MAXI upper limits of the electromagnetic counterpart of GW170817

Abstract

We report the MAXI observation of the gravitational-wave (GW) event GW170817 and the electromagnetic counterpart of GW170817. GW170817 is a binary neutron star coalescence candidate detected by the Advanced LIGO and Advanced Virgo detectors, and it is the first event for which the optical counterpart has been discovered. In the MAXI observation, the Gas Slit Camera (GSC) covered approximately 62% of the sky region of the GW event within 90% probability during the first 92 min of orbit after the trigger. No significant X-ray transient was detected in the error region, and the upper limit of the average flux with a significance of 3 σ in the 2-10 keV band was 53/26 mCrab (one-orbit observation/one-day observation). In the optical counterpart of GW170817, the observational window of GSC at the position started at 20 s after the GW trigger, but the high voltage of GSC was unfortunately off at the time because the ISS was entering a high-particle-background region. The first observation of the position by GSC was eventually performed at 16797 sec (4.6 hours) since the GW trigger, yielding the 3 σ upper limit of 8.60×10 −9 erg cm −2 s −1 in the 2-10 keV band, though it was the earliest X-ray observation of the counterpart.

ALMA and GMRT Constraints on the Off-axis Gamma-Ray Burst 170817A from the Binary Neutron Star Merger GW170817

“…Although the chance coincidence of finding both transients quasi-contemporaneous and in the same region of the sky is very small, the credible region of the γ-ray localization had a size of ∼1100deg 2 (90% confidence; Blackburn et al 2017). To firmly establish the connection between GRB 170817A and GW170817 by detecting the afterglow of the GRB in the X-ray and radio bands, numerous groups carried out large follow-up campaigns to very deep limits, but without success (e.g., Alexander et al 2017a;Bannister et al 2017;Cenko et al 2017;De et al 2017;Deller et al 2017;Evans et al 2017a;Kaplan et al 2017;Margutti et al 2017;Resmi et al 2017;Sugita et al 2017). It was not until nine days after GW170817 that a brightening X-ray source was detected at the position of AT2017gfo (Troja et al 2017a).…”

Multi-messenger astrophysics with THESEUS in the 2030s

“…In the case of GW170817/GRB 170817A, no evidence for a SDPT was found in the soft X-ray band. However, the first deep pointed observations at ∼keV photon energies only started as late as ∼ 15 h after merger with Swift/XRT [96], and the earlier constraints provided by MAXI 4.6 h after merger with a flux limit of 8.6 × 10 −9 erg/(cm 2 s) [97] were not able to exclude a SDPT. The combination of the THESEUS/SXI sensitivity at keV energies and its field of view about 10 4 times larger than Swift/XRT will offer much better prospects for a detection within minutes/hours after a GW trigger.…”

Multi-Messenger Astrophysics with THESEUS in the 2030s

“…In the case of GW170817/GRB 170817A, no evidence for a SDPT was found in the soft X-ray band. However, the first deep pointed observations at ∼keV photon energies only started as late as ∼ 15 h after merger with Swift/XRT [94], and the earlier constraints provided by MAXI 4.6 h after merger with a flux limit of 8.6 × 10 −9 erg/(cm 2 s) [95] were not able to exclude a SDPT. The combination of the THESEUS/SXI sensitivity at keV energies and its field of view about 10 4 times larger than Swift/XRT will offer much better prospects for a detection within minutes/hours after a GW trigger.…”

“…Radioactive decay of the newlyformed and unstable heavy nuclei powers a rapidly evolving, nearly isotropic thermal transient known as a ''kilonova'', the observation of which not only witnesses cosmic nucleosynthesis of heavy elements, but can also probe the physical conditions during and after the merger phase [92]. So far, the only robust observation of a kilonova, among a few other candidates [93], was the optical and infrared counterpart of GW170817, named AT2017gfo ( [94], [95], [96], [97]). With an exposure of ~150 s, an AT2017gfo-like kilonova would be detectable by THESEUS/IRT for a NS-NS merger up to ~200 Mpc away (Figure 2-17).…”