TITLE: GCN CIRCULAR NUMBER: 36289 SUBJECT: LIGO/Virgo/KAGRA S240422ed: Archival BlackGEM/MeerLICHT detections of AT 2024hdr & AT 2024hdq DATE: 24/04/24 21:10:06 GMT FROM: Danielle Pieterse at Radboud U. d.pieterse@astro.ru.nl

D.L.A. Pieterse (Radboud), H. Tranin (Barcelona), J. van Roestel (Amsterdam), P.J. Groot (Radboud, UCT, SAAO), P.M. Vreeswijk (Radboud), S. Bloemen (Radboud) and P.G. Jonker (Radboud) report on behalf of the BlackGEM/MeerLICHT Consortium:

Following the DECam candidate counterparts to S240422ed reported by (Hu et al., GCN 36273), we looked at archival data of the the 0.6m BlackGEM/MeerLICHT telescope array located at the ESO La Silla, Chile and SAAO Sutherland, South Africa observatories.

We detect DECam candidates AT 2024hdr and AT 2024hdq as nuclear transients in archival 60s q-band (440-720 nm) images of BlackGEM and MeerLICHT. We therefore conclude that these are not the GW counterpart. No Name night range q_mag range 1 AT 2024hdr 2023/12/06-2024/04/23 19.0-19.5 2 AT 2024hdq 2022/12/31-2024/12/03 18.6-19.2

We report transient limiting magnitudes for the other DECam candidates from (Hu et al., GCN 36273): No Name limmag filter date-obs 1 AT 2024hdk >19.6 i 2024-04-08 00:12:33 2 AT 2024hdn >19.6 q 2024-04-23 21:25:02 3 AT 2024hdm >19.9 q 2024-04-23 21:20:59 4 AT 2024hdl >20.0 i 2024-04-17 23:46:19 5 AT 2024hdo >20.3 q 2024-04-23 23:26:45 6 AT 2024hdp >19.9 q 2024-04-23 19:39:27

Transient candidates were extracted using the BlackBOX/ZOGY pipeline, where astrophotometric calibrations are performed using Gaia DR3 photometry and astrometry. Possible asteroids are filtered using the daily-updated lists of known asteroids from the Minor Planet Center. All magnitudes quoted are on the AB system.

The BlackGEM/MeerLICHT telescope are designed, installed and operated by a consortium of the following universities and institutions: Radboud University, Netherlands Research School for Astronomy NOVA, KU Leuven, Armagh Observatory and Planetarium, Technical University of Denmark, Hebrew University of Jerusalem, South African Astronomical Observatory, Tel Aviv University, Texas Tech University, University of Amsterdam, University of Barcelona, University of California at Davis, University of Cape Town, University of Durham, University of Hamburg, University of Manchester, University of Oxford, University of Potsdam, University of Valparaiso, University of Warwick, Weizmann Institute

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