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SPLOT: a Snapshot survey for Polarised Light in Optical Transients

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posted on 04.02.2019, 14:35 by AB Higgins, K Wiersema, S Covino, RLC Starling, HF Stevance, Ł Wyrzykowski, ST Hodgkin, JR Maund, PT O'Brien, NR Tanvir
We present SPLOT, a small-scale pilot survey to test the potential of snapshot (single epoch) linear imaging polarimetry as a supplementary tool to traditional transient follow-up. Transients exist in a vast volume of observational parameter space and polarimetry has the potential to highlight sources of scientific interest and add value to near real-time transient survey streams. We observed a sample of ∼50 randomly selected optical transients with the EFOSC2 (ESO Faint Object Spectrograph and Camera v2) and SofI (Son of ISAAC) instruments, on the 3.6 m New Technology Telescope to test the feasibility of the survey. Our sample contained a number of interesting individual sources: a variety of supernovae, X-ray binaries, a tidal disruption event, blazar outbursts and, by design, numerous transients of unknown nature. We discuss the results, both for the individual sources and the survey in detail. We provide an overview on the success and limitations of SPLOT and also describe a novel calibration method for removing instrumental polarization effects from Nasymth-mounted telescopes. We find that a SPLOT-like survey would be a benefit to the large-scale future transient survey streams such as Large Synoptic Survey Telescope. The polarimetric measurements have added scientific value to a significant number of the sources and, most importantly, have shown the potential to highlight unclassified transient sources of scientific interest for further study.


Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 097.D-0891(A) and 099.D-0262(A). This research made use of data from the Steward Observatory spectropolarimetric monitoring project which is supported by Fermi Guest Investigator grants NNX08AW56G, NNX09AU10G, NNX12AO93G, and NNX15AU81G. This work has also made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, and the Gaia, DPAC and the Photometric Science Alerts Team ( Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. ABH is supported by a Science and Technology Facilities Council (STFC) studentship granted by the University of Leicester. KW, RLCS, and NRT acknowledge support from STFC. RLCS acknowledges support from Royal Society Research Grant RG170230. HFS is supported by a PhD studentship granted by the University of Sheffield. ŁW acknowledges the Polish National Science Centre (NCN) grant OPUS 2015/17/B/ST9/03167. We are grateful to all ESO support staff at La Silla, for their assistance and encouragement and we particularly thank Ivo Saviane for allowing us to use SofI when EFOSC2 was unusable. We thank Cristina Baglio for her kind assistance with SofI OBs. KW thanks Dipali Thanki and Ray McErlean for their excellent support of science operations at the University of Leicester observatory (UL50). This research made extensive use of the app iObserve, written by C. Foellmi ( We are grateful to Dr Foellmi for his commitment to this app. This research made use of ASTROPY, a community-developed core PYTHON package for Astronomy (Astropy Collaboration et al. 2018). We acknowledge ESA Gaia, DPAC, and the Photometri



Monthly Notices of the Royal Astronomical Society, 2019, 482(4), pp. 5023–5040

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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Monthly Notices of the Royal Astronomical Society


Oxford University Press (OUP), Royal Astronomical Society



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Accepted in MNRAS. 20 pages, 10 figures, 3 tables. Also contains a 10 page, two part appendix with unpolarised standard star measurements used for calibration (A) and individual source information and light curves (B). Corrected more typos



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