TITLE: GCN CIRCULAR NUMBER: 39934 SUBJECT: LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 1) DATE: 25/03/29 22:30:24 GMT FROM: Isaac McMahon at University of Zürich isaac.mcmahon@ligo.org
S. MacBride (UZH), I. McMahon (UZH), M. Soares-Santos (UZH), reporting on behalf of the Dark Energy Survey Gravitational Wave (DESGW) Team:
At 01:43 UTC, March 29th, the Dark Energy Camera (DECam) began the first epoch of observations in response to the LVK alert issued for the candidate gravitational-wave event S250328ae (GCN 39898). We observed eight fields centered on the following ICRS coordinates: (145.286221, 10.615360) (145.996500, 12.108130) (143.786221, 10.715360) (144.496500, 12.208130) (144.069167, 9.115670) (143.344621, 7.609550) (145.900667, 13.593470) (142.620092, 6.103430) These pointings cover the 90% localization region of candidate gravitational-wave event S250328ae.
All fields were observed in DECam r, i, and z filters with 90-second exposures. The limiting magnitude achieved is ~22.7 in r-band, ~22.1 in i-band, and ~21.4 in z-band.
We process the images with our difference imaging pipeline (Herner et al. 2020) using DES and public DECam images as templates. We employ the autoscan machine learning code (Goldstein et al 2015) to reject subtraction artifacts. Candidates were selected by requiring at least two high signal to noise detections. We also require an autoscan score of at least 0.7 on at least one of those detections. We also match our candidates against the ALLWISE, Milliquas, and Quaia AGN catalogs (Secrest et al 2015, Flesch 2023, Storey-Fisher et al 2024) within the LVK localization volume to determine if any correspond to known active galactic nuclei.
After candidate selection, we report the 20 high confidence candidates listed below. After vetting and identification, 8 candidates are classified as nuclear candidates (likely active galactic nuclei), 8 candidates as possible supernovae, and 3 other candidates do not fall in either category. 1 additional candidate (2292763) has been identified as a known AGN WISEA J093710.05+082057.2. We have numerous other transient candidates which require further observation to confidently classify. Further observations are ongoing, and we encourage followup of the 20 candidates identified herein.
| TYPE | ID | ATNAME | RA | DEC | MAG_R | MAG_R_ERR | MAG_I | MAG_I_ERR | MAG_Z | MAG_Z_ERR | | -------- | ------- | --------- | ---------- | ---------- | ----- | ---- | ----- | ---- | ----- | ---- | | SN_LIKE | 2290892 | AT2025gei | 143.636743 | 9.980209 | N/A | N/A | 20.59 | 0.03 | N/A | N/A | | OTHER | 2292987 | AT2025gej | 143.183373 | 6.893136 | 21.37 | 0.04 | 21.45 | 0.08 | N/A | N/A | | AGN_LIKE | 2290036 | AT2025gek | 145.199481 | 10.828527 | 20.77 | 0.04 | 20.62 | 0.03 | 20.69 | 0.1 | | SN_LIKE | 2290467 | AT2020woa | 144.388798 | 10.255536 | 19.87 | 0.02 | N/A | N/A | 20.1 | 0.04 | | SN_LIKE | 2290524 | AT2025gel | 144.524917 | 10.199936 | N/A | N/A | N/A | N/A | 20.47 | 0.06 | | OTHER | 2290001 | AT2025avp | 144.806008 | 10.632223 | 20.36 | 0.02 | 20.19 | 0.02 | 20.22 | 0.06 | | SN_LIKE | 2291473 | AT2025gem | 144.706509 | 11.560317 | 20.92 | 0.03 | N/A | N/A | 21.22 | 0.1 | | AGN_LIKE | 2293190 | AT2025cvb | 144.191297 | 10.828462 | 20.86 | 0.03 | 20.87 | 0.03 | N/A | N/A | | AGN_LIKE | 2290623 | AT2025gen | 144.112464 | 11.641817 | 21.4 | 0.04 | 21.3 | 0.08 | 21.37 | 0.12 | | SN_LIKE | 2292782 | AT2025geo | 144.928578 | 10.349243 | 20.92 | 0.04 | 21.07 | 0.04 | N/A | N/A | | SN_LIKE | 2291779 | AT2025gej | 143.182187 | 6.894174 | N/A | N/A | N/A | N/A | 20.76 | 0.06 | | OTHER | 2290762 | AT2025gep | 144.259773 | 11.511316 | 21.29 | 0.04 | N/A | N/A | N/A | N/A | | SN_LIKE | 2290334 | AT2025geq | 145.235616 | 12.469694 | 20.22 | 0.02 | 20.57 | 0.03 | N/A | N/A | | AGN_LIKE | 2290970 | AT2025ger | 142.543835 | 6.090899 | 21.71 | 0.05 | 21.43 | 0.06 | 21.28 | 0.09 | | AGN_LIKE | 2292040 | AT2025ges | 144.438216 | 9.885617 | 21.72 | 0.07 | 21.75 | 0.11 | 21.93 | 0.17 | | SN_LIKE | 2292645 | AT2025get | 144.053408 | 11.422277 | N/A | N/A | 22.67 | 0.21 | N/A | N/A | | AGN_LIKE | 2293517 | AT2025geu | 145.956024 | 12.381673 | 21.73 | 0.08 | 21.65 | 0.07 | N/A | N/A | | AGN_LIKE | 2291833 | AT2025gev | 143.241035 | 8.651865 | 22.16 | 0.09 | 21.99 | 0.13 | 22.22 | 0.22 | | AGN_LIKE | 2294074 | AT2025gew | 144.291829 | 8.349302 | 22.23 | 0.1 | 21.85 | 0.11 | N/A | N/A | | AGN | 2292763 | AT2025gex | 146.071329 | 11.839902 | 21.89 | 0.11 | 21.92 | 0.12 | 21.05 | 0.1 |
The DECam Search & Discovery Program for Optical Signatures of Gravitational Wave Events (DESGW) is carried out by the Dark Energy Survey (DES) collaboration in partnership with wide-ranging groups in the community. DESGW uses data obtained with the Dark Energy Camera (DECam), which was constructed by the DES collaboration with support from the Department of Energy and member institutions, and utilizes data as distributed by the Science Data Archive at NOIRLAB. NOIRLAB is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. We thank the Cerro Tololo observatory staff for their support in acquiring these observations.
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