SUZAKU X-RAY IMAGING OF THE EXTENDED LOBE IN THE GIANT RADIO GALAXY NGC 6251 ASSOCIATED WITH THE FERMI-LAT SOURCE 2FGL J1629.4+8236
SUZAKU X-RAY IMAGING OF THE EXTENDED LOBE IN THE GIANT RADIO GALAXY NGC 6251 ASSOCIATED WITH THE FERMI-LAT SOURCE 2FGL J1629.4+8236
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DOI：
10.1088/0004-637x/749/1/66
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发表时间：
2012-02
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通讯作者：
Y. Takeuchi;J. Kataoka;Ł. Stawarz;Ł. Stawarz;Y. Takahashi;K. Maeda;T. Nakamori;C. Cheung;C. Cheung;A. Celotti;Yasuyuki T. Tanaka;Tadayuki Takahashi
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作者：
Y. Takeuchi;J. Kataoka;Ł. Stawarz;Ł. Stawarz;Y. Takahashi;K. Maeda;T. Nakamori;C. Cheung;C. Cheung;A. Celotti;Yasuyuki T. Tanaka;Tadayuki Takahashi
我们报告了NGC 6251的朱雀X射线成像研究结果，NGC 6251是一个邻近的巨型射电星系，具有中等FR I/II射电性质。我们的指向集中在最近用费米大面积望远镜（LAT）发现的γ射线发射峰上，该峰位于西北（NW）射电瓣的位置，距离核15弧分。在减去邻近射电瓣的两个“离源”点并去除X射线成像光谱仪视场中可能的污染物后，我们发现显著的残余X射线发射很可能在自然界中扩散。过剩X射线辐射的光谱符合幂律，光子指数Γ = 1.90 ± 0.15，0.5-8 keV的通量为4 × 10−13 erg cm−2 s−1。我们解释这个扩散的X射线发射分量是由于逆康普顿上散射的宇宙微波背景光子的超相对论电子内的瓣，只有一个小的贡献，从大规模的喷流的光束发射。利用源的存档无线电数据，我们通过宽带谱模拟证明，费米LAT源2FGL J1629.4+8236的γ射线通量可以很好地由波瓣的逆康普顿连续谱的高能尾部来解释。因此，NGC 6251西北瓣的γ射线与最近的半人马座A扩展瓣的费米-LAT成像一起，表明粒子可能被有效地（再）加速到超相对论能量，通常在附近射电星系的扩展射电瓣内。
We report the results of a Suzaku X-ray imaging study of NGC 6251, a nearby giant radio galaxy with intermediate FR I/II radio properties. Our pointing direction was centered on the γ-ray emission peak recently discovered with the Fermi Large Area Telescope (LAT) around the position of the northwest (NW) radio lobe 15 arcmin offset from the nucleus. After subtracting two “off-source” pointings adjacent to the radio lobe and removing possible contaminants in the X-ray Imaging Spectrometer field of view, we found significant residual X-ray emission most likely diffuse in nature. The spectrum of the excess X-ray emission is well fitted by a power law with a photon index Γ = 1.90 ± 0.15 and a 0.5–8 keV flux of 4 × 10−13 erg cm−2 s−1. We interpret this diffuse X-ray emission component as being due to inverse Compton upscattering of the cosmic microwave background photons by ultrarelativistic electrons within the lobe, with only a minor contribution from the beamed emission of the large-scale jet. Utilizing archival radio data for the source, we demonstrate by means of broadband spectral modeling that the γ-ray flux of the Fermi-LAT source 2FGL J1629.4+8236 may well be accounted for by the high-energy tail of the inverse Compton continuum of the lobe. Thus, this claimed association of γ-rays from the NW lobe of NGC 6251, together with the recent Fermi-LAT imaging of the extended lobes of Centaurus A, indicates that particles may be efficiently (re-)accelerated up to ultrarelativistic energies within extended radio lobes of nearby radio galaxies in general.