TITLE: GCN CIRCULAR NUMBER: 36311 SUBJECT: LIGO/Virgo/KAGRA S240422ed: Magellan Follow-up Observations of Swift/XRT candidates DATE: 24/04/26 01:28:33 GMT FROM: Ryan Foley at UC Santa Cruz foley@ucsc.edu

A. L. Piro, J. D. Simon (Carnegie), A. Polin (Carnegie/Purdue), D. A. Coulter (STScI), M. R. Drout (Toronto), R. J. Foley, and C. Rojas-Bravo (UC Santa Cruz)

report on behalf of the Carnegie Gravitational wave ElectroMagnetic follow-up (CGEM) and the One-Meter Two-Hemisphere (1M2H) collaborations:

As part of our ongoing search for optical counterparts to the candidate gravitational wave event S240422ed using the 6.5m Magellan Clay telescope with the LDSS-3 imager, we have obtained optical imaging of the Swift/XRT sources S240422ed_X61 (GCN 36278, GCN 36259, GCN 36262, GCN 36271, GCN 36293), 240422ed_X101 (GCN 36278, GCN 36287, GCN 36293), and S240422ed_X190 (GCN 36278, GCN 36293, GCN 36305).

Based on comparison with DECaPS2 images, we do not detect transient sources within the XRT error circle in any of these fields. We estimate the following 5-sigma limiting magnitudes:

+----------------+---------------------+--------+-----------------+ | ID | UT observation date | filter | magnitude limit | +----------------+---------------------+--------+-----------------+ | S240422ed_X61 | 2024-04-24T00:40:24 | i | 23.6 | | S240422ed_X101 | 2024-04-25T00:30:25 | i | 23.2 | | S240422ed_X190 | 2024-04-25T00:33:35 | i | 23.1 | +----------------+---------------------+--------+-----------------+

We thank Marcelo Mora, Povilas Palunas, and the rest of the LCO staff for making these observations possible.

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