一种估算微弱源AstroSat/LAXPC背景的替代方案
An alternative scheme to estimate AstroSat/LAXPC background for faint sources
摘要：
描述了一种替代方案，用于估计第1层LAXPC 20的微弱源背景，其中源对50-80 keV计数率的贡献小于0.25计数/秒（15毫克拉或$6 \times 10^{-11}$尔格/秒/厘米$^2$）。我们考虑12空白天空观测和基于他们的50-80千电子伏计数率在100秒的时间箱，产生四个模板光谱，然后用于估计背景光谱和光曲线为一个给定的微弱源观测。12个空白天空观测的估计背景扣除光谱的方差被视为能量依赖的系统不确定性，其将在超过5 ksec的曝光的统计上占主导地位。在4-20 keV波段估算的100秒时槽背景光曲线与空白天空光曲线相吻合，系统误差为3%.对于具有通量$\gtrapprox 1$毫蟹的源，可以约束4-20 keV谱。对于在100秒处分组的$\sim 5$毫蟹源光变曲线，可以确定10\%的分数r.m.s变异性。为了说明这一方案，本文给出了三个不同的空天观测结果，即三个活动星系核源（Mrk 0926、Mrk 110、NGC 4593）和大麦哲伦星系X-1的光变曲线和光谱。
英文摘要：
An alternative scheme is described to estimate the layer 1 LAXPC 20 background for faint sources where the source contribution to the 50-80 keV count rate is less than 0.25 counts/sec (15 milli-crabs or $6 \times 10^{-11}$ ergs/s/cm$^2$). We consider 12 blank sky observations and based on their 50-80 keV count rate in 100 second time-bins, generate four template spectra which are then used to estimate the background spectrum and lightcurve for a given faint source observation. The variance of the estimated background subtracted spectra for the 12 blank sky observations is taken as the energy dependent systematic uncertainty which will dominate over the statistical one for exposures longer than 5 ksecs. The estimated 100 second time bin background lightcurve in the 4-20 keV band with a 3\% systematic error matches with the blank sky ones. The 4-20 keV spectrum can be constrained for a source with flux $\gtrapprox 1$ milli-crab. Fractional r.m.s variability of 10\% can be determined for a $\sim 5$ milli-crab source lightcurve binned at 100 seconds. To illustrate the scheme, the lightcurves, and spectra of three different blank sky observations, three AGN sources (Mrk 0926, Mrk 110, NGC 4593), and LMC X-1 are shown.
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