论文标题

用Swift-XRT从Cygnus Cocoon发出的Leptonic TeV发射的限制

Limits on Leptonic TeV Emission from the Cygnus Cocoon with Swift-XRT

论文作者

Guevel, David, Beardmore, Andrew, Page, Kim L, Lien, Amy, Fang, Ke, Tibaldo, Luigi, Casanova, Sabrina, Huentemeyer, Petra

论文摘要

Cygnus Cocoon是Cygnus X恒星形成区域的扩展源的$γ$ - 射线观测,这表明存在宇宙射线加速器的存在,达到了最多可达的能量。高能(VHE; 0.1-100〜TEV)$γ$ -Ray的发射可以通过宇宙射线Hadron与茧内部物质的相互作用来解释,但是不能排除相对论电子逆向辐射的起源。 VHE的倒数compton $γ$ -rays伴随着同步辐射在X射线中达到峰值。因此,X射线观测可能会探测源的电子总体和磁场。我们在Cygnus Cocoon内或附近观察到110 ksec的Cygnus Cocoon或附近的11个田地。我们将磁场拟合到银河系和半河外背景模型,并为其他漫射剂组件进行了对数可能性比率测试。我们发现没有明显的额外排放,并且在每个磁场中建立了上限。通过假设X射线强度跟踪TEV强度并遵循$ dn/de \ propto e^{ - 2.5} $ spectrum,我们获得了$ f_x <8.7 \ 8.7 \ times 10^{ - 11} { - 11} \ rm〜erg \ rm〜erg \ erg^erg \ erg \,cm^,cm^{ - 2}的90 \%上限, 10^{ - 11} \ rm〜Erg \,cm^{ - 2} \,s^{ - 1} $在整个Cygnus Cocoon的X射线通量上,取决于2至10 keV之间的X射线通量,具体取决于选择氢柱密度模型的选择。这表明,当假定$ \ sim 20 \,μ$ g时,在1 TEV处的$γ$ ray通量的四分之一是由compton散射产生的。

$γ$-ray observations of the Cygnus Cocoon, an extended source surrounding the Cygnus X star-forming region, suggest the presence of a cosmic ray accelerator reaching energies up to a few PeV. The very-high-energy (VHE; 0.1-100~TeV) $γ$-ray emission may be explained by the interaction of cosmic-ray hadrons with matter inside the Cocoon, but an origin of inverse Compton radiation by relativistic electrons cannot be ruled out. Inverse Compton $γ$-rays at VHE are accompanied by synchrotron radiation peaked in X-rays. Hence, X-ray observations may probe the electron population and magnetic field of the source. We observed eleven fields in or near the Cygnus Cocoon with the Neil Gehrels Swift Observatory's X-Ray Telescope (Swift-XRT) totaling 110 ksec. We fit the fields to a Galactic and extra-galactic background model and performed a log-likelihood ratio test for an additional diffuse component. We found no significant additional emission and established upper limits in each field. By assuming that the X-ray intensity traces the TeV intensity and follows an $dN/dE\propto E^{-2.5}$ spectrum, we obtained a 90\% upper limit of $F_X < 8.7\times 10^{-11}\rm~erg\,cm^{-2}\,s^{-1}$ or $< 5.2\times 10^{-11}\rm~erg\,cm^{-2}\,s^{-1}$ on the X-ray flux of the entire Cygnus Cocoon between 2 and 10 keV depending on the choice of hydrogen column density model. This suggests that no more than one quarter of the $γ$-ray flux at 1 TeV is produced by inverse Compton scattering, when assuming an equipartition magnetic field of $\sim 20\,μ$G.

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