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arXiv 1203.6545astro-ph.HE
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探索未识别的VHE gamma-ray源HESS J1507-622的性质

Exploring the nature of the unidentified VHE gamma-ray source HESS J1507-622

Wilfried Domainko, Stefan Ohm

摘要:

第一个身份不明的VHE伽马射线源的性质与显着的角度偏离银河平面的3.5度,HESS J1507-622,进行了探讨。利用34个月收集的高能(He,100 MeV < E < 100 GeV)γ射线的Fermi-LAT数据描述了源的能谱分布(SED)。HESS J1507-622在费米能区被探测到,它的光谱最好用能量的幂律来描述,伽马=1.7 +/- 0.1 stat +/- 0.2_sys,积分通量在(0.3-300)GeV之间,F =(2.0 +/-0.5_stat +/- 1.0_sys)x 10^-9 cm^-2 s^-1。根据现有的数据,不可能区分HESS J1507-622的强子和轻子情况。源的位置和紧凑性表明该物体从银河平面有相当大的物理偏移。在数kpc距离的情况下,这对HESS J1507-622的脉冲星风星云(PWN)起源提出了挑战,因为在银河系盘中出生的脉冲星到达这样一个位置的旅行时间将超过能量足以产生VHE伽马射线的电子的逆康普顿(IC)冷却时间。然而,这个伽马射线源的起源与一颗脉冲星有关,而这颗脉冲星是在一颗超高速恒星的爆炸中从银河系平面诞生的。到目前为止,HESS J1507-622的性质仍然未知,一般不能排除PWN场景。相反,HESS J1507-622可能是第一个被发现的代表空间扩展的VHE伽马射线发射器与HE伽马射线对应物的种群,它们位于距离银河平面相当大的偏移处。未来的调查在VHE伽马射线范围是必要的,以探测存在或不存在这样的源人口。(节略)

英文摘要:

The nature of the first unidentified VHE gamma-ray source with significant angular offset from the Galactic plane of 3.5 degrees, HESS J1507-622, is explored. Fermi-LAT data in the high-energy (HE, 100 MeV < E < 100 GeV) gamma-ray range collected over 34 month are used to describe the spectral energy distribution (SED) of the source. HESS J1507-622 is detected in the Fermi energy range and its spectrum is best described by a power law in energy with Gamma=1.7 +/- 0.1 stat +/- 0.2_sys and integral flux between (0.3-300) GeV of F = (2.0 +/-0.5_stat +/- 1.0_sys) x 10^-9 cm^-2 s^-1. With the available data it is not possible to discriminate between a hadronic and a leptonic scenario for HESS J1507-622. The location and compactness of the source indicate a considerable physical offset from the Galactic plane for this object. In case of a multiple-kpc distance, this challenges a pulsar wind nebula (PWN) origin for HESS J1507-622 since the time of travel for a pulsar born in the Galactic disk to reach such a location would exceed the inverse Compton (IC) cooling time of electrons that are energetic enough to produce VHE gamma-rays. However, an origin of this gamma-ray source connected to a pulsar that was born off the Galactic plane in the explosion of a hypervelocity star cannot be excluded. The nature of HESS J1507-622 is still unknown to date, and a PWN scenario cannot be ruled out in general. On the contrary HESS J1507-622 could be the first discovered representative of a population of spatially extended VHE gamma-ray emitters with HE gamma-ray counterpart that are located at considerable offsets from the Galactic plane. Future surveys in the VHE gamma-ray range are necessary to probe the presence or absence of such a source population.(abridged)

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