{
  "submitter": "Sam Shilling at Lancaster University <shilling.sam@gmail.com>",
  "submittedHow": "web",
  "format": "text/plain",
  "circularId": 40047,
  "eventId": "GRB 250402A",
  "body": "S. P. R. Shilling (Lancaster U.)  and S. R. Oates (Lancaster U.) report on behalf of the Swift UVOT team:\n\nSwift/UVOT observed the field of SVOM/ECLAIRs GRB 250402A (Chen et al. GCN Circ. 40014) for 2521 seconds in the U-band starting at 12:48:12 UT on 25/04/03, ~13 hours after the detection by SVOM/ECLAIRs.\n\nNo optical afterglow is detected within a 5\" radius of the position of the uncatalogued X-ray source\ndetected by Swift/XRT (Dichiara et al., GCN Circ. 40027) and SVOM/MXT (Maggi et al., GCN circ. 40019) or the optical afterglow detected by SVOM/VT (Xin et al., GCN Circ. 40015), LCOGT (Pérez-Fournon et al., GCN Circ. 40020), and the SVOM/COLIBRÍ (Magnani et al., GCN Circ. 40023). \n\nThe Swift/UVOT non-detection in the U-band has a preliminary 3-sigma upper limit of >21.1, calculated using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373).",
  "createdOn": 1743771060423,
  "subject": "GRB 250402A: Swift/UVOT Upper Limits",
  "bibcode": "2025GCN.40047....1S"
}