//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 11941 SUBJECT: GRB 110420A: Swift detection of a burst with optical counterpart DATE: 11/04/20 11:17:43 GMT FROM: David Burrows at PSU/Swift V. Mangano (INAF-IASFPA), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), S. Campana (INAF-OAB), J. R. Cummings (NASA/UMBC), P. A. Evans (U Leicester), J. M. Gelbord (PSU), B. Gendre (ASDC), C. Guidorzi (U Ferrara), S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU), P. T. O\'Brien (U Leicester), C. Pagani (U Leicester), P. Romano (INAF-IASFPA), A. Rowlinson (U Leicester), B. Sbarufatti (INAF-OAB/IASFPA), M. H. Siegel (PSU), M. Stamatikos (OSU/NASA/GSFC) and R. L. C. Starling (U Leicester) report on behalf of the Swift Team: At 11:02:24 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 110420A (trigger=451757). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 2.165, -37.855 which is RA(J2000) = 00h 08m 40s Dec(J2000) = -37d 51' 17" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single peak structure with a duration of about 20 sec. The peak count rate was 4000 counts/sec (15-350 keV), at 10 sec after the trigger. The XRT began observing the field at 11:03:51.6 UT, 87.6 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 2.16337, -37.88696 which is equivalent to: RA(J2000) = 00h 08m 39.21s Dec(J2000) = -37d 53' 13.1" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 115 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. We cannot determine whether the source is fading at the present time. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (1.26 x 10^20 cm^-2, Kalberla et al. 2005), with an excess column of 2.8 (+2.08/-1.84) x 10^21 cm^-2 (90% confidence). The initial flux in the 2.5 s image was 8.02e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 97 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 00:08:39.27 = 2.16364 DEC(J2000) = -37:53:12.0 = -37.88667 with a 90%-confidence error radius of about 0.75 arc sec. This position is 1.3 arc sec. from the center of the XRT error circle. The estimated magnitude is 17.77 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.01. Burst Advocate for this burst is V. Mangano (vanessa AT ifc.inaf.it). 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: 11942 SUBJECT: GRB 110420A: Enhanced Swift-XRT position DATE: 11/04/20 17:26:35 GMT FROM: Phil Evans at U of Leicester A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team. Using 1599 s of XRT Photon Counting mode data and 2 UVOT images for GRB 110420A, 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 = 2.16355, -37.88627 which is equivalent to: RA (J2000): 00h 08m 39.25s Dec (J2000): -37d 53' 10.6" with an uncertainty of 1.5 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: 11943 SUBJECT: GRB 110420A: Swift-XRT refined Analysis DATE: 11/04/20 20:28:46 GMT FROM: Vanessa Mangano at INAF-IASFPA V. Mangano (INAF-IASFPA) and B. Sbarufatti (INAF OAB/INAF-IASFPA) report on behalf of the Swift-XRT team: We have analysed 1.9 ks of XRT data for GRB 110420A (Mangano et al. GCN Circ. 11941), from 77 s to 17.0 ks after the BAT trigger. The data comprise 57 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN. Circ 11942). The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=3.87 (+0.31, -0.29). At T+181 s the decay flattens to an alpha of 0.23 (+0.08, -0.09) before breaking again at T+11.0 ks to a final decay with index alpha=3.9 (+1.8, -2.1). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 4.2 (+0.5, -0.4). The best-fitting absorption column is 1.9 (+0.6, -0.5) x 10^21 cm^-2, in excess of the Galactic value of 1.3 x 10^20 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a photon index of 2.37 (+0.16, -0.15) and a best-fitting absorption column of 2.1 (+/-0.4) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (6.4 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.1 (+/-0.4) x 10^21 cm^-2 Galactic foreground: 1.3 x 10^20 cm^-2 Excess significance: 8.8 sigma Photon index: 2.37 (+0.16, -0.15) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00451757. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 11945 SUBJECT: GRB 110420A: Swift-BAT refined analysis DATE: 11/04/20 23:59:45 GMT FROM: Scott Barthelmy at NASA/GSFC GRB 110420A: Swift-BAT refined analysis H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), V. Mangano (INAF-IASFPA), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-61 to T+242 sec from recent telemetry downlinks, we report further analysis of BAT GRB 110420A (trigger #451757) (Mangano, et al., GCN Circ. 11941). The BAT ground-calculated position is RA, Dec = 2.164, -37.877 deg which is RA(J2000) = 00h 08m 39.3s Dec(J2000) = -37d 52' 35.5" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 15%. The mask-weighted light curve shows a single peak with some structure starting at ~T-15 sec, peaking at ~T+8 sec, and ending at ~T+35 sec. T90 (15-350 keV) is 11.8 +- 0.9 sec (estimated error including systematics). The time-averaged spectrum from T-0.1 to T+16.0 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.30 +- 0.07. The fluence in the 15-150 keV band is 5.9 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+8.04 sec in the 15-150 keV band is 14.0 +- 0.9 ph/cm2/sec. 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/451757/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 11948 SUBJECT: GRB 110420A Swift/UVOT Observations DATE: 11/04/21 10:10:04 GMT FROM: Samantha Oates at MSSL S. R. Oates (MSSL-UCL) & V. Mangano (INAF-IASFPA) report on behalf of the Swift-UVOT team The Swift/UVOT began settled observations of the field of GRB 110420A 97s after the trigger (Mangano et al., GCN Circ. 11941). We detect a source at a refined position of RA(J2000), DEC(J2000)= 2.16363deg,-37.88664deg. This is equivalent to: RA (J2000) 00:08:39.27 Dec (J2000) -37:53:11.9 with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence). This is consistent with the position of the X-ray afterglow (Beardmore et al., GCN Circ. 11942). The afterglow is detected in all filters providing a photometric redshift limit of z~<1.6. Preliminary magnitudes using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) for the finding chart (FC) and summed exposures at the location of the optical afterglow are: Filter T_start(s) T_stop(s) Exp(s) Mag ##################################################### wh (FC) 97 247 147 17.81 +/- 0.05 wh 761 781 19 18.10 +/- 0.17 u (FC) 309 559 246 17.46 +/- 0.07 u 712 732 19 17.96 +/- 0.36 v 811 831 19 18.20 +/- 0.67 b 737 757 19 18.04 +/- 0.28 uvw1 688 707 19 17.08 +/- 0.24 uvm2 663 683 19 17.73 +/- 0.41 uvw2 614 634 19 17.91 +/- 0.35 ##################################################### The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.01 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 11951 SUBJECT: Konus-Wind observation of GRB 110420A DATE: 11/04/21 13:41:09 GMT FROM: Valentin Pal'shin at Ioffe Inst S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind team, report: The long soft GRB 110420A (Swift-BAT trigger #451757: Mangano et al., GCN 11941; Krimm et al., GCN 11945) triggered Konus-Wind at T0(KW)=39750.543 s UT (11:02:30.543). The burst light curve shows a single pulse started at ~T0(KW)-9 s with a duration of ~18 s. As observed by Konus-Wind the burst had a fluence of 6.54(-0.53, +0.64)x10^-6 erg/cm2, and a 256-ms peak flux measured from T0-0.320 s of (1.11 +/- 0.17)x10^-6 erg/cm2/s (both in the 20 - 500 keV energy range). The time-integrated spectrum of the burst (from T0 to T0+8.448 s) is well fitted (in the 20 - 500 keV range) by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.71(-0.26, +0.31), and Ep = 43(-18, +17) keV (chi2 = 31.1/39 dof). Fitting by GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.61 (chi2 = 31.1/38 dof). All the quoted errors are at the 90% confidence level. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB110420_T39750/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 11954 SUBJECT: GRB110420A: GROND detection of the Optical/NIR Afterglow Candidate DATE: 11/04/21 14:18:16 GMT FROM: Jonny Elliott at MPE/GROND P. Afonso, J. Elliott, and J. Greiner (MPE Garching) report on behalf of the GROND team: We observed the field of GRB 110420A (Swift trigger 451757; Mangano et al., GCN #11941) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPI/ESO telescope at La Silla Observatory (Chile). Observations started at 09:34 UT on April 21, 22.5 hours after the GRB trigger. They were performed at an average seeing of 1.8'' and at an average airmass of 2.3. We confirm the detection of the single point source reported by Oates et al. (GCN #11948). Based on the first 142-s exposures in r', we estimate a preliminary magnitude (AB system) of r' = 20.6 +/- 0.1 mag. In combination with the early UVOT detection, this would imply a decay slope of 0.85 between 700 s and 22.5 hours. Given magnitudes are calibrated against GROND zeropoints and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.014 mag in the direction of the burst (Schlegel et al. 1998).