Gamma-ray Burst 000830

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN notice #779
  K. Hurley, on behalf of the Ulysses GRB team, T. Cline, on behalf of the Konus-Wind and NEAR GRB teams, and E. Mazets and S. Golenetskii, on behalf of the Konus-Wind GRB team, report:
  Ulysses, Konus, and NEAR observed this burst at 85793 s UT. As observed by Ulysses, it had a duration ~9 s, a 25-100 keV fluence of ~5.2x10^-6 erg/cm^2, and a peak flux over 0.5 s of ~1.3x10^-6 erg/cm^2 s. We have triangulated this burst to a preliminary, 3 sigma error box with area ~38 sq. arcmin., whose coordinates are:
  

      RA(2000)                 DEC(2000)
   23 h 34 m 12.08 s      6 o 20 '  47.07 "  (CENTER)
   23 h 34 m 22.60 s      6 o 20 '  31.35 "  (CORNER)
   23 h 33 m 41.31 s      6 o 14 '  35.26 "  (CORNER)
   23 h 34 m 42.79 s      6 o 27 '   0.40 "  (CORNER)
   23 h 34 m  1.57 s      6 o 21 '   2.92 "  (CORNER)
  

  This error box may be improved.
• GCN notice #780
  Paul Price, Tim Axelrod and Brian Schmidt (RSAA, ANU) report:
  We have observed the error box of GRB000830 (Hurley et al., GCN #779) with 3 x 300s exposures with the 50-inch telescope at Mount Stromlo Observatory starting 31.73 August 2000 UT, i.e. 17.8 hr after the burst. Our R_MACHO and B_MACHO images cover all but the eastern-most half arcminute of the error box, and are slightly deeper than the Digital Sky Survey (DSS). We find no optical afterglow candidate as compared with the DSS to a 3-sigma limiting magnitude of R_MACHO ~ 20.5 mag.
• GCN notice #781
  James Rhoads reports:
  I recently proposed that GRB afterglows can be found in single epoch observations using optical color-color diagrams (Rhoads 2000, astro-ph/0008461). This is possible because afterglows generally have power law spectra, which can be distinguished from curved stellar spectra in color-color plots.
  GRB 000830 may be a good test case to try this method, given its medium-sized error box and the nearly moonless sky.
  The required observations would include I band, either U or B band, and either V or R band. The approximate colors expected for an afterglow are U-B=-0.75, B-V=+0.35, V-R=+0.4, R-I=+0.5 (for standard Johnson-Cousins magnitudes and an f_nu ~ nu^-1 power law spectrum). The relative depth required in different filters can be estimated from these colors. Absolute photometric calibration is not strictly needed so long as enough area is covered to get a clearly defined stellar locus in the color-color plane.
  The required photometric accuracy depends on the spectral coverage. With U, V and I filters, the afterglows are expected to lie about 0.7 magnitudes from the stellar locus. Using instead B, V, R, I filters gives a smaller offset of about 0.2 magnitudes. The large color-plane offset with the U filter approximately balances the extra difficulties of obtaining U band data.
  The middle filter (i.e., V or R) should be observed last, so that fading behavior will serve to increase the apparent offset of the afterglow from the stellar locus rather than reducing it.
  Given the 38 square arcminute error box of GRB 000830, one might expect about one quasar of magnitude R ~ 22 in the error box; any brighter point source with the expected colors of an afterglow is unlikely to be a quasar, while at fainter magnitudes multiple candidates (most of them quasars) would be expected.
  More details of the method are available from http://xxx.lanl.gov/abs/astro-ph/0008461 .
• GCN notice #784
  V.Rumjantsev and I.Savanov (on behalf of Crimean Observatory and Space Research Institute (Moscow) GRB follow-up teams) report:
  We have obtained on 2000 Sept. 01 21:24:15 (UT) images of the IPN error box (Hurley, et al. GCN 779) for GRB 000830 with the AT-64 telescope (D=640, F/1.4) with a SBIG ST-8 1530x1020 CCD and without filter in visible light. Conditions were not so good. Our images cover all but the square half degree. We find no optical afterglow candidate as compared with the Digital Sky Survey (DSS) to a 3-sigma limiting magnitude of ~ 20.0 mag.
• GCN notice #785
  A. Henden (USRA/USNO) reports on behalf of the USNO GRB team:
  We have acquired preliminary BVRcIc all-sky photometry for an 11x11 arcmin field that covers the center of the error box for GRB000830 with the USNOFS 1.0-m telescope on one photometric night. Stars brighter than V=14 are saturated and should be used with care. We have placed the photometric data on our anonymous ftp site: ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb000830.dat. The current photometry has a potential external zero-point error of less than two percent. The astrometry in this file is based on linear plate solutions with respect to USNO-A2.0. The internal errors are less than 100mas. Further calibration of this field will be performed if an optical afterglow is identified.
• GCN notice #786
  E. Palazzi, N. Masetti (ITESRE, CNR, Bologna), A. Magazzu, M. Pedani, S. Benetti (TNG) and E. Pian (OATs, Trieste), on behalf of a larger collaboration, report:
  We acquired optical B-band images of the central part of the GRB000830 error box (Hurley et al., GCN #779) on 2000 Aug. 31.99, Sep. 2.03 and Sep. 3.16 UT (i.e. 24, 49 and 76 hours after the GRB) with TNG+Dolores. The total exposure time was 15 minutes for each epoch. Seeing was 1.2, 1.1 and 1.5 arcsec on the three epochs, respectively. The pointings covered about 75% of the GRB error box.
  Photometric calibration was performed using USNO-A2.0 catalog stars. No new object brighter than the DSS-II limit is detected inside the GRB error box in any of the three images (note however that the DSS-II plates are in the R-band filter). Also, the comparison between pairs of epochs does not reveal any object with significant brightness variation down to a 3-sigma limiting magnitude B ~ 24.0.
• GCN notice #787
  P. Price, I. Cotoros, A. Diercks, J. S. Bloom, R. Gal and S. G. Djorgovski report on behalf of the larger Caltech-NRAO-CARA GRB collaboration:
  We have imaged the error box of GRB000830 (Hurley et al., GCN #779) with the Palomar 60-inch telescope at Sep 3.25 and Sep 4.28 UT. Our images cover the entire error box in two pointings, each of total integration time 3600s. There is substantial overlap (approximately 21.26 sq arcmin) between the two pointings in the central region of the error box. The magnitude limits (based on Henden, GCN #785) in this central region are R = 23.6 mags and R = 23.9 mags (3 sigma) for the first and second epochs respectively. We do not detect any object with significant variability between the two epochs.
• GCN notice #788
  B. L. Jensen, H. Pedersen, J. Hjorth (U. of Copenhagen) J. Gorosabel (DSRI, Copenhagen), J. P. U. Fynbo (ESO, Garching) and W. Nowotny (U. of Vienna), on behalf of a larger European GRB collaboration, report:
  We have obtained images covering the error box of GRB 000830 (Hurley et al, GCN #779) with the 2.56-m Nordic Optical Telescope (NOT) (+ALFOSC) on La Palma, and the 1.54-m Danish Telescope (+DFOSC) on La Silla, as follows:
  

  Start (UT)   Tel.  Filter  Exp.time  Seeing Lim.Mag
  ===================================================
  Aug. 31.98   NOT      R      6x600s   0.9"   ~24.5
  Sept. 1.00   NOT      I      4x300s   0.8"   ~23.3      
    "   1.02   NOT      U      3x300s   1.1"   ~23.5
    "   1.09   DK1.5m   R     8x1200s   1.6"   ~24.2
    "   1.21   DK1.5m   V     6x1200s   1.7"   ~24.5
  Sept. 2.06   NOT      R      7x600s   0.8"   ~24.6
    "   2.09   DK1.5m   R    10x1200s   1.3"   ~24.5
    "   2.24   DK1.5m   V     6x1200s   1.4"   ~24.7
  Sept. 3.13   NOT      R      7x600s   1.1"   ~24.3
    "   3.15   DK1.5m   R     8x1200s   1.2"   ~24.5
  Sept. 4.09   DK1.5m   R     5x1200s   1.5"   ~23.6
  

  The NOT images covered the central 70%, and the DK1.5-m images, about 95% of the error box. The photometric calibration in VRI-bands is based on the photometry reported by Henden (GCN #785). Comparison of the images reveal no significantly variable object down to R=24.5 (3 sigma).