TITLE:   GCN CIRCULAR
NUMBER:  36279
SUBJECT: LIGO/Virgo/KAGRA S240422ed: MOSFIRE imaging of the DECam GW-MMADS candidate AT 2024hdm
DATE:    24/04/24 09:01:56 GMT
FROM:    Viraj Karambelkar at Indian Inst of Tech,Bombay <karambelkarvraj21197@gmail.com>

Viraj Karambelkar (Caltech), Jacob Jencson (IPAC), Samaporn Tinyanont
(NARIT), Mansi Kasliwal (Caltech) report on behalf of a larger
collaboration.

We imaged the DECam GW-MMADS source AT2024hdm (GCN 36273), reported as a
candidate optical counterpart to the LVK gravitational wave event S240422ed
(GCN 36236) in the near-IR J-band with MOSFIRE on the Keck-I telescope on
UTC 2024-04-24T07:48:25. This transient is close to a galaxy with photoz ~
0.048 (Bilicki et al. 2014), suggesting an absolute magnitude of M_r ~ -16
mag at discovery (GCN 36273, https://www.wis-tns.org/object/2024hdm).

We detect AT2024hdm in the J-band with m_J ~ 20.4 +/- 0.1 mag (AB). Based
on the r-band discovery magnitude,  the r - J color of this transient is ~
0.3 mag. Correcting for Galactic extinction of E(B-V) ~ 0.1 along this
direction gives a corrected (r-J)_corr ~ 0.15 +/- 0.1 mag, suggesting that
the intrinsic color is not particularly red at this phase.

This transient may be consistent with a supernova. We encourage
spectroscopic classification to determine the true nature of the source.