{
  "bibcode": "1998GCN...157....1R",
  "body": "James Rhoads, Arjun Dey, Buell Jannuzi, and Megan Sosey (on behalf of\nthe KPNO GRB followup team); Sylvio Klose; Daniel Reichart; Andrew\nFruchter; and Francisco Castander report:\n \nWe have used data obtained by Rhoads on the night of 980403 UT to\ncalibrate Klose's I band measurement of the optical transient\nassociated with GRB 980329 (GCNC #43).  We find an optical transient\nmagnitude I=20.8 +- 0.3 on March 29.8-30.0 (cf. Reichart et al, in\npreparation).  The corresponding flux density is 11 +- 3 microJansky.\nThe data consisted of 1200 seconds integration per filter on the GRB\n980329 field in R band (April 3.147) and I band (April 3.167) at\nairmass 1.1, plus brief R and I band observations of the SA107 field\nat airmass 1.4.  The data were taken with the 4 meter Mayall telescope\nand Mosaic CCD Imager at Kitt Peak National Observatory.  Weather was\nphotometric with poor image quality (from 1.25 to 1.75 arcsec).\nDetails of the photometric calibration and a table of reference star\nmagnitudes in the GRB 980329 field are at the end of this circular.\n\nWe used the same data to measure the flux at the location of the\ntransient.  No obvious source is present at the location of the\ntransient (7:02:38.0 +38:50:44 J2000.0) in either filter.  R band\nphotometry using a 0.75 and 1.25 arcsecond radius apertures, corrected\nfor aperture losses using the curve of growth, yield flux estimates\nof 0.40 +- 0.25 and 0.80 +- 0.25 microJansky, where the error bar\nincludes contributions from photon counting noise and from sky\nsubtraction uncertainties only.  Conservatively, this gives a 3 sigma\nupper limit of 1.50 microJansky (for a one-sided confidence interval\nwith probability 99.73%) and R > 23.3 magnitudes.\n\nFor the I band, the aperture-corrected point source fluxes measured in \n0.75 and 1.25 arcsecond radius apertures are 0.06 +- 0.51 and -0.12 +- 0.44\nmicroJansky.  The first implies a 3 sigma upper limit of 1.48 microJansky\nand to I > 23.0, while the second gives an upper limit of 1.10 microJansky\nand I > 23.3 magnitudes.\n\nIn addition, we report a K band upper limit using data obtained by\nDey, Jannuzi, and Sosey (on behalf of the NOAO Deep Widefield Survey\nteam) on 1998 April 3.205 using the Kitt Peak National Observatory 2.1\nmeter telescope and ONIS camera.  No point source is apparent at the\nlocation of the transient.  The RMS counts in the image imply a 3\nsigma upper limit of 13.4 microJansky for a point source (in a 1\narcsec radius aperture and corrected using the curve of growth),\nwhich corresponds to K > 19.2 at the 3 sigma level.\n\n - Details of the photometric calibrations - \nReliable optical fluxes were measured for the Landolt standard stars\nSA107-212, 213, 357, 359, 351, 457, 456, 600, 599, 612, 626, and 627.\nStandard star and GRB field photometry was done in a similar fashion,\nwith growth curves derived from multiaperture photometry used to\ncorrect all magnitudes to an effective 7\" radius.  The photometric\nerrors in the GRB frame were taken from the IRAF \"mkapfile\" task,\nwhich applies the aperture corrections.  Additional errors were added\nin quadrature to account for uncertainties in the photometric zero\npoint (+- 0.004 mag in both R and I), color correction terms (+-\n0.07*[R-I - 0.42]), and airmass correction term (+- 0.01 mag for I\nband and +- 0.024 mag for R band).\n \nThe table of measured magnitudes for objects near GRB 980329:\n# RA (J2000) Dec        R     err(R)      I    err(I)\n#\n7:02:39.0 38:50:32.7  15.7     1.0      15.300  0.2 \n7:02:37.5 38:50:33.5  15.85    1.0      15.450  0.12\n7:02:35.1 38:50:23.2  16.30    0.3      15.988  0.036 \n7:02:40.1 38:50:11.8  16.9664  0.0314   16.647  0.0155\n7:02:39.4 38:50:03.1  18.4428  0.0275   18.093  0.0175\n7:02:38.7 38:50:26.9  20.655   0.0646   19.473  0.0623\n7:02:36.6 38:50:36.3  20.3862  0.0536   19.331  0.0478\n7:02:36.3 38:50:19.8  20.5135  0.0464   19.625  0.0459 \n7:02:38.4 38:50:50.7  21.2876  0.0688   20.026  0.0711 \n7:02:51.0 38:49:31.0  17.6592  0.0456   16.668  0.0399 \n7:02:50.4 38:49:57.1  17.9663  0.0258   17.539  0.0161\n#\nUsers of this table should be aware that the magnitude uncertainties\nfor the different stars include some sources of systematic error\n(airmass and color terms) that are not independent from star to star.\nAlso, the first two entries are substantially saturated in R and I;\nthe third is substantially saturated in R and perhaps marginally in I;\nand the fourth may be marginally saturated in R.  Photometric errors\nquoted for saturated stars are approximate guesses.\n \nMore detail, and sections of the processed R and I band images, are\navailable from  http://www.noao.edu/noao/grb/980329.html .\nThis report is citable.",
  "circularId": 157,
  "createdOn": 911457864000,
  "email": "rhoads@noao.edu",
  "subject": "GRB980329 R,I flux calibration and R,I,K upper limits",
  "submitter": "James Rhoads at KPNO  <rhoads@noao.edu>",
  "eventId": "GRB 980329"
}