TITLE: GCN GRB OBSERVATION REPORT NUMBER: 157 SUBJECT: GRB980329 R,I flux calibration and R,I,K upper limits DATE: 98/11/19 06:44:24 GMT FROM: James Rhoads at KPNO James Rhoads, Arjun Dey, Buell Jannuzi, and Megan Sosey (on behalf of the KPNO GRB followup team); Sylvio Klose; Daniel Reichart; Andrew Fruchter; and Francisco Castander report: We have used data obtained by Rhoads on the night of 980403 UT to calibrate Klose's I band measurement of the optical transient associated with GRB 980329 (GCNC #43). We find an optical transient magnitude I=20.8 +- 0.3 on March 29.8-30.0 (cf. Reichart et al, in preparation). The corresponding flux density is 11 +- 3 microJansky. The data consisted of 1200 seconds integration per filter on the GRB 980329 field in R band (April 3.147) and I band (April 3.167) at airmass 1.1, plus brief R and I band observations of the SA107 field at airmass 1.4. The data were taken with the 4 meter Mayall telescope and Mosaic CCD Imager at Kitt Peak National Observatory. Weather was photometric with poor image quality (from 1.25 to 1.75 arcsec). Details of the photometric calibration and a table of reference star magnitudes in the GRB 980329 field are at the end of this circular. We used the same data to measure the flux at the location of the transient. No obvious source is present at the location of the transient (7:02:38.0 +38:50:44 J2000.0) in either filter. R band photometry using a 0.75 and 1.25 arcsecond radius apertures, corrected for aperture losses using the curve of growth, yield flux estimates of 0.40 +- 0.25 and 0.80 +- 0.25 microJansky, where the error bar includes contributions from photon counting noise and from sky subtraction uncertainties only. Conservatively, this gives a 3 sigma upper limit of 1.50 microJansky (for a one-sided confidence interval with probability 99.73%) and R > 23.3 magnitudes. For the I band, the aperture-corrected point source fluxes measured in 0.75 and 1.25 arcsecond radius apertures are 0.06 +- 0.51 and -0.12 +- 0.44 microJansky. The first implies a 3 sigma upper limit of 1.48 microJansky and to I > 23.0, while the second gives an upper limit of 1.10 microJansky and I > 23.3 magnitudes. In addition, we report a K band upper limit using data obtained by Dey, Jannuzi, and Sosey (on behalf of the NOAO Deep Widefield Survey team) on 1998 April 3.205 using the Kitt Peak National Observatory 2.1 meter telescope and ONIS camera. No point source is apparent at the location of the transient. The RMS counts in the image imply a 3 sigma upper limit of 13.4 microJansky for a point source (in a 1 arcsec radius aperture and corrected using the curve of growth), which corresponds to K > 19.2 at the 3 sigma level. - Details of the photometric calibrations - Reliable optical fluxes were measured for the Landolt standard stars SA107-212, 213, 357, 359, 351, 457, 456, 600, 599, 612, 626, and 627. Standard star and GRB field photometry was done in a similar fashion, with growth curves derived from multiaperture photometry used to correct all magnitudes to an effective 7" radius. The photometric errors in the GRB frame were taken from the IRAF "mkapfile" task, which applies the aperture corrections. Additional errors were added in quadrature to account for uncertainties in the photometric zero point (+- 0.004 mag in both R and I), color correction terms (+- 0.07*[R-I - 0.42]), and airmass correction term (+- 0.01 mag for I band and +- 0.024 mag for R band). The table of measured magnitudes for objects near GRB 980329: # RA (J2000) Dec R err(R) I err(I) # 7:02:39.0 38:50:32.7 15.7 1.0 15.300 0.2 7:02:37.5 38:50:33.5 15.85 1.0 15.450 0.12 7:02:35.1 38:50:23.2 16.30 0.3 15.988 0.036 7:02:40.1 38:50:11.8 16.9664 0.0314 16.647 0.0155 7:02:39.4 38:50:03.1 18.4428 0.0275 18.093 0.0175 7:02:38.7 38:50:26.9 20.655 0.0646 19.473 0.0623 7:02:36.6 38:50:36.3 20.3862 0.0536 19.331 0.0478 7:02:36.3 38:50:19.8 20.5135 0.0464 19.625 0.0459 7:02:38.4 38:50:50.7 21.2876 0.0688 20.026 0.0711 7:02:51.0 38:49:31.0 17.6592 0.0456 16.668 0.0399 7:02:50.4 38:49:57.1 17.9663 0.0258 17.539 0.0161 # Users of this table should be aware that the magnitude uncertainties for the different stars include some sources of systematic error (airmass and color terms) that are not independent from star to star. Also, the first two entries are substantially saturated in R and I; the third is substantially saturated in R and perhaps marginally in I; and the fourth may be marginally saturated in R. Photometric errors quoted for saturated stars are approximate guesses. More detail, and sections of the processed R and I band images, are available from http://www.noao.edu/noao/grb/980329.html . This report is citable.