GROND multi-color imaging of the GRB 161219B / SN 2016jca field.

This folder contains optical/near-infrared imaging of the field of GRB 161219B (Swift trigger 727541; D'Ai, GCN #20296) collected simultaneously with the Gamma-Ray Burst Optical/Near Infrared imager (GROND; Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPG telescope on ESO's LaSilla observatory. These data include a time-series of SN 2016jca following GRB 161219B with nearly daily monitoring around peak, and are published in Cano et al. 2017 (arXiv:1704.05401).<br><br>The data were obtained in the grizJHK photometric bands. They were collected over a period of several nights starting from 2016-12-20, and consisted of several dithered images that are stacked to yield one fits image per epoch per band. <br><br>Data were automatically processed with the GROND pipeline, which uses standard procedures in python/pyraf/IRAF (see e.g., Kruehler et al. 2008, ApJ, 685, 376). The data are sky-subtracted and astrometrically calibrated against the Pan-STARRS or GAIA catalogs.<br><br>Critical information can be found in the fits header, the following keywords are particularly useful:<br><br>- EXPTIME = Exposure time of a single image<br>- NIMGS = Total number of images combined<br>- COMBINE = How the images were combined<br>- IMGEXP = Summed exposure of the image<br>- MJD-MID = Midtime of the image<br>- FILTER = Filter band of the observation<br>- AIRMASS = Average airmass of the observation<br>- FWHM = FWHM of the stellar PSF<br>- ASTRRMS1 = Uncertainty of the astrometric solution in RA<br>- ASTRRMS2 = Uncertainty of the astrometric solution in DEC<br>- MAGLIM = Limiting magnitude of the image<br>- INTERPSM = Individual images are resampled during shifting and adding, this number describes an empirical estimate by what factor the noise is smoothed (i.e., too low as estimated by the rms in the image). In particular in the NIR bands, standard procedure will underestimate the photometric error by this factor.<br>

本文件夹包含GRB 161219B天区（Swift触发727541；D'Ai，GCN #20296）的光学/近红外成像数据，该数据由安装在欧洲南方天文台（ESO）拉西拉天文台2.2米MPG望远镜上的伽马射线暴光学/近红外成像仪（GROND; Greiner et al. 2008, PASP 120, 405）同步获取。本数据集包含伴随GRB 161219B的超新星SN 2016jca的时间序列观测，在光变峰值附近实现了近乎每日的监测，相关研究成果发表于Cano et al. 2017（arXiv:1704.05401）。

本次观测采用grizJHK测光波段进行数据采集，观测时段从2016年12月20日起持续数个夜晚，通过对多幅抖动（dithered）图像进行堆叠处理，得到每个观测历元、每个滤光波段对应的单幅FITS（Flexible Image Transport System）图像。

数据通过GROND数据处理管道自动完成定标，该管道采用python/pyraf/IRAF中的标准流程（参见Kruehler et al. 2008, ApJ, 685, 376）。所有数据均已扣除天空背景，并基于Pan-STARRS或GAIA星表完成天体测量定标。

关键观测信息可在FITS文件头中查询，以下关键字尤为实用：
- EXPTIME：单幅图像的曝光时间
- NIMGS：合并的总图像数量
- COMBINE：图像合并方法
- IMGEXP：该图像的总曝光时间
- MJD-MID：图像观测的中间时刻
- FILTER：观测所用的滤光片波段
- AIRMASS：观测的平均大气质量
- FWHM：恒星点扩散函数（Point Spread Function, PSF）的半高全宽（Full Width at Half Maximum, FWHM）
- ASTRRMS1：天体测量解在赤经（Right Ascension, RA）方向的不确定度
- ASTRRMS2：天体测量解在赤纬（Declination, DEC）方向的不确定度
- MAGLIM：图像的极限星等
- INTERPSM：单幅图像在移位与叠加过程中会被重采样，该数值为噪声平滑因子的经验估计值（即根据图像均方根误差估算的偏低值）。尤其在近红外波段，标准流程会按此因子低估测光误差。