//////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4397 SUBJECT: GRB 051227: Swift detection of a burst DATE: 05/12/27 18:59:47 GMT FROM: Scott Barthelmy at NASA/GSFC L. Barbier (GSFC), S. Barthelmy (GSFC), A. Beardmore (U Leicester), D. Burrows (PSU), J. Cummings (GSFC/NRC), A. Falcone (PSU), N. Gehrels (GSFC), K. Page (U Leicester), A. Retter (PSU), P. Roming (PSU), T. Sakamoto (GSFC) on behalf of the Swift team: At 18:07:16 UT, Swift-BAT triggered and located GRB 051227 (trigger=174738). The spacecraft slewed immediately. The BAT on-board calculated location is RA,Dec 125.270d,+31.929d {08h 21m 05s,+31d 55' 44"} (J2000), with an uncertainty of 3 arcmin (radius, 90% containment, stat+sys). The BAT light curve shows a multi-peak structure with a total duration of at least 8 sec. The peak count rate was ~3500 counts/sec (15-350 keV), at 0 seconds after the trigger. The XRT began observing the GRB at 18:08:49 UT, 93s after the BAT trigger. A bright fading uncataloged source was found by the on-board centroiding algorithm at: RA(J2000)= 08h 20m 57.6s DEC(J2000)= +31d 55' 33.5" with an uncertainty of 7 arcseconds radius (90% containment). This position has not been corrected for the XRT boresight and retains a 4-5 arcsecond residual systematic error, which is included in the 7 arcsecond error radius. This position lies 95 arcseconds from the centre of the BAT error circle. The initial X-ray flux is estimated to be 1.1e-9 erg/cm2/sec (0.2-10keV). UVOT took a finding chart exposure of nominal 200 seconds with the V filter starting 96 seconds after the BAT trigger. No afterglow candidate has been found in the initial data products. Image catalog data are not available at this time. The overlap of the 8'x8' region for the list of sources generated on-board and the XRT error circle is uncertain. No correction has been made for the expected visual extinction of about 0.1 magnitudes. We note that according to SIMBAD, there is a galactic cluster NSC J082047+315700 within 2.7 arcmin from this location, but this is definitely a long burst (not a short GRB). //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4398 SUBJECT: GRB 051227, optical observation DATE: 05/12/27 20:04:04 GMT FROM: Eri Sonoda at U of Miyazaki/Japan E.Sonoda,S.Maeno,S.Masuda,Y.Nakamura,M.Yamauchi (University of Miyazaki) "We have observed the field covering the error circle of GRB 051227 (GCN 4397) with the unfiltered CCD camera on the 30-cm telescope at University of Miyazaki. The observation was started 18:27:18 UT on Dec.27. After co-adding a set of 6 images (18:27:18 - 18:36:21 UT) of 30 sec exposures, we have compared with the USNO A2.0 catalog. Preliminary analysis shows there is no new source brighter than 17.6 mag." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4399 SUBJECT: GRB051227: SDSS pre-burst observations DATE: 05/12/27 21:36:11 GMT FROM: Richard J. Cool at U.of AZ/Steward Obs Richard J. Cool (Arizona), Daniel J. Eisenstein (Arizona), David W. Hogg (NYU), Michael R. Blanton (NYU), J. Brinkmann (Apache Point Observatory), Donald P. Schneider (PSU), and Daniel E. Vanden Berk (PSU) report on behalf of the Sloan Digital Sky Survey (SDSS) Collaboration: The Sloan Digital Sky Survey (SDSS) imaged the field of burst GRB051227 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/GRB051227 We supply FITS images in each of the 5 SDSS bands of a 8'x8' region centered on the GRB position (ra=125.270 (08:21:04.8), dec=31.9290 (31:55:44.4); Swift-BAT TRIGGER 174738), 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 GRB051227_sdss.calstar.dat, we report photometry and astrometry of 825 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 GRB051227_sdss.objects_flux.dat and GRB051227_sdss.objects_magnitudes.dat, we report photometry of 2481 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 GRB051227_sdss.objects_flux.dat are in nanomaggies while the magnitudes listed in GRB051227_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=0.213 mag, A_g=0.157 mag, A_r = 0.114 mag, A_i=0.086 mag, and A_z=0.061 mag. The file GRB051227_sdss.spectro.dat contains a list of the 4 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. See the SDSS DR4 documentation for more details: http://www.sdss.org/dr4 //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4400 SUBJECT: GRB 051227: Refined analysis of the Swift-BAT burst DATE: 05/12/27 22:16:06 GMT FROM: Scott Barthelmy at NASA/GSFC D. Hullinger (GSFC/UMD), L. Barbier (GSFC), S. Barthelmy (GSFC), P. Boyd (GSFC-UMBC), J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS), J. Tueller (GSFC), W. Voges (MPE) on behalf of the Swift-BAT team: Using the full data set from the recent telemetry downlink, we report further analysis of Swift-BAT GRB 051227 (trigger #174738) (Barbier, et al., GCN 4397). The ground-analysis position is RA,Dec 125.230,+31.953 {08h 20m 55.2s,+31d 57' 12"} (J2000) with an uncertainty of 1.8 arcmin (radius, 90%, stat+sys). T90 is 8.0 +- 0.2 sec. The partial coding fraction is 97%. The lightcurve has an initial multi-peak structure at T+0.00 sec (FWHM of ~3.5 sec) and there is a smaller broad softer peak spanning T+30 to T+50 sec. Fitting a simple power law over the full interval from T-1 to T+8 sec, the photon index is 1.31 +/- 0.22 with a fluence of 2.3 +/- 0.3 X 10^-7 erg/cm^2. The peak flux in a 1-sec wide window starting at T-0.008 sec is 0.97 +/- 0.13 ph/cm^2/sec. All values are in the 15-150 keV band at the 90% confidence level. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4401 SUBJECT: GRB 051227: Further analysis of the Swift-BAT burst DATE: 05/12/28 01:53:51 GMT FROM: Scott Barthelmy at NASA/GSFC S. Barthelmy (GSFC), N. Gehrels (GSFC), J. Norris (GSFC), T. Sakamoto (GSFC/NRC) on behalf of the Swift-BAT team: Continuing the analysis of GRB 051227, we point out the possibility that this is a short burst. We do not have the full data set downloaded for this burst yet (only T-60 to T+120 sec), but we wish to get this speculation out to the follow-up community to facilitate observations as soon as possible (i.e. CA coast and Hawaii big glass). We base this on 2 observations: 1) The spectral lag is negligible, 2+-10 ms (1 sigma), between the 25-50 and 100-350 keV energy bands -- typical of spectral lags in short bursts (Norris & Bonnell, submitted to ApJ). The median lag for long bursts is 50 ms, and only 1% of long bursts have a lag less than 2 ms. 2) The overall shape of the lightcurve of GRB 051227 is similar to the lightcurve of the short hard burst GRB 050724. The initial hard spike is followed by 1 or 2 smaller short peaks at delays of one to several seconds. Then a period of hiatus, followed by a broad low-level soft emission emission that starts at a few tens of seconds out to 100+ seconds. However, we can not rule out that this is a FRED-like profile with a very long low-statistics decay tail. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4402 SUBJECT: GRB 051227: XRT refined analysis DATE: 05/12/28 03:25:11 GMT FROM: David Burrows at PSU/Swift A. Beardmore (U. Leicester), D. N. Burrows (PSU), K. Page (U. Leicester), F. Marshall (GSFC), M. Chester (PSU) report on behalf of the Swift XRT team: We have analysed the first 3 orbits of XRT data from GRB 051227. A 2.8ks photon counting mode image provides a refined XRT position: RA(J2000) = 08h 20m 57.92s, Dec(J2000) = +31d 55m 30.43s with an uncertainty of 3.5 arcsec (90% containment). This position is 5.1 arcsec away from the on-board XRT position quoted in Barbier et al. (GCN4397) and includes the latest XRT boresight correction. This position is 106 arcseconds from the refined BAT position (Hullinger et al., GCN 4400). The X-ray light curve displays multiple small flares, with the largest peaking at a count rate of approximately 25 counts/s at T + 115s (where T is the BAT trigger time). The underlying decay can be fit with a broken power-law with an initial decay slope of -2.2+/-0.2, a break at 475+235-80s, and a post-break slope of -0.95+/-0.15. A power-law fit to the X-ray spectrum from T + 101s to T + 180s gave a photon index of 1.4+/-0.2 and a column density of (1.8+/-1.0)e21 cm**-2. We note the galactic hydrogen column density in the direction of the burst is 4.3e20cm**-2. The 0.2-10.0keV observed flux was 4.2e-10 ergs cm**-2 s**-1, which corresponds to an unabsorbed flux of 5.0e-10 ergs cm**-2 s**-1. If the burst continues decaying at the current rate we estimate an XRT count rate of 0.0022 counts/s at T + 24hr, which corresponds to an observed 0.2-10.keV flux of 1.1e-13 ergs cm**-2 s**-1. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4403 SUBJECT: GRB 051227: Joint Swift-HETE Spectral Analysis DATE: 05/12/28 03:50:13 GMT FROM: Don Lamb at U.Chicago GRB 051227: Joint Swift-HETE Spectral Analysis T. Sakamoto, J-L. Atteia, G. Ricker, N. Kawai, D. Lamb, and S. Woosley, on behalf of the HETE Science Team; M. Arimoto, T. Donaghy, E. Fenimore, M. Galassi, C. Graziani, N. Ishikawa, A. Kobayashi, J. Kotoku, M. Maetou, M. Matsuoka, Y. Nakagawa, R. Sato, T. Shimokawabe, Y. Shirasaki, S. Sugita, M. Suzuki, T. Tamagawa, K. Tanaka, and A. Yoshida, on behalf of the HETE WXM Team; N. Butler, G. Crew, J. Doty, G. Prigozhin, R. Vanderspek, J. Villasenor, J. G. Jernigan, A. Levine, G. Azzibrouck, J. Braga, R. Manchanda, G. Pizzichini, and S. Gunasekera, on behalf of the HETE Operations and HETE Optical-SXC Teams; M. Boer, J-F Olive, J-P Dezalay, and K. Hurley, on behalf of the HETE FREGATE Team; L. Barbier, S. Barthelmy, J. Cummings, N. Gehrels, and J. Norris, on behalf of the Swift BAT team; report: The HETE FREGATE instrument detected the initial peak of GRB 051227 (Swift Trigger 174738; Barbier, et al., GCN 4397) as an untriggered event. Carrying out a fit to the FREGATE spectral data alone, the spectrum of the initial peak is adequately fit by a power-law (PL) model, with photon index alpha = 1.3 +0.4/-0.6 (90% confidence level). This confirms the result reported by Hullinger et. al (GCN 4400). Carrying out a joint fit to the BAT plus FREGATE spectral data, the best-fit cutoff PL model yields an improvement in ch^i2 over the best-fit PL model of 5.2 for one additional parameter, corresponding to a significance of 2.3E-02. Thus the joint spectral fit provides evidence of curvature in the spectrum. Adopting the best-fit cutoff PL model yields a best-fit value of Epk = 100 +219/-41.3 keV (90% confidence level) and a fluence ratio S(2 keV-30 keV)/S(30 keV-400 keV) = 0.19. The event is therefore a hard GRB. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4404 SUBJECT: GRB 051227: R-band object in the XRT error circle DATE: 05/12/28 05:39:12 GMT FROM: Daniele Malesani at SISSA-ISAS,Trieste,Italy D. Malesani (SISSA), S. Piranomonte, L.A. Antonelli (INAF/OAR), E. Depagne, C. Lidman, C. Melo (ESO), S. Campana, S. Covino, G. Tagliaferri (INAF/OABr), G. Chincarini (Univ. Milano-Bicocca), M. Della Valle (INAF/OAA), F. Fiore, and L. Stella (INAF/OARm), report on behalf of the MISTICI collaboration: We observed the field of the hard (and possibly short) GRB 051227 (Barbier et al., GCN 4397; Barthelmy et al., GCN 4401; Sakamoto et al., GCN 4403) using the ESO VLT-UT2 (Kueyen) equipped with the FORS1 instrument. Observations started on 2005 Dec 28, 04:22 UT (~10.3 h after the GRB), in the R band. Observations were conducted at high airmass and moderate seeing (1.5"). Coadding three 5-min images, we detect inside the revised XRT error circle (Beardmore et al., GCN 4402) one single, faint source, at the coordinates (J2000): alpha = 08:20:58.14 delta = +31:55:31.7 The astrometric error is about 0.5". This object is not seen in the r-band SDSS images provided by Cool et al. (GCN 4399). However, it is significantly fainter than the limit of these images. We propose this object as a candidate afterglow or host for GRB 051227. We also note a further, fainter object slightly outside the XRT error circle, at the coordinates: alpha = 08:20:57.54 delta = +31:55:32.47 We acknowledge the excellent support from the ESO staff. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4405 SUBJECT: GRB 051227: MDM Observation DATE: 05/12/28 05:39:41 GMT FROM: Jules Halpern at Columbia U. J. P. Halpern & S. Tyagi (Columbia U.) report on behalf of the MDM Observatory GRB follow-up team: "We are observing the Swift XRT position (Beardmore et al., GCN 4402) of GRB 051227 in the SDSS r filter with RETROCAM on the MDM 2.4m, a medium-sized telescope on Kitt Peak, Arizona. Beginning on Dec. 28 03:55 UT, or 9.9 hours after the burst, our first 15 minutes of exposure yields no detection to a limit R > 23, referenced to the SDSS photometry in the field (Cool et al., GCN 4399)." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4406 SUBJECT: GRB 051227: P60 Observations DATE: 05/12/28 08:13:51 GMT FROM: S. Bradley Cenko at Caltech S. Bradley Cenko, Alicia M. Soderberg, Eran Ofek (Caltech) and Derek B. Fox (Penn State) report on behalf of the Caltech-NRAO-Carnegie GRB Collaboration: We have imaged the field of GRB 051227 (Barbier et al., GCN 4397; Hullinger et al., GCN 4400; Barthelmy et al., GCN 4401; Sakamoto et al., GCN 4403) with the automated Palomar 60-inch telescope. Observations consisted of 30 x 180 s images in the Kron R filter taken at a mean epoch of approximately UT 28 December 05:50 (11.7 hours after the burst). In a coaddition of all our images, we find no sources inside the revised XRT error circle (Beardmore et al., GCN 4402) to a limiting magnitude of R > 22.5 (calculated with respect to several nearby sources in the Guide Star Catalog). In particular we note the candidate afterglow/host proposed by Malesani et al. (GCN 4404) is not detected in our images to the above limit. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4407 SUBJECT: GRB 051227: refined analysis of VLT images DATE: 05/12/28 09:49:46 GMT FROM: Daniele Malesani at SISSA-ISAS,Trieste,Italy D. Malesani (SISSA), S. Piranomonte, L.A. Antonelli (INAF/OARm), S. Campana (INAF/OABr), G. Chincarini (Univ. Milano-Bicocca), and L. Stella (INAF/OARm), report on behalf of the MISTICI collaboration: The field of GRB 051227 (Barbier et al., GCN 4397; Barthelmy et al., GCN 4401; Sakamoto et al., GCN 4403) was observed at two epochs with the ESO-VLT UT2, equipped with FORS1. Exposure was 20 minutes per epoch, with mean times 10.4 and 12.5 h after the GRB trigger. Coaddition of all images confirms the presence of a single, faint source (Malesani et al., GCN 4404) at the edge of the revised XRT error circle (Beardmore et al., GCN 4402). A finding chart is posted at the following link: http://www.sissa.it/~malesani/GRB/051227/GRB051227_finder.jpg The source inside the XRT error circle (S1) shows a marginal dimming in the R band between the two epochs, by 0.34 +- 0.20 mag. The error was estimated by looking at the variations of several objects with brightness comparable to that of S1. We note that the seeing slightly worsened between the two epochs, passing from 1.3" to 1.6". //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4408 SUBJECT: GRB 051227: Magellan r'-band Imaging/Astrometry DATE: 05/12/28 10:30:02 GMT FROM: Josh Bloom at UC Berkeley J. S. Bloom (UC Berkeley), P. Challis (CfA), A. Garg (CfA), and R. Foley (UC Berkeley) report: "Starting at 2005-12-28 06:16:19 UT, we began imaging the field of GRB 051227 (GCNs 4397, 4400, 4401, 4403) with the Magellan 6.5m + LDSS3 instrument (*). At an airmass of 2.1 the effective seeing was 0.62 arcsec. In each five minute exposure we detect the faint VLT sources noted by Malesani et al. (GCNs 4404, 4407) near the XRT localization (Beardmore et al., GCN 4402). Photometric analysis is ongoing. We fit an astrometric world coordinate system using more than one hundred objects common between the LDSS3 imaging and SDSS (Cool et al. 4399) with an rms of 85 mas in each coordinate. Our location of the possibly transient source (Malesani et al.; GCN 4407) is (J2000): RA 08:20:58.109 DEC +31:55:31.89 with a statistical uncertainty of 210 mas in each coordinate from centroiding uncertainty. The absolute uncertainty is ~250 mas, assuming 100 mas error in the absolute SDSS WCS. This is 1.89" S and 4.28" W of an apparent galaxy (SDSS J082058.46+315533.4; r = 22.9 mag; 08:20:58.445 +31:55:33.78). If the galaxy and the apparent counterpart are at the redshift of the cluster (NSC J082047+315700 as noted by Barbier GCN# 4397; z = 0.1753; Gal et al. 2003), then this offset would amount to 13.7 kpc in projection." A comparison finding chart between tonight's imaging with SDSS can be found at: http://astro.berkeley.edu/~jbloom/grb051227-ldss.ps This message may be cited. (*) http://www.ociw.edu/lco/magellan/instruments/LDSS3/ //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4409 SUBJECT: GRB 051227: Keck Spectroscopy DATE: 05/12/28 14:04:14 GMT FROM: Ryan Foley at UC Berkeley R. J. Foley, J. S. Bloom (UC Berkeley), J. X. Prochaska, G. D. Illingworth, B. P. Holden, D. Magee (UCO/Lick), P. Challis, and A. Garg (CfA) report: "We obtained 2x1500 sec spectra of the object found inside, S1 (GCN 4404, 4407, 4408), and the galaxy north-east, G1 (GCN 4408), of the XRT error box of GRB 051227 (GCN 4402) with Keck II (+ DEIMOS). We detect absorption lines at the position of the galaxy which we identify as Ca II H&K at z = 0.714. We also detect emission lines which we identify as [O II] 3727 and H beta. If the GRB afterglow is S1 and at this redshift, then the offset from G1 to S1 would amount to 33.7 kpc in projection." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4410 SUBJECT: GRB 051227: Gemini observations DATE: 05/12/28 17:56:26 GMT FROM: Edo Berger at Carnegie Obs E. Berger (Carnegie Observatories) reports: "We imaged the error circle of GRB 051227 (GCNs 4397,4401) with GMOS on the Gemini-north telescope starting on 2005, Dec. 28.33 UT (13.88 hr after the burst). A total of 25 min were obtained in r-band in good seeing conditions (0.75"). Within the refined XRT position (GCN 4402) we detect source S1 (GCNs 4404,4407,4408) at coordinates (J2000): RA = 08:20:58.107 DEC= +31:55:32.01 We also detect an additional faint source about 0.7" outside of the XRT error circle (S2) which is not clearly visible in the finders provided by Malesani et al. (GCN 4407) and Bloom et al. (GCN 4408) at coordinates: RA = 08:20:57.773 DEC= +31:55:26.67 Using several nearby stars with SDSS calibration (GCN 4399) we determine that source S1 has r=24.8+/-0.15 mag, while source S2 has r=25.5+/-0.25 mag. Since previous GCNs do not provide photometry of source S1 we are unable to determine whether it has varied in brightness compared to earlier observations. A finding chart showing objects S1 and S2 is available at: http://www.ociw.edu/~eberger/grb051227-gemini.ps Further Gemini observations are planned." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4411 SUBJECT: GRB 051227: Swift/UVOT Upper Limits (Possible U-band DATE: 05/12/28 19:40:53 GMT FROM: Pete Roming at PSU P. Roming (PSU), L. Barbier (GSFC), M. Trippico (GSFC-SSAI), J. Nousek (PSU) on behalf of the Swift/UVOT team We have created summed images from Swift UVOT exposures of GRB051227 (Barbier et al., GCN 4397) taken through each of the broadband filters. No source was detected at the XRT position (Beardmore et al. GCN 4402) or the R-band VLT position (Malesani, GCN 4404) down to the following 5-sigma upper limits (no correction has been made for the expected visual extinction of about 0.14 magnitudes): Filter T_range(s) Tot Exp(s) 5sigUL(mag) V 96-4092 496 19.0 B 462-10250 617 20.2 U 408-6370 502 19.6 UVW1 354-5904 950 19.6 UVM2 300-4996 950 19.7 UVW2 571-3988 113 18.5 White 516-565 100 19.2 We note that from the U-band summed image a source is detected by the Swift analysis tool, uvotsource, at the 4.0-sigma confidence coincident with the position reported by Malesani. The magnitude is 19.8+/-0.3. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4412 SUBJECT: GRB 051227: optical afterglow DATE: 05/12/29 05:45:00 GMT FROM: Daniele Malesani at SISSA-ISAS,Trieste,Italy D. Malesani (SISSA), S. Covino (INAF/OABr), E. Depagne, C. Lidman, C. Melo (ESO), S. Piranomonte, L.A. Antonelli (INAF/OARm), S. Campana, G. Tagliaferri (INAF/OABr), G. Chincarini (Univ. Milano-Bicocca), M. Della Valle (INAF/OAA), F. Fiore and L. Stella (INAF/OAR), report on behalf of the MISTICI collaboration: We observed again the field of GRB 051227 (Barbier et al., GCN 4397; Hullinger et al., GCN 4400; Barthelmy et al., GCN 4401) with the ESO VLT-UT2 equipped with FORS1. Observations started on 2005 Dec 29.1899 (1.4 d after the GRB), and secured 1 hour of net exposure in the R band. Analysis of the first 6 frames (30 min exposure) reveals that the source S1 individuated in the previous VLT images (Malesani et al., GCN 4404, 4407; see also Bloom et al., GCN 4408; Berger et al., GCN 4410; Roming et al., GCN 4411) has dimmed by 1.1 +- 0.3 mag in the R band. Assuming a power law decay, the decay slope is alpha = 0.9 +- 0.3. This suggests that very likely S1 is the optical afterglow of GRB 051227. This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4413 SUBJECT: GRB051227: further analysis of VLT images DATE: 05/12/29 18:30:10 GMT FROM: Paolo D'Avanzo at INAF-OAB P. D'Avanzo, S. Covino (INAF/OABr), D. Malesani (SISSA), S. Piranomonte, L.A. Antonelli (INAF/OAR), S. Campana (INAF/OABr), report on behalf of the MISTICI collaboration: We further analyzed our VLT images (Malesani et al., GCN 4404, 4412) of GRB 051227 (Barbier et al., GCN 4397; Hullinger et al., GCN 4400; Barthelmy et al., GCN 4401). Optimal subtraction performed with the ISIS package on our two set of images (taken on Dec 28.2 and 29.2 UT) clearly shows a dimming of the source S1 (Malesani et al., GCN 4404). A figure showing the result of the subtraction can be found at the following URL: http://www.sissa.it/~malesani/GRB/051227/subtraction.jpg This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4414 SUBJECT: GRB 051227: Confirmed fading from Gemini observations DATE: 05/12/29 18:42:02 GMT FROM: Alicia Soderberg at Caltech A. M. Soderberg (Caltech) and E. Berger (Carnegie Observatories) report: "We re-observed the error circle of GRB 051227 with Gemini/GMOS starting on 2005 Dec. 29.36 UT (38.6 hr after the burst) for a total of 25 min in r-band. Digital image subtraction performed on this image and the one obtained on the previous night (13.9 hr after the burst; GCN 4410) confirms that source S1 has faded, as indicated by Malesani et al. (GCN 4412) and D'Avanazo et al. (GCN 4413)." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4415 SUBJECT: GRB051227: Radio Observations DATE: 05/12/29 22:37:11 GMT FROM: Dale A. Frail at NRAO Dale A. Frail (NRAO) reports on behalf of a larger collaboration: "We used the Very Large Array to observe the Swift burst GRB051227 (GCN 4397) at a frequency of 8.46 GHz on 2005 December 28.57 UT and December 29.22 UT. No radio emission is detected within the XRT error circle (GCN 4402). At the position of the optical afterglow (GCN 4408) the formal flux density values are -21 +/- 28 uJy and 18 +/- 25, 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." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4418 SUBJECT: GRB 051227: optical observation DATE: 05/12/30 12:08:31 GMT FROM: Nobuyuki Kawai at Tokyo Tech Kenshi Yanagisawa, Tsuyoshi Sakamoto (OAO/NAOJ), and N. Kawai (Tokyo Tech) report on behalf of the MITSUME Collaboration: "The field of GRB051227 (Barbier et al., GCN 4397) was observed with the 3-color Mitsume 50cm Telescope at Okayama, Japan from 19:13 UT to 19:21 UT (1.1 to 1.4 hours after the burst), until the observation was terminated by the cloudy weather. Coadding the 14 frames of 60 sec exposure, we did not detect a source at the position of the afterglow candidate noted by Malesani et al. (GCN 4404, 4407, 4412), Bloom et al. (GCN 4408), Berger et al. (GCN 4410) and Roming et al. (GCN 4411). The 10-sigma upper limits are g'=18.5, Rc=17.7, and Ic=17.1, which were calibrated using the pre-burst SDSS observations (stars in the file GRB051227_sdss.objects_magnitudes.dat, Cool et al., GCN 4399), where the Rc and Ic magnitudes were converted from the g', r', and i' magnitudes using the formula by Smith et al. (2002)." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4419 SUBJECT: GRB 051227: Likely host galaxy underlying afterglow position DATE: 05/12/30 20:12:59 GMT FROM: Edo Berger at Carnegie Obs E. Berger (Carnegie Observatories) and A. M. Soderberg (Caltech) report: "We re-observed the error circle of GRB 051227 with Gemini/GMOS starting on 2005 Dec. 30.35 UT (62.6 hr after the burst) for a total of 30 min in r-band. Source S1 is clearly detected in our summed image with r=25.8+/-0.2 mag. Digital subtraction performed on this image and the previous two Gemini images obtained on nights 1 and 2 (13.9 and 38.6 hr after the burst, respectively; GCN 4414) reveals that following a decline of about 1 mag between nights 1 and 2 (CGNs 4412,4413,4414), there has been no change in flux between nights 2 and 3. This suggests that unless there has been a significant flatenning in the afterglow decay, our detection of source S1 on night 3 represents the host galaxy of GRB 051227 and that the galaxy at z=0.714 located 4.7" to the NE (GCNs 4408,4409) is unrelated to the burst. Thus, the offset of GRB 051227 relative to its host is negligible, and the actual redshift of the burst is most likely higher than z=0.7. Therefore, GRB 051227 is either one of the highest redshift short GRBs detected to date, or given the similarity in brightness to the hosts of long GRBs, and the ambiguity as to the nature of the burst (GCN 4401), it is in fact a long GRB." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4421 SUBJECT: GRB051227: SARA Observations DATE: 05/12/30 22:50:51 GMT FROM: Autumn Homewood at Clemson U K.V. Garimella, A.L. Homewood, D.H. Hartmann (Clemson University), and G.D. Henson (ETSU) on behalf of the SARA Consortium and the Clemson GRB Follow-Up Team: We began observations of GRB 051227 (Barbier et al, GCN 4397) beginning December 28th, 06:20:31UT and ending 07:36:35UT approximately 12 hours after the Swift Trigger (trigger=174738). We obtained 15 300-second exposures in R-band with the SARA 0.9m telescope on Kitt Peak. Coadding all exposures and comparing with the USNO A2.0 catalog reveals no new source down to a detection limit of R=21.55 +/- 0.20 mag. The SARA website can be found at http://www.saraobservatory.org . The Clemson University GRB Response Site can be found at http://people.clemson.edu/~kgarime/burst/ . This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5191 SUBJECT: GRB 051227 : WIDGET simultaneous optical observations DATE: 06/05/31 11:50:03 GMT FROM: Toru Tamagawa at RIKEN N. Kodaka, Y. Urata, M. Tashiro, K. Abe, K. Onda, K. Masuno (Saitama-U), F. Usui (ISAS/JAXA), M. Kuwahara (TUS/RIKEN), T. Tamagawa (RIKEN) report: "We observed the error region of GRB 051227 (Barbier et al. GCN 4397) with the very wide-field camera WIDGET located at Akeno, Japan. WIDGET monitored the region continuously with repeat of unfiltered 5-second exposures between 187 minutes before and 12 minutes after the burst trigger. We did not find any optical emission at the Swift XRT source position (Beardmore et al. GCN 4402). The 1-sigma limiting magnitude of each frame derived by the Tycho-2 catalog was around V=10.9 magnitudes." This message may be cited.