* Astronomy

Title: A tale of two transients: GW170104 and GRB170105A
Author: V. Bhalerao, M. M. Kasliwal, D. Bhattacharya, A. Corsi, E. Aarthy, S. M. Adams, N. Blagorodnova, T. Cantwell, S. B. Cenko, R. Fender, D. Frail, R. Itoh, J. Jencson, N. Kawai, A. K. H. Kong, T. Kupfer, A. Kutyrev, J. Mao, S. Mate, N. P. S. Mithun, K. Mooley, D. A. Perley, Y. C. Perrott, R. M. Quimby, A. R. Rao, L. P. Singer, V. Sharma, D. J. Titterington, E. Troja, S. V. Vadawale, A. Vibhute, H. Vedantham, S. Veilleux

We present multi-wavelength follow-up campaigns by the AstroSat-CZTI and GROWTH collaborations to search for an electromagnetic counterpart to the gravitational wave event GW170104. At the time of the GW170104 trigger, the AstroSat CZTI field-of-view covered 50.3% of the sky localization. We do not detect any hard X-ray (>100 keV) signal at this time, and place an upper limit of \approx 4.5 x 10^-7 erg cm^-2 s-1 for a 1s timescale. Separately, the ATLAS survey reported a rapidly fading optical source dubbed ATLAS17aeu in the error circle of GW170104. Our panchromatic investigation of ATLAS17aeu shows that it is the afterglow of an unrelated long, soft GRB 170105A, with only a fortuitous spatial coincidence with GW170104. We then discuss the properties of this transient in the context of standard long GRB afterglow models.

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