Rapid-response and High-precision Wide-field Photometry of Transients and Gravitational Wave Counterparts

Roberts, Dean (2020). Rapid-response and High-precision Wide-field Photometry of Transients and Gravitational Wave Counterparts. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.00010f77


This work focuses on the use of the small-aperture PIRATE robotic telescope, built with off the shelf components at a relatively low cost, in the observation of numerous astrophysical objects. This includes both the follow-up of gravitational wave alerts released by the LIGO/Virgo collaboration, but also the long term monitoring of Luminous Blue Variable (LBV) stars in the nearby Triangulum galaxy (M33). A new pipeline was developed to fully automate the follow-up of gravitational wave alerts, which enables PIRATE to respond promptly without human intervention. This resulted in the detailed follow-up of four gravitational wave alerts, all of which were as a result of a binary black hole merger. Although no optical counterparts were detected, upper limits were placed on the magnitude of any potential counterpart. However, this work did produce dozens of serendipitously discovered candidate variable stars; and had it not been due to bad luck, PIRATE would have been able to follow-up the famous binary neutron star merger event GW170817.

Additionally, PIRATE was used to monitor several candidate LBV stars in the Triangulum galaxy for a continuous period of 4 months, to search for signs of an S Dor cycle that’s indicative of an LBV. This was used in conjunction with new spectroscopic data taken with the WHT to analyse the behaviour of these stars and reclassify them accordingly. In total, three stars were re-classified as bona fide LBVs as a result of this work, and a further four were given new classifications as Cool Hypergiants. Although no LBV was photometrically observed undergoing an outburst, PIRATE was able to detect several of them in M33 and would have consequently observed such a rare event had one occurred during its observing window.

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