TITLE: GCN CIRCULAR NUMBER: 42722 SUBJECT: LIGO/Virgo/KAGRA S251112cm: WFST follow-up observations and preliminary results DATE: 25/11/17 15:38:01 GMT FROM: Zhengyan Liu at USTC <ustclzy@mail.ustc.edu.cn> Z. Y. Liu, W. Zhao, J.-A. Jiang, Z. L. Xu, D. Z. Meng, M. X. Cai, T. G. Wang, X. Kong, Z. G. Dai, L. L. Fan (USTC), Z. P. Jin, Y. Z. Fan (PMO) report on behalf of the WFST Collaboration: Following the detection of the sub-solar mass merger candidate S251112cm (the LIGO-Virgo-Kagra Collaboration, GCN 42650), we conducted follow-up observations focused on the northern region of the initial bayestar skymap (GCN 42650) using the newly deployed 2.5-meter Wide Field Survey Telescope (WFST Collaboration; Wang et al., 2023) at the Lenghu Astronomical Observation Base (Qinghai province, China). Observations began at UTC 2025-11-13T11:29:36, corresponding to ~20.2 hours after the merger event (UTC 2025-11-12T15:18:45). The follow-ups lasted for three nights until UTC 2025-11-15T23:16:16. We observed in WFST g, r, and i bands with exposure times of 45-90 seconds. A total area of about 727.4 square degrees of the 90% skymap (GCN 42650) was observed, covering ~64% of the event localization. Additionally, ~7.5% skymap was covered in 30s g- and r-band exposures through the WFST wide-field survey (WFS) 6.35 hours after the merger event. The follow-up observation data were processed using the WFST pipeline. For images localized in WFS, image subtraction was performed using the WFST stacking images taken berfore the event as templates. The search for the counterpart of S251112cm was performed mainly through visual inspection based on the locations of nearby galaxies, considering the distance estimate of 93 +/- 27 Mpc (redshift ~ 0.02; the LIGO-Virgo-Kagra Collaboration, GCN 42690) and the uncertainty of the potential electromagnetic counterpart. All extragalactic transient candidates detected by WFST during follow-ups were reported to the IAU Transient Name Server (TNS). After excluding sources with pre-merger detections reported in TNS, only one candidate was found to be located near a galaxy with spectroscopic redshift below 0.045: AT2025aebp was first detected at 60992.93 (+1.3 days post-merger) with 21.5 +/- 0.1 mag in r-band, and the spectroscopic redshift of its possible host galaxy SDSS J103703.20+231142.2 is 0.043. Additionally, we report three other sources without pre-merger detections. These sources have possible host galaxies with SDSS DR16 photometric redshift (Csabai et al., 2007; Ahumada et al., 2019) less than 0.1: | AT Name | MJD | RA | Dec | Filter | Mag | Host | photoZ | |------------|-----------|----------|----------|--------|----------|--------------------------|------------| | AT2025aebk | 60992.86 | 156.5043 | 24.9277 | g | 21.8 ± 0.1 | SDSS J102601.47+245542.1 | 0.06 ± 0.02 | | AT2025aebl | 60992.92 | 152.3554 | 18.2025 | r | 21.4 ± 0.1 | SDSS J100925.32+181207.3 | 0.09 ± 0.03 | | AT2025aebq | 60992.94 | 172.3128 | 36.6438 | r | 21.4 ± 0.1 | SDSS J112914.78+363832.0 | 0.09 ± 0.03 | We also checked the aforementioned candidates reported through TNS and GCN Circulars (GCN 42658, GCN 42666, GCN 42677, GCN 42691, GCN 42707). Ten public sources were detected in our difference images. Difference photometric results are listed as follows: | AT Name | MJD | RA | Dec | Filter | Mag | |------------|-----------|----------|----------|--------|------------| | AT2025adjd | 60992.96 | 190.8110 | 56.8036 | r | 21.31 ± 0.04 | | AT2025adie | 60992.83 | 185.3958 | 56.5862 | g | 21.7 ± 0.1 | | AT2025adhu | 60992.83 | 181.8041 | 55.6536 | g | 21.4 ± 0.1 | | AT2025adtj | 60990.94 | 172.5489 | 38.6207 | r | 19.64 ± 0.03 | | AT2025adia | 60992.85 | 169.5689 | 35.9858 | g | 21.6 ± 0.1 | | AT2025adln | 60989.89 | 168.0373 | 30.42659 | g | 21.2 ± 0.2 | | AT2025adlk | 60989.93 | 159.2667 | 19.30616 | g | 20.1 ± 0.1 | | AT2025adic | 60989.89 | 169.5444 | 41.0946 | g | 21.8 ± 0.2 | | AT2025adtq | 60990.94 | 175.6142 | 34.0085 | r | 21.2 ± 0.1 | | AT2025adtk | 60990.93 | 174.3825 | 31.3606 | r | 18.98 ± 0.02 | We thank the WFST staff for supporting these observations. Subsequent WFST observations and a systematic search for potential transients are ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/42722. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...