//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6330 SUBJECT: GRB 070420: Swift detection of a burst with optical afterglow DATE: 07/04/20 06:56:57 GMT FROM: David Palmer at LANL M. Stamatikos (NASA/ORAU), D. N. Burrows (PSU), G. Cusumano (INAF-IASFPA), P. A. Evans (U Leicester), C. Gronwall (PSU), V. Mangano (INAF-IASFPA), C. B. Markwardt (GSFC/UMD), P. T. O'Brien (U Leicester), D. M. Palmer (LANL), A. M. Parsons (GSFC), M. Perri (ASDC) and G. Stratta (ASDC) report on behalf of the Swift Team: At 06:18:13 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 070420 (trigger=276321). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 121.253, -45.561 which is RA(J2000) = 08h 05m 01s Dec(J2000) = -45d 33' 38" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multiply-peaked structure with a duration of at least 70 sec starting at T-50s. The peak count rate was ~4000 counts/sec (15-350 keV), at ~7 sec after the trigger. XRT began observing the field at 06:19:52 UT, 99 seconds after the BAT trigger. XRT found a bright, fading, previously uncatalogued X-ray source in the field of view at the following coordinates: RA(J2000) = 08h 04m 55.3s Dec(J2000)= -45d 33' 23.2" with an uncertainty of 4 arcseconds radius (90% containment). This is a ground calculated position based on prompt downlinked data. This position lies 62 arcseconds from the center of the BAT error circle. UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 108 seconds after the BAT trigger. An afterglow candidate has been found in the initial data products. The 2.7'x2.7' region for the list of sources generated on-board covers 100% of the XRT error circle. A source is detected at RA(J2000) = 08h 04m 55.25s Dec(J2000)= -45d 33' 21.0" with an estimated uncertainty of +/-0.5 arcsec. This position is 2.0 arcsec from the XRT position. The estimated magnitude in the White filter is 17.3. No correction has been made for the expected extinction correspondingto E(B-V) of 0.52. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6331 SUBJECT: GRB 070420: NIR and optical afterglow confirmed DATE: 07/04/20 07:18:55 GMT FROM: Stefano Covino at Brera Astronomical Observatory P. D'Avanzo, L.A. Antonelli, L. Calzoletti, S. Campana, G. Chincarini, M.L. Conciatore, S. Covino, S. Cutini, P. D'Avanzo, V. D'Elia, F. Dalessio, F. Fiore, D. Fugazza, P. Goldoni, D. Guetta, C. Guidorzi, G.L. Israel, D. Malesani, N. Masetti, A. Melandri, E. Meurs, L. Nicastro, E. Palazzi, E. Pian, S. Piranomonte, D. Rizzuto, L. Stella, G. Stratta, G. Tagliaferri, G. Tosti, V. Testa, S.D. Vergani, F. Vitali report on behalf of the REM team: We observed the field of the GRB 070420 (Stamatikos et al. GCN 6330) with the robotic 60-cm REM telescope located at La Silla (Chile). A set of observations was performed automatically in the optical and near infrared filters (V, R, I and J, H, K, z) starting on 2007 April 20 at 06:19:32 UT, 42s after the Swift trigger and 79s after the GRB time. Although the observations were performed under thin clouds and at very high airmass (~ 7.5) we clearly detect the NIR and optical afterglow at the coordinates reported by UVOT (GCN 6330). Preliminary analysis gives an approximate magnitude about 5 minutes after the burst time was H = 13.1 +/- 0.2. Observations were then soon interrupted due to excessive airmass. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6332 SUBJECT: GRB 070420: TAROT La Silla observatory optical observations DATE: 07/04/20 11:32:28 GMT FROM: Alain Klotz at CESR-CNRS Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report: We imaged the field of GRB 070420 detected by SWIFT (trigger 276321) with the TAROT robotic telescope (D=25cm) located at the European Southern Observatory, La Silla observatory, Chile. The observations started 34s after the GRB trigger (8s after the notice) when the GRB was still active. The elevation of the field decreased from from 7 degrees above horizon and weather conditions were good but with some thin clouds in the sky. The date of trigger : t0 = 2007-04-20T06:18:13.824 The first image is trailed with a duration of 60.0s (see the description in Klotz et al., 2006, A&A 451, L39). We do not detect the OT mentioned by Stamatikos et al. (GCNC 6330) with a limiting magnitude of: t0+34s to t0+94s : R > 16.1 The second image is 30.0s exposure in tracking mode. We detect the OT: t0+100s to t0+130s : R = 16.2 The third image is 30.0s exposure in tracking mode: t0+136s to t0+166s : R = 16.4 Magnitudes were estimated with the nearby USNO-B1 stars and are not corrected for galactic dust extinction. It seems that this afterglow is very red compared to values published by Stamatikos et al. (GCNC 6330) and by D'Avanzo et al. GCNC 6331). N.B. Galactic coordinates are lon=260.8667 lat= -7.4088 and the galactic extinction in R band is 0.7 magnitudes estimated from D. Schlegel et al. 1998ApJ...500..525S. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6334 SUBJECT: GRB 070420: Faulkes Telescope South Observations DATE: 07/04/20 14:02:57 GMT FROM: Cristiano Guidorzi at INAF-OAB C. Guidorzi (Uni-Bicocca/INAF-OAB), R.J. Smith, D.F. Bersier, I.A. Steele, C.G. Mundell, S.N. Fraser, C.J. Mottram, A. Melandri, M.F. Bode (Liverpool JMU), A. Gomboc (Ljubljana), P. O'Brien, E. Rol, N. Tanvir (U. Leicester) report on behalf of the RoboNet GRB collaboration: "The 2-m Faulkes Telescope South (Australia) started observing the field of the Swift burst GRB 070420 (Stamatikos et al. GCN Circ. 6330) about 3 hours after the trigger time in BVRi filters. We detect the UVOT optical transient reported by Stamatikos et al (GCN Circ. 6330) and confirmed in IR by REM (D'Avanzo et al., GCN Circ. 6331) in V, R and i' band filters at the following position: RA(J2000) = 08:04:55.18 Dec(J2000)= -45:33:20.0 with an error of 0.7", and 1.2" away from the UVOT position. Start Time End Time Exposure Filter Mag (min) (min) (s) -------------------------------------------------------- 175.5 185.9 4x150 R 19.7 ± 0.4 211.3 221.8 4x150 i' 19.3 ± 0.5 -------------------------------------------------------- Magnitudes are calibrated with respect to USNOB1 R2 and I magnitudes. Further observations are ongoing." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6336 SUBJECT: GRB070420: Swift UVOT continuing observations DATE: 07/04/20 16:57:52 GMT FROM: Stefan Immler at NASA/GSFC S. Immler (USRA/GSFC), F. E. Marshall (NASA/GSFC), S. T. Holland (CRESST/USRA/GSFC), and M. Stamatikos (NASA/ORAU) report on behalf of the Swift/UVOT team: The UVOT position sent out as a GCN notice gave an invalid position while GCN 6330 had the correct position. We regret any confusion this might have caused. The revised UVOT position of the afterglow is RA(J2000) = 08h04m55.17s, Dec(J2000) = -45d33'20.0". We estimate a statistical accuracy of 0.2 arcsec radius (90% confidence) but with a systematic uncertainty of the aspect solution of about 0.5 arcsec. The Swift/UVOT began taking data in the field of GRB070420 90s after the BAT trigger (Stamatikos et al., GCN 6330). The afterglow is detected in all UVOT optical filters. The large reddening, E(B-V) = 0.52, might explain the non-detection in the UV. The flux is decaying with t**-0.7 in the White for times between T+500 and T+10000 seconds. The photometry results are given for the 7 UVOT filters below. V T+(s) Exp(s) Mag White 109 99 17.4+/-0.1 7125 197 20.8+/-0.1 V 90 10 17.9+/-0.1 B 693 10 18.8+/-0.1 U 669 20 21.1+/-0.1 UVW1 645 20 >20.4 (3-sigma) UWM2 620 20 >20.8 (3-sigma) UVW2 723 20 >20.8 (3-sigma) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6337 SUBJECT: GRB 070420: Swift XRT refined analysis DATE: 07/04/20 18:34:49 GMT FROM: Giulia Stratta at ASDC G. Stratta (ASDC), M. Perri (ASDC), D.N. Burrows (PSU) and M. Stamatikos (NASA/ORAU) report on behalf of the Swift XRT team: We have analyzed the first four orbits of Swift-XRT data on GRB 070420 (Stamatikos et al. GCN 6330), with a total exposure of 573 s in Windowed Timing (WT) mode and of 7.5 ks in Photon Counting (PC) mode. This provides a refined XRT position at RA,Dec(deg)=121.230194683,-45.5562815181 which is: RA(J2000)=08h 04m 55.22s Dec(J2000)=-45d 33' 22.6" with an estimated error radius of 3.5 arcseconds (90% confidence). This position is 62.3 arcseconds from the BAT position (Stamatikos et al. GCN 6330), 0.8 arcseconds from the initial XRT position (Stamatikos et al. GCN 6330) and 2.6 arcseconds from the UVOT refined optical counterpart position (Holland et al. GCN 6336). The 0.3-10 keV X-ray light curve presents a steep decay between T+106 s and T+300 s followed by a plateau phase up to about T+2ks (end of the first orbit). The last three orbits of data taken in PC mode show a new steepening of the light curve, from T+5ks to T+18.5 ks (end of the third orbit). The light curve from T+106 s to T+18.5 ks is well fit by a double broken power law model with decay indices: d1=-4.4+/-0.2, d2=-0.2+/-0.1 and d3=-1.5+/-0.1 and with the first break at about t1=230s and the second break at about t2=3200s. The 0.3-10.0 keV X-ray spectrum from the XRT/WT data during the decay phase is well fit by an absorbed power law with a photon index of 2.6 +/- 0.1 and a total column density of NH=(4.1+/-0.3)e21 cm**-2. The X-ray spectrum from the XRT/PC data during the flat decay phase (corrected from the pileup effects) can be fit by an absorbed power law with a photon index of 2.0+/-0.2 and a total column density of NH=(5.0+/-1.0)e21 cm**-2. We note that the Galactic column density in the direction of the source is 3.7e21 cm**-2 (Dickey & Lockman 1990). Assuming the X-ray emission continues to decline with decay index d3, we predict a 0.3-10.0 keV XRT count rate of 1.3e-2 count/s at T+24h and 4.7e-3 count/s at T+48h, which corresponds to an observed 0.3-10.0 keV flux of 7e-13 erg/cm**2/s and 2.5e-13 erg/cm**2/s, respectively. This circular is an official product of the Swift Team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6338 SUBJECT: GRB 070420: optical rebrightening observed at Mt. John DATE: 07/04/20 18:43:44 GMT FROM: Martin Jelinek at Inst.Astrophys.Andalucia,Granada M. Jelínek (IAA-CSIC Granada), P. Tristram (MOA, Univ. of Canterbury), A. de Ugarte Postigo, J. Gorosabel, (IAA-CSIC), F. Hale (Earth & Sky, Tekapo), A. Gilmore, P. Kilmartin (Univ. of Canterbury) and A. J. Castro-Tirado (IAA-CSIC), on behalf of a larger collaboration, report: "Following the detection by Swift of the GRB070420 (Stamatikos et al. GCNC 6330), we obtained V(26), R (14) and I (1) -band images at the 0.6m B&C telescope at the Mt. John Observatory on Lake Tekapo. They were taken starting on Apr 20.33 UT (i.e. 1.6 hr post-burst) and continued until Apr 20.51 UT (~6 hours after the burst). Our preliminary V-band lightcurve shows a simple powerlaw decay between 1.6 and 3.5 hours after the burst with alpha~-1.2+-0.2 which is somewhat stee- per than the value reported from UVOT (Immler et al. GCNC 6336). At 4 hours after the GRB we see a sudden rebrigh- tening of the order of 1 magnitude in 40min above the value extrapolated from the previous decay. Further analysis is in progress." This message can be quoted. [GCN OPS NOTE(22apr07): Per author's request, the "(Stamatikos et al. GCNC 6330)" was changed to "(Immler et al GCNC 6336)".] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6342 SUBJECT: GRB 070420 Swift-BAT Refined Analysis DATE: 07/04/21 02:16:48 GMT FROM: Michael Stamatikos at GSFC A. Parsons (GSFC), L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) on behalf of the Swift-BAT team: Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 070420 (trigger #276321) (Stamatikos, et al., GCN Circ. 6330). The BAT ground-calculated position is RA, Dec = 121.245, -45.564 deg which is RA(J2000) = 8h 4m 58.7s Dec(J2000) = -45d 33' 50.6" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 8%. The light curve is described by a slow rise to double-peaks at T+2 and T+8 sec, with subsequent gradual decay spanning from T-50 to T+70 sec. The T90 (15-350 keV) is 77 +- 4 sec (estimated error including systematics). The time-averaged spectrum from T-29 to T+100 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.16 +- 0.24, and Epeak of 114 +- 42 keV (chi squared 50.74 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 1.40 +- 0.04 x 10-5 erg/cm2 and the 1-sec peak flux measured from T+1.40 sec in the 15-150 keV band is 7.1 +- 0.8 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.59 +- 0.05 (chi squared 61.25 for 57 d.o.f.). All the quoted errors are at the 90% confidence level. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6344 SUBJECT: Konus-Wind observation of GRB 070420 DATE: 07/04/23 15:22:20 GMT FROM: Valentin Pal'shin at Ioffe Inst S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, and T. Cline on behalf of the Konus-Wind team report: The long GRB 070420 (Stamatikos et al., GCN 6330; Parsons et al., GCN 6342), triggered Konus-Wind at T0=22693.706 s UT (06:18:13.706). The burst started at T-T0 ~-50 s and had a duration of ~120 s. As observed by Konus-Wind the burst had a fluence of 2.64(-0.88, +0.11)x10^-5 erg/cm2, and a 256-ms peak flux measured from T0-0.144 s 1.28(-0.29, +0.19)x10^-6 erg/cm2/s (both in the 20 keV - 1 MeV energy range). The spectrum of the most intense part integrated from T0 to T0+16.640 s is well fitted (in the 20 keV - 1 MeV range) by a power law with exponential cutoff model: dN/dE ~ E^(-alpha) * exp(-(2-alpha)*E/Ep) with alpha = 1.08(-0.13, +0.12) and Ep = 167(-16, +20) keV (chi2 = 40/52 dof). The fluence of this part is 1.06(-0.19, +0.04)x10^5 erg/cm2. The spectrum integrated from T0 to T0+65.792 s is well fitted (in the 20 keV - 1 MeV range) by a power law with exponential cutoff model with alpha = 1.23(-0.18, +0.17) and Ep = 147(-19, +29) keV (chi2 = 54/52 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.rssi.ru/LEA/GRBs/GRB070420_T22693/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6345 SUBJECT: GRB 070420: pseudo-z~1.56 from spectral parameters of the prompt DATE: 07/04/23 16:01:10 GMT FROM: Alexandre Pelangeon at LATT,OMP,Toulouse A. Pelangeon & J-L. Atteia (LATT-OMP) report: We have used the spectral parameters of the most intense part of GRB 070420 provided by Golenetskii et al. (GCNC 6344) to compute the spectral pseudo-redshift** of this burst detected by SWIFT-BAT (Stamatikos et al., GCNC 6330). We find a pseudo-redshift pz= 1.56 +/- 0.35 ** cf. http://www.ast.obs-mip.fr/grb/pz //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6347 SUBJECT: GRB 070420, SMARTS optical/IR afterglow observations DATE: 07/04/23 20:40:38 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 070420 (GCN 6330, Stamatikos et al.) with a mid-exposure time of 2007-04-21 01:15 UT (~18.9 hrs post-burst) and again at 2007-04-23 00:52 UT (~66.6 hrs post-burst). For each set of observations, total summed exposure times amounted to 36 minutes in I and 30 minutes in J. The afterglow of GRB 070420 (GRB 6330, Stamatikos et al.) is detected in the first epoch images and is observed to fade between the first and second epochs by approximately 1 magnitude. This indicates a decay rate of alpha ~ 0.7 (afterglow flux proportional to t^-alpha), which is consistent with early-time UVOT observations (GCN 6336, Immler et al.). We note that there is a source with constant brightness only 1 arcseconds West and 0.7 arcseconds North of the afterglow of GRB 070420. This source has magnitudes I~20 and J~18.5 (magnitudes are calibrated using USNO-B1.0 values in the optical and 2MASS stars in the IR.). The source appears to have a stellar profile and is most likely just a coincident star.