Gamma-ray Burst 000528

A GRB was detected on May 28, 2000 at 08:46:35 UT with BeppoSAX, Ulysses and NEAR, and localized to better than 2 armin.

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• BeppoSAX mail n.00/10
  On May 28 at 08:46:35 UT a strong and long burst (GRB000528) was detected by GRBM and WFC2 (2-26 keV).
  The position is:

  R.A.= 161.354
  Decl.= -34.002
  

  with an error radius of 4'.
  The follow-on is technically feasible, but the unavailability of Mission Planners during Sunday and the switching-off of instruments during weekend nights doesn't allow a useful and fast repointing of satellite (see GCN 634).
• BeppoSAX MAIL n. 00/11
  Refined coordinates from WFC are:

  R.A.(2000)= 161.276
  DEC(2000)= -33.983
  

  i.e. 4' off from the preliminary position. The error radius is 2'.
  Thanks to BeppoSAX staff personal efforts we are planning a NFI follow-on, with the instruments switched on during the whole night.
• GCN notice #674
  B. L. Jensen, J. Hjorth, H. Pedersen (University of Copenhagen), J. Gorosabel (DSRI), J. A. L. Aguerri (IAC), and A. A. Kaas (NOT) report on behalf of a larger European collaboration:
  We have imaged the error circle of GRB 000528 (Piro & Gandolfi, BeppoSAX Mail ## 00/10, 00/11) with the 2.5-m Nordic Optical Telescope. Two 300-s R-band exposures were obtained with ALFOSC on 28.90 May 2000 UT. The data were obtained at high (2.7) airmass but in fairly good seeing (1.4" FWHM) and reach a limiting magnitude of about R = 22.3. No obvious candidate optical counterpart to GRB 000528 is found down to a limit of R ~ 21.5 by comparison with the Digitized Sky Survey (DSS-2, AAO SES red). The NOT image is posted at http://www.astro.ku.dk/~brian_j/grb/grb000528/ .
• GCN notice #675
  C. Guidorzi, E. Montanari, F. Frontera (Department of Physics, University of Ferrara, Italy) and M. Feroci (IAS/CNR, Rome) on behalf of a larger collaboration report:
  With reference to the GRB000528 occurred on May 28.366 UT and localized with the BeppoSAX WFC no. 2 (see BeppoSAX Mails ## 00/10 and 00/11), a preliminary analysis of the GRBM data shows a complex time profile of this GRB with two main peaks of decreasing intensity. The peak flux is of 1.7E3 cts/s in the 40-700 keV energy band corresponding to 1.44 +/- 0.04) x 10^(-6) erg/cm2/s . The GRB duration is of about 80 s. A preliminary spectral analysis reveals an evident softening evolution with an average power law photon index of about 1.9. We are now able to derive rough GRB positions from the GRBM data. The GRBM position obtained for this GRB is R.A.(2000)= 160 and DEC(2000) = -29 with an error radius of 5 deg, that is fully consistent with that given with the WFC.
• GCN notice #677
  J. in 't Zand and J. Heise, Space Research Organization of the Netherlands (SRON), Utrecht; E. Kuulkers, SRON and Astronomical Institute, Utrecht University; G. D'Andreta and G. Celidonio, BeppoSAX Science Operations Center, Telespazio, Rome; J.M. Muller, SRON and BeppoSAX Science Data Center, Telespazio, Rome; G. Gandolfi and E. Costa, Istituto di Astrofisica Spaziale, CNR, Rome; and F. Frontera, Istituto Tecnologie e Studio Radiazioni Extraterrestri, Bologna, report: "GRB 000528, which was detected by the BeppoSAX Gamma-Ray Burst Monitor on May 28.366 UT (GCN Circ. 675), was simultaneously detected with Wide Field Camera (WFC) unit 2. While the burst lasted for about 80 s in gamma-rays (40-700 keV), it lasted about 120 s in x-rays (2-26 keV). The WFC-determined position is R.A. = 10h45m06.3s, Decl. = -33o58'59" (equinox 2000.0), with an error radius of 2' (99-percent confidence level). The 2-26 keV peak flux is 1.9 Crab units.
• GCN notice #681
  K. Hurley, on behalf of the Ulysses GRB team, T. Cline and E. Mazets, on behalf of the Konus-Wind GRB team, and F. Frontera, C. Guidorzi, and E. Montanari, on behalf of the BeppoSAX GRBM team, report:
  Ulysses, Konus, and the BeppoSAX GRBM observed this burst (GCN #677). Triangulation gives a preliminary annulus centered at RA(2000)=129.532, Decl.(2000)=-33.150, with radius 26.478 +/- 0.111 degr. (3 sigma). This annulus intersects the BeppoSAX WFC error circle at two points (RA, Decl.=161.292, -34.013, and RA, Decl.=161.283, -33.950), reducing its area by over a factor of two. A map has been posted at ssl.berkeley.edu/ipn3/000528. This localization can be improved.
  In addition, we call attention to the fact that the Ulysses data clearly show a second episode of emission which follows the burst by ~600 seconds, with intensity approximately as great as that in the burst itself. It is possible that this is from the same source as the burst; we are investigating whether the Konus or GRBM data can be used to verify this. The time history has been posted at the same site.
• GCN notice #683
  A BeppoSAX follow up of GRB000528 with the Narrow Field Instruments started around May 28 at 20:50 UT, i.e. about 12 hours after the GRB.
  Preliminary analysis of the MECS (1.6-10 keV) data shows two previously unknown sources inside the field. The preliminary WFC error box (BeppoSAX Mail #10) contains both objects, while the refined one (BeppoSAX Mail #11 and GCN 677) only the second.

  Object #1:
   
    R.A.(2000)= 161.365
    DEC(2000)= -33.975
   
  Object #2:
   
    R.A.(2000)= 161.287
    DEC(2000)= -33.986
   

  both with an error radius of 1.5'.
  The source #1 is possibly fading, while the #2 seems to be consistent with a constant flux. Further and more detailed analysis are in progress.
• GCN notice #686
  E. Berger (Caltech) and D. A. Frail (NRAO) report on behalf of a larger collaboration:
  On June 1.11 UT we used the VLA at 8.46 GHz to observe the field centered on the refined position provided by the SAX WFC (GCN 677). There are no obvious radio candidates brighter than 0.14 mJy (3.5 sigma) inside the 1.5' region centered on object #2, which was identified by the SAX NFI (GCN 683). The 1.5' region centered on object #1 contains one bright source which is also present in the NRAO VLA Sky Survey (NVSS). Further observations are planned.
• GCN notice #691
  E. Palazzi, N. Masetti, E. Pian, F. Frontera (ITESRE, CNR, Bologna), A.J. Castro-Tirado (LAEFF, IAA), J. Hjorth (Univ. of Copenhagen), P.M. Vreeswijk, E.P.J. van den Heuvel (Univ. of Amsterdam), J. Greiner (AIP), P. Francois, J. Brewer and O. Hainaut (ESO) and L. Piro (IAS, CNR, Rome), on behalf of a larger collaboration, report:
  We obtained optical R-band images of the field of GRB000528 (BeppoSAX Mails #00/10, #00/11) on 2000 May 29.10, May 29.96 and June 4.02 UT (i.e. 18 hr, 38 hr and 160 hr after the GRB, respectively) with the 1.54-meter Danish telescope (plus DFOSC) at ESO - La Silla (Chile). These images contain the BeppoSAX WFC error box of this GRB (GCNs #677, #681) and the two MECS sources reported in GCN #683. Seeing was ~1.3 arcsec on the three epochs. Exposure times were 15 min for the first observation, 10 min for the second and 45 min for the third.
  Photometric calibration was performed using standard stars in the Landolt field SA107 (Landolt 1992, AJ 104, 340). The comparison between pairs of images does not reveal any object with significant brightness variation down to a 3-sigma limiting magnitude of R ~ 23.3.
• GCN notice #700
  E. Kuulkers, L. Kuiper, J.J.M. in 't Zand, J. Heise (Space Research Organization Netherlands), L.A. Antonelli (Osservatorio Astronomico di Roma), K. Hurley (University of California, Berkeley), L. Salotti (ASI, Rome), M. Stornelli, G. Celidonio (Telespazio, Rome), E. Costa, M. Feroci, G. Gandolfi (IAS-CNR, Rome), F. Frontera (ITESRE-CNR, Bologna, and University of Ferrara) L. Nicastro (IFCAI-CNR, Palermo), T. Cline (NASA Goddard Space Flight Center), E Mazets (Ioffe Physici-Technical Institute, St. Petersburg), C. Guidorzi, and E. Montanari (University of Ferrara) report:
  The BeppoSAX narrow-field instruments observed the region of GRB000528 twice: from May 28.71 to May 29.57 UT (TOO1, 8.3-28.9 hours after the burst) and from May 31.65 to June 1.49 (TOO2). The total exposure time obtained with the Medium-Energy Concentrator Spectrometers (MECS) is 58 ksec. Two X-ray sources close to one another were detected in the field, one at R.A. = 10h 45h 28m, Dec. = -33d 58' 14" (J2000.0), which we designate as 1SAX J1045.5-3358 (object 1 in GCN 683), and the other at R.A. = 10h 45m 08s, Dec. = -33d 59' 26", which we designate as 1SAX J1045.1-3359 (object 2 in GCN 683). Both sources have a conservative positional error of 1.5'. Object 2 is inside the WFC error region (GCN 677) while the centroid of object 1 is 2.5 arcmin outside that region. We note that a bright and archival radio source has been reported coincident with object 1 (GCN 686). A refined IPN analysis using Ulysses, BeppoSAX, and Konus data indicates that object 1 is far less consistent with the IPN annuli than object 2. The countrates for object 1 in MECS units 2 and 3 combined are (2.10+/-0.44)E-3 and (1.21+/-0.36)E-3 c/s for TOO1 and TOO2 respectively and for object 2 (2.40+/-0.46)E-3 and (0.65+/-0.32)E-3 c/s. Object 2 shows the strongest fading. Based on all pieces of information, we identify object 2 (1SAX J1045.1-3359) as the likely X-ray afterglow of GRB 000528.
  For maps of the error regions, see URL http://wfc.sron.nl/GRB000528/
  Contour maps of source detection significances in he MECS 2-10 keV data for TOO1 (26.6 ks exposure, upper map) and TOO2 (31.2 ks, lower map). The contours start at 3sigma and go up in steps of 1sigma. The two axes are in instrument coordinates (in units of arcsec). The dark-shaded area designates the overlap between the refined Ulysses/BeppoSAX annulus and the Ulysses/Konus annulus, the light-shaded circle inside this area is the WFC error region. The positions of the two sources were determined using TOO1 and are indicated by the square (object 1) and triangle (object 2). Object 1 is coincident with an archival radio source (GCN 686) and is apparent in both TOOs. Object 2 is not present in TOO2 and is the proposed X-ray afterglow.

  Neither the WFC nor the GRBM observed the delayed emission 600 s after the burst (GCN 681); the source was unocculted at this time, and this emission would have been detected with high significance if it had originated from this source. We conclude that this emission was either solar in origin, or possibly from a different GRB.