The focus of all gravitational-wave data-analysis tools, both for ground-based instruments as well as lisa, has been on using gravitational- wave data alone. However, a crucial aspect of optimizing data analysis will be the use of complementary electromagnetic observations. Although this is widely acknowledged[1], very little actual work has been done in this area.
The postdoc will use the techniques developed for different gravitational-wave data-analysis problems (ligo/Virgo double neutronstar inspirals, different lisa sources) to analyze the different simulated gravitational-wave data sets and will make an inventory of the possible electromagnetic data (radio, infrared, optical, UV and X-ray). Ideally, the candidate would have a background in gravitationalwave data analysis and have to familiarize himself/herself with the astronomical data. Alternatively, it could be an astronomer who first has to learn gravitational-wave data analysis.
The main part of the project will be to develop data-analysis techniques that use the electromagnetic data, either as priors, or for joint optimization of parameters. First application will be to high-frequency Virgo/ligo data, investigating the use of possible electromagnetic data from neutron-star and black-hole mergers, such as gamma-ray bursts or low-frequency radio transients[2]. After that the techniques will be applied to Galactic ultra-compact binaries and super-massive black-hole mergers in the lisa data, building on the strong track record of both the gravitational-wave and electromagnetic expertise[3]. The aim is to investigate the improvements in parameter estimation that are possible with complementary electromagnetic observations and the (astro)physical questions that come within reach with these tools.
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Closely related to project VI, one PhD student will use the joint gravitational-wave and electromagnetic data analysis to study the Galactic compact binaries, in particular the lisa verification binaries. The estimated population of ultra-compact binaries in the Galaxy is around 100 million, of which several thousand might be detectable with lisa[1]. At present, using electromagnetic tools, only several tens have been discovered, although the number is increasing rapidly. For a handful of the currently known systems the electromagnetic observations have provided enough information to derive reasonably accurate system parameters, which makes it possible to estimate their lisa signal[2]. These objects should be easily detectable and thus can be used as verification binaries for the mission. The first project of the PhD student will be to update these estimates, both for any new electromagnetic data, as well as using the joint gw-em data analysis.
These techniques will then be applied to all ultra-compact binaries, working closely together with the (nwo-ew funded) current PhD students working on Galactic populations of binary stars. In particular it will be investigated to what extent the lisa measurements will allow us to constrain the different uncertainties in the formation of ultra-compact binaries, such as the exact outcome of mass transfer between stars. This will most likely depend strongly on the available complementary electromagnetic data. Therefore different scenarios will be developed, depending on the availability of several future (radio, infrared, optical, UV and X-ray) instruments.
This project will bridge the gap between the gravitational-wave data analysis efforts in Nijmegen and the observational astrophysics groups.
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For both high-frequency, as well as low-frequency gravitational-wave detectors, many sources are stellar mass compact objects, often in binary systems. Binary systems containing neutron stars and black holes can evolve from sources for low-frequency detectors into sources for high-frequency detectors. Relatively little attention has been paid to the synergy between the two types of detections. For most expected sources (neutron stars or stellar mass black holes with masses around 10 solar mass) the shortest time between observation in the low-frequency band (i.e. below 0.1 Hz) and the high-frequency band (above 10 Hz) is several tens to hundreds of years. In addition, the estimated number of such sources in the Galaxy is small enough that most likely the shortest observed binary has a significantly lower frequency than 0.1 Hz. Therefore, the chance of seeing the same source in lisa as well as et is not very large. However, statistically the et merger rates and the lisa detection numbers should provide independent constraints on the formation of neutron star and black hole binaries, in particular they can test the predictions that many double neutron stars systems are formed at very short periods, and thus do not show up in the radio pulsar surveys[1].
More speculatively, but also much more interesting, is the possibility of forming close pairs of intermediate mass black holes (with masses between 100 and 1000 solar mass) or intermediate mass – stellar mass black hole pairs[2]. These have low enough masses to still be detectable with et, but their evolution time from the low-frequency to the high-frequency band is only of the order of years. In addition, they are detectable for lisa to much larger distances, greatly increasing the probability of finding them. These intermediate mass black holes may form from the first population of stars formed in the Universe, or in the centers of dense star clusters, where frequent stellar collisions lead to very massive central objects. In particular the cluster environment is interesting, as further interactions between stars or stellar mass black holes and the intermediate mass black holes can lead to the formation of close pairs[3].
The aim of this project is to estimate potential rates and simulate the data analysis for joint detections between lisa and et. For the stellar mass objects, the constraints obtained on the formation of neutron star binaries will be determined, using simulated populations for different astrophysical assumptions. For the intermediate mass systems, it will be derived what (extra) constraints/test of general relativity can be obtained when combining the relatively long lisa observations with the short et observations.
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