Gamma-ray Burst 971227

A moderate Gamma-Ray Burst (BATSE trigger No. 6546, 3760 cts/s peak intensity) was detected by BATSE and BeppoSAX WFC on December 27, 1997 at 08:23:06 UT. With the BeppoSAX WFC the location could be deduced to a 8 arcmin error circle centered at R.A. = 194.395, Decl. = +59.256 degrees (2000.0).
A follow-up observation with the BeppoSAX NFI instruments has been performed 14 hrs. after the GRB (see IAUC 6797). Out of two X-ray sources detected within the WFC error circle, one is variable: 1SAX J1257.3+5924 (R.A. = 12h57m15s, Decl. = +59o24'02"; +/-1.5') had 0.0032+/-0.001 cts/s during first 8 hrs, while afterwards <0.002 cts/s. Unfortunately, the GRB location is not reachable for ROSAT due to Sun angle constraints. There exists no serendipituous ROSAT pointing towards the GRB location. (All information courtesy of the instrument teams and GCN messages.)

Previous IAU Circulars

• IAUC 6796 BeppoSAX WFC detection and localisation
• IAUC 6797 BeppoSAX NFI detection of 2 X-ray sources; 1SAX J1257.3+5924 probable X-ray afterglow
• IAUC 6798 GRB properties as seen with BATSE
• IAUC 6800 fading optical object within 1SAX J1257.3+5924 error box
• IAUC 6803 no object brighter than R=22 mag at position of OT in IAUC 6800
• IAUC 6806no object brighter than I=22 mag on Jan. 6
• IAUC 6807 URL address for IAUC 6803 images

• Archive of GCN Messages for GRB971227
• GCN3 message Dec. 29, 1997
  Paul Groot, Titus Galama (Univeristy of Amsterdam), Jan van Paradijs (UoA and University of Alabama in Hunstville), Chryssa Kouveliotou (AURA at NASA/MSFC), Nic Walton, (ING La Palma), Penny Sackett (Groningen), Arlin Crotts (Columbia University, NY), Simone Bianchi and Jonathan Davies (Cardiff, UK) report: " Visual comparison of optical R-band observations made on December 28.237 UT (1800s) and December 29.108 UT (900s) with the 2.5m Isaac Newton Telescope at La Palma of the inner 12'x12' region of the SAX WFC errorbox of GRB971227 shows no obvious varying object. Preliminary photometry shows that this corresponds to an upper limit on variability of 0.3 mags down to a limiting magnitude of R=22.8"
• GCN3 message Dec. 29, 1997
  A.J. Castro-Tirado and J. Gorosabel, Laboratorio de Astrofisica Espacial y Fisica Fundamental (LAEFF-INTA), Madrid; J. Greiner, Astrophysikalisches Institut (AIP), Potsdam; M. R. Zapatero-Osorio, Instituto de Astrofisica de Canarias (IAC), Tenerife and E. Costa, Istituto di Astrofisica Spaziale, Frascati (on behalf of the BeppoSAX team) report: following the detection of GRB 971227 by BeppoSAX, R-band images were obtained by Y. Aguilar and R. Kohley (Sternwarte der Universitat, Bonn) with the 2.2-m CAHA telescope (+CAFOS) at the German- Spanish Calar Alto Observatory, on Dec 27.91, Dec 28.16 and Dec 29.12 . A careful visual inspection of the three frames reveals no variable object (by more than 0.5 mag) above a R = 21.5 limiting magnitude within the entire BeppoSAX WFC error box (8' radius). Further observations are in progress.
• GCN3 message Dec. 30, 1997
  H. S. Park on behalf of the LOTIS collaboration: R. Bionta, E. Ables, L. Ott, E. Parker (LLNL); G. Williams, D. Hartmann (Clemson University); S. Barthelmy, P. Butterworth, N. Gehrels, T. Cline (NASA/GSFC); C. Kouveliotou, J. Fishman, C. Meegan (NASA/MSFC); D. Band (U.C. San Diego); K. Hurley (U. C. Berkeley); D. Ferguson (CalState, Hayward): LOTIS (the Livermore Optical Transient Imaging System), an automated, wide-field-of-view telescope system dedicated to the search for simultaneous GRB optical counterparts, was on-line on the night of Dec. 27 when BATSE detected GRB971227. LOTIS received GCN coordinates derived from BATSE telemetry approximately 4 seconds after the start of the burst and obtained its first 10 second exposure, centered on the GCN coordinates 6 seconds later (10 sec after the burst began: 27.3495 UT) LOTIS continued taking 10 second exposures at the rate of 1 image every 20 seconds for the next 20 minutes, then at the rate of once per minute for the rest of the night. Because of LOTIS's large, 17.4 x 17.4 degree field of view, the recorded images fully contain the error box of the location of the associated x-ray transient detected by BeppoSAX's NFI despite the 6.7 degree difference between the location of the BeppoSAX NFI position and the GCN BATSE-Original coordinates. A computer-aided visual examination of the area within the BeppoSAX NFI/WFC position error circle (8' radius) revealed 10 objects brighter than a visual magnitude of mV ~ 12.3 +/- 0.3; all of which were identified with known objects in the Guide Star Catalog and the Digital Sky Survey, and none showing variations in brightness. Further analysis is in progress.
• GCN3 message Dec. 31, 1997
  T.J. Galama, P.J. Groot (University of Amsterdam), T. von Hippel (University of Wisconsin) and A. Diercks (University of Washington, Seattle), J. van Paradijs (UoA and University of Alabama in Huntsville), C. Kouveliotou (USRA at NASA/MSFC) report: "R-band observations of the proposed OT to GRB971227 (Castro-Tirado et al., IAUC 6800) taken with the Kitt Peak 0.9m telescope at December 29.53 UT and the 3.5m Apache Point Telescope at December 30.44 UT show this object at a constant level of R=20.4 +/- 0.1 mag, at a position RA=12h57m08.65s, Dec=+59d24'40" (J2000). It is 1.4 magnitudes fainter than a relatively bright (R=19.0) star located at RA=12h57m04.8s, Dec=+59d24'42.0" (J2000). Both object appear in the Digital Sky Survey with a relative magnitude difference comparable to this value. In the Apache Point image the source appears to be slightly extended, which indicates it may be a galaxy.
  No object in the SAX NFI error box (Piro et al., IAUC 6797) appears to vary at a level of more than 0.3 mag, down to a limiting magnitude of R=21.5".
• GCN3 message Jan. 2, 1998
  Howard E. Bond (Space Telescope Science Institute) David Balam (University of Victoria) Kailash C. Sahu (Space Telescope Science Institute) report: There seems to have been some confusion about possible optical counterparts of GRB 971227 in recent GCN e-mails. We believe that this is because THREE different optical objects have been mentioned in recent communications, as follows:

  Object   RA    (J2000)    Dec       Remarks
  
     1     12h57m10.6s   +59o24'43"   proposed as GRB counterpart by 
                                      Castro-Tirado et al., IAUC 6800
  
     2     12h57m08.6s   +59d24'40"   described as non-variable at 
                                      R=20.4 by Galama et al. (GCN 
                                      notice Dec 31) based on KPNO and 
                                      APO data
  
     3     12h57m04.8s   +59d24'42"   reference star with R=19.0 used 
                                      by Galama et al.
  

  We note that objects 1 and 2 ARE NOT IDENTICAL. Object 2 is in fact faintly visible on direct examination of POSS-II films, in accordance with the above report of non-variability. Object 1 is NOT visible on POSS-I prints nor the POSS-II films.
  A 630-sec CCD R-band exposure on the field was obtained on 1997 Dec 31.44 by D. Balam under poor observing conditions with the 1.8-m Plaskett reflector of the Dominion Astrophysical Observatory; the limiting magnitude (S/N=3) is R=20.5 (assuming Object 3 to have R=19.0). Object 2 is faintly visible, in accordance with the above.
  Object 1, visible at R=19.5 in a Calar Alto image of Dec 27.91 posted on the WWW by Castro-Tirado et al. (see IAUC 6800), and reported as NOT seen above R=20.5 on Dec 30.16 by Bartolini et al. (GCN notice, Dec 30), is likewise NOT visible above R=20.5 in Balam's image of Dec 31.44. This observation would appear to strengthen the reported variability of Object 1 and its identification with the GRB afterglow. Deeper images should urgently be obtained and monitoring should continue.
• GCN3 message Jan. 2, 1998
  Dave Balam additionally reports: A precise optical position of Object 3 in our previous report has been determined as follows:

                12h 57m 04s.93 +59o 24' 39".1 (J2000)
  

  The astrometric solution was obtained using 17 USNO catalog stars, m.e. 0".41 (RA) and 0".32 (Dec)
• GCN3 message Jan. 2, 1998
  A. N. Ramaprakash, S. R. Kulkarni, S. G. Djorgovski, R. R. Gal (Caltech), and S. Perlmutter and B. Grossan (UCB/LBL), report on behalf of the Caltech GRB collaboration: "We have analyzed R-band images of the field of 1SAX J1257.3+5924, proposed as the x-ray counterpart of GRB 971227, obtained at the Keck-II telescope, on UT 1997 Dec 30.8 and UT 1998 Jan 01.8. Our analysis shows no objects brighter than R = 23 mag which have varied significantly by more than 0.2 mag over this 2-day interval (conservative limits). For comparison, a source declining with a standard 1/t power-law would have faded by about 0.5 mag in the same time interval. This upper limit is at least a factor of 10 fainter than the optical transient associated with GRB 970508 at the same time interval.
  In addition, we have obtained r-band images at Palomar 60-inch telescope on UT 1997 Dec 28.4, covering about 80 percent of the 1.5-arcmin radius error circle quoted for the x-ray source. They show no objects brighter than about R = 21 mag which were not also detected in the subsequent Keck images.
  More refined analysis is in progress."
• GCN3 message Jan. 3, 1998
  S. G. Djorgovski, S. R. Kulkarni, A. N. Ramaprakash, (Caltech), and D. Frail (NRAO) report on behalf of the Caltech GRB collaboration: "There has been some confusion regarding various objects in the field of 1SAX J1257.3+5924, the proposed x-ray counterpart of GRB 971227. Keck R-band images of the field (obtained on UT 1997 Dec 30.8, limiting magnitude R ~ 25.5) can be obtained at the following URL: http://astro.caltech.edu/~george/grb/grb971227.html (see also below). There we mark several objects, whose positions (good to 0.4 arcsec, on the basis of USNO A1.0 catalog) are:

  Object   type      RA(J2000)     DEC(J2000)   R mag
  
     A     star     12 57 13.68   +59 23 36.7   19.1
     B     star     12 57 11.15   +59 24 45.4   22.1
     C     galaxy   12 57 08.74   +59 24 35.7   20.6
     D     star     12 57 04.95   +59 24 39.2   19.4
     E     galaxy   12 57 08.22   +59 24 52.4   21.4
     F     galaxy   12 57 08.30   +59 25 00.5   21.25
  

  The magnitudes have been zero-pointed using a set of APM objects in the field; the zero-point is uncertain by at least 0.2 mag.
  Star B is the closest object to the detection claimed by Castro-Tirado et al. (GCN 30Dec97 [#020], and IAUC 6800), even though it is 4.8 arcsec away from their estimated position. In particular, no object was detected within their nominal (3 arcsec radius) error circle down to a magnitude of R ~ 24 or even fainter in the Keck images of Dec 30.8 UT. Star B remains constant in brightness over the time span of our data (cf. our earlier GCN note [#024]), and indeed we detect no significantly variable objects in the entire error circle of the x-ray source down to the limits of our data. If the detection claimed by Castro-Tirado et al. was real, it would imply a fading with a power-law slope of t^(-2.5) or steeper.
  D is the comparison star mentioned by Galama et al. (GCN 31Dec97 [#021]), even though it is about 3 arcsec away from their quoted position, and galaxy C is almost certainly the object they propose as the possible identification of the claimed detection by Castro-Tirado et al.
  A is a convenient comparison/offset star. E and F are random galaxies in the same area, also given here as comparisons.
  We conclude that there is thus far no evidence for an optical transient associated with this gamma-ray burst down to significantly faint magnitude limits, similar to the cases of GRB 970815 and 970828.
  The above is the Keck R-band image from UT Dec 30.8, field size = 218 arcsec, centered on the position of the X-ray source 1SAX J1257.3+5924. The center coordinates (J2000) are: RA = 12h 57m 15.0s, DEC = +59d 24' 02" The limiting magnitude is R ~ 25.5.
  This is a zoom-in on the same image, field size = 109 arcsec, centered on the position of a detection claimed by Castro-Tirado et al. (IAUC 6800). The center coordinates (J2000) are: RA = 12h 57m 10.6s, DEC = +59d 24' 43"
• GCN3 message Jan. 4, 1998
  T.J. Galama, P.J. Groot (University of Amsterdam), S. Bianchi and J. Davies (Cardiff), T. von Hippel (University of Wisconsin) and A. Diercks (University of Washington, Seattle), J. van Paradijs (UoA and University of Alabama in Huntsville), C. Kouveliotou (USRA at NASA/MSFC) report: "As noted by many, the identification (GCN #21) of a galaxy with the optical counterpart to GRB971227 proposed by Castro-Tirado et al (GCN note #20, IAUC 6800), is incorrect. The galaxy is unrelated to the proposed counterpart. We sincerely apologize for the confusion this has caused to the community. Comparison of the images taken with the Kitt Peak 0.9m telescope at Dec. 29.53 UT, the Apache Point Observatory 3.5m Telescope at Dec 30.44 UT and a 2700s exposure with the 2.5m Isaac Newton Telescope at La Palma at Jan 03.10 UT of the region around the proposed OT, shows no variable object at a level of more than 0.3mag down to R=21.5.
• GCN3 message #027 (Jan. 12, 1998)
  S. R. Kulkarni, A. N. Ramaprakash, J. Bloom, S. Djorgovski, Caltech; R. Goodrich, Keck Observatory/CARA and D. Frail, VLA/NRAO report on behalf of the Caltech GRB effort: "The optical transient (IAUC 6788) of GRB 971214 (IAUC 6787; IAUC 6792) was observed by J. Aycock using the LRIS instrument on Keck II. The observations were conducted between 1400--1600 UT of January 10, 1998 and images were obtained in the R band. The seeing was consistently 0.86 arcsec and 12 frames each of five minute duration were obtained. A source is clearly detected at the position of the OT. This source is fainter by 5.5 +/- 0.17 mag compared to object 2 of Henden et al. (GCN note [#016] of Dec 24, 1997). We measured pixel offsets between this source and object 2 and compared to similar offsets in the LRIS I-band image of Dec 15.47 1997 UT (see GCN note of Dec 17, 1997). The offsets and images were obtained in the R band. The seeing was consistently 0.86 arcsec and 12 frames each of five minute duration were obtained. A source is clearly detected at the position of the OT. This source is fainter by 5.5 +/- 0.17 mag compared to object 2 of Henden et al. (GCN note [#016] of Dec 24, 1997). We measured pixel offsets between this source and object 2 and compared to similar offsets in the LRIS I-band image of Dec 15.47 1997 UT (see GCN note of Dec 17, 1997). The offsets match to better than 0.15 arcsec in each axis. A power law fit to the I-band data of Halpern et al. (IAUC 6788) and our LRIS I-band data of Dec 16.52 and Dec 17.45 UT predict an I-band magnitude between 26.2 and 27.0 on January 10, 1998. The uncertainty represents maximum errors in the extrapolation. Diercks et al. (IAUC 6791) note that the OT had R-I=1.0+/-0.4 on Dec 15.5 1997 UT. The subsequent two R band measurements (IAUC 6791) appear to track the I-band points (to within errors). Thus, if there is no color evolution in the OT then the predicted R band magnitude on 10 January 1998 UT is between 27.2 and 28.0 mag with an offset uncertainty of 0.4 mag. We conclude that either the OT has stopped its power law decay or more likely the host of the OT has an R magnitude of 25.6 mag."
• GCN3 message #028 (Jan. 13, 1998)
  S. Klose, Thueringer Landessternwarte Tautenburg, Germany (klose@tls-tautenburg.de) reports: The 1.5 arcmin radius error box of GRB 971227 (Piro et al., IAUC 6797) was imaged with the Calar Alto 2.2-m telescope on January 9.1 UT using one of the MAGIC near-infrared cameras. The total integration time was 5000 seconds in the K'-band and 5000 seconds in the J-band, centered at RA, DEC (J2000) = 12:57:15.0, 59:24:02. MAGIC was used in its wide-field mode giving a field of view of 415 times 415 arcsec. The sky was clear, but the sky conditions presumably not very photometric. Final images and final results of the data reduction will be published within about 2-4 weeks. Preliminary results of the image reduction can already be obtained via http://www.tls-tautenburg.de/research/grb.html. Both, the J and the K'-band image are obtained by combining 1000 frames taken at 5 overlapping positions. If the optical counterpart of the GRB afterglow is strongly affected by extinction, then the most promising candidates for the NIR counterpart might be very red and faint objects. Two such objects are visible in the GRB error box. Both have only a faint counterpart on the Keck R-band image published by Djorgovski et al. (GCN #025). Coordinates are (+/- 2"):

  
      Object A: RA, DEC (J2000) = 12:57:10.3, 59:24:14
      Object B: RA, DEC (J2000) = 12:57:22.8, 59:23:48.
  

  A photometry has still not been performed, but one can guess that both objects might have K' = 19.0 +/- 1.0. The most promising object is object A. Currently, it seems unlikely that this is an artifact, but remind please, these are preliminary data. At the moment it is impossible to decide whether one object is physically related to GRB 971227, or whether both objects are only very red objects in the field. To be careful, one should assume the latter. ROSAT/HRI data could help.