Studies On The Detection Capability And Observation Strategy For Kilonovae

With the construction and running of the second generation of laser gravitational waves detectors,LIGO and Virgo,people succeeded in observing gravitational waves directly and verified the general relativity directly.As a new method of observation,gravitational waves help people to detect and study the binary compact stars merger in a new messenger way.Till now,for the binary compact stars mergers that are detected by gravitational waves detectors,LIGO and Virgo,the masses range of compact stars vary from neutron star of stellar mass to black holes of hundreds of stellar masses.On August 17,2017,LIGO and Virgo detected a binary neutron star merger event via gravitational waves emission and a short gamma-ray burst was detected 1.74 s after the gravitational waves signal.After this merger event,people successfully observed its optical counterpart in the UV,optical,and NIR for 30 days.The luminosity of binary compact stars(binary neutron stars or neutron star black hole)merger is usually 1000 times brighter than classical nova.This transient astronomical event is called kilonova.In this paper,kilonova is referred to the transient astronomical event resulting from binary neutron stars merger.This is the first time that people observed a kilonova that is testified by gravitational waves and short gamma-ray bursts.The observation of electromagnetic counterpart could help people constrain neutron star’s equation of state and study the evolution of chemical elements.This kind of sources could also be used as standard sirens to constrain the cosmological parameters.Combining the observation of kilonova with the results of numerical relativity,it’s possible to predict light curves of kilonova through the gravitational waves detected in the future.With the joining of Kamioka Gravitational Waves Detector(KAGRA)in Japan and the Wide-Field Survey Telescope(WFST)to be constructed in Lenghu,Qinghai Province,the wild field of WFST could make it be good at searching for the following optical counterpart of binary neutron stars’ gravitational waves in the incoming 04 runs.In this paper,we simulate the sources of binary neutron stars mergers at redshift z<0.2 and calculate the light curve of merger events through a kilonova model with shock-heated cocoon and another kilonova model with several kinds of disk wind.With these light curves,we investigate the detectability of these simulated kilonovae with redshift z<0.2 using WFST,large synoptic survey telescope(LSST),and Chinese space station telescope(CSST).We determine that whichever kilonova model is used,the best observing band for WFST and LSST is always the g band,which could detect most sources.Moreover,when adopting the two-band-observing strategies,the best observing strategies predicted by both kilonova models are searching for events through the g/r band first and then searching for events via the r/i band.However,the time of switching filters is different for different kilonova models.The switching time predicted by the kilonova model with shock-cocoon and the kilonova model with two kinds of disk winds are 1.5 days and 3.5 days after merger respectively.As for CSST which will observe via deep slitless spectrum,the kilonova model with shock-cocoon and the kilonova model with two kinds of disk winds predict that events could only be detected via the GU band in the first 1.5 and 2.0 days,via the GV band in the first 3.5 and 4.0 days and via the GI band in the longest time.The distribution of observable events on bands predicted by two models are different.Taking CSST as an example,the kilonova model with shock-cocoon predicts that the events that could be detected by the GV and the GI band are comparable.However,the kilonova model with two kinds of disk winds predicts that the GI band could detect the most sources which is 30%more than the GV band.For the kilonova model with shock cocoon,we investigate the effect of observer viewing angle on light curve.We determine that for the sources with mass ratio q>0.8,the change of light curve is significant when the viewing angle is different.