A low-latency pipeline for GRB light curve and spectrum using Fermi/GBM near real-time data

14 pages, 8 figures. The paper has been accepted by Research in Astronomy and Astrophysics (RAA)Rapid response and short time latency are very important for Time Domain Astronomy, such as the observations of Gamma-ray Bursts (GRBs) and electromagnetic (EM) counterparts of gravitational waves (GWs). Based on near real-time Fermi/GBM data, we developed a low-latency pipeline to automatically calculate the temporal and spectral properties of GRBs. With this pipeline, some important parameters can be obtained, such as T and fluence, within ∼ 20 min after the GRB trigger. For ∼ 90% of GRBs, T and fluence are consistent with the GBM catalog results within 2σ errors. This pipeline has been used by the Gamma-ray Bursts Polarimeter (POLAR) and the Insight Hard X-ray Modulation Telescope (Insight-HXMT) to follow up the bursts of interest. For GRB 170817A, the first EM counterpart of GW events detected by Fermi/GBM and INTEGRAL/SPI-ACS, the pipeline gave T and spectral information 21 min after the GBM trigger, providing important information for POLAR and Insight-HXMT observations. © 2018 National Astronomical Observatories, CAS and IOP Publishing Ltd..We thank the anonymous reviewer for helpful comments and suggestions. This work is supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB23040400), the National Natural Science Foundation of China (Grant Nos. 11403026, 11503028 and 11673023) and the National Basic Research Program of China (973 program, Grant No. 2014CB845800). BBZ acknowledges support from the National Thousand Young Talents programof China. We gratefully acknowledge support from the collaboration team of POLAR, a project funded by China National Space Administration (CNSA), the Chinese Academy of Sciences (CAS) and the University of Geneva (UNIGE). The authors would also like to thank Jing Jin, Jinlu Qu, Xiaobo Li, Youli Tuo, Zijian Li, Mingyu Ge, Jinyuan Liao, Guangcheng Xiao, Yue Huang and Chengkui Li for their suggestions on data analysis and the revision of this paper

X-ray reprocessing in accreting pulsar GX 301-2 observed with Insight-HXMT

We investigate the absorption and emission features in observations of GX 301-2 detected with Insight-HXMT/LE in 2017-2019. At different orbital phases, we found prominent Fe Kα, Kβ, and Ni Kα lines, as well as Compton shoulders and Fe K-shell absorption edges. These features are due to the X-ray reprocessing caused by the interaction between the radiation from the source and surrounding accretion material. According to the ratio of iron lines (Kα and Kβ), we infer the accretion material is in a low ionization state. We find an orbital-dependent local absorption column density, which has a large value and strong variability around the periastron. We explain its variability as a result of inhomogeneities of the accretion environment and/or instabilities of accretion processes. In addition, the variable local column density is correlated with the equivalent width of the iron Kα lines throughout the orbit, which suggests that the accretion material near the neutron star is spherically distributed

Switches between accretion structures during flares in 4U 1901+03

We report on our analysis of the 2019 outburst of the X-ray accreting pulsar 4U 1901+03 observed with Insight-HXMT and NICER. Both spectra and pulse profiles evolve significantly in the decaying phase of the outburst. Dozens of flares are observed throughout the outburst. They are more frequent and brighter at the outburst peak. We find that the flares, which have a duration from tens to hundreds of seconds, are generally brighter than the persistent emission by a factor of -1.5. The pulse-profile shape during the flares can be significantly different from that of the persistent emission. In particular, a phase shift is clearly observed in many cases. We interpret these findings as direct evidence of changes of the pulsed beam pattern, due to transitions between the sub- and supercritical accretion regimes on a short time-scale. We also observe that at comparable luminosities the flares’ pulse profiles are rather similar to those of the persistent emission. This indicates that the accretion on the polar cap of the neutron star is mainly determined by the luminosity, i.e. the mass accretion rate

Very early photo of Alta Lodge about 1940

Very early photo of Alta Lodge about 194