J-GEM follow-up observations to search for an optical counterpart of the first gravitational wave source GW150914

Gravitational waves from a merger of two neutron stars (NSs) were discovered for the first time in GW170817, together with diverse electromagnetic (EM) counterparts. To make constraints on a relativistic jet from the NS merger, we calculate the EM signals in (1) the short gamma-ray burst sGRB 170817A from an off-axis jet, (2) the optical-infrared macronova (or kilonova), especially the blue macronova, from a jetpowered cocoon, and (3) the X-ray and radio afterglows from the interaction between the jet and interstellar medium. We find that a typical sGRB jet is consistent with these observations, and there is a parameter space to explain all the observations in a unified fashion with an isotropic energy ∼ 10 51 -10 52 erg, opening angle ∼ 20 • , and viewing angle ∼ 30 • . The off-axis emission is less de-beamed than the point-source case because the viewing angle is comparable to the opening angle. We also analytically show that the jet energy accelerates a fair fraction of the merger ejecta to a sub-relativistic velocity ∼ 0.3-0.4c as a cocoon in a wide parameter range. The ambient density might be low ∼ 10 −3 -10 −6 cm −3 , which can be tested by future observations of radio flares and X-ray remnants.

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“…Then the cross section of the jet at the breakout time is Σ j ∼ π(∆θcβ e t br ) 2 , so that Eqs. (12), (13), and (14) yield…”

Section: /25mentioning

confidence: 99%

Can an off-axis gamma-ray burst jet in GW170817 explain all the electromagnetic counterparts?

Ioka

Nakamura

2018

Progress of Theoretical and Experimental Physics

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“…We conducted coordinated observations in the framework of Japanese collaboration for Gravitational-wave Electro-Magnetic follow-up (J-GEM) (Morokuma et al 2016;Yoshida et al 2017;Utsumi et al in press) immediately after the discovery of the strong candidate SSS17a and investigated the characteristics of the optical and NIR emission. In this paper, we present the results of the J-GEM follow-up observations of SSS17a.…”

Section: Introductionmentioning

confidence: 99%

J-GEM observations of an electromagnetic counterpart to the neutron star merger GW170817

Utsumi¹,

Tanaka²,

Tominaga³

et al. 2017

Publications of the Astronomical Society of Japan

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198

105

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The first detected gravitational wave from a neutron star merger was GW170817. In this study, we present J-GEM follow-up observations of SSS17a, an electromagnetic counterpart of GW170817. SSS17a shows a 2.5-mag decline in the z-band from 1.7 days to 7.7 days after the merger. Such a rapid decline is not comparable with supernovae light curves at any epoch. The color of SSS17a also evolves rapidly and becomes redder for later epochs; the z − H color changed by approximately 2.5 mag in the period of 0.7 days to 7.7 days. The rapid evolution of both the optical brightness and the color are consistent with the expected properties of a kilonova that is powered by the radioactive decay of newly synthesized r-process nuclei. Kilonova models with Lanthanide elements can reproduce the aforementioned observed properties well, which suggests that r-process nucleosynthesis beyond the second peak takes place in SSS17a. However, the absolute magnitude of SSS17a is brighter than the expected brightness of the kilonova models with the ejecta mass of 0.01 M ⊙ , which suggests a more intense mass ejection (∼ 0.03M ⊙ ) or possibly an additional energy source.

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“…TRIPOL should be especially useful to investigate variability phenomena on timescales from a few seconds to years or longer. These include, but not limited to, gravitational-wave counterparts (Morokuma et al 2016), gammaray bursts, cataclysmic variables, eclipsing binaries, Cepheids, novae, supernovae, blazars, Miras, and T Tauri stars (Chen et al 2015;Huang et al 2019).…”

Section: Scientific Demonstrationmentioning

confidence: 99%

Triple Range Imager and POLarimeter (TRIPOL)—a compact and economical optical imaging polarimeter for small telescopes

Sato

Huang

Chen

et al. 2019

Res. Astron. Astrophys.

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We report the design concept and performance of a compact, light-weight, and economic imaging polarimeter, TRIPOL (the Triple Range Imager and POLarimeter), capable of simultaneous optical imagery and polarimetry. TRIPOL splits the beam from wavelength 400 to 830 nm into g ′ -, r ′ -, and i ′ -bands with two dichroic mirrors, and measures polarization with an achromatic half-waveplate and a wire-grid. The simultaneity makes TRIPOL a useful tool for small telescopes for photometry and polarimetry of time variable and wavelength dependent phenomena. TRIPOL is devised for a Cassegrain telescope of an aperture of ∼1 m. This paper presents the engineering considerations of TRIPOL and compares the expected with the observed performance. Using the Lulin 1-m telescope and 100 seconds integration, the limiting magnitudes are g ′ ∼ 19.0 mag, r ′ ∼ 18.5 mag and i ′ ∼ 18.0 mag with a signal-to-noise of 10, in agreement with design expectation. The instrumental polarization is measured to be ∼ 0.3% at three bands. Two applications, one to the star-forming cloud IC 5146, and the other to the young variable GM Cep, are presented as demonstration.

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J-GEM follow-up observations to search for an optical counterpart of the first gravitational wave source GW150914

Cited by 32 publications

References 58 publications

Can an off-axis gamma-ray burst jet in GW170817 explain all the electromagnetic counterparts?

Can an off-axis gamma-ray burst jet in GW170817 explain all the electromagnetic counterparts?

J-GEM observations of an electromagnetic counterpart to the neutron star merger GW170817

Triple Range Imager and POLarimeter (TRIPOL)—a compact and economical optical imaging polarimeter for small telescopes

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