Gamma-ray Burst 060123

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #4584
  D. Palmer (LANL), J. Kennea (PSU), J. Cummings (GSFC), D. N. Burrows (PSU), N. Gehrels (GSFC), F. Marshall (GSFC), C. Markwardt (GSFC/UMD), J. A. Nousek (PSU), A. Parsons (GSFC) report on behalf of the Swift team:
  At 22:22:40 UT, the Swift Burst Alert Telescope (BAT) located GRB 060123. The burst did not trigger GCN notices because the source was found in a long-term (5 minute) image, for which triggers are not currently enabled. The BAT ground-calculated location is RA,Dec 179.750, +45.513 {11h 59m 00s, +45d 30' 47"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi-peaked structure with a duration of about 900 +- 100 sec. The peak count rate was ~160 counts/sec (15-50 keV, note the unusual energy interval), at ~300 sec after the trigger. We note that this is a very long duration burst, which suggests the possibility of a high-z event.
  At 19:14:14 on Jan 24th, 2006 (75.1 ks after the event) Swift began a target of opportunity observation of this source. Analysis of XRT data reveals a faint, fading, uncataloged point source at the following coordinates:

  RA(J2000):  11h 58m 47.9s
  Dec(J2000): +45d 30' 45.5"
  

  with an error circle of 6 arcseconds (90% containment). This position lies 128 arcseconds from the BAT position of this source. The fading X-ray lightcurve of this object strongly suggests that this is a GRB afterglow.
  UVOT took a 210 second exposure with the V filter starting at 19:14:14 UT. No source was detected with a 3-sigma upper limit of 20.0 mag. at the XRT position.
• GCN Circular #4585
  Richard J. Cool (Arizona), Daniel J. Eisenstein (Arizona), David W. Hogg (NYU), Michael R. Blanton (NYU), David J. Schlegel (LBNL), J. Brinkmann (APO), Donald P. Schneider (PSU), and Daniel E. Vanden Berk (PSU) report:
  The Sloan Digital Sky Survey (SDSS) imaged the field of burst GRB060123 prior to the burst. As these data should be useful as a pre-burst comparison and for calibrating photometry, we are supplying the images and photometry measurements for this GRB field to the community.
  Data from the SDSS, including 5 FITS images, 3 JPGS, and 3 files of photometry and astrometry, are being placed at http://mizar.as.arizona.edu/~grb/public/GRB060123
  We supply FITS images in each of the 5 SDSS bands of a 8'x8' region centered on the GRB position (ra=179.700 (11:58:47.9), dec=45.5126 (45:30:45.5); GCN 4584), as well as 3 gri color-composite JPGs (with different stretches). The units in the FITS images are nanomaggies per pixel. A pixel is 0.396 arcsec on a side. A nanomaggie is a flux-density unit equal to 10^-9 of a magnitude 0 source or, to the extent that SDSS is an AB system, 3.631e-6 Jy. The FITS images have WCS astrometric information.
  In the file GRB060123_sdss.calstar.dat, we report photometry and astrometry of 182 bright stars (r<20.5) within 15' of the burst location. The magnitudes presented in this file are asinh magnitudes as are standard in the SDSS (Lupton 1999, AJ, 118, 1406). Beware that some of these stars are not well-detected in the u-band; use the errors and object flags to monitor data quality.
  In the files GRB060123_sdss.objects_flux.dat and GRB060123_sdss.objects_magnitudes.dat, we report photometry of 428 objects detected within 6' of the GRB position. We have removed saturated objects and objects with model magnitudes fainter than 23.0 in the r-band. The fluxes listed in GRB060123_sdss.objects_flux.dat are in nanomaggies while the magnitudes listed in GRB060123_sdss.objects_magnitudes.dat are asinh magnitudes.
  All quantities reported are standard SDSS photometry, meaning that they are very close to AB zeropoints and magnitudes are quoted in asinh magnitudes. Photometric zeropoints are known to about 2% rms. None of the photometry is corrected for dust extinction. The Schlegel, Finkbeiner, and Davis (1998) predictions for this region are A_U=0.077 mag, A_g=0.057 mag, A_r = 0.041 mag, A_i=0.031 mag, and A_z=0.022 mag.
  The file GRB060123_sdss.spectro.dat contains a list of the 1 objects with SDSS spectroscopy within 6 arcminutes of the GRB position. In addition to the redshift and 1-sigma error for each object, this file also lists the object spectroscopic classification.
  SDSS astrometry is generally better than 0.1 arcsecond per coordinate. Users requiring high precision astrometry should take note that the SDSS astrometric system can differ from other systems such as those used in other notices; we have not checked the offsets in this region.
  More detailed information pertaining to our SDSS GRB releases can be found in our initial data release paper (Cool et al. 2006, astro-ph/0601218). See the SDSS DR4 documentation for more details: http://www.sdss.org/dr4.
  These data have been reduced using a slightly different pipeline than that used for SDSS public data releases. We cannot guarantee that the values here will exactly match those in the data release in which these data are included. In particular, we expect the photometric calibrations to differ by of order 0.01 mag.
  This note may be cited, but please also cite the SDSS data release paper, Adelman-McCarthy et al. (2006, ApJS, in press, astro-ph/0507711), when using the data or referring to the technical documentation.
• GCN Circular #4594
  S. B. Cenko (Caltech), W. Reach, and D. Faied (JPL / IPAC) report on behalf of the Caltech-NRAO-Carnegie Collaboration:
  We have imaged the field of GRB060123 (Palmer et al., GCN 4584) with the Large Format Camera mounted on the Palomar 200-inch Hale Telescope. Observations consisted of 300 s frames in r' and i' beginning at approximately 8:35 January 25 UT (~ 34.2 hours after the burst). In single r' and i' exposures, we find no new sources in the XRT error circle to a limiting magnitude of r',i' > 22.0. This limiting magnitude was calculated with reference to the SDSS calibration stars provided by Cool et al. (GCN 4585).
• GCN Circular #4595
  J. S. Bloom, F. Marchis (UCB), K Smalley, E. E. Falco, C. Blake (CfA), N. Bulter, and R. Foley (UCB) report:
  With high winds and poor transmission on Mt. Hopkins we observed the field of GRB 060123 (Palmer et al., GCN 4584) both with the PAIRITEL 1.3m and the 48" telescope equipped with Keplercam. At time 25.3 Jan 2006 UT we find no significantly new source in i, z, J, H, Ks within the XRT error circle when compared with SDSS (Cool et al. GCN 4585). Imaging in I and z' under better conditions at the Lick 3m + PFCam on Mt. Hamilton began at 25.3 Jan 2006 UT: analysis is still in progress but we confirm the conclusion of Cenko et al. (GCN 4594) that there is no evidence for a new optical source to the SDSS limits. We do note that there is a faint (z_AB = 19.87 mag) apparent galaxy (SDSS J115847.6+453050.8) on the northern outskirts of the 90% containment XRT error circle at J2000: 11:58:47.59, +45:30:50.8."
  A SDSS-PAIRITEL-PFCam triptych may be found at: http://astro.berkeley.edu/~jbloom/grb060123.ps
• GCN Circular #4600
  N. Butler and J. S. Bloom (UC Berkeley):
  We determine a refined XRT positions for GRB060123 (Palmer et al., GCN 4584) by matching the positions of X-ray sources to positions of SDSS sources. A similar procedure was employed in GCN 4500 to refine the XRT position for GRB060108. Using 4 X-ray sources detected in 4.5 ksec of PC mode data and 6 SDSS sources, we determine a frame offset for the XRT of:
  Frame Offset: RA -2.28 ; Dec 2.0 , 90% Conf. Error: 2.7"
  Our refined XRT position for GRB060123 is then:
  RA 11h 58m 47.66s ; DEC +45d 30' 50.55" +/- 3.1" (90% Conf.)
  This refined XRT position is coincident with the SDSS galaxy noted in Bloom et al. (GCN 4595). Given this, we suggest that this coincidence appears to disfavor the high-redshift hypothesis for the burst (Palmer et al., GCN 4584)."
  The X-ray/optical source offsets are shown at: http://astro.berkeley.edu/~nat/060123/crosscor_sdss.jpg
  The XRT overlap atop the SDSS and PAIRITEL images is: http://astro.berkeley.edu/~jbloom/grb060123-nat.ps.gz
  We thank Dave Burrows at PSU for his assistance.
  
• GCN Circular #4608
  J. Cummings (GSFC/ORAU), V. Mangano (INAF-IASFPA), L. Angelini (GSFC), L. Barbier (GSFC), S. Barthelmy (GSFC), D.N. Burrows (PSU), M. Chester (PSU), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (UMD), J. Kennea (PSU), H. Krimm (GSFC/USRA), V. La Parola (INAF-IASFPA), A. Levan (U. Leicester), C. Markwardt (GSFC/UMD), T. Mineo (INAF-IASFPA), J. Norris (GSFC), P. O'Brien (U. Leicester), D. Palmer (LANL) A. Parsons (GSFC), E. Rol (U. Leicester), P. Romano (INAF-OAB), T. Sakamoto (GSFC/ORAU), G. Sato (ISAS), J. Tueller (GSFC), on behalf of the Swift team:
  Using Swift-BAT survey data from T-23 to T+877 sec and target of opportunity (ToO) Swift-XRT observations, we report further analysis of Swift-BAT GRB 060123 (Palmer, et al., GCN 4584).
  T90 was 900 +- 100 seconds (estimated one-sigma error), with multiple peaks but an overall gradual profile. Peak flux was 0.04 +- 0.01 photons/cm2/sec in the 15-150 keV band.
  The prompt emission time-averaged spectrum is well fitted by a simple power law model. The power law index is 1.9 +- 0.6. The fluence in the 15-150 keV band was (3.0 +- 1.2) x 10^-7 erg/cm2.
  A Swift ToO observation started at 19:14:14 on Jan 24th, 2006 (75.1 ks after the event). XRT detected a point source within the BAT error box (Palmer et al, GCN 4584). Subsequent ToO observations revealed that, after an initially flat phase, this source is steadily decaying with a slope of -2.2 +/- 0.4. The initial flat phase extended to ~1.1 x 10^5 sec. Further observations are ongoing.
  The average XRT spectrum accumulated in the time interval from 75.1 ksec to 291 ksec after the event (20 ksec of net exposure) was fitted, using Cash statistics, with an absorbed power law. The best fit photon index is 2.1 +/- 0.2. The spectrum shows evidence of absorption at the level of (2 +/- 1)e21 cm^-2, in excess of the estimated Galactic value (1.6e20 cm^-2, Dickey & Lockman 1990). The average unabsorbed 0.2-10 keV flux is 7.0e-13 ergs cm^-2 s^-1.
  All the quoted errors are at the 90% confidence level except as noted.
  This was an unusual event. It was very long and very gradual, having the longest duration and weakest peak flux of any BAT burst. The GRB nature of the event would be uncertain on the basis of the BAT data alone, but is highly probable given the fading XRT light curve. The flat decay phase extends very late for a GRB. Followup observations are strongly encouraged.
• GCN Circular #4621
  Dale A. Frail (NRAO) reports on behalf of a larger collaboration:
  "We used the Very Large Array to observe the Swift burst GRB 060123 (GCN 4584; GCN 4608) at a frequency of 8.46 GHz on 2006 January 26.47 and January 30.52 UT. No radio emission was detected within the refined 3-arcsec XRT error circle (GCN 4600) above a 4-sigma level at either epoch, with sigma noise values of 26 uJy and 18 uJy, respectively.
  No further observations are planned.
  The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc."
• GCN Circular #4622
  E. Berger (Carnegie Observatories), P. A. Price (IfA, Hawaii), and D. B. Fox (Penn State) report on behalf of a larger collaboration:
  "We obtained 2x1500 sec spectra of the putative host galaxy located inside the XRT error circle of GRB 060123 (GCNs 4584,4595,4600) with GMOS on the Gemini-N 8-m telescope starting on 2006 Jan 30.60 UT. The spectra cover the range 6400-9100 A and reveal one strong and resolved emission line at an observed wavelength of 7826.0A, and a possible weaker line at 7590.8A. The latter line is located on the edge of the atmospheric A-band and and its reality is therefore questionable. We find three possible interpretations for the redshift:
  [1] The broad line is the (barely resolved) [OII] 3727 doublet at z=1.099. In this case there is no obvious interpretation for the second line.
  [2] The broad line is H-alpha and the weak line line is [OI] 6364 at z=0.193. In this case we may expect to detect the [NII] and [SII] doublets, which we do not.
  [3] The broad line is [OIII] 5007 and the weak line is H-beta at z=0.562. In this case we expect to detect [OIII] 4959, which we do not.
  Given that the weak line may not be real, and the lack of detection of various other lines expected in scenarios [2] and [3], we favor the first interpretation and a redshift z=1.099.
  We note that spectra with bluer coverage may be able to confirm or rule out options [2] and [3] through the detection (or lack thereof) of [OII], [OIII], and H-beta at their corresponding redshifts."
• GCN Circular #4627
  Richard J. Cool (University of Arizona) reports:
  Based upon feedback from users of our online releases of SDSS photometry and astrometry of GRB fields, we have discovered an error in several past releases. In preparing the releases, we inadvertently neglected to remove duplicate listings of several objects from the online catalogs. Several of the secondary observations of the objects included are of lower photometric quality than the primary observation and thus photometric zeropoints derived with them may shift slightly. We removed all duplicate observations from the online catalogs for past bursts located at http://mizar.as.arizona.edu/grb/public/.
  We apologize for any inconvenience.
• D. Perley's Keck GRB Host project: suggests host galaxy at redshift z=0.56 (OII, Hbeta, OIII)