//////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4966 SUBJECT: GRB 060418: Swift detection of a burst with bright x-ray and optical afterglow DATE: 06/04/18 03:23:03 GMT FROM: Scott Barthelmy at NASA/GSFC A. D. Falcone (PSU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), J. R. Cummings (NASA/ORAU), N. Gehrels (NASA/GSFC), S. D. Hunsberger (PSU), J. A. Kennea (PSU) and D. M. Palmer (LANL) report on behalf of the Swift Team: At 03:06:08 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 060418 (trigger=205851). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 236.420, -3.643 {15h 45m 41s, -03d 38' 35"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a broad smooth peak starting at T-8 sec. It decays almost to background, and then a bright peak at T+27 sec (FWHM ~3 sec). There is possibly emission at T+130 sec. The peak count rate was ~6000 counts/sec (15-350 keV), at ~27 sec after the trigger. The XRT began observing the field at 03:07:26 UT, 78 seconds after the BAT trigger. XRT found a bright, variable, uncatalogued X-ray source located at RA(J2000) = 15h 45m 42.8s, Dec(J2000) = -03d 38' 26.1", with an estimated uncertainty of 5.8 arcseconds (90% confidence radius). This location is 32 arcseconds from the BAT on-board position, within the BAT error circle. The initial flux in the 0.1s image was 1.6e-08 erg/cm2/s (0.2-10 keV). UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 88 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at (RA,DEC) (J2000) of (236.4275,-3.6389) or (15h45m42.60s,-03o38'20.0") with a 1-sigma error radius of about 0.5 arc sec. This position is 7.2 arc sec. from the center of the XRT error circle. The estimated V magnitude is 14.5 with a 1-sigma error of about 0.5 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.22. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4967 SUBJECT: GRB 060418: REM candidate afterglow DATE: 06/04/18 03:34:35 GMT FROM: Stefano Covino at Brera Astronomical Observatory S. Covino, L.A. Antonelli, S.D. Vergani, E. Molinari, G. Chincarini, F.M. Zerbi, V. Testa, G. Tosti, F. Vitali, P. Conconi, G. Cutispoto, G. Malaspina, L. Nicastro, E. Palazzi, E. Meurs, P. Goldoni, report on behalf of the REM/ROSS Team: We imaged the field of GRB 060418 (Falcone et al. GCN 4966) with the robotic 60-cm REM telescope located at La Silla (Chile). Observations were performed automatically in the near infrared (J, H, K, z bands) soon after the GRB alert. We find a single bright source in the XRT error circle, not visible in the 2MASS survey. Its H magnitude is about 11.25. Further observations are still in progress. This message is citeable. [GCN OPS NOTE(18apr06): Per author's request, Vergani was added to the author list.] //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4968 SUBJECT: GRB060418 : LT optical afterglow observation DATE: 06/04/18 03:46:33 GMT FROM: Andrea Melandri at Liverpool John Moores U A. Melandri, A. Gomboc, C.G. Mundell, C. Guidorzi, A. Monfardini, C.J. Mottram, R.J. Smith, I.A. Steele, D. Carter, M. Burgdorf, S. Kobayashi, D. Bersier, M.F. Bode (Liverpool JMU) report: "The 2-m Liverpool Telescope immediately observed the field of GRB060418 (Falcone et al. 4966) and started observing its position about 5.0 minutes after the GRB. The automatic "detection mode" procedure clearly detected the optical afterglow candidate at the XRT position reported by Falcone et al. (GCN 4966). This source has a R magnitude of ~14.0 after ~6 minutes from 3x10-s images and clearly show a rapid early optical decay. Further analysis and observation are still ongoing." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4969 SUBJECT: GRB060418: Magellan/MIKE Spectroscopic Redshift DATE: 06/04/18 05:04:41 GMT FROM: Hsiao-Wen Chen at U Chicago A. K. Dupree, E. Falco (Harvard-Smithsonian CfA), J. X. Prochaska (UCO/Lick Observatory), H.-W. Chen (U Chicago), and J. S. Bloom (UC Berkeley) report on behalf of the GRAASP collaboration: "We observed the afterglow of GRB060418 reported by Falcone et al. (GCN 4966) using the MIKE echelle spectrograph on the Magellan Clay telescope with a 0.7-arcsec slit. The observations started at UT 03:34:02 on April 18, 2006, ~ 28 minutes after the inital Swift/BAT trigger. The first exposure had a total integration of 1200 sec under a mean seeing condition of 0.4 arcsec. The mean signal-to-noise of the single exposure was S/N > 20 over the entire 3500 Ang to 9000 Ang spectral coverage. We observed the strongest absorption feaures at 6978 Ang and 6959 Ang, which we identify as the MgII absorption doublet originated in the host of the GRB at z=1.49. We therefore adopt this as the redshift of the GRB host due to the absense of any other absorption features beyond 7100 Ang. Further analysis is underway. This message may be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4970 SUBJECT: GRB 060418, SMARTS optical/IR afterglow observations DATE: 06/04/18 05:05:45 GMT FROM: Bethany Cobb at Yale U B. E. Cobb (Yale), part of the larger SMARTS consortium, reports: Using the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained optical/IR imaging of the error region of GRB 060418 (Falcone et al. GCN 4966) beginning ~1 hours post-burst (2006-04-18 04:05 UT). Several dithered images were obtained in each filter, with total summed exposure times of 180s in each of BRIYJK and 120s in each of H and V. The afterglow candidate reported by Falcone et al. and confirmed by Covino et al. (GCN 4967) and Melandri et al. (GCN 4968) is visible in all wavebands, from B to K. At a mid-exposure time of 1.2 hrs post-burst, the preliminary K-band magnitude of the afterglow candidate is K = 14.1 +/- 0.1. This value is obtained by comparison with nearby 2MASS standards. The lack of a Lyman-alpha forest absorption break suggest this GRB has a redshift of z<~3. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4971 SUBJECT: GRB 060418: PROMPT Detections DATE: 06/04/18 06:05:55 GMT FROM: Melissa Nysewander at UNC,Chapel Hill M. Nysewander, K. Ivarsen, A. Foster, D. Reichart, J. Haislip, A. LaCluyze, A. Trotter, J. A. Crain, J. Kirschbrown, and C. MacLeod report on behalf of the UNC team of the FUN GRB Collaboration: Skynet observed the localization of GRB 060418 (Falcone et al., GCN 4966) with one of the 16-inch PROMPT telescopes at CTIO beginning 40 sec after the burst (15 sec after notification). We weakly detect the afterglow (Falcone et al., GCN 4966) at z = 15.3 +/- 0.3 mag (calibrated to three USNO-B1.0/NOMAD stars) in a 5-sec exposure taken at this time. Observations were then interrupted until about 16 minutes after the burst due to an unfortunately scheduled operating system update. Skynet resumed observations with three of the PROMPT telescopes in Ugriz (three simultaneously), with clear detections in 80-sec griz exposures. At 16.6 minutes after the burst, we measure z = 14.44 +/- 0.02 mag, implying a brightening of the afterglow at early times. At 1.3 hours after the burst, we measure z = 16.2 +/- 0.1 mag. If fading as a power law between these times, this implies a temporal index of about -1.1. PROMPT is currently being built and commissioned. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4972 SUBJECT: GRB 060418, SMARTS continuing afterglow observations DATE: 06/04/18 07:22:10 GMT FROM: Bethany Cobb at Yale U B. E. Cobb (Yale), part of the larger SMARTS consortium, reports: Continuing ANDICAM observations (see GCN 4970 for observing details) of the afterglow of GRB 060418 (Falcone et al. GCN 4966) record the steady fading behavior of the afterglow between all 45-second individual I-band exposures, as shown below. These preliminary magnitudes were calibrated using several USNO-B1.0 stars and the error in the photometric calibration is ~0.2 mag. The relative error is ~0.05 magnitudes. time post-burst I-magnitude 1.09 16.50 1.17 16.66 1.41 16.79 1.48 16.85 2.25 17.44 2.32 17.49 2.57 17.61 2.64 17.71 3.17 17.79 (225-second exposure) 3.34 17.99 (225-second exposure) The decay rate is, therefore, approximately alpha = -1.2 between about 1 and 3 hours post-burst. This is similar to the power law index calculated by Nysewander et al. (GCN 4971) during the first hour post-burst and suggests that no jet break has yet been observed. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4973 SUBJECT: GRB060418: Swift XRT Team Refined Analysis DATE: 06/04/18 12:05:19 GMT FROM: Abe Falcone at PSU/Swift A. D. Falcone, D. N. Burrows, Jamie Kennea (PSU), report on behalf of the Swift XRT team: Following the Malindi gap, we have analyzed the initial Swift XRT data from GRB 060418 (Falcone et al., GCN4966), with a total exposure of 1.4 ks. The refined XRT position is: RA(J2000) = 15 45 42.4 Dec(J2000) = -03 38 22.8 We estimate an uncertainty of 4 arcseconds radius (90% containment). In addition to the afterglow decay, the early light curve has bright flaring. The largest flare has a peak of about 460 c/s at approximately 128 s after the trigger time. Aside from the flaring, the light curve is clearly fading, but the rate is difficult to estimate due to the flaring and the limited data available at this time. A preliminary estimate of the power law decay index is approximately 0.6 ± 0.3. This Circular is an official product of the Swift XRT Team. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4974 SUBJECT: VLT/UVES observations of GRB060418 DATE: 06/04/18 12:10:35 GMT FROM: Paul Vreeswijk at ESO Paul Vreeswijk (U. of Chile/ESO) and Andreas Jaunsen (U. of Oslo) report on behalf of a larger collaboration: "Following the Swift detection of GRB060418 (Falcone et al., GCN 4966), we triggered observations with the Ultraviolet and Visual Echelle Spectrograph (UVES), mounted at Kueyen (UT2) of ESO's Very Large Telescope (VLT). The observations were performed using the Rapid-Response Mode, which allows for robotic VLT observations without any human intervention, except for the slit alignment. Starting at 3:16 UT (10min after the Swift/BAT trigger), a series of exposures with increasing integration times (3, 5, 10, 20, and 40min) were performed with central wavelengths 390nm in the blue arm and 564nm in the red, covering 330-670nm at a resolving power of ~43000. This was followed by a 90min exposure with central wavelengths 437nm in the blue and 860nm in the red, extending the wavelength coverage up to 950nm. A preliminary analysis of the spectra shows various absorption features, which can be identified with typical metal lines originating in at least four intervening absorbers at redshifts: z=0.602, z=0.655, z=1.106 and the highest at z=1.489. This confirms the GRB060418 host-galaxy redshift determination by Dupree et al. (GCN 4969). We are very grateful for the excellent support of the Paranal staff, and in particular that of Stefano Bagnulo, Nancy Ageorges and Stan Stefl." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4975 SUBJECT: GRB 060418: Refined Analysis of the Swift-BAT burst DATE: 06/04/18 15:17:40 GMT FROM: Louis M Barbier at NASA/GSFC/Swift J. Cummings (GSFC/ORAU), L. Barbier (GSFC), S. Barthelmy (GSFC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (UMD), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD),D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (ISAS), J. Tueller (GSFC), on behalf of the Swift-BAT team: Using the data set from T-119 to T+183 sec from the recent telemetry downlink, we report further analysis of BAT GRB 060418 (trigger #205851) (Falcone, et al. GCN 4966). The BAT ground-calculated position is RA,Dec = 236.428, -3.642 deg {15h 45m 42.6s, -3d 38' 31.5"} (J2000) +- 0.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 30%. The mask-weighted lightcurve shows three overlapping peaks - a slow rise beginning at T-8 to a broad peak at T+10, a smaller peak at T+18, followed by the largest spike at T+27. There is a small bump in the lightcurve at T+130 which coincides with a flare seen in the XRT data. (Falcone et al. GCN 4973). T90 (15-350 keV) is 52 +- 1 s. The time-averaged spectrum from T-19.2 to T+136.6 is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.66 +- 0.05. The fluence in the 15-150 keV band is 8.1 +- 0.2 x 10-06 erg/cm2. The 1-sec peak photon flux measured from T+27.45 sec in the 15-150 keV band is 6.7 +- 0.4 ph/cm2/sec. Eiso is 5.3e+52 ergs in the 37.35 - 373.5 keV range at the GRB rest frame using z = 1.49 (Dupree et al. GCN 4969, Vreeswijk et al. GCN 4974). All the quoted errors are at the 90% confidence level. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4976 SUBJECT: GRB 060418: FRAM early afterglow observation DATE: 06/04/18 19:04:46 GMT FROM: Martin Jelinek at Inst.Astrophys.Andalucia,Granada Martin Jelínek (IAA Granada, Spain), Petr Kubánek (ISDC Versoix, Switzerland and ASU Ondrejov, Czech Rep.) and Michael Prouza (Columbia University, USA and FZU Praha, Czech Rep.) on behalf of the FRAM team, coordinated by FZU Praha, Czech Rep. report: The robotic telescope FRAM (part of the Pierre Auger Observatory) located in Malargue, Argentina, observed the Swift GRB 060418 (Falcone et al., GCN 4966) in fully automatic mode (under control of RTS2), starting 51s after the GRB trigger under thin cirrus. We detect the OT reported by UVOT at 5 combined images (220s integration time) with mean exposure time 3:11:12UT (~300s after the trigger) with R-band magnitude 14.2+-0.2. We note, that our lightcurve seems to peak at about this time - in agreement with observation of PROMPT (Nysewander et al., GCN 4971). //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4977 SUBJECT: GRB060418: Optical Observations DATE: 06/04/18 19:48:15 GMT FROM: AAVSO GRB Network at AAVSO M. Koppelman (Starhouse Observatory and University of Minnesota) reports on behalf of the AAVSO International High Energy Network on optical observations of GRB060418 (GCN #4966, Falcone et al.) and its reported optical afterglow (GCN #4968, Melandri et al.; GCN #4971, Nysewander et al.; GCN #4972, Cobb et al.): Koppelman reports the following Rc-band measurement: 03:46:20 UT Rc=16.47+/-0.14. Rc magnitudes are untransformed and differential with respect to a two-star ensemble with USNO B1.0 stars 0863-0300553 (R=14.86) and 0864-0294924 (R=14.22). Scatter in the check star was 0.05 mag. A detailed report of these observations follows at the end of this report. M. Nicholson (International Consortium of Robotic Astronomical Researchers) reports V-band observations of this afterglow approximately three hours after the burst. Analysis of these observations is continuing. The AAVSO thanks the Curry Foundation for their continued support of the AAVSO International High Energy Network. Rc-band observations by M. Koppelman, Starhouse Observatory: ----------------------- Name: Michael Koppelman email: michael at aps.umn.edu Observer: Michael Koppelman (KMP) Site: Starhouse Observatory Location: Cologne, MN LatitudeLongitude: 45N 93W Elevation: 800' Scope: Newtonian 0.212m ScopeFocalRatio: f/3.9 CCDVendor: SBIG ST-7XME CCDDetector: Kodak KAF-0402ME CCDSize: 765x510 CCDPixelScale: 2.26"/px CCDFOV: 30x20 Object: GRB060418A ObsDate: 2006-04-18 ObsMidPointTime: 2006-04-18 03:46:22 TimePerFrame: 60, 120 and 180s NumberOfFrames: 10 Filters: Rc Processing: bias, dark, flat Seeing: LimitingMag: Sky: Good afterglowmag: 16.47 afterglowerr: 0.14 compstars: B1.0 0863-0300553 and 0864-0294924 Report: I observed the afterglow at high air mass (~5) with an Rc filter. Plate solution yields a position of 15:45:42.54 -03:38:21 with an error of about 1". The afterglow is visible on 1 of 10 images but reliably detected above the sky background on 2 other images for a total of 3 positive detections. JD Rc Err 2453843.6530 16.44 0.39 2453843.6600 16.57 0.22 2453843.6621 16.37 0.22 Rc magnitudes are untransformed and differential with respect to a two-star ensemble with USNO B1.0 stars 0863-0300553 (R=14.86) and 0864-0294924 (R=14.22). Scatter in check star was 0.05m. Fits images and photometry available upon request to michael at aps.umn.edu. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4978 SUBJECT: GRB060418: Swift/UVOT Observations DATE: 06/04/18 20:46:46 GMT FROM: Patricia Schady at MSSL/Swift P. Schady (UCL-MSSL), A. D. Falcone (PSU), report on behalf of the Swift/UVOT team: The Swift/UVOT began taking data on the field of GRB060418 at 2006-04-18T03:07:36, 88 s after the BAT trigger (Falcone et al., GCN 4966). The source is observed to decay in six of the UVOT filters, but was not detected in the UVW2 filter down to a 3-sigma limiting magnitude of UVW2 > 20.4 in a 949s coadded image. This is consistent with the reported redshift of z=1.49 (Dupree et al. 2006; GCN 4969). The magnitudes for the filters in which there was a detection are as follows: Filter T_mid(s) Exp(s) Mag V 393 393 14.99 +/- 0.02 5996 197 18.84 +/- 0.33 B 675 10 16.22 +/- 0.13 10765 295 19.87 +/- 0.27 U 656 20 15.83 +/- 0.09 6610 197 18.55 +/- 0.20 UVW1 632 20 16.47 +/- 0.19 6405 197 19.04 +/- 0.40 UVM2 608 20 17.30 +/- 0.30 4343 197 > 19.30 White 137 10 14.32 +/- 0.03 11676 295 19.23 +/- 0.16 These magnitudes are uncorrected for the estimated Galactic reddening of E_{B-V} = 0.224 mag (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4979 SUBJECT: GRB060418, BVRcIc field calibration DATE: 06/04/18 21:48:53 GMT FROM: Arne A. Henden at AAVSO A. Henden (AAVSO) reports on behalf of the AAVSO High Energy Network and Sonoita Research Observatory (SRO): We have acquired BVRcIc all-sky photometry for a 20x20arcmin field centered on the coordinates of the afterglow for GRB060418 (Falcone et al. GCN 4966) with the SRO 0.35m telescope on one marginally photometric night. The current zeropoint error is approximately 0.04mag and will be improved with additional nights of photometry. As opposed to previous calibrations, this one is quite shallow, saturating at about V=11. Further reductions will extend this calibration about two magnitudes fainter. We have placed the photometric data on our anonymous ftp site: ftp://ftp.aavso.org/public/grb/grb060418.dat Note#1: the USNO-FS ftp site (ftp.nofs.navy.mil) that used to contain all of the calibrations by Henden had a hard disk failure about a month ago. All of the calibrations have been moved to the AAVSO site, where they will be maintained for the forseeable future. Note#2: the grb060418 file has a modified format that includes (V-Ic). This will be the format for subsequent calibrations. As always, you should check the dates on the .dat file prior to final publication to get the latest photometry. There is a README file on the ftp directory to give you information about the procedures used to calibrate these fields. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4980 SUBJECT: GRB 060418: Radio Observations DATE: 06/04/19 16:19:03 GMT FROM: Alicia Soderberg at Caltech A. M. Soderberg (Caltech) and D. A. Frail (NRAO) report: "Using the Very Large Array, we observed the field of GRB 060418 (GCN 4966) at 8.5 GHz on Apr 19.50 UT. We detect no source above our detection limit of 78 uJy (2-sigma) at the position of the X-ray/optical afterglow (GCN 4966). 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: 4981 SUBJECT: GRB 060418: JHKs PAIRITEL Observations of Afterglow DATE: 06/04/20 00:06:36 GMT FROM: Daniel Kocevski at UC Berkeley Daniel Kocevski, J. S. Bloom (UC Berkeley), and C. H. Blake (Harvard/ CfA), on behalf of a larger collaboration, report: "We began observations of GRB 060417 (Falcone et. al. GCN 4966) with the PAIRITEL 1.3m at 2006-04-18 05:25:34. UTC, 2hr32min after the GRB trigger. The transient reported by Falcone et al. (GCN 4966) is well detected in 300s mosaics simultaneously in JHKs bands, and is seen to fade between mosaics. A series of 13 simultaneous JHKs mosaics taken over 6 hours of observations shows a power law decline in J with a slope of about alpha = 1.11 +/- 0.10 ( F(t)~t^(-alpha) ). The decay slopes measured in H and Ks are consistent with the J band slope within error. This slope is consistent with that reported by Nysewander et al. (GCN 4971) and Cobb et al. (GCN 4972). No break was seen in the observed decay out to at least 08:09:31 UTC. An animated gif of the observations can be found at: http://lyra.berkeley.edu/~kocevski/GCN/GRB060418.gif This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4982 SUBJECT: GRB 060418 : Lulin Optical follow-up DATE: 06/04/20 08:59:37 GMT FROM: Yuji Urata at RIKEN B.A. Chen (NCKU), C.S. Lin, K.Y. Huang, W.H. Ip (NCU), Y. Urata (Saitama-U) on behalf of EAFON report: "We have made B, R, I band imaging for GRB 060418 optical afterglow (Falcone et al. GCN 4966) using Lulin 1m telescope started from 14:38 (UT) on April 18. Preliminary our photometry is below. ================================= Delay(d) Filter mag. --------------------------------- 0.496 R 20.7 +/- 0.1 ================================= This message may be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4983 SUBJECT: GRB 060218 : IR afterglow observations DATE: 06/04/20 09:01:02 GMT FROM: Yuji Urata at RIKEN K. Y. Huang, W.H. Ip(NCU), Y. Urata (Saitama-U) on behalf of EAFON report: " We performed IR follow-up observations with CFHT/WIRCam from 8 hours after the GRB. The afterglow was detected in JHKs bands clearly. The afterglow brightness estimated from 2MASS catalog is Ks = 16.8 +/-0.1 at 8.11 hours after the burst. During our observational period, the decay index is about 1 in Ks band. " This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4984 SUBJECT: Erratum of GCN 4983 for GRB 060418 IR follow-up DATE: 06/04/20 09:15:38 GMT FROM: Yuji Urata at RIKEN K. Y. Huang, W.H. Ip(NCU), Y. Urata (Saitama-U) on behalf of EAFON report: The report of GCN 4983 is for "GRB 060418". Below is correct one. GRB 060418 : IR afterglow observations " We have performed IR follow-up observations for GRB 060418 (Falcone et al. GCN 4966) with CFHT/WIRCam at 8 hours after the GRB. The afterglow was detected in JHKs bands clearly. The afterglow brightness estimated from 2MASS catalog is Ks = 16.8 +/-0.1 at 8.11 hours after the burst. During our observational period, the decay index is about 1 in Ks band. " //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4989 SUBJECT: Konus-Wind observation of GRB 060418 DATE: 06/04/21 12:27:00 GMT FROM: Valentin Pal'shin at Ioffe Inst S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, M. Ulanov, and T. Cline on behalf of the Konus-Wind team report: The long GRB 060418 (Swift-BAT trigger=205851; Falcone et al. GCN 4966; Cummings et al. GCN 4975) was observed by Konus-Wind in the waiting mode. The emission is clearly seen in the three K-W bands: G1 (18-70 keV), G2 (70-360 keV) and G3 (360-1360 keV) with high S/N. Using an approximation the time-integrated 3-channel K-W spectrum by a power law with exponential cutoff model: dN/dE ~ E^(-alpha)*exp(-E*(2-alpha)/Ep), we have found alpha ~1.5, and Ep ~230 keV. As observed by Konus-Wind, the burst had a duration of ~44 s, and fluence ~1.6x10^-5 erg/cm2 (in the 20 - 1100 keV energy range). Assuming z = 1.49 (Dupree et al. GCN 4969; Vreeswijk and Jaunsen GCN 4974) and a standard cosmology model with H_0 = 70 km/s/Mpc, Omega_M = 0.3, Omega_\Lambda = 0.7, the isotropic energy release is E_iso ~9x10^52 erg. ~1200 s after the BAT GRB 060418, Konus-Wind detected another burst. Whether the second event relates to the first GRB or whether it is a different GRB detected by chance close to first one is not clear at this time. The available data cannot confirm or rule out the possibility that the second event came from the same location as the Swift GRB: a) the Konus-Wind ecliptic latitude response for the second event is consistent with the ecliptic latitude response for the Swift GRB. b) BAT does not see a rate increase at ~03:26. At this time, GRB 060418 was out of the BAT FOV (~57 degrees off axis), but a little above the Earth horizon (J. Cummings, private communication). So, the BAT data do not rule out the possibility the second event came from GRB 060418. c) Neither burst was detected by Odyssey, but both bursts are Mars-blocked, if the second one comes from the same direction as the first. RHESSI observed the first (Swift) burst, but not the second one. The RHESSI detection of the first burst was rather weak, and as observed by Konus, the second burst was weaker than the first one, so it could have missed. the second one (K. Hurley, private communication). d) The second event was not detected by Suzaku-WAM. The position of GRB 060418 was occulted by the Earth from Suzaku at the time of the second event (K. Yamaoka, private communication). Hence, the situation is ambiguous. Possibly, the data from optical telescopes can clarify this issue, if there were some optical observations of the GRB 060418 afterglow during the time of the second event. The K-W light curves of these events are available at http://www.ioffe.rssi.ru/LEA/GRBs/GRB060418/ //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4990 SUBJECT: GRB060418: optical observations DATE: 06/04/21 14:00:18 GMT FROM: Alexei Pozanenko at IKI, Moscow B. Hafizov (MAO), D. Sharapov (MAO and NOT, La Palma), A. Pozanenko (IKI), M. Ibrahimov (MAO) on behalf of larger GRB follow up collaboration report: We observed the afterglow of GRB060418 (Falcone et al. GCN 4966) with 1.5m telescope of Maidanak Astronomical Observatory (MAO) in BRI-bands on April 18. A series of BRI images (B: 8x180s, R: 7x120s, I: 9x120s) were taken on April 18 (UT) 19:54 - 21:07 and 9x120s I-images were taken between 22:14 - 22:37. We detect OT (Falcone et al. GCN 4966) on single images in I and R; preliminary OT brightness estimation of the first I-image (UT=19:54) is ~20.5. Data reduction is continuing. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4991 SUBJECT: GRB 060418: prediction of t_break DATE: 06/04/21 15:09:37 GMT FROM: Gabriele Ghisellini at Obs.Astro. di Brera G. Ghisellini, G. Ghirlanda and F. Tavecchio report: The long GRB 060418 detected by Swift (Falcone et al. GCN 4966; Cummings et al. GCN 4975) whose spectral parameters have been reported by Golenetskii et al. (GCN 4989), as observed by Konus-Wind, is consistent with the E_peak-E_iso (Amati) correlation. If the light curve will show a break at t=3+-1 days, this burst would also be consistent with the E_p-E_gamma (Ghirlanda) relation. Therefore multiwavelength observations are encouraged. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5002 SUBJECT: GRB060418: Further Analysis of MIKE Spectroscopy DATE: 06/04/24 17:27:34 GMT FROM: Jason Prochaska at UCO/Lick Obs J. X. Prochaska (UCO/Lick Observatory), H.-W. Chen (U Chicago), J. S. Bloom (UC Berkeley), E. Falco, and A. K. Dupree (Harvard-Smithsonian CfA) report on behalf of the GRAASP collaboration: "We have further analyzed the echelle spectra of GRB060418 (Falcone et al. GCN 4966), obtained using MIKE on the Magellan Clay telescope (Dupree et al. GCN 4969). We report the detection of ZnII, SiII, SiII*, FeII, FeII*, MgII, MgI, AlIII, CIV and NiII transitions among others at a redshift z=1.4901 +/- 0.0001. The relative populations of the excited FeII levels are similar to GRB051111 (PHB06, astro-ph/0601057); the J=7/2 to J=1/2 states follow a Boltzmann distribution with T=1000-5000K. But, following GRB051111 and GRB050730, we interpret the FeII excitation as the result of indirect UV pumping by the GRB afterglow. The detection of strong MgI absorption places this gas (and presumably the majority of low-ion gas) at a distance r>50pc from the GRB. Finally, we measure [Si/Fe]=+0.5dex indicating a modest dust-to-metals ratio. This message may be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5009 SUBJECT: GRB060418: Swift XRT Team Further Refined Analysis DATE: 06/04/27 17:05:58 GMT FROM: Abe Falcone at PSU/Swift A. D. Falcone, D. N. Burrows, D. Morris, J. Racusin (PSU), P. T. O'Brien, J. P. Osborne (U Leicester), N. Gehrels (GSFC) report on behalf of the Swift XRT team: We have performed more analysis on recent Swift XRT data from GRB 060418 (Falcone et al., GCN4966). As reported by Falcone et al. (GCN4973), the early afterglow decay has bright flaring. This flaring made it difficult to estimate the afterglow decay index at the time of the previous report, which made use of only the initial flare-dominated data. Here we give a better estimate of this decay, along with some preliminary spectral information. From 78 s until about 115 s after the burst trigger time, the light curve had a steep power law decay index of alpha = 4.6 +/- 0.2. A large flare begins at T+115 s, peaking at T+135 s (where T is the BAT trigger time) with a maximum count rate of ~560 c/s. Flaring continues to at least T+6000 s. No flares are evident after T+40,000 s, at which point the count rate has dropped to less than 0.01 c/s. The temporal decay of the underlying afterglow was fit using two time regions that showed no evidence of flaring (T+350 to T+530 s, and T+40,000 to T+190,000 s). The underlying afterglow has a power law decay index of alpha = 1.4 ± 0.1 from T+350 s until the last detection at T+700,000 s. There is no evidence for a break in the underlying decay curve up to 9 days after the trigger. In particular, we do not detect the break predicted by Ghisellini et al. (GCN 4991), although we have only a single 2 sigma data point after the predicted break time. Due to a normal orbital gap, we have no data during the time of the potential second burst reported by Konus-Wind (Golenetskii et al. GCN4989). A preliminary light curve can be viewed at http://www.astro.psu.edu/users/afalcone/grb060418/falcone_grb060418.gif The observed spectra of the underlying afterglow can be described by a simple absorbed power law, with photon index 2.04 +/- 0.13 and total N_H = (19 +/- 4)e20 cm^-2, with a chi2/dof of 1.22 (75 dof). This fit assumes all absorption is local to the observer. The Galactic N_H at this position is ~9e20 cm^-2 (Dickey and Lockman 1990). We fit the time period during the large flare with a spectral model that was the sum of two power laws; one was the underlying afterglow frozen to the values shown above (with the normalization changed based on the measured temporal decay) and the other was a power law that was free to vary. This fit resulted in a chi2/dof of 1.07 (321 dof), with the following flare power law component parameters: photon index 2.04 +/- 0.05 and N_H = (29 +/-2)e20 cm^-2. For the flare component, we also tried a cutoff power law, a Band function, and a blackbody model. In all cases, the fits were equivalently acceptable, with chi2/dof always falling in the range from 1.05 to 1.07. The cutoff power law was equivalent to the simple power law since the cutoff reached a maximum value in excess of 500 keV. The Band function and the blackbody models both resulted in harder energy spectral indices, with an N_H that was consistent (within 1 sigma error bars) with that of the underlying afterglow. This is in contrast to the simple power law that implies an N_H increase during the flare (relative to the underlying afterglow value). This Circular is an official product of the Swift XRT Team. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5112 SUBJECT: GRB060418: optical observations DATE: 06/05/11 11:04:51 GMT FROM: Alexei Pozanenko at IKI, Moscow R. Karimov, B. Hafizov (MAO), A. Pozanenko (IKI), M. Ibrahimov (MAO) on behalf of larger GRB follow up collaboration report: We observed the afterglow of GRB060418 (Falcone et al. GCN 4966) with 1.5m telescope of Maidanak Astronomical Observatory (MAO) in BRI-bands on April 18 between (UT) 19:54 and 22:37 (Hafizov et al. GCN 4990). A photometry of the afterglow is following: Mid_Time(UT), Filter, Exposure, Magnitude 18.857 B 7x180 s 22.38 +/- 0.10 18.853 R 7x120 s 21.14 +/- 0.05 18.855 I 9x120 s 20.66 +/- 0.04 18.934 I 9x120 s 20.35 +/- 0.04 The photometry is based on field stars calibration by Henden (GCN 4979) and not corrected for Galaxy extinction. We note our I-observations indicate a possible re-brighntening of the afterglow. This message may be cited.