arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1707.08653astro-ph.HEastro-ph.GA
收藏

分子云作为费米Gamma-Ray GeV-Excess的起源

Molecular Clouds as the Origin of the Fermi Gamma-Ray GeV-Excess

Wim de Boer, Leo Bosse, Iris Gebauer, Alexander Neumann, Peter Biermann

摘要:

用基于能谱的谱模板拟合研究了银河系弥散γ射线辐射的所谓“GeV-过剩”。光谱模板可以从伽马射线数据中以数据驱动的方式获得,这避免了使用发射率模型从数据中减去标准背景过程。相反,人们可以用任何天空方向的任何“信号”同时确定这些背景,包括银河系盘和银河系中心。使用光谱模板拟合的“GeV过量”的两个假设进行了测试:暗物质(DM)假设的过量是由DM湮灭和分子云(MC)假设的“GeV过量”是与消耗的伽马射线低于2 GeV,是直接观察到的中央分子区(CMZ)。这两种假设都提供了可接受的拟合,如果考虑以银河系中心周围20 $^\circ$为中心的有限视场,并对能量范围进行削减和/或排除低纬度,DM假设的支持者通常会采用这种削减。然而,如果考虑整个伽马射线天空,并包括高达100 GeV的伽马射线能量,我们发现MC假设优于DM假设,原因有几个:i)MC假设提供了明显更好的拟合; ii)“GeV过量”的形态遵循CO图的形态,这是MC的示踪剂,也就是说,在银河系盘中存在着一个强的“GeV-过剩”,在大半径处也是如此; iii)具有$l \times b = 3.5^{\circ} \times 0.5^{\circ}$的矩形视场的大质量CMZ示出了在2 GeV处扩散伽马射线谱中的每个对数箱的最大能通量,即“GeV过量”,已经在原始数据中没有任何分析。矩形轮廓与DM湮灭所预期的球形形态相矛盾。

英文摘要:

The so-called "GeV-excess" of the diffuse Galactic gamma-ray emission is studied with a spectral template fit based on energy spectra. The spectral templates can be obtained in a data-driven way from the gamma-ray data, which avoids the use of emissivity models to subtract the standardbackground processes from the data. Instead, one can determine these backgrounds simultaneously with any "signals" in any sky direction, including the Galactic disk and the Galactic center. Using the spectral template fit two hypothesis of the "GeV-excess" were tested: the dark matter (DM) hypothesis assuming the excess is caused by DM annihilation and the molecular cloud (MC) hypothesis assuming the "GeV-excess" is related to a depletion of gamma-rays below 2 GeV, as is directly observed in the Central Molecular Zone (CMZ). Both hypotheses provide acceptable fits, if one considers a limited field-of-view centered within 20$^\circ$ around the Galactic center and applies cuts on the energy range and/or excludes low latitudes, cuts typically applied by the proponents of the DM hypothesis. However, if one considers the whole gamma-ray sky and includes gamma-ray energies up to 100 GeV we find that the MC hypothesis is preferred over the DM hypothesis for several reasons: i) The MC hypothesis provides significantly better fits; ii) The morphology of the "GeV-excess" follows the morphology of the CO-maps, a tracer of MCs, i.e. there exists a strong "GeV-excess" in the Galactic disk also at large longitudes; iii) The massive CMZ with a rectangular field-of-view of $l \times b = 3.5^{\circ} \times 0.5^{\circ}$ shows the maximum of the energy flux per log bin in the diffuse gamma-ray spectrum at 2 GeV, i.e. the "GeV-excess", already in the raw data without any analysis. The rectangular profile contradicts the spherical morphology expected for DM annihilation.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑