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SCIENCE CHINA Physics, Mechanics & Astronomy, Volume 61 , Issue 3 : 031011(2018) https://doi.org/10.1007/s11433-017-9107-5

Insight-HXMT observations of the first binary neutron star merger GW170817

(The Insight-HXMT team) , TiPei Li 1,2,3, ShaoLin Xiong 1, ShuangNan Zhang 1,3,*, FangJun Lu 1, LiMing Song 1, XueLei Cao 1, Zhi Chang 1, Gang Chen 1, Li Chen 4, TianXiang Chen 1, Yong Chen 1, YiBao Chen 2, YuPeng Chen 1, Wei Cui 1,2, WeiWei Cui 1, JingKang Deng 2, YongWei Dong 1, YuanYuan Du 1, MinXue Fu 2, GuanHua Gao 1,3, He Gao 1,3, Min Gao 1, MingYu Ge 1, YuDong Gu 1, Ju Guan 1, ChengCheng Guo 1,3, DaWei Han 1, Wei Hu 1, Yue Huang 1, Jia Huo 1, ShuMei Jia 1, LuHua Jiang 1, WeiChun Jiang 1, Jing Jin 1, YongJie Jin 5, Bing Li 1, ChengKui Li 1, Gang Li 1, MaoShun Li 1, Wei Li 1, Xian Li 1, XiaoBo Li 1, XuFang Li 1, YanGuo Li 1, ZiJian Li 1,3, ZhengWei Li 1, XiaoHua Liang 1, JinYuan Liao 1, CongZhan Liu 1, GuoQing Liu 2, HongWei Liu 1, ShaoZhen Liu 1, XiaoJing Liu 1, Yuan Liu 1, YiNong Liu 5, Bo Lu 1, XueFeng Lu 1, Tao Luo 1, Xiang Ma 1, Bin Meng 1, Yi Nang 1,3, JianYin Nie 1, Ge Ou 1, JinLu Qu 1, Na Sai 1,3, Liang Sun 1, Yin Tan 1, Lian Tao 1, WenHui Tao 1, YouLi Tuo 1,3, GuoFeng Wang 1, HuanYu Wang 1, Juan Wang 1, WenShuai Wang 1, YuSa Wang 1, XiangYang Wen 1, BoBing Wu 1, Mei Wu 1, GuangCheng Xiao 1,3, He Xu 1, YuPeng Xu 1, LinLi Yan 1,3, JiaWei Yang 1, Sheng Yang 1, YanJi Yang 1, AiMei Zhang 1, ChunLei Zhang 1, ChengMo Zhang 1, Fan Zhang 1, HongMei Zhang 1, Juan Zhang 1, Qiang Zhang 1, Shu Zhang 1, Tong Zhang 1, Wei Zhang 1,3, WanChang Zhang 1, WenZhao Zhang 4, Yi Zhang 1, Yue Zhang 1,3, YiFei Zhang 1, YongJie Zhang 1, Zhao Zhang 2, ZiLiang Zhang 1, HaiSheng Zhao 1, JianLing Zhao 1, XiaoFan Zhao 1,3, ShiJie Zheng 1, Yue Zhu 1, YuXuan Zhu 1, ChangLin Zou 1
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  • ReceivedOct 9, 2017
  • AcceptedOct 13, 2017
  • PublishedOct 16, 2017
PACS numbers

Abstract

Finding the electromagnetic (EM) counterpart of binary compact star merger, especially the binary neutron star (BNS) merger, is critically important for gravitational wave (GW) astronomy, cosmology and fundamental physics. On Aug. 17, 2017, Advanced LIGO and Fermi/GBM independently triggered the first BNS merger, GW170817, and its high energy EM counterpart, GRB 170817A, respectively, resulting in a global observation campaign covering gamma-ray, X-ray, UV, optical, IR, radio as well as neutrinos. The High Energy X-ray telescope (HE) onboard Insight-HXMT (Hard X-ray Modulation Telescope) is the unique high-energy gamma-ray telescope that monitored the entire GW localization area and especially the optical counterpart (SSS17a/AT2017gfo) with very large collection area (~1000 cm2) and microsecond time resolution in 0.2-5 MeV. In addition, Insight-HXMT quickly implemented a Target of Opportunity (ToO) observation to scan the GW localization area for potential X-ray emission from the GW source. Although Insight-HXMT did not detect any significant high energy (0.2-5 MeV) radiation

from GW170817, its observation helped to confirm the unexpected weak and soft nature of GRB 170817A. Meanwhile, Insight-HXMT/HE provides one of the most stringent constraints (~10‒7 to 10‒6 erg/cm2/s) for both GRB170817A and any other possible precursor or extended emissions in 0.2-5 MeV, which help us to better understand the properties of EM radiation from this BNS merger. Therefore the observation of Insight-HXMT constitutes an important chapter in the full context of multi-wavelength and multi-messenger observation of this historical GW event.


Funded by

This work made use of the data from the Insight-HXMT mission

a project funded by China National Space Administration(CNSA)

Chinese Academy of Sciences (CAS). the National Program on Key Research and Development Project(2016YFA0400800) from the Minister of Science and Technology of China (MOST)

Strategic Priority Research Program of the Chinese Academy of Sciences(XDB23040400)

the Hundred Talent Program of Chinese Academy of Sciences

National Natural Science Foundation of China(11233001,11503027,11403026)


Acknowledgment

This work made use of the data from the Insight-HXMT mission, a project funded by China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). This work was supported by the National Program on Key Research and Development Project (Grant No. 2016YFA0400800) from the Ministry of Science and Technology of China (MOST), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB23040400), the Hundred Talent Program of Chinese Academy of Sciences, the National Natural Science Foundation of China (Grant Nos. 11233001, 11503027, 11403026, 11473027, and 11733009).


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  • Figure 1

    (a) Insight-HXMT is composed of HE, ME and LE telescopes. Coordinates used in this paper are shown on the upper left. Incident angle theta is the angle between line-of-sight to the source and the Z axis. Azimuthal angle phi equals 0 deg for the X axis, and 90 deg for the Y axis. (b) The design of NaI/CsI detector. Slat collimators (not shown) are placed above the Be window.

  • Figure 2

    Simulated total effective area of 18 HE CsI detectors for GRB detection in regular mode (a) and GRB mode (b). Each line represents the effective area for each theta angle averaged in azimuthal (phi angle from 0 to 360 deg).

  • Figure 3

    Light curves of GRB 170904A (a) and GRB 170921C (b) detected by Insight-HXMT/HE.

  • Figure 4

    (a) The sky area monitored by HE for gamma-ray transients when GW170817 happened. The whole area of Fermi/GBM localization, LVC location and the optical counterpart SSS17a was not occulted by the Earth. (b) Evolution of the Earth angle of the GW source within T0±5000 s. Earth angle < 67.3 means the source was occulted by the Earth. Gray area indicates the SAA passage when HE was turned off. Blue lines are time intervals when HE monitored the GW source (SSS17a).

  • Figure 5

    Light curves of 18 HE CsI detectors around GW170817 and GRB 170817A. From (a) to (d) the time ranges and bin widths are: [T0‒2.5 s, T0+1.5 s] and 0.05 s; [T0‒5 s, T0+5 s] and 0.2 s; [T0‒50 s, T0+50 s] and 1 s; [T0‒650 s, T0+450 s] and 5 s, respectively. No significant excess above background variation is found. The bump from T0‒100 s to T0+100 s is caused by charged particles in orbit, as indicated by the bump in the same time interval in the ACD light curve (gray).

  • Figure 6

    Simulated counts rate of 18 CsI detectors for GRB170817A using the GBM spectrum [20], GW incident angles and the corrected effective area (see sect. 2.3). In the 2 s duration of GRB170817A, the total count expected to be detected by HE is ~50, which is well within the 1-σ statistical fluctuation (~120) of the background in Figure 5.

  • Figure 7

    Crab pulse profile accumulated in the calibration observation, normalized with the maximum 1 and minimum 0. Phase 0 represents the position of the X-ray main peak observed by the HE NaI detector.

  • Figure 8

    Insight-HXMT upper limits (3σ) for GRB170817A, precursor and extended emission with various time-scales (width of the upper limit bar). Only results for three Comptonized models (see Table 1) are shown. See Table 2 for comprehensive upper limit results for all spectral models.

  • Table 1   Spectral models are used for the upper limits calculation

    Spectral model

    Alpha

    Beta

    Epeak (keV)

    Band_1

    ‒1.9

    ‒3.7

    70

    Band_2

    ‒1.0

    ‒2.3

    230

    Band_3

    0.0

    ‒1.5

    1000

    Comp_1

    ‒1.9

    70

    Comp_2

    ‒1.0

    230

    Comp_3

    0.0

    1000

    PL_1

    ‒2.0

    PL_2

    ‒1.5

    PL_3

    ‒1.0

  • Table 2   Insight-HXMT upper limits in 0.2-5 MeV (3) for different time-scales and spectral models (see ) for GRB170817A and other possible precursor and extended emission. _start and _end are the start and end time (relative to T0) of the assumed emission component to calculate the upper limits

    Upper limits

    (erg/cm2/s)

    T_start (s)

    T_end (s)

    Band_1

    Band_2

    Band_3

    Comp_1

    Comp_2

    Comp_3

    PL_1

    PL_2

    PL_3

    GRB170817A

    ‒0.30

    0.00

    1.4×10‒6

    1.9×10‒6

    3.4×10‒6

    1.3×10‒6

    1.2×10‒6

    3.0×10‒6

    2.2×10‒6

    2.8×10‒6

    2.1×10‒6

    GRB170817A

    0.00

    0.25

    1.6×10‒6

    2.2×10‒6

    3.6×10‒6

    1.6×10‒6

    1.4×10‒-6

    3.3×10‒6

    2.6×10‒6

    3.1×10‒6

    2.3×10‒6

    Precursor

    ‒400.05

    ‒399.95

    2.3×10‒6

    3.1×10‒6

    4.8×10-6

    2.3×10‒6

    2.1×10‒6

    4.4×10‒6

    3.6×10‒6

    4.1×10‒6

    2.9×10‒6

    Precursor

    ‒400.5

    ‒399.5

    7.7×10‒7

    1.1×10‒6

    1.8×10‒6

    7.5×10‒7

    6.8×10‒7

    1.7×10‒6

    1.3×10‒6

    1.7×10‒6

    1.1×10‒6

    Extended

    299.5

    300.5

    8.9×10‒7

    1.2×10‒6

    2.0×10‒6

    8.7×10‒7

    7.9×10‒7

    1.8×10‒6

    1.4×10‒6

    1.8×10‒6

    1.2×10‒6

    Extended

    295

    305

    3.1×10‒7

    4.3×10‒7

    6.4×10‒7

    3.0×10‒7

    2.8×10‒7

    6.1×10‒7

    5.2×10‒7

    6.1×10‒7

    4.1×10‒7