Observations of the GRB afterglow ATLAS17aeu and its possible association with GW170104

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We report the discovery and multi-wavelength data analysis of the peculiar optical transient, ATLAS17aeu.

• This transient was identified in the skymap of the LIGO gravitational wave event GW170104 by our ATLAS and Pan-STARRS coverage.
• ATLAS17aeu was discovered 23.1hrs after GW170104 and rapidly faded over the next 3 nights, with a spectrum revealing a blue featureless continuum.
• The transient was also detected as a fading x-ray source by Swift and in the radio at 6 and 15 GHz.