{
  "bibcode": "2010GCN.10720....1M",
  "body": "F.E. Marshall (NASA/GSFC) and S.T. Holland (CRESST/USRA/GSFC) \nreport on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT has monitored the optical flux from GRB 100418A \nsince shortly after the BAT trigger (Marshall et al., GCN Circ. 10612).\nThe highest flux was seen at about T+50 ks, followed by a power-law\ndecay with an index of -1.0 +/- 0.1 in the UVOT white filter \n(Siegel et al., GCN Circ. 10645). The power-law decay continued\nuntil about T+700 ks, after which time the flux has remained\napproximately constant at about 22.3 mag in the white filter\nthrough the latest observation at about T+1.2 Ms.\nThis late plateau may be due to flux from the host galaxy\n(Malesani, GCN Circ. 10621). We note that the white magnitude is 0.6 mag\nbrighter than the SDSS g magnitude, but this may be due to\nthe very different filter responses. Other possibilities for the plateau\ninclude a very bright SN (Malesani, GCN Circ. 10621; Filgas et al.,\nGCN Circ. 10644) or optical flaring, which was seen earlier\nin the light curve (Bikmaev, GCN Circ. 10635; Covino et al.,\nGCN Circ. 10646). \n\nSwift continues to monitor GRB 100418A and observations with other\ntelescopes are encouraged.\n\nThe above magnitudes are not corrected for the Galactic extinction\ncorresponding to a reddening of E_{B-V} = 0.07 (Schlegel et al.,\n1998, ApJS, 500, 525). The photometry is on the UVOT photometric\nsystem described in Poole et al. (2008, MNRAS, 383, 627).",
  "circularId": 10720,
  "createdOn": 1273090236000,
  "email": "marshall@milkyway.gsfc.nasa.gov",
  "subject": "GRB 100418A: Flattening of the Swift/UVOT Optical Light Curve",
  "submitter": "Frank Marshall at GSFC  <marshall@milkyway.gsfc.nasa.gov>",
  "eventId": "GRB 100418A"
}