[论文解读] A Persistent High-Energy Flux from the Heart of the Milky Way : Integral's view of the Galactic Center

G. Bélanger, A. Goldwurm+7 more|ArXiv.org|Aug 4, 2005

Astrophysics and Cosmic Phenomena参考文献 67被引用 52

一句话总结

本文基于国际伽马射线天文台（INTEGRAL）卫星的高能X射线与软伽马射线观测，揭示了银河系中心Sgr A*附近1角分内存在一个持续的、弥漫的、非热辐射区域。结合Isgri与XMM-Newton的数据，首次获得了20–400 keV能量范围内的精确宽能谱，其光度为(5.37 ± 0.21) × 10³⁵ erg s⁻¹，且无显著变异性，表明该源并非点状天体，而是一个紧凑的扩展发射区，很可能与超新星遗迹Sgr A East相关。

ABSTRACT

The Ibis/Isgri imager on Integral detected for the first time a hard X-ray source, IGR J17456-2901, located within 1' of Sgr A* over the energy range 20-100 keV. Here we present the results of a detailed analysis of ~7 Ms of Integral observations of the GC. With an effective exposure of 4.7 Ms we have obtained more stringent positional constraints on this HE source and constructed its spectrum in the range 20-400 keV. Furthermore, by combining the Isgri spectrum with the total X-ray spectrum corresponding to the same physical region around SgrA* from XMM data, and collected during part of the Integral observations, we constructed and present the first accurate wide band HE spectrum for the central arcmins of the Galaxy. Our complete analysis of the emission properties of IGR shows that it is faint but persistent with no variability above 3 sigma contrary to what was alluded to in our first paper. This result, in conjunction with the spectral characteristics of the X-ray emission from this region, suggests that the source is most likely not point-like but, rather, that it is a compact, yet diffuse, non-thermal emission region. The centroid of IGR is estimated to be R.A.=17h45m42.5, decl.=-28deg59'28'', offset by 1' from the radio position of Sgr A* and with a positional uncertainty of 1'. Its 20-400 keV luminosity at 8 kpc is L=5.4x10^35 erg/sec. Very recently, Hess detected of a source of ~TeV g-rays also located within 1' of Sgr A*. We present arguments in favor of an interpretation according to which the photons detected by Integral and Hess arise from the same compact region of diffuse emission near the central BH and that the supernova remnant Sgr A East could play an important role as a contributor of very HE g-rays to the overall spectrum from this region.

研究动机与目标

• 利用长时间的INTEGRAL观测，表征银河系中心的高能辐射特征。
• 确定探测到的硬X射线源IGR J17456–2901是否为点状源或扩展源，以及其是否随时间变化。
• 结合INTEGRAL与XMM-Newton数据，为银河系中心区域构建从1 keV到400 keV的连续宽能谱。
• 探究高能辐射的起源，特别是其与已知结构（如Sgr A East）及HESS探测到的TeV伽马射线源之间的关联。
• 排除热等离子体、X射线暂现源或Sgr A*耀发活动等其他解释。

提出的方法

• 分析为期两年、总计4.7 × 10⁶秒的INTEGRAL Isgri观测数据，聚焦于20–400 keV能量范围。
• 利用精确天球测量（赤经 = 17h45m42.5s，赤纬 = -28°59′28″ J2000）将硬X射线源IGR J17456–2901与射电源Sgr A*进行交叉识别。
• 将Isgri数据与XMM-Newton X射线谱（1–10 keV）结合，生成银河系中心区域的连续宽能谱。
• 应用谱拟合技术，将辐射建模为热辐射或非热辐射，并利用显著性阈值（3σ）评估变异性。
• 将观测谱与已知源（包括1E 1743.1–2853和Sgr A East）进行比较，评估其对总通量的贡献。
• 利用JEM-X数据（3′角分辨率）检验是否存在点状发射，未检测到信号，支持该源为弥漫源的解释。

实验结果

研究问题

• RQ1 基于形态与变异性特征，硬X射线源IGR J17456–2901是点状源还是扩展源？
• RQ2 银河系中心持续的20–400 keV辐射的起源是什么？其与已知源相比有何特征？
• RQ3 观测谱是否可由热等离子体、X射线暂现源或Sgr A*耀发活动解释？
• RQ4 INTEGRAL与HESS在Sgr A*附近探测到的TeV伽马射线之间是否存在物理关联？
• RQ5 超新星遗迹Sgr A East是否可能是高能辐射的主要贡献者？

主要发现

• 硬X射线源IGR J17456–2901并非点状源，而是一个尺寸为数角分的紧凑、弥漫发射区。
• 在两年观测期间，该源在3σ以上无显著变异性，表明其通量具有持续性。
• IGR J17456–2901在20–400 keV能量范围的光度为(5.37 ± 0.21) × 10³⁵ erg s⁻¹，距离为8 kpc。
• 结合Isgri与XMM-Newton的谱数据排除了人马座复合体中热等离子体作为主要辐射源的可能性。
• 该源无法由已知的X射线暂现源或Sgr A*耀发活动解释，因其软X射线通量远低于类似双星系统（如1E 1743.1–2853）的水平。
• 对511 keV电子-正电子湮灭线通量设定3σ上限为1.9 × 10⁻⁴ ph cm⁻² s⁻¹。