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An advanced numerical scheme for computing the free surface flow about a ship is presented. The present approach is a higher order panel method which employs a parabolic quadrilateral as a basic element. It can represent an actual curved ship hull surface more accurately with a smaller number of panels than is possible with a flat panel approximation. Singularity strength can vary linearly or quadratically across the panel. A sample unbounded flow problem with an analytical solution was considered first to validate the present approach and examine the characteristics of accuracy and convergence compared with those of the conventional low-order approaches (constant source strength across flat panel). The Wigley hull and the Series 60, C sub B=0.60 hull, which have been studied extensively, were selected for sample free surface flow computations. Comparisons between calculated and experimental results show good agreement. A modified body boundary condition was suggested to simulate a dry transom stern numerically, and calculated results show good correspondence with test data. Keywords: Ship hulls; Wave profile; Wave-making resistance; Higher-order panel method.

Between 2011 March and 2014 August Swift responded to 20 triggers from the IceCube neutrino observatory, observing the IceCube 50% confidence error circle in X-rays, typically within 5 hours of the trigger. No confirmed counterpart has been detected. We describe the Swift follow up strategy and data analysis and present the results of the campaign. We discuss the challenges of distinguishing the X-ray counterpart to a neutrino trigger from serendipitous uncatalogued X-ray sources in the error circle, and consider the implications of our results for future strategies for multi-messenger astronomy, with particular reference to the follow up of gravitational wave triggers from the advanced-era detectors.

swift

Binary neutron star (NS) mergers are among the most promising astrophysical sources of gravitational wave emission for Advanced LIGO and Advanced Virgo, expected to be operational in 2015 . Finding electromagnetic counterparts to these signals will be essential to placing them in an astronomical context. The Swift satellite carries a sensitive X-ray telescope (XRT), and can respond to target-of-opportunity requests within 1-2 hours, and so is uniquely poised to find the X-ray counterparts to LIGO / Virgo triggers. Assuming NS mergers are the progenitors of short gamma-ray bursts (GRBs), some percentage of LIGO/Virgo triggers will be accompanied by X-ray band afterglows that are brighter than 10(exp -12) ergs/s/sq cm in the XRT band one day after the trigger time. We find that a soft X-ray transient of this flux is bright enough to be extremely rare, and so could be confidently associated with even a moderately localized GW signal. We examine two possible search strategies with the Swift XRT to find bright transients in LIGO/Virgo error boxes. In the first strategy, XRT could search a volume of space with a approx.100 Mpc radius by observing approx 30 galaxies over the course of a day, with sufficient depth to observe the expected X-ray afterglow. For an extended LIGO / Virgo horizon distance, the XRT could employ very short 100 s exposures to cover an area of approx 35 square degrees in about a day, and still be sensitive enough to image GW discovered GRB afterglows. These strategies demonstrate that the high X-ray luminosity of short GRBs and the relatively low X-ray transient background combine to make high confidence discoveries of X-ray band counterparts to GW triggers possible, though challenging, with current satellite facilities.

Binary neutron star (NS) mergers are among the most promising astrophysical sources of gravitational wave emission for Advanced LIGO and Advanced Virgo, expected to be operational in 2015. Finding electromagnetic counterparts to these signals will be essential to placing them in an astronomical context. The Swift satellite carries a sensitive X-ray telescope (XRT), and can respond to target-of-opportunity requests within 1-2 hours, and so is uniquely poised to find the X-ray counterparts to LIGO/Virgo triggers. Assuming NS mergers are the progenitors of short gamma-ray bursts (GRBs), some percentage of LIGO/Virgo triggers will be accompanied by X-ray band afterglows that are brighter than 10^-12 erg/s/cm^2 in the XRT band one day after the trigger time. We find that a soft X-ray transient of this flux is bright enough to be extremely rare, and so could be confidently associated with even a moderately localized GW signal. We examine two possible search strategies with the Swift XRT to find bright transients in LIGO/Virgo error boxes. In the first strategy, XRT could search a volume of space with a ~100 Mpc radius by observing ~30 galaxies over the course of a day, with sufficient depth to observe the expected X-ray afterglow. For an extended LIGO/Virgo horizon distance, the XRT could employ 100 s exposures to cover an area of ~ 35 square degrees in about a day, remain sensitive enough to image GW discovered GRB afterglows. These strategies demonstrate that discovery of X-ray band counterparts to GW triggers will be possible.

Binary neutron star (NS) mergers are among the most promising astrophysical sources of gravitational wave emission for Advanced LIGO and Advanced Virgo, expected to be operational in 2015. Finding electromagnetic counterparts to these signals will be essential to placing them in an astronomical context. The Swift satellite carries a sensitive X-ray telescope (XRT), and can respond to target-of-opportunity requests within 1-2 hours, and so is uniquely poised to find the X-ray counterparts to LIGO/Virgo triggers. Assuming NS mergers are the progenitors of short gamma-ray bursts (GRBs), some percentage of LIGO/Virgo triggers will be accompanied by X-ray band afterglows that are brighter than 10^-12 erg/s/cm^2 in the XRT band one day after the trigger time. We find that a soft X-ray transient of this flux is bright enough to be extremely rare, and so could be confidently associated with even a moderately localized GW signal. We examine two possible search strategies with the Swift XRT to find bright transients in LIGO/Virgo error boxes. In the first strategy, XRT could search a volume of space with a ~100 Mpc radius by observing ~30 galaxies over the course of a day, with sufficient depth to observe the expected X-ray afterglow. For an extended LIGO/Virgo horizon distance, the XRT could employ 100 s exposures to cover an area of ~ 35 square degrees in about a day, remain sensitive enough to image GW discovered GRB afterglows. These strategies demonstrate that discovery of X-ray band counterparts to GW triggers will be possible.

One of the most exciting near-term prospects in physics is the potential discovery of gravitational waves by the advanced LIGO and Virgo detectors. To maximise both the confidence of the detection and the science return, it is essential to identify an electromagnetic counterpart. This is not trivial, as the events are expected to be poorly localised, particularly in the near-term, with error regions covering hundreds or even thousands of square degrees. In this paper we discuss the prospects for finding an X-ray counterpart to a gravitational wave trigger with the Swift X-ray Telescope, using the assumption that the trigger is caused by a binary neutron star merger which also produces a short gamma-ray burst. We show that it is beneficial to target galaxies within the GW error region, highlighting the need for substantially complete galaxy catalogues out to distances of 300 Mpc. We also show that nearby, on-axis short GRBs are either extremely rare, or are systematically less luminous than those detected to date. We consider the prospects for detecting afterglow emission from an an off-axis GRB which triggered the GW facilities, finding that the detectability, and the best time to look, are strongly dependent on the characteristics of the burst such as circumburst density and our viewing angle.