）的积分场光谱仪SINFONI进行的。结果：在2年的观察期间（24.8小时生存时间），HESS检测到VHE信号，约10个标准差。在300 GeV以上的积分通量为（4.6 +- 0.6{stat} +- 0.9{syst}）x 10^{-12} cm^{-2} s^{-1}，相当于蟹状星云超过相同阈值的通量的3.4%。测量的时间平均能谱从225 GeV到~1.3 TeV，其特征在于非常软的幂律（伽马的光子指数= 4.5 +- 0.3{stat} +- 0.1{syst}）。在VHE数据中的任何采样时间尺度上都没有发现任何通量或光谱变化的证据。PG 1553+113的红移无法确定。事实上，即使测量的SINFONI光谱是有史以来报道的该物体在近红外波长下最灵敏的光谱，并且灵敏度与其他波长下的最佳光谱相当，但在这里呈现的H+K光谱中没有发现吸收或发射线。

英文摘要：

AIMS: The properties of the very high energy (VHE; E>100 GeV) gamma-ray emission from the high-frequency peaked BL Lac PG 1553+113 are investigated. An attempt is made to measure the currently unknown redshift of this object. METHODS: VHE Observations of PG 1553+113 were made with the High Energy Stereoscopic System (HESS) in 2005 and 2006. H+K (1.45-2.45 micron) spectroscopy of PG 1553+113 was performed in March 2006 with SINFONI, an integral field spectrometer of the ESO Very Large Telescope (VLT) in Chile. RESULTS: A VHE signal, ~10 standard deviations, is detected by HESS during the 2 years of observations (24.8 hours live time). The integral flux above 300 GeV is (4.6 +- 0.6{stat} +- 0.9{syst}) x 10^{-12} cm^{-2} s^{-1}, corresponding to ~3.4% of the flux from the Crab Nebula above the same threshold. The time-averaged energy spectrum is measured from 225 GeV to ~1.3 TeV, and is characterized by a very soft power law (photon index of Gamma = 4.5 +- 0.3{stat} +- 0.1{syst}). No evidence for any flux or spectral variations is found on any sampled time scale within the VHE data. The redshift of PG 1553+113 could not be determined. Indeed, even though the measured SINFONI spectrum is the most sensitive ever reported for this object at near infrared wavelengths, and the sensitivity is comparable to the best spectroscopy at other wavelengths, no absorption or emission lines were found in the H+K spectrum presented here.

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