//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10034 SUBJECT: GRB 091018: Swift detection of a burst with optical afterglow DATE: 09/10/18 21:08:34 GMT FROM: David Palmer at LANL M. Stamatikos (OSU/NASA/GSFC), D. N. Burrows (PSU), J. R. Cummings (NASA/UMBC), V. D'Elia (ASDC), N. Gehrels (NASA/GSFC), C. Gronwall (PSU), C. Guidorzi (U Ferrara), S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU), W.B Landsman (GSFC), C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester), D. M. Palmer (LANL), M. Perri (ASDC), J. L. Racusin (NASA/GSFC/ORAU) and G. Stratta (ASDC) report on behalf of the Swift Team: At 20:48:19 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 091018 (trigger=373172). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 32.211, -57.526 which is RA(J2000) = 02h 08m 51s Dec(J2000) = -57d 31` 34`` with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single smooth FRED peak a duration of about 10 sec. The peak count rate was ~16000 counts/sec (15-350 keV), at ~2 sec after the trigger. The XRT began observing the field at 20:49:20.5 UT, 60.9 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 32.18587, -57.54749 which is equivalent to: RA(J2000) = 02h 08m 44.61s Dec(J2000) = -57d 32' 51.0" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 91 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (2.81e+20 cm^-2, Kalberla et al. 2005), with an excess column of 1.4 (+1.00/-0.93) x 10^21 cm^-2 (90% confidence). The initial flux in the 2.5 s image was 4.40e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 68 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7`x2.7` sub-image at RA(J2000) = 02:08:44.61 = 32.18588 DEC(J2000) = -57:32:53.8 = -57.54827 with a 90%-confidence error radius of about 0.61 arc sec. This position is 3.8 arc sec. from the center of the XRT error circle. The estimated magnitude is 14.60 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.03. Burst Advocate for this burst is M. Stamatikos (Michael.Stamatikos-1 AT nasa.gov). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10036 SUBJECT: GRB 091018: ROTSE-III Detection of Optical Counterpart DATE: 09/10/18 21:34:32 GMT FROM: Brad Schaefer at LSU B. E. Schaefer (Louisiana State) and S. B. Pandey (U Mich), report on behalf of the ROTSE collaboration: ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia, responded to GRB 091018 (Swift trigger 373172, Stamatikos et al., GCN 10034). The first image was at 20:57:36.1 UT, 556.6 s after the burst (11.1 s after the GCN notice time). The unfiltered images are calibrated relative to USNO A2.0. We detect a new object, not visible in the DSS (second epoch), with coordinates: 02:08:44.6 -57:32:53.6 (J2000), with positional uncertainty of 1" or better start UT mag mlim(of image) ---------------------------------- 20:57:36.1 15.4 16.4 With this, we confirm the optical afterglow reported in GCN 10034 as a UVOT detection. The source is rapidly fading. A jpeg image is available at http://www.rotse.net/images/gsb373172_3c01_img.jpg Note that the object numbered 14 (in the lower of the two circles) is the candidate in question. Continuing observations are in progress. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10037 SUBJECT: GRB 091018: Enhanced Swift-XRT position DATE: 09/10/19 00:31:06 GMT FROM: Phil Evans at U of Leicester J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team. Using 1175 s of XRT Photon Counting mode data and 2 UVOT images for GRB 091018, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 32.18588, -57.54825 which is equivalent to: RA (J2000): 02h 08m 44.61s Dec (J2000): -57d 32' 53.7" with an uncertainty of 1.7 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10038 SUBJECT: GRB091018: Magellan Echellette Observations DATE: 09/10/19 01:49:14 GMT FROM: Hsiao-Wen Chen at U Chicago Hsiao-Wen Chen, Jennifer Helsby (UChicago), Stephen Shectman, Ian Thompson, Jeffrey Crane (Carnegie Observatory) report on behalf of a larger collaboration: "We observed the afterglow of GRB091018 reported by Stamatikos et al. (GCN 10034) and confirmed by Schaefer et al. (GCN10036) using the MagE echellette spectrograph on the Magellan Clay Telescope. The observations started at UT 00:28 on October 19, 2009, ~ 3.5 hours after the inital trigger. We obtained 2x900s exposures. Our preliminary reduction shows that the afterglow spectrum displays strong absorption transitions due to MgII, FeII, MnII at redshift z=0.971, which we tentatively identify as the host redsdhift of the GRB. Further analysis is underway. This message may be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10039 SUBJECT: GRB 091018: GROND observations DATE: 09/10/19 02:13:51 GMT FROM: Robert Filgas at MPI R. Filgas, T. Kruehler, A. Yoldas (all MPE Garching), S. Klose (TLS Tautenburg), and J. Greiner (MPE Garching), report on behalf of the GROND team: GROND (Greiner et al. 2008, PASP 120, 405), the 7-channel imager mounted at the 2.2m ESO/MPI telescope at La Silla Observatory (Chile), started follow-up observations of GRB 091018 (Stamatikos et al. 2009, GCN 10034) on October 18, at 23:47 UTC (~4 hrs after the burst). For the afterglow candidate reported by Stamatikos et al. we estimate the following preliminary magnitudes (in the AB system): g'= 19.061 +/- 0.010 r'= 18.853 +/- 0.007 i'= 18.732 +/- 0.013 z'= 18.70 +/- 0.10 J = 18.3 +/- 0.1 H = 18.2 +/- 0.1 K = 17.9 +/- 0.1 calibrated against GROND zeropoints. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10040 SUBJECT: GRB 091018: Swift-BAT refined analysis DATE: 09/10/19 02:57:39 GMT FROM: Scott Barthelmy at NASA/GSFC C. B. Markwardt (GSFC/UMD), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), D. M. Palmer (LANL), A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 091018 (trigger #373172) (Stamatikos, et al., GCN Circ. 10034). The BAT ground-calculated position is RA, Dec = 32.191, -57.546 deg, which is RA(J2000) = 02h 08m 45.9s Dec(J2000) = -57d 32' 45.0" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 84%. The mask-weighted light curve shows the FRED peak starting at ~T-5 sec, peaking at T+1.1 sec, and ending at ~T+20 sec. T90 (15-350 keV) is 4.4 +- 0.6 sec (estimated error including systematics). The time-averaged spectrum from T-0.3 to T+7.7 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.77 +- 0.24, and Epeak of 19.2 +18,-11 keV (chi squared 40.01 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 1.4 +- 0.1 x 10^-6 erg/cm2 and the 1-sec peak flux measured from T+0.80 sec in the 15-150 keV band is 10.3 +- 0.4 ph/cm2/sec. A fit to a simple power law gives a photon index of 2.30 +- 0.06 (chi squared 52.2 for 57 d.o.f.). All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/373172/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10041 SUBJECT: GRB091018: Swift/UVOT observations DATE: 09/10/19 04:12:08 GMT FROM: Wayne Landsman at GSFC/SSAI W.B. Landsman (NASA/GSFC) and M. Stamatikos (OSU/NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 091018 69s after the BAT trigger (Stamatikos et al., GCN 10034). The afterglow is well-detected in all seven UVOT filters at the position reported by Stamatikos et al. The initial magnitudes are as follows: Filter T_start(s) Exp(s) Mag white 69 147 14.57 ± 0.012 white 860 147 16.48 ± 0.018 u 281 246 15.07 ± 0.017 u 6911 197 18.04 ± 0.08 v 610 19 16.4 ± 0.14 b 536 19 16.4 ± 0.08 uvw1 660 20 15.9 ± 0.12 uvm2 635 20 15.7 ± 0.16 uvw2 586 20 16.1 ± 0.15 The detection in the uvw2 filter indicates a redshift less than z = 1.1, consistent with the value of z= 0.971 reported by the Magellan group ( Chen et al., GCN 10038). The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.029 in the direction of the burst (Schlegel et al. 1998). The photometry is on the UVOT photometric system described in Poole et al. (2008, MNRAS, 383, 627). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10042 SUBJECT: GRB 091018: VLT/X-shooter spectra DATE: 09/10/19 16:24:15 GMT FROM: Antonio Deugarte at IAA-CSIC A. de Ugarte Postigo (OAB-INAF), P. Goldoni (APC/Univ. Paris 7 and SAp/CEA), C.C. Thoene (OAB-INAF), N. Tanvir (Univ. Leicester), P. Jakobsson (Univ. of Iceland), S.D. Vergani (APC/Univ. Paris 7), H. Flores (Paris Obs.) D. Malesani (DARK/NBI), A. Levan (Univ. Warwick) and J.P.U. Fynbo (DARK/NBI) report on behalf of the X-shooter GRB collaboration: X-shooter observed the afterglow of GRB 091018 (Stamatikos et al. CGN 10034) starting at 23:58 UT of the 18th Oct 2009. The observation consisted of 4 x 600s exposures, having a mean epoch of October 19.0148 UT, 3.53 hours after the burst. In the spectra we detect the continuum in the complete range from 3000 to 24800 Angstroms. On a preliminary analysis we find several absorption features including AlII (1670), AlIII (1854, 1862), FeII (2260, 2344, 2374, 2382, 2586, 2600) MnII (2576, 2594, 2606), MgII (2797, 2803), MgI (2852), CaII (3934, 3969) at a common redshift of 0.9710 +/- 0.0003, consistent with the observation reported by Chen et al. (GCN 10038). There is also a tentative detection of [OII], [OIII] and H-alpha emission lines from the host galaxy at the same redshift. Further analysis is ongoing. We thank the ESO observing staff, in particular A. Smette, C. Martayan and C. Cid. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10043 SUBJECT: GRB 091018: BOOTES-3 observations DATE: 09/10/19 19:49:59 GMT FROM: Antonio Deugarte at IAA-CSIC A. de Ugarte Postigo (INAF-OAB), P. Kubanek (U. Valencia, IAA-CSIC), M. Jelinek, A.J. Castro-Tirado, J. Gorosabel, R. Cunniffe, S. Guziy (IAA-CSIC), B.A. Allen (Vintage Lane Obs.) and P. Yock (Auckland Univ.) report: We have observed the afterglow of GRB 091018 (Stamatikos et al. CGN 10034) with the 0.6m Yock-Allen telescope (BOOTES-3) located in Blenheim (New Zealand). A combination of 21x30s unfiltered images with mean epoch Oct. 19.625 UT (18.2 hours after the burst) shows the afterglow at a magnitude of R=20.0+/-0.3. The photometry has been obtained using as comparison 5 USNO-B1.0 stars. This magnitude implies a rough decay slope of alpha = 0.7 +/- 0.2 (with F ~ t^(-alpha)) as compared to the values of Filgas et al. (GCN 10039). Further analysis is ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10044 SUBJECT: GRB 091018 : Faulkes Telescope South Observations DATE: 09/10/19 20:37:10 GMT FROM: Zach Cano at ARI/John Moores Liverpool Z. Cano (Liverpool JMU), C. Guidorzi (U. Ferrara), D. Bersier, N.R. Clay, S. Kobayashi, A. Melandri, C.G. Mundell, C.J. Mottram, R.J. Smith, I.A. Steele (Liverpool JMU), A. Gomboc (U. Ljubljana), N.R. Tanvir (U. Leicester) on behalf of a larger collaboration report: The Faulkes Telescope South (Australia) observed the field of GRB 091018 (Swift trigger=373172, Stamatikos et al., GCN 10034) on 2009 October 19. We clearly detect the afterglow candidate (Schaefer & Pandey, GCN 10036; Chen et al., GCN 10038; Filgas et al., GCN 10039; Landsman & Stamatikos, GCN 10041; A. de Ugarte Postigo et al., GCN 10042 & GCN 10043) in the Ri' filters with the following magnitudes: Filter mag merr T-To (hr) --------------------------------------- I 19.73 0.06 15.17 I 20.13 0.08 20.95 R 19.67 0.06 15.72 R 20.06 0.08 20.95 As calibrated against nearby USNO object 0342-0026807 (R2 = 16.34, I2 = 16.22). From the images obtained on FTS we derive preliminary decay rates of: alpha_I = 1.1 +/- 0.3 & alpha_R = 1.2 +/- 0.3. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10045 SUBJECT: Konus-RF observation of GRB 091018 DATE: 09/10/19 21:35:13 GMT FROM: Valentin Pal'shin at Ioffe Inst S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, P. Oleynik, M. Ulanov, and D. Svinkin on behalf of the Konus-RF team, report: The soft GRB 091018 (Swift-BAT trigger #373172: Stamatikos et al., GCN 10034, Markwardt et al., GCN 10040) triggered Konus-RF at T0=74900.651 s UT (20:48:20.651). The burst light curve shows a single pulse with a duration of ~5 s. As observed by Konus-RF the burst had a fluence of 1.44(-0.16, +0.19)x10^-6 erg/cm2, and a 256-ms peak flux measured from T0-0.280 s of 4.32(-0.94, +0.97)x10^-7 erg/cm2/s (both in the 20 keV - 1 MeV energy range). The time-integrated spectrum of the burst (from T0-2s to T0+3s) is well fitted (in the 10 keV - 1 MeV range) by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep), with alpha = -1.53(-0.39, +0.59), and Ep = 28(-16, +10) keV (chi2 = 83.4/94 dof). Fitting by GRB (Band) model yields the same alpha and Ep, and only an upper limit on the high energy photon index: beta < -2.44 (chi2 = 81.7/93 dof). All the quoted values are preliminary. All the quoted errors are at the 90% confidence level. Assuming z = 0.971 (Chen et al., GCN 10038) and a standard cosmology model with H_0 = 70 km/s/Mpc, Omega_M = 0.27, Omega_Lambda = 0.73, the isotropic energy release E_iso ~3.7x10^51 erg, the peak luminosity (L_iso)_max ~2.2x10^51 erg/s, and Ep_rest ~55 keV. The Konus-RF light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB091018_T74900/KRF/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10046 SUBJECT: GRB 091018: Skynet/PROMPT Observations of Fading DATE: 09/10/19 23:59:19 GMT FROM: Aaron LaCluyze at U.North Carolina A. LaCluyze, D. Reichart, J. Haislip, K. Ivarsen, R. Egger, A. Foster, J. Moore, A. Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M. Nysewander report: Skynet observed the Swift/BAT localization of GRB 091018 (Stamatikos et al., GCN 10034) with four of the 16" PROMPT telescopes at CTIO beginning 3.0 hours after the the trigger in BVRI. We detect the afterglow (Stamatikos et al., GCN 10034) in all filters. Between 3.0 and 12.3 hours after the trigger, the afterglow faded with periods of rebrightening (1) beginning around 5 hours and peaking around 6 hours, and (2) beginning around 8 hours and peaking around 9 hours. Overall, if fitted with a power law, the afterglow faded with a power-law index of about -0.95 in BVR but only about -0.65 in I. I - R brightened by about 0.45 mag over the course of 12 hours. At 12.3 hours after the trigger, the afterglow's magnitude was R = 19.82 +0.14 -0.12 (statistical) +/- 0.56 (systematic; calibrated to 115 USNO B1 stars). Skynet's most recent BVRI light curve, calibrated to USNO B1 and NOMAD stars, can be found here: http://skynet.unc.edu/grb/grb091018.png //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10047 SUBJECT: GRB 091018: miniTAO/ANIR Observations DATE: 09/10/20 05:47:04 GMT FROM: Takeo Minezaki at U.of Tokyo/Astro K. Motohara, M. Konishi, K. Toshikawa, N. Mitani, T. Minezaki, S. Koshida, D. Kato, Y. Yoshii$B!!(B(University of Tokyo), Y. Ita (National Astronomical Observatory of Japan) on behalf of the TAO project team: We report the NIR imaging observation of GRB 091018 carried out from October 19 2:09 to 2:57 (UTC), using NIR Camera ANIR (Motohara et al. 2008, Proc. SPIE 7014, 70142T) mounted on the 1.0m miniTAO telescope (Sako et al. 2008, Proc. SPIE7012, 70122T) at the University of Tokyo Atacama Observatory on the summit of Co. Chajnantor (5640m altitude) in the northern Chile. The preliminary magnitudes (AB system) for the afterglow candidate reported by Stamatikos et al. 2009 (GCN 10034) are ; Y = 18.98 +/- 0.14 J = 19.40 +/- 0.19 H = 18.93 +/- 0.17 Ks = 18.22 +/- 0.07 which are taken with the MKO filter system. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10055 SUBJECT: GRB 091018: Swift XRT refined analysis DATE: 09/10/21 11:55:55 GMT FROM: Giulia Stratta at ASDC G. Stratta (ASDC) reports on behalf of the Swift-XRT team: The Swift-XRT began observing GRB 091018 (trigger=373172) on 2009-10-18 at 20:49:20.5 UT, 60.9 seconds after the BAT trigger (Stamatikos et al., GCN Circ. 7226). The data have been taken in Windowed Timing (WT) mode from T + 67 s to T + 144 s and in Photon Counting (PC) mode later on. Enhanced position of the detected, bright X-ray afterglow was given by Osborne et al. (GCN Circ. 10037) The X-ray light curve from T + 67 s to T + 53.3 ks is well fit by a broken power law model (chi^2 = 115 for 128 degrees of freedom) with a temporal break at tb = T + (500 +/- 100) s and decay indices alpha1 = -0.4 +/- 0.1 and alpha2 = -1.17 +/- 0.03 before and after the break, respectively. The 0.3-10 keV spectrum from T + 156 s to T + 7.1 ks is well fit by an absorbed power law (reduced chi2 of 1.0, with 50 degrees of freedom). The best fit photon index is 1.9 +/- 0.1, with an hydrogen column density at the burst rest frame (z=0.971, Hsiao-Wen Chen et al. GCN Circ.10038) of NHz = (1.4 +/- 0.8)e21 cm^-2 in addition to the Galactic column along the line of sight, that is NH = 2.8e20 cm^-2 (Kalberla et al. 2005). Errors are given at 90% confidence level. The observed (unabsorbed) flux in the 0.3-10 keV band is 1.5(1.8)e-10 erg cm^-2 s^-1. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10061 SUBJECT: GRB 091018: Skynet/PROMPT Continued Observations of Fading DATE: 09/10/23 14:36:01 GMT FROM: Aaron LaCluyze at U.North Carolina A. LaCluyze, D. Reichart, J. Haislip, K. Ivarsen, R. Egger, A. Foster, J. Moore, A. Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M. Nysewander report: Skynet has continued to observed the afterglow (Stamatikos et al., GCN 10034) of GRB 091018 (Stamatikos et al., GCN 10034) with four of the 16" PROMPT telescopes at CTIO in BVRI. After fading with a power-law index of about -0.95 in BVR between 3 and 12 hours after the trigger (LaCluyze et al., GCN 10046), the afterglow faded with a steeper power-law index of about -1.3 in BR between 12 hours and 1.5 days after the trigger, which is consistent with the findings of Cano et al. (GCN 10044). However, between 1.5 days and 3.4 days after the trigger, the afterglow faded with a shallower power-law index of about -0.9 in R. The I - R color of the afterglow, which brightened by about 0.45 mag between 3 and 12 hours after the trigger (LaCluyze et al., GCN 10046), has faded by about 0.1 +/- 0.3 mag between 12 hours and 3.4 days after the trigger, which is consistent with no additional color change, but the uncertainty is large. At 3.4 days after the trigger, the afterglow's magnitude was R = 22.27 +0.28 -0.23 (statistical) +/- 0.56 (systematic; calibrated to 115 USNO B1 stars). Skynet's most recent BVRI light curve, calibrated to USNO B1 and NOMAD stars, can be found here: http://skynet.unc.edu/grb/grb091018.png Continued observations with larger telescopes are encouraged. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10110 SUBJECT: GRB 091018, SMARTS optical/IR afterglow observations DATE: 09/10/29 21:47:42 GMT FROM: Bethany Cobb at UC Berkeley B. E. Cobb (UC Berkeley) reports: Using the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained optical/IR imaging of the error region of GRB 091018 (GCN 10034, Stamatikos et al.) over several epochs, starting ~3.9 hours post-burst. For the first epoch, several dithered images were obtained in each filter, with total summed exposure times of 180s in each of BRIJK and 120s in each of H and V. For later epochs, total summed exposure times amounted to 15 minutes in I and V and 12 minutes in J and K. At a mid-exposure time of 2009-10-19 00:57 UT (4.1 hrs post-burst), the GRB afterglow (e.g. GCN 10034, Stamatikos et al., GCN 10036, Schaefer et al., GCN 10039, Filgas et al.) is detected with the following magnitudes: B = 19.59 +/- 0.04 V = 19.27 +/- 0.05 R = 18.88 +/- 0.04 I = 18.44 +/- 0.04 J = 18.0 +/- 0.2 H = 17.1 +/- 0.2 K = 16.1 +/- 0.2 Between 4.1 hrs and 33.0 hrs post-burst, the GRB afterglow fades with a decay rate of approximately alpha = -1.3 (where afterglow flux is proportional to t^alpha). time post-burst I-band magnitude 4.1 hrs 18.44 +/- 0.04 5.5 hrs 18.82 +/- 0.04 8.0 hrs 19.26 +/- 0.04 9.7 hrs 19.49 +/- 0.05 28.6 hrs 21.04 +/- 0.06 33.0 hrs 21.27 +/- 0.08 (Optical photometry is calibrated against Landolt standard stars and IR photometry is calibrated against 2MASS stars in the field.) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10112 SUBJECT: GRB 091018: Skynet/PROMPT Observations of Possible Host Galaxy DATE: 09/10/30 04:17:19 GMT FROM: Aaron LaCluyze at U.North Carolina A. LaCluyze, D. Reichart, J. Haislip, K. Ivarsen, R. Egger, A. Foster, J. Moore, A. Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M. Nysewander report: Skynet has continued to observed the afterglow (Stamatikos et al., GCN 10034) of GRB 091018 (Stamatikos et al., GCN 10034) with two of the 16" PROMPT telescopes at CTIO in RI (LaCluyze et al., GCNs 10046, 10061). Between 3.2 and 7.5 days after the trigger, the light curve is consistent with constant emission, which suggests that we are observing the host galaxy. If so, we measure its brightness to be: R = 22.30 +/- 0.11 (statistical) +/- 0.56 (systematic; calibrated to 115 USNO B1 stars). and I = 21.78 +/- 0.16 (statistical) +/- 0.54 (systematic; calibrated to 67 USNO B1 stars).