{
  "bibcode": "2007GCN..6572....1B",
  "body": "J. S. Bloom (UC Berkeley), L. Pollack (UC Santa Cruz), D. A. Perley  \n(UC Berkeley) report:\n\n\"We observed the field of GRB 070621 (GCN #6560) in the K-prime  \nfilter using\nthe Laser Guide Star (LGS) Adaptive Optics (AO) system + NIRC2 on the\nKeck II telescope.  With integrations of 60 sec per frame, we stacked\n45 frames with a mean time since GRB trigger of 13.8 hr.  The brighter\ncompact sources in the field have typical FWHM of 130 mas, and the\npreliminary 5 sigma detection threshold is K-prime = 21.5 mag.  With\nfurther refinements we expect this limit to improve.\n\nA number of sources mentioned in previous circulars are detected (*)\nas well as a few red and faint sources near the XRT position. In\nparticular, we note source l1 (ra=21:35:10.22, dec=-24:49:07.4, J2000)\nwhich is 0.8 arcseconds East of apparent galaxy s1 (Bloom et al. GCN\n#6568 = Malesani et al. source #1 GCN #6565?).  The source near the\nEastern edge of the XRT position (l2) is nearly coincident with the\nposition of s4 (Bloom et al. GCN #6568 = Tanvir et al. source #2 GCN\n#6570) but appears only marginally extended at K-prime. Both l1 (being\nquite red and close to a galaxy) and l2 (appearing nearly point-like\nand close to the XRT position) are of prime interest in the search for\nthe afterglow of this GRB.  Given the large number of sources in the\nfield and the quality of the laser AO images, if either l1 or l2 are\nconfirmed as the GRB afterglow then the astrometric accuracy will be\ncomparable to that obtained previously with early and late HST\nimaging of other afterglows.\"\n\n(*) http://lyra.berkeley.edu/~jbloom/grb070621_bloom_kecklaser.pdf\n\nWe thank the WMKO staff for their assistance in obtaining these\nobservations, especially Randy Campbell and Al Conrad.",
  "circularId": 6572,
  "createdOn": 1182531708000,
  "email": "jbloom@astron.berkeley.edu",
  "subject": "Keck Laser Guide Star Adaptive Optics Imaging of GRB 070621",
  "submitter": "Josh Bloom at UC Berkeley  <jbloom@astron.berkeley.edu>",
  "eventId": "GRB 070621"
}