Fermi-GBM Data Release Related to Searches for Neutrinos from Gamma-Ray Bursts using the IceCube Neutrino Observatory

This data release includes Fermi Gamma-ray Burst Monitor (GBM) localizations used in searches for neutrinos from gamma-ray bursts (GRB) by the IceCube Neutrino Observatory. These localizations are provided publicly to the community since they are generally useful for any analysis that needs the Fermi-GBM localization for a GRB. <strong>Full Details:</strong> The files contained herein are HEALPix representations of GRB localizations from the Fermi-GBM stored as FITS files and produced according to the automated method described in [1]. Each file represents the probability density (statistical + systematic) for the true source location. By definition, this excludes the Earth occulted region of the sky, which is set to 0 due to the fact that real sources are not visible through the Earth. These files cover a time range spanning the first detection of GRBs by GBM in July 2008 through July 2019 and should be considered preliminary. The files are preliminary in the sense that they contain some key differences to the official files hosted at HEASARC FTP server through the Fermi Science Support Center (FSSC; https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/). We list the key differences here: Fermi began production HEALPix FITS files in early 2018, and files prior to that have not been officially provided. The files in this archive are currently the only version of HEALPix files pre-2018.<br> These files were not produced via the standard GBM operational pipeline; however they were produced with the same functional code that is used to make the files. The result of this is that the standard quality checks on the FITS headers by uploading to the FSSC were skipped. The primary header is most affected, with some null values, but these null values do not affect the HEALPix data.<br> These localizations may have centroids that are slightly different than reported in the online catalog. This is because an automated algorithm for localization (RoboBA) was used to localize the GRBs and produce these files as opposed to the manual Human-in-the-Loop localization performed for every GRB prior to 2016, and ~15% of GRBs thereafter [1].<br> These localizations contain an updated and improved systematic uncertainty model compared to the pre-July 2019 localizations at the FSSC. The new systematic uncertainty model is explained in [1], while the older localizations at the FSSC contain a systematic uncertainty model from [2].<br> In general, the official localizations hosted at the FSSC currently do not remove localization probability that overlaps the Earth, but these files do remove the probability that overlaps the Earth and renormalizes the remaining PDF. This encodes the assertion that the localization is indeed of an astrophysical nature. The FITS files are organized with two HDUs: PRIMARY HDU with some basic metadata about the mission from which the data originated<br> HEALPIX HDU containing header information about the GBM detector pointings, as well as the Sun and Geocenter localizations with respect to Fermi. There are two data fields contained in the extension: PROBABILITY: the differential localization probability per pixel (NSIDE=128) SIGNIFICANCE: integrated probability for estimating confidence intervals (NSIDE=128) Furthermore, we provide images of each localization. The images are a Mollweide projection of the sky, with the 50% and 90% localization confidence regions marked in shaded purple. The location of the Earth from Fermi's perspective is marked in shaded blue. The GBM trigger number associated with each FITS file and image is listed in the filename. <strong>References:</strong> [1] Goldstein, A. et al. 2020, ApJ, 895, 40<br> [2] Connaughton, V. et al. 2015, ApJS, 216, 32本数据集公开包含费米伽马射线暴监测器（Fermi Gamma-ray Burst Monitor, GBM）定位结果，此类结果被用于冰立方中微子天文台（IceCube Neutrino Observatory）开展的伽马射线暴（gamma-ray bursts, GRB）中微子搜寻研究。由于这类定位结果可广泛应用于任何需要伽马射线暴费米-GBM定位信息的分析工作，故本数据集面向全球天文社区共享。 <strong>详细说明：</strong>本数据集包含的文件为费米-GBM生成的伽马射线暴定位结果的HEALPix表示形式，以FITS格式存储，其生成方法遵循文献[1]中所述的自动化流程。每个文件均对应伽马射线暴真实源位置的概率密度分布（包含统计不确定度与系统不确定度）。根据定义，此类文件不包含地球掩蔽的天区区域，该区域的概率密度被设为0，因为真实天体无法穿透地球被观测到。本数据集覆盖的时间范围为2008年7月费米-GBM首次探测到伽马射线暴至2019年7月，且所有数据均为预发布版本。 本数据集文件为预发布版本，与费米科学支持中心（Fermi Science Support Center, FSSC）通过HEASARC FTP服务器托管的官方文件存在若干关键差异，官方文件地址为：https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/。现将关键差异说明如下： 费米于2018年初开始生成HEALPix格式的FITS文件，此前的伽马射线暴定位HEALPix文件从未正式发布。本存档中的文件是目前仅有的2018年之前的HEALPix格式定位文件。 本数据集文件并非通过费米-GBM标准运行流程生成，但所用代码与官方文件的生成代码完全一致。由于未通过FSSC上传进行FITS文件头的标准质量校验，主文件头存在部分空值，但此类空值不会影响HEALPix数据本身。 本数据集的定位结果质心可能与在线目录中公布的数值存在小幅偏差，原因在于本数据集采用自动化定位算法（RoboBA）完成伽马射线暴定位并生成文件；而2016年之前的所有伽马射线暴以及2016年之后约15%的伽马射线暴均采用人工参与的人机协同定位流程[1]。 与FSSC托管的2019年7月之前的官方定位结果相比，本数据集的定位结果采用了更新优化的系统不确定度模型。新的系统不确定度模型详见文献[1]，而FSSC托管的旧版定位结果采用的系统不确定度模型来自文献[2]。 总体而言，FSSC目前托管的官方定位结果并未移除与地球重叠的定位概率，但本数据集文件会移除该部分概率并对剩余的概率密度函数（Probability Density Function, PDF）进行重归一化，以此明确该定位结果仅针对天体物理源。 本数据集的FITS文件包含两个数据扩展单元（HDU）： PRIMARY HDU：包含数据来源任务的基础元数据 HEALPIX HDU：包含费米-GBM探测器指向、太阳以及相对于费米望远镜的地心定位相关的头文件信息。 该扩展单元包含两个数据字段： PROBABILITY：单个像素的微分定位概率（NSIDE=128） SIGNIFICANCE：用于估算置信区间的积分概率（NSIDE=128） 此外，本数据集还为每个定位结果提供了可视化图像。图像采用摩尔维德投影（Mollweide projection）绘制天区，其中50%和90%的定位置信区域以紫色阴影标注，费米望远镜视角下的地球位置以蓝色阴影标注。每个FITS文件及对应图像的GBM触发编号均包含在文件名中。 <strong>参考文献：</strong> [1] Goldstein, A. 等. 2020, 《天体物理学杂志》(ApJ), 895, 40 [2] Connaughton, V. 等. 2015, 《天体物理学杂志增刊》(ApJS), 216, 32