On joint analysing XMM-NuSTAR spectra of active galactic nuclei  

活动星系核XMM-NuSTAR光谱的联合分析

作　　者：Jialai Kang Junxian Wang 康嘉来;王俊贤(中国科学技术大学天文学系中国科学院星系宇宙学重点实验室,安徽合肥230026;中国科学技术大学天文与空间科学学院,安徽合肥230026)

机构地区：[1]CAS Key Laboratory for Research in Galaxies and Cosmology,Department of Astronomy,University of Science and Technology of China,Hefei 230026,China [2]School of Astronomy and Space Science,University of Science and Technology of China,Hefei 230026,China

出　　处：《中国科学技术大学学报》2024年第7期19-33,18,I0002,共17页JUSTC

基　　金：supported by the National Natural Science Foundation of China(12033006,12192221,123B2042).

摘　　要：A recently released XMM-Newton note revealed a significant calibration issue between nuclear spectroscopic telescope array(NuSTAR)and XMM-Newton European Photon Imaging Camera(EPIC)and provided an empirical correction to the EPIC effective area.To quantify the bias caused by the calibration issue in the joint analysis of XMM-NuSTAR spectra and verify the effectiveness of the correction,in this work,we perform joint-fitting of the NuSTAR and EPIC-pn spectra for a large sample of 104 observation pairs of 44 X-ray bright active galactic nuclei(AGN).The spectra were extracted after requiring perfect simultaneity between the XMM-Newton and NuSTAR exposures(merging good time intervals(GTIs)from two missions)to avoid bias due to the rapid spectral variability of the AGN.Before the correction,the EPIC-pn spectra are systematically harder than the corresponding NuSTAR spectra by■subsequently yielding significantly underestimated cutoff energy E_(cut)and the strength of reflection component R when performing joint-fitting.We confirm that the correction is highly effective and can commendably erase the discrepancy in best-fitΓ,E_(cut),and R.We thus urge the community to apply the correction when joint-fitting XMM-NuSTAR spectra,but note that the correction is limited to 3–12 keV and therefore not applicable when the soft X-ray band data are included.Besides,we show that as merging GTIs from two missions would cause severe loss of NuSTAR net exposure time,in many cases,joint-fitting yields no advantage compared with utilizing NuSTAR data alone.Finally,We present a technical note on filtering periods of high background flares for XMM-Newton EPIC-pn exposures in the small window(SW)mode.XMM-Newton望远镜近期发布的技术说明指出NuSTAR望远镜与XMM-Newton EPIC设备之间存在一显著的校准问题,并提供了一种对EPIC有效面积的经验性改正方法。为了定量刻画这种校准问题给联合分析XMMNuSTAR光谱带来的偏差并确认相应改正方法的有效性,在本工作中我们针对包含44个X射线明亮的活动星系核的104次观测对开展了NuSTAR和XMM EPIC-pn光谱的联合拟合。所抽取的XMM-NuSTAR光谱具有绝对的同时性(通过合并两个设备的GTI文件),以避免活动星系核快速光谱光变带来的影响。在改正之前,EPIC-pn的光谱比相应的NuSTAR光谱系统性的硬(ΔΓ~0.1),因此在联合拟合时导致了显著被低估的截断能量E_(cut)及反射成分强度R。我们确认了经验性改正非常有效,很好地消除了Γ,E_(cut)及R的最佳拟合值的偏差。因此,我们呼吁社群在联合拟合XMM-NuSTAR光谱时应用此改正;不过需要注意此改正仅对3–12 keV的数据有效,因此在使用软X射线波段数据时不适用。此外,我们展示了由于匹配两个设备的GTI会导致NuSTAR净曝光时间的严重损失,联合拟合相对于只利用NuSTAR数据在许多情况下并没有优势。最后,我们提供了一个过滤XMM-Newton EPIC-pn小窗模式下高背景时间段的技术说明。

关 键 词：active galactic nuclei X-ray spectroscopy XMM-NEWTON NuSTAR cross-calibration issue 

分 类 号：P141.5[天文地球—天体物理]