A gravitational-wave (GW) transient was identified in data recorded by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) detectors on 2015 September 14. The event, initially designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground-and space-based facilities. In this Letter we describe the low-latency analysis of the GW data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network circulars, giving an overview of the participating facilities, the GW sky localization coverage, the timeline, and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic (EM) signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the EM data and results of the EM follow-up campaign are being disseminated in papers by the individual teams.
ABSTRACTwhich falls in the planetary-mass regime. This is the first discovery of a planetary companion orbiting a G-type giant star.
We report a development of a multi-color simultaneous camera for the 188cm telescope at Okayama Astrophysical Observatory in Japan. The instrument, named MuSCAT, has a capability of 3-color simultaneous imaging in optical wavelength where CCDs are sensitive. MuSCAT is equipped with three 1024×1024 pixel CCDs, which can be controlled independently. The three CCDs detect lights in g ′ 2 (400-550 nm), r ′ 2 (550-700 nm), and z s,2 (820-920 nm) bands using Astrodon Photometrics Generation 2 Sloan filters. The field of view of MuSCAT is 6.1×6.1 arcmin 2 with the pixel scale of 0.358 arcsec per pixel. The principal purpose of MuSCAT is to perform high precision multi-color transit photometry. For the purpose, MuSCAT has a capability of self autoguiding which enables to fix positions of stellar images within ∼1 pix. We demonstrate relative photometric precisions of 0.101%, 0.074%, and 0.076% in g ′ 2 , r ′ 2 , and z s,2 bands, respectively, for GJ436 (magnitudes in g ′ =11.81, r ′ =10.08, and z ′ =8.66) with 30 s exposures. The achieved precisions meet our objective, and the instrument is ready for operation.
We present optical (g ′ , R c , and I c ) to near-infrared (J) simultaneous photometric observations for a primary transit of GJ3470b, a Uranus-mass transiting planet around a nearby M dwarf, by using the 50-cm MITSuME telescope and the 188-cm telescope both at Okayama Astrophysical Observatory. From these data, we derive the planetary mass, radius, and density as 14.1 ± 1.3 M ⊕ , 4.32 +0.21 −0.10 R ⊕ , and 0.94 ± 0.12 g cm −3 , respectively, thus confirming the low density that was reported by Demory et al. based on the Spitzer/IRAC 4.5-µm photometry (0.72 +0.13 −0.12 g cm −3 ). Although the planetary radius is about 10% smaller than that reported by Demory et al., this difference does not alter their conclusion that the planet possesses a hydrogen-rich envelope whose mass is approximately 10% of the planetary total mass. On the other hand, we find that the planet-to-star radius ratio (R p /R s ) in the J band (0.07577 +0.00072 −0.00075 ) is smaller than that in the I c (0.0802 ± 0.0013) and 4.5-µm (0.07806 +0.00052 −0.00054 ) bands by 5.8% ± 2.0% and 2.9% ± 1.1%, respectively. A plausible explanation for the differences is that the planetary atmospheric opacity varies with wavelength due to absorption and/or scattering by atmospheric molecules. Although the significance of the observed R p /R s variations is low, if confirmed, this fact would suggest that GJ3470b does not have a thick cloud layer in the atmosphere. This property would offer a wealth of opportunity for future transmission-spectroscopic observations of this planet to search for certain molecular features, such as H 2 O, CH 4 , and CO, without being prevented by clouds. Subject headings: planetary systems -planets and satellites: atmosphere -planets and satellites:individual(GJ3470b) -stars: individual(GJ3470) -techniques: photometric
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