{
  "bibcode": "2007GCN..6765....1M",
  "body": "F.E. Marshall (NASA/GSFC) and A. Moretti (INAF-OAB)\nreport on behalf of the Swift team:\n\nThe Swift/UVOT observed the field of GRB 070731 starting 144 ks \nafter the BAT trigger (Tueller et al., GCN Circ. 6691), which\noccurred at 09:33:22 UT (Moretti et al., GCN Report 79.1). \nAll of the UVOT exposures used the White (160-650 nm) filter, \nand the final exposure started 219 ks after the trigger. \nNo XRT source was detected (Moretti et al., GCN Report 79.1) \ninside the BAT error circle, and we do not find any afterglow \ncandidate inside the BAT error circle in the UVOT observations. \nThe first long (1154 s) exposure that covered the entire \nBAT error circle started 155 ks after the BAT trigger. \nThe 3-sigma upper limit for detecting a source is 20.9 mag. \n(uncorrected for the expected Galactic extinction corresponding \nto a reddening of E(B-V) = 0.04 mag in the direction of the burst \n(Schlegel et al. 1998)).",
  "circularId": 6765,
  "createdOn": 1188220913000,
  "email": "marshall@milkyway.gsfc.nasa.gov",
  "subject": "GRB 070731: Swift/UVOT Upper Limit",
  "submitter": "Frank Marshall at GSFC  <marshall@milkyway.gsfc.nasa.gov>",
  "eventId": "GRB 070731"
}