Gamma-ray Burst 080825B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #8133
  Y. Evangelista, P. Soffitta, E. Del Monte, I. Donnarumma, M. Feroci, F. Lazzarotto, L. Pacciani, E. Costa, I. Lapshov, M. Rapisarda (INAF/IASF Rome), A. Giuliani, S. Vercellone, A. Chen, S. Mereghetti, A. Pellizzoni, F. Perotti, F. Fornari, P. Caraveo (INAF/IASF Milan), A. Bulgarelli, F. Gianotti, M. Trifoglio, G. Di Cocco, C. Labanti, F. Fuschino, M. Marisaldi, M. Galli, (INAF/IASF Bologna), M. Tavani, G. Pucella, F. D'Ammando, V. Vittorini, A. Argan, A. Trois (INAF/IASF Rome), G. Barbiellini, F. Longo (INFN Trieste), P. Picozza, A. Morselli (INFN Roma-2), M. Prest, E. Vallazza (Universita` dell'Insubria), P. Lipari, D. Zanello (INFN Roma-1), and P. Giommi, C. Pittori, B. Preger, P. Santolamazza, F. Verrecchia (ASDC) and L. Salotti (ASI), on behalf of the AGILE Team, report:
  "SuperAGILE detected a gamma ray burst on 25 August 2008, at 17:46:40 UT. The event was approximately 10 degrees off-axis, with a duration of about 50 s in the 20-60 keV energy range, with a multi-peaked structure. The burst position was reconstructed as (RA, Dec) (209.281 deg, -68.943 deg), which is:

  RA(J2000)  = 13h 57m 07.42s
  Dec(J2000) = -68d 56' 34.0"
  

  with an uncertainty of 3' radius. The given uncertainty accounts for both the statistical and systematic errors.
  An analysis of the AGILE Gamma Ray Imager (GRID) data is in progress."
  This message may be cited.
• GCN/BACODINE POSITION NOTICE
  

  TITLE:           GCN/SuperAGILE NOTICE
  NOTICE_DATE:     Mon 25 Aug 08 21:08:50 UT
  NOTICE_TYPE:     SuperAGILE GRB Ground Position
  TRIGGER_NUM:     599
  GRB_RA:          209.281d {+13h 57m 07s} (J2000),
                   209.453d {+13h 57m 49s} (current),
                   208.294d {+13h 53m 11s} (1950)
  GRB_DEC:         -68.943d {-68d 56' 33"} (J2000),
                   -68.985d {-68d 59' 05"} (current),
                   -68.699d {-68d 41' 55"} (1950)
  GRB_ERROR:       3.00 [arcmin radius, statistical plus systematic]
  GRB_INTEN:       1071.739   919.802 [X & Y cnts]
  GRB_SIGNIF:      17.51  16.30 [sigma]
  GRB_DATE:        14703 TJD;   238 DOY;   08/08/25
  GRB_TIME:        64000.00 SOD {17:46:40.00} UT
  SUN_POSTN:       154.96d {+10h 19m 51s}  +10.40d {+10d 23' 48"}
  SUN_DIST:         87.91 [deg]   Sun_angle= -3.6 [hr] (East of Sun)
  MOON_POSTN:       87.83d {+05h 51m 18s}  +27.46d {+27d 27' 25"}
  MOON_DIST:       126.68 [deg]
  MOON_ILLUM:      29 [%]
  GAL_COORDS:      308.80, -6.82 [deg] galactic lon,lat of the burst (or transient)
  ECL_COORDS:      239.52,-51.84 [deg] ecliptic lon,lat of the burst (or transient)
  COMMENTS:        SuperAGILE GRB Coordinates.  
  COMMENTS:        This is a GRB.  
  COMMENTS:        SuperAGILE ground GRB coordinates  
  

• red DSS finding chart ps-file
  
  
• GCN Circular #8135
  Christina C. Thoene (DARK/NBI), Antonio de Ugarte Postigo (ESO) and Davide Ricci (Univ. of Liege) report:
  We observed the complete 3' error box of the SuperAGILE GRB 080825B (Evangelista et al., GCN 8133) using the Danish 1.54m + DFOSC at La Silla (Chile) starting Aug. 25 at 23:18:31 UT (5.53 hours after the burst). In the first I-band frame we detect a new source not present in the DSS-2 catalogue at the following coordinates (J2000.0 +/- 0.7"):

  RA: 13:56:48.22
  DEC: -68:57:18.5
  

  for which we measure an I-band magnitude of 17.4 +/- 0.2 as compared to several USNO-B1 stars.
  A finding chart can be found at: http://www.sc.eso.org/~adeugart/GRB/080825/080825.jpg
  Further observations and analysis are ongoing to establish the connection to the GRB and the fading of the object.
• GCN Circular #8137
  Antonio de Ugarte Postigo (ESO), Christina C. Thoene (DARK/NBI) and Davide Ricci (Univ. of Liege) report:
  We obtained further observations of the candidate optical counterpart of GRB 080825BB (Evangelista et al., GCN 8133) in Bessel-UBVRI bands. The object is found to be fading in a series of I band images. From 23:18 UT to 01:41 UT, the candidate afterglow faded from 17.4+/-0.2 to 18.1+/-0.2 mag compared to several USNO-B stars, confirming the reality of the afterglow proposed by Thoene et al. (GCN 8135). Furthermore the object is detected in V, R and I band, but not in U and B. We therefore derive a redshift limit of z>3 if the nondetection is due to Lyman alpha absorption or z>4.3 if due to the Lyman limit.
  Further analysis is ongoing.
• GCN Circular #8140
  C. Pagani reports on behalf of the Swift-XRT team:
  We have analyzed the Swift XRT data on the field of the AGILE detected GRB 080825B (Evangelista et al., GCN Circ. 8133), consisting of 7.5 ks of Photon Counting data collected from T0+44 ks to T0+78 ks.
  We detect a point source at the position of the optical afterglow (Thoene et al., GCN Circ. 8135). During the XRT observations the source faded from an initial count rate of 0.05 counts/s to a later count rate of 0.01 counts/s.
  The spectrum from the PC data can be fitted by an absorbed power law model with photon index of 2.1 and the absorption consistent with the Galactic value along the line of sight (2.10e21 cm^-2, Kalberla et al. 2005). The average observed (unabsorbed) flux of the PC mode data is 5.8e-13 (9.0e-13) ergs cm^-2 s^-1.
  This Circular is an official product of the Swift-XRT team.
• GCN Circular #8142
  S. Golenetskii, R. Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, P. Oleynik, D. Svinkin, M. Ulanov and T. Cline, on behalf of the Konus-Wind team report:
  The most intense part of the GRB 080825B localized by SuperAGILE (Evangelista et al., GCN 8133) triggered Konus-Wind at T0=64012.487 s UT (17:46:52.487).
  The burst light curve shows a weak emission starting at ~T0-70s, the main multipeaked part (from ~T0-5s to ~T0+15s), and an extended emission seen up to ~T0+40s.
  As observed by Konus-Wind the burst had a fluence of 7.81(-0.70, +0.83)x10^-6 erg/cm2, and a 256-ms peak flux measured from T0-0.080 s of 1.21(-0.31, +0.32)x10^-6 erg/cm2/s (both in the 20 keV - 1 MeV energy range).
  The spectrum of the most intense part (from T0 to T0+16.640 s) is well fitted (in the 20 keV-1 MeV range) by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.13(-0.36, +0.40), and Ep = 72(-9, +11) keV (chi2 = 40.0/51 dof). Fitting by GRBM (Band) model yields: the low-energy photon index is alpha = -1.05(-0.38, +0.56), the high energy photon index beta < -2.52, the peak energy Ep = 71(-9, +11) keV (chi2 = 38.8/50 dof). All the quoted errors are at the 90% confidence level.
  The Konus-Wind light curve of this GRB is available at http://www.ioffe.rssi.ru/LEA/GRBs/GRB080825_T64012/
• GCN Circular #8143
  We used the spectral parameters of GRB 080825B provided by Golenetskii et al. (GCNC 8142) to compute the spectral pseudo-redshift(**) of this burst localized by SuperAGILE (Evangelista et al., GCN 8133).
  We find a pseudo-redshift pz=3D 0.83 =B1 0.30
  (**) cf. http://www.ast.obs-mip.fr/grb/pz
• GCN Circular #8158
  P. J. Brown (PSU) reports on behalf of the Swift/UVOT team:
  The Swift/UVOT observed the field of GRB 080825B starting about 45 ks after the SuperAGILE detection (Evangelista et al., GCN Circ. 8133). We do not detect the optical afterglow seen by Thoene et al. (GCN Circ. 8135) in any of the UVOT filters down to the following 3 sigma upper limits.

  Filter  T_start(s) T_stop  Exp(s)   MagLimit
  white   49916      50823   885      >22.1
  uvw2    44237      78448   1903     >21.5
  uvm2    61477      67242   988      >20.8
  uvw1    67248      73020   1036     >20.9
  u       73027      73522   483      >20.8
  b       49004      49911   885      >21.2
  v       45144      61472   1234     >20.5
  

  The above magnitudes are not corrected for the Galactic extinction corresponding to a reddening of E(B-V) ~ 0.25 mag (Schlegel et al., 1998, ApJS, 500, 525). The photometry is on the UVOT photometric system described in Poole et al. (2008, MNRAS, 383,627).
• 1011.1205 from 5 Nov 10
  T. Krühler et al.: Photometric redshifts for GRB afterglows from GROND and Swift/UVOT
  We present a framework to obtain photometric redshifts (photo-zs) for gamma-ray burst afterglows. Using multi-band photometry from GROND and Swift/UVOT, photo-zs are derived for five GRBs for which spectroscopic redshifts are not available. We use UV/optical/NIR data and synthetic photometry based on afterglow observations and theory to derive the photometric redshifts of GRBs and their accuracy. Taking into account the afterglow synchrotron emission properties, we investigate the application of photometry to derive redshifts in a theoretical range between z~1 and z~12. The measurement of photo-zs for GRB afterglows provides a quick, robust and reliable determination of the distance scale to the burst, particularly in those cases where spectroscopic observations in the optical/NIR range cannot be obtained. Given a sufficiently bright and mildly reddened afterglow, the relative photo-z accuracy is better than 10% between z=1.5 and z~7 and better than 5% between z=2 and z=6. We detail the approach on 5 sources without spectroscopic redshifts observed with UVOT on-board Swift and/or GROND. The distance scale to those same afterglows is measured to be $z=4.31^{+0.14}_{-0.15}$ for GRB 080825B, $z=2.13^{+0.14}_{-0.20}$ for GRB 080906, $z=3.44^{+0.15}_{-0.32}$ for GRB 081228, $z=2.03^{+0.16}_{-0.14}$ for GRB 081230 and $z=1.28^{+0.16}_{-0.15}$ for GRB 090530. Combining the response from UVOT with ground-based observatories and in particular GROND operating in the optical/NIR wavelength regime, reliable photo-zs can be obtained from z ~ 1.0 out to z ~ 10, and possibly even at higher redshifts in some favorable cases, provided that these GRBs exist, are localized quickly, have sufficiently bright afterglows and are not heavily obscured.