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GCN Circular 33974

LIGO/Virgo/KAGRA S230615az: GROWTH-India candidates
2023-06-15T23:47:06Z (a year ago)
Vishwajeet Swain at IIT Bombay <>
H. Kumar (IITB), V. Swain (IITB), A. Salgundi (IITB), K. Angail (IAO), V. Bhalerao (IITB), G. C. Anupama (IIA), S. Barway (IIA) report on behalf of the GIT team:

We followed up the sky localisation of the gravitational wave trigger S230615az with the 0.7m GROWTH-India telescope. We obtained multiple 300-sec exposures in the r' filter starting at 2023-06-15T17:56:40 UT, 6.55 minutes after the trigger. By targeting galaxies in the region, we covered 0.4% of the source probability on the sky, based on the "bayestar.multiorder.fits,1" map. After performing image subtraction, vetting, and a cross-check with minor planet centre, we obtained the following two transient candidates within the 90% localisation region of the event:

| Name         | JD             | RA(J2000)   | Dec(J2000)  | Filter | Mag (AB)       |
| GIT230615aa  | 2460111.271145 | 12:50:03.64 | 20:53:21.77 |   r'   | 20.05 +/- 0.06 |
| GIT230615ab  | 2460111.286931 | 12:42:11.65 | 22:03:25.08 |   r'   | 19.81 +/- 0.05 |

GIT230615aa was detected in two images separated by 17 minutes. There is no significant fading between the two images. We could not get a second confirmation image for GIT230615ab as the source was set soon after the first image.

The magnitudes are calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.

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 (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at
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