Antonia Rowlinson Personal Website

Late time follow-up of transients

In addition to the LOFAR Rapid Response Mode, my team and I also conduct late time follow-up of a wide range of multi-messenger transient sources. Here are two key examples.

Recurrent Novae

Recurrent Novae are systems comprising of one white dwarf and a larger companion star. The white dwarf is accreting material from its companion and, when sufficient material builds up on the surface of the white dwarf, they go into a bright outburst. Recurrent Novae have been seen to do this at least two times.

Using observations by LOFAR and MeerKAT, we were able to model the evolution of an outburst of the recurrent nova RS Ophiuchi at low radio frequencies (de Ruiter et al. 2023). This monitoring showed that the emission is most likely from a non-thermal mechanism that is consistent with originating from two lobes of emission.

Radio light curves of the RS Oph 2021 eruption including model fits. The left-hand panel shows the best fitting radio supernova models, as described in Appendix  A, as a dashed line. The right-hand panel shows the fit resulting from a model where two synchrotron components are allowed. The dashed lines show the total fit, which is the sum of the two components shown with the dotted lines. Figure and Caption from de Ruiter et al. (2023).
Simple geometry sketch of RS Oph (not to scale) of the expanding and bipolar arrangement of the RS Oph ejecta. The radio brightest parts of the eastern and western lobe are shown in yellow. Figure and Caption from de Ruiter et al. (2023).

Gravitational Wave Events

Gravitational wave events are typically from the inspired and merger of two compact objects (black holes and/or neutron stars). If there is at least one neutron star involved, we would expect to observe a bright multi-wavelength afterglow. Our team has been involved in following up gravitational wave events from the very first detection of gravitational waves by Advanced LIGO.

LOFAR is capable of both obtaining targeted observations of candidate counterparts (Broderick et al. 2020) and using the wide field its to conduct large sky area searches for candidate counterparts (Gourdji et al. 2022 and Gourdji et al. 2023)

Part of the three-detector GW location probability density map of G299232 (LIGO Scientific Collaboration/Virgo Collaboration 2017). Contours enclose 50 and 90 per cent of the probability density (though additional regions in the Southern hemisphere are not included here). The full extent of the area searched in this analysis is enclosed by the blue dashed line, and corresponds to 47 overlapping LOFAR beams each searched out to a radius of 3.5°. The blue circles denote beam coverage of radius 1.4°, and the resulting unique sky area covered by these radii is 289.4 deg2. Figure and caption from Goudji et al. (2022)