{
  "bibcode": "2005GCN..2933....1G",
  "body": "B. M. Gaensler (CfA), C. Kouveliotou (NASA/MSFC, NSSTC), R. Wijers\n(U. Amsterdam), M. Garrett (JIVE), M. Finger, P. Woods, S. Patel (USRA,\nNSSTC), M. McLaughlin (Jodrell Bank), R. Fender (U. Southampton),\nT. Delaney (CfA) report on behalf of a larger team:\n\nWe observed the soft gamma-ray repeater SGR 1806-20 with the Very Large\nArray (VLA) in the A-configuration for a second time on January 4,\n2005 for one hour (14:15-15:15 UT). We detect the source at the same\ncoordinates as reported by Gaensler et al. (GCN 2929). Preliminary flux \nlevels, including improved estimates of the fluxes reported in GCN 2929, \nare as follows (the numbers in parentheses indicate 3 sigma errors in the \nlast decimal points):\n\nFrequency   Flux (2005 Jan 03.8)   Flux (2005 Jan 04.6)\n (GHz)               (mJy)                 (mJy)\n---------   --------------------   --------------------\n  1.4               172(4)               135(10)\n  4.9                80(1)                66(2)    \n  8.5                53(1)                38(5) \n\nThese results indicate a decay in the flux at a rate of approximately\n1.9 mJy/hour at 1.4 GHz. At the same time the spectrum has remained constant. \nOn Jan 3, 2005 the spectral index (in the sense F_nu ~ nu^alpha) was alpha =\n-0.65+/-0.05, while on Jan 4, 2005 the spectral index was -0.61+/-0.06.\n\nA reanalysis of the VLA data from 3 Jan 2004 (GCN 2928, 2929) suggests that \nthe radio source associated with SGR 1806-20 is slightly extended at both 4.9 \nand 8.5 GHz. Assuming that the underlying geometry is an optically thin, spherical \nthin shell, both data-sets independently suggest a source of approximate \ndiameter 50-100 milliarcseconds. This implies a projected expansion speed of \napprox (0.3-0.6)c over the 7 days since the initial Giant SGR flare (assuming \na source distance of 15.1 kpc; Eikenberry, S. et al., ApJ 616, 506, 2004).\n\nFurther radio observations of this source with the Westerbork Synthesis\nRadio Telescope (WSRT), the MERLIN VLBI network and the Parkes Radio\nObservatory are currently underway or are being scheduled and will be \nreported as they are analyzed. We will continue monitoring the source with \nthe VLA until it fades below detection level.",
  "circularId": 2933,
  "createdOn": 1104851700000,
  "email": "chryssa.kouveliotou-1@nasa.gov",
  "subject": "Second-epoch VLA observations of SGR 1806-20",
  "submitter": "Chryssa Kouveliotou at MSFC  <chryssa.kouveliotou-1@nasa.gov>"
}