FERMI LARGE AREA TELESCOPE OBSERVATIONS OF THE SUPERNOVA REMNANT W28 (G6.4−0.1)
FERMI LARGE AREA TELESCOPE OBSERVATIONS OF THE SUPERNOVA REMNANT W28 (G6.4−0.1)
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DOI：
10.1088/0004-637x/718/1/348
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发表时间：
2010-05
期刊：
影响因子：
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通讯作者：
T. F. C. A. A. Abdo-T.-F.-C.-A.-A.-Abdo-102611352;et al.
中科院分区：
文献类型：
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作者：
T. F. C. A. A. Abdo-T.-F.-C.-A.-A.-Abdo-102611352;et al.
我们对两个伽马射线源 1FGL J1801.3−2322c 和 1FGL J1800.5−2359c 进行了详细分析，这两个伽马射线源是通过费米伽马射线太空望远镜上的大面积望远镜 (LAT) 在超新星遗迹 (SNR) W28 附近发现的。 1FGL J1801.3−2322c被发现是SNR W28边界内的扩展源，并且与TeV伽马射线源HESS J1801−233广泛重叠，后者与与SNR相互作用的致密分子云有关。使用 LAT 在 0.2 至 100 GeV 范围内测量的伽马射线能谱可以通过断断续续的幂律函数来描述，断断点为 ~1 GeV，断点以下的光子指数为 2.09 ± 0.08 (stat) ± 0.28 (sys)，断点以上的光子指数为 2.74 ± 0.06 (stat) ± 0.09 (sys)。鉴于 HESS J1801−233 与冲击分子云之间的明确关联以及 GeV-TeV 波段中平滑连接的光谱，我们认为 GeV 和 TeV 范围内的伽马射线发射的起源是在 SNR 中加速的粒子与分子云之间的相互作用。加速强子和致密分子气体之间相互作用产生的中性π介子的衰变为宽带伽马射线谱提供了合理的解释。 1FGL J1800.5−2359c 位于 SNR W28 南部边界之外，无法解析。假设表面亮度均匀的圆形，使用~2 GeV以上的事件，伽马射线发射尺寸的上限估计为~16'。它似乎与 TeV 源 HESS J1800−240B 一致，后者被认为与包含超致密 H ii 区域 W28A2 (G5.89−0.39) 的致密分子云有关。我们在 TeV 源 HESS J1800−230A 和 HESS J1800−230C 位置的 LAT 能带中没有发现明显的伽马射线发射。 HESS J1800−230A 的 LAT 数据与 TeV 数据点相结合表明 10 GeV 和 100 GeV 之间存在光谱中断。
We present detailed analysis of two gamma-ray sources, 1FGL J1801.3−2322c and 1FGL J1800.5−2359c, that have been found toward the supernova remnant (SNR) W28 with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. 1FGL J1801.3−2322c is found to be an extended source within the boundary of SNR W28, and to extensively overlap with the TeV gamma-ray source HESS J1801−233, which is associated with a dense molecular cloud interacting with the SNR. The gamma-ray spectrum measured with the LAT from 0.2 to 100 GeV can be described by a broken power-law function with a break at ∼1 GeV and photon indices of 2.09 ± 0.08 (stat) ± 0.28 (sys) below the break and 2.74 ± 0.06 (stat) ± 0.09 (sys) above the break. Given the clear association between HESS J1801−233 and the shocked molecular cloud and a smoothly connected spectrum in the GeV–TeV band, we consider the origin of the gamma-ray emission in both GeV and TeV ranges to be the interaction between particles accelerated in the SNR and the molecular cloud. The decay of neutral pions produced in interactions between accelerated hadrons and dense molecular gas provides a reasonable explanation for the broadband gamma-ray spectrum. 1FGL J1800.5−2359c, located outside the southern boundary of SNR W28, cannot be resolved. An upper limit on the size of the gamma-ray emission was estimated to be ∼16′ using events above ∼2 GeV under the assumption of a circular shape with uniform surface brightness. It appears to coincide with the TeV source HESS J1800−240B, which is considered to be associated with a dense molecular cloud that contains the ultra compact H ii region W28A2 (G5.89−0.39). We found no significant gamma-ray emission in the LAT energy band at the positions of TeV sources HESS J1800−230A and HESS J1800−230C. The LAT data for HESS J1800−230A combined with the TeV data points indicate a spectral break between 10 GeV and 100 GeV.