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Register a new userRATIR Followup of LIGO/Virgo Gravitational Wave Events
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Recently we have witnessed the first multi-messenger detection of colliding neutron stars through Gravitational Waves (GWs) and Electromagnetic (EM) waves (GW170817), thanks to the joint efforts of LIGO/Virgo and Space/Ground-based telescopes. In this paper, we report on the RATIR followup observation strategies and show the results for the trigger G194575. This trigger is not of astrophysical interest; however, is of great interests to the robust design of a followup engine to explore large sky error regions. We discuss the development of an image-subtraction pipeline for the 6-color, optical/NIR imaging camera RATIR. Considering a two band ($i$ and $r$) campaign in the Fall of 2015, we find that the requirement of simultaneous detection in both bands leads to a factor $sim$10 reduction in false alarm rate, which can be further reduced using additional bands. We also show that the performance of our proposed algorithm is robust to fluctuating observing conditions, maintaining a low false alarm rate with a modest decrease in system efficiency that can be overcome utilizing repeat visits. Expanding our pipeline to search for either optical or NIR detections (3 or more bands), considering separately the optical $riZ$ and NIR $YJH$ bands, should result in a false alarm rate $approx 1%$ and an efficiency $approx 90%$. RATIRs simultaneous optical/NIR observations are expected to yield about one candidate transient in the vast 100 $mathrm{deg^2}$ LIGO error region for prioritized followup with larger aperture telescopes.
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We investigate the effects of observatory locations on the probability of discovering optical/infrared counterparts of gravitational wave sources. We show that for the LIGO--Virgo network, the odds of discovering optical/infrared (OIR) counterparts show some latitude dependence, but weak or no longitudinal dependence. A stronger effect is seen to arise from the timing of LIGO/Virgo observing runs, with northern OIR observatories having better chances of finding the counterparts in northern winters. Assuming identical technical capabilities, the tentative mid-2017 three-detector network observing favors southern OIR observatories for discovery of EM counterparts.
The Super-Kamiokande detector can be used to search for neutrinos in time coincidence with gravitational waves detected by the LIGO-Virgo Collaboration (LVC). Both low-energy ($7-100$ MeV) and high-energy ($0.1-10^5$ GeV) samples were analyzed in order to cover a very wide neutrino spectrum. Follow-ups of 36 (out of 39) gravitational waves reported in the GWTC-2 catalog were examined; no significant excess above the background was observed, with 10 (24) observed neutrinos compared with 4.8 (25.0) expected events in the high-energy (low-energy) samples. A statistical approach was used to compute the significance of potential coincidences. For each observation, p-values were estimated using neutrino direction and LVC sky map ; the most significant event (GW190602_175927) is associated with a post-trial p-value of $7.8%$ ($1.4sigma$). Additionally, flux limits were computed independently for each sample and by combining the samples. The energy emitted as neutrinos by the identified gravitational wave sources was constrained, both for given flavors and for all-flavors assuming equipartition between the different flavors, independently for each trigger and by combining sources of the same nature.
In this work we continue a line of inquiry begun in Kanner et al. which detailed a strategy for utilizing telescopes with narrow fields of view, such as the Swift X-ray Telescope (XRT), to localize gravity wave (GW) triggers from LIGO/Virgo. If one considers the brightest galaxies that produce ~50% of the light, then the number of galaxies inside typical GW error boxes will be several tens. We have found that this result applies both in the early years of Advanced LIGO when the range is small and the error boxes large, and in the later years when the error boxes will be small and the range large. This strategy has the beneficial property of reducing the number of telescope pointings by a factor 10 to 100 compared with tiling the entire error box. Additional galaxy count reduction will come from a GW rapid distance estimate which will restrict the radial slice in search volume. Combining the bright galaxy strategy with a convolution based on anticipated GW localizations, we find that the searches can be restricted to about 18+/-5 galaxies for 2015, about 23+/-4 for 2017, and about 11+/-2 for 2020. This assumes a distance localization at or near the putative NS-NS merger range for each target year, and these totals are integrated out to the range. Integrating out to the horizon would roughly double the totals. For nearer localizations the totals would decrease. The galaxy strategy we present in this work will enable numerous sensitive optical and X-ray telescopes with small fields of view to participate meaningfully in searches wherein the prospects for rapidly fading afterglow place a premium on a fast response time.
The field of gravitational-wave astronomy has been opened up by gravitational-wave observations made with interferometric detectors. This review surveys the current state-of-the-art in gravitational-wave detectors and data analysis methods currently used by the Laser Interferometer Gravitational-Wave Observatory in the United States and the Virgo Observatory in Italy. These analysis methods will also be used in the recently completed KAGRA Observatory in Japan. Data analysis algorithms are developed to target one of four classes of gravitational waves. Short duration, transient sources include compact binary coalescences, and burst sources originating from poorly modelled or unanticipated sources. Long duration sources include sources which emit continuous signals of consistent frequency, and many unresolved sources forming a stochastic background. A description of potential sources and the search for gravitational waves from each of these classes are detailed.
The detection of the gravitational wave events GW150914, GW151226, LVT 151012 and GW170104 by the Advanced LIGO antennas has opened a new possibility for the study of fundamental physics of gravitational interaction. We suggest a new method for determining the polarization state of a gravitational wave, which is independent of the nature of a GW source. For this, we calculate the allowed sky positions of GW sources along apparent circles. This is done for each polarization state by considering the sensitivity pattern of each antenna and relative amplitudes of detected signals. The positions of circles are calculated with respect to the line joining both LIGO antennas using the observed arrival time delay of the signal between them. The apparent circles (AC) on the sky for allowed positions of the GW sources for the GW150914, GW151226 and LVT151012 events are parallel to the plane of the disc-like large scale structure known as the Local Super-Cluster (LSC) of galaxies which extends up to radius $sim 100$ Mpc and having thickness $sim 30$ Mpc. For the GW170104 event, the AC is perpendicular to the LSC plane but the predicted position of the source may also belong to the LSC plane, which is consistent with detection of possible optical counterpart ATLAS17aeu. The next aLIGO-aVirgo observing runs are proposed to test the possibility of clustering the GW sources along the LSC plane.
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