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Register a new userJ-GEM Follow-Up Observations of The Gravitational Wave Source GW151226
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We report the results of optical--infrared follow-up observations of the gravitational wave (GW) event GW151226 detected by the Advanced LIGO in the framework of J-GEM (Japanese collaboration for Gravitational wave ElectroMagnetic follow-up). We performed wide-field optical imaging surveys with Kiso Wide Field Camera (KWFC), Hyper Suprime-Cam (HSC), and MOA-cam3. The KWFC survey started at 2.26 days after the GW event and covered 778 deg$^2$ centered at the high Galactic region of the skymap of GW151226. We started the HSC follow-up observations from 12 days after the event and covered an area of 63.5 deg$^2$ of the highest probability region of the northern sky with the limiting magnitudes of 24.6 and 23.8 for i band and z band, respectively. MOA-cam3 covered 145 deg$^2$ of the skymap with MOA-red filter 2.5 months after the GW alert. Total area covered by the wide-field surveys was 986.5 deg$^2$. The integrated detection probability of all the observed area was $sim$29%. We also performed galaxy-targeted observations with six optical and near-infrared telescopes from 1.61 days after the event. Total of 238 nearby (<100 Mpc) galaxies were observed with the typical I band limiting magnitude of $sim$19.5. We detected 13 supernova candidates with the KWFC survey, and 60 extragalactic transients with the HSC survey. Two third of the HSC transients were likely supernovae and the remaining one third were possible active galactic nuclei. With our observational campaign, we found no transients that are likely to be associated with GW151226.
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We present our optical follow-up observations to search for an electromagnetic counterpart of the first gravitational wave source GW150914 in the framework of the Japanese collaboration for Gravitational wave ElectroMagnetic follow-up (J-GEM), which is an observing group utilizing optical and radio telescopes in Japan, as well as those in New Zealand, China, South Africa, Chile, and Hawaii. We carried out a wide-field imaging survey with Kiso Wide Field Camera (KWFC) on the 1.05-m Kiso Schmidt telescope in Japan and a galaxy-targeted survey with Tripole5 on the B&C 61-cm telescope in New Zealand. Approximately 24 deg2 regions in total were surveyed in i-band with KWFC and 18 nearby galaxies were observed with Tripole5 in g-, r-, and i-bands 4-12 days after the gravitational wave detection. Median 5-sigma depths are i~18.9 mag for the KWFC data and g~18.9 mag, r~18.7 mag, and i~18.3 mag for the Tripole5 data. Probability for a counterpart to be in the observed area is 1.2% in the initial skymap and 0.1% in the final skymap. We do not find any transient source associated to an external galaxy with spatial offset from its center, which is consistent with the local supernova rate. We summarize future prospects and ongoing efforts to pin down electromagnetic counterparts of binary black hole mergers as well as neutron star mergers.
The Advanced LIGO observatory recently reported the first direct detection of gravitational waves (GW) which triggered ALIGO on 2015 September 14. We report on observations taken with the Swift satellite two days after the trigger. No new X-ray, optical, UV or hard X-ray sources were detected in our observations, which were focussed on nearby galaxies in the GW error region and covered 4.7 square degrees (~2% of the probability in the rapidly-available GW error region; 0.3% of the probability from the final GW error region, which was produced several months after the trigger). We describe the rapid Swift response and automated analysis of the X-ray telescope and UV/Optical Telescope data, and note the importance to electromagnetic follow up of early notification of the progenitor details inferred from GW analysis.
Gravitational Wave (GW) events are physical processes that significantly perturbate space-time, e.g. compact binary coalescenses, causing the production of GWs. The detection of GWs by a worldwide network of advanced interferometers offer unique opportunities for multi-messenger searches and electromagnetic counterpart associations. While carrying extremely useful information, searches for associated electromagnetic emission are challenging due to large sky localisation uncertainties provided by the current GW observatories LIGO and Virgo. Here we present the methods and procedures used within the High Energy Stereoscopic System (H.E.S.S.) in searches for very-high-energy (VHE) gamma-ray emission associated to the emission of GWs from extreme events. To do so we create several algorithms dedicated to schedule GW follow-up observations by creating optimized pointing paterns. We describe algorithms using 2-dimensional GW localisation information and algorithms correlating the galaxy distribution in the local universe, by using galaxy catalogs, with the 3-dimensional GW localisation information and evaluate their performances. The H.E.S.S. automatic GW follow-up chain, described in this paper, is optimized to initiate GW follow-up observations within less than 1 minute after the alert reception. These developements allowed H.E.S.S. observations of 6 GW events out of the 67 non-retracted GW events detected during the first three observation runs of LIGO and Virgo reaching VHE $gamma$-ray coverages of up to 70% of the GW localisation.
The electromagnetic (EM) emission associated with a gravitational wave (GW) signal is one of the main goal of future astronomy. Merger of neutron stars and/or black holes and core-collapse of massive stars are expected to cause rapid transient electromagnetic signals. The EM follow-up of GW signals will have to deal with large position uncertainties. The gravitational sky localization is expected to be tens to hundreds of square degrees. Wide-field cameras and rapid follow-up observations will be crucial to characterize the EM candidates for the first EM counterpart identification. We present some of the activities that we are currently carrying on to optimize the response of the INAF network of facilities to expected GW triggers. The INAF network will represent an efficient operational framework capable of fast reaction on large error box triggers and direct identification and characterization of the candidates.
The Laser Interferometer Gravitational-wave Observatory Scientific Collaboration and Virgo Collaboration (LVC) sent out 56 gravitational-wave (GW) notices during the third observing run (O3). Japanese collaboration for Gravitational wave ElectroMagnetic follow-up (J-GEM) performed optical and near-infrared observations to identify and observe an electromagnetic (EM) counterpart. We constructed web-based system which enabled us to obtain and share information of candidate host galaxies for the counterpart, and status of our observations. Candidate host galaxies were selected from the GLADE catalog with a weight based on the three-dimensional GW localization map provided by LVC. We conducted galaxy-targeted and wide-field blind surveys, real-time data analysis, and visual inspection of observed galaxies. We performed galaxy-targeted follow-ups to 23 GW events during O3, and the maximum probability covered by our observations reached to 9.8%. Among them, we successfully started observations for 10 GW events within 0.5 days after the detection. This result demonstrates that our follow-up observation has a potential to constrain EM radiation models for a merger of binary neutron stars at a distance of up to $sim$100~Mpc with a probability area of $leq$ 500~deg$^2$.
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