TITLE: GCN CIRCULAR NUMBER: 25632 SUBJECT: LIGO/Virgo S190901ap: GROWTH-India follow-up of ZTF19abvionh DATE: 19/09/03 16:40:09 GMT FROM: Gaurav Waratkar at IIT Bombay Harsh Kumar (IITB), Anirban Dutta (IIA), Gaurav Waratkar (IITB), Kunal Deshmukh (IITB), Maitreya Khandagale (IITB), Avinash Singh (IIA), Erik Kool (OKC), Varun Bhalerao (IITB), G. C. Anupama (IIA), Urgain Stanzin (IIA) report on behalf of the GROWTH collaboration: We observed the optical counterpart candidate ZTF19abvionh (Erik Kool et al. GCN 25616, M. J. B. Rosell et al. GCN 25622, GCN 25624) of the gravitational wave trigger S190901ap (LVC et al. GCN 25606, GCN 25614) with the 0.7m GROWTH-India telescope. We obtained a series of exposures, each 600 sec long, in SDSS-r filter starting from 2458729.15950926 JD. We used PS1 catalog images for image subtraction. The candidate was clearly detected in the subtracted images. Photometry of the subtracted images is reported below: ------------------------------------------------------------------ JD(Start) | Name | Filter | Mag | Mar_err| ------------------------------------------------------------------ 2458729.15950926 | ZTF19abvionh | r | 20.81 | 0.117 2458729.16622148 | ZTF19abvionh | r | 20.83 | 0.088 2458729.20642199 | ZTF19abvionh | r | 20.56 | 0.108 2458729.21345010 | ZTF19abvionh | r | 20.50 | 0.088 ------------------------------------------------------------------ Our measurements indicate a rise in the r-band brightness of the candidate. Further observations are planned. We encourage further monitoring of this candidate. The GROWTH India Telescope (GIT) is a 70-cm telescope with a 0.7 degree field of view, set up by the Indian Institute of Astrophysics and the Indian Institute of Technology Bombay with support from the Indo-US Science and Technology Forum (IUSSTF) and the Science and Engineering Research Board (SERB) of the Department of Science and Technology (DST), Government of India (https://sites.google.com/view/growthindia/). It is located at the Indian Astronomical Observatory (Hanle), operated by the Indian Institute of Astrophysics (IIA).