//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6210 SUBJECT: GRB 070318: Swift detection of a burst with an optical afterglow DATE: 07/03/18 07:49:43 GMT FROM: Scott Barthelmy at NASA/GSFC J. R. Cummings (NASA/UMBC), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), G. Cusumano (INAF-IASFPA), N. Gehrels (NASA/GSFC), C. Gronwall (PSU), V. La Parola (INAF-IASFPA), T. Mineo (INAF-IASFPA) and D. M. Palmer (LANL) report on behalf of the Swift Team: At 07:28:56 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 070318 (trigger=271019). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 48.540, -42.962 which is RA(J2000) = 03h 14m 10s Dec(J2000) = -42d 57' 42" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single FRED-like peak with a duration of about 70 sec. The peak count rate was ~4000 counts/sec (15-350 keV), at ~2 sec after the trigger. The XRT began observing the field at 07:29:59 UT, 64 seconds after the BAT trigger. XRT found a bright, fading, uncatalogued X-ray source located at RA, Dec 48.4856, -42.9468 which is RA(J2000) = 03h 13m 56.5s Dec(J2000) = -42d 56' 48.4" with an uncertainty of 4.7 arcseconds (radius, 90% containment). This location is 153 arcseconds from the BAT on-board position, within the BAT error circle. The initial flux in the 2.5s image was 2.6e-09 erg/cm2/s (0.2-10 keV). UVOT took a finding chart exposure of 400 seconds with the V filter starting 180 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 03:13:56.83 = 48.4868 DEC(J2000) = -42:56:46.3 = -42.9462 with a 1-sigma error radius of about 0.5 arc sec. This position is 3.8 arc sec. from the center of the XRT error circle. The estimated magnitude is 15.4 with a 1-sigma error of about 0.5 mag. No correction has been made for the expected extinction of about 0.1 magnitudes. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6212 SUBJECT: GRB 070318, Swift-BAT refined analysis DATE: 07/03/18 13:59:03 GMT FROM: Scott Barthelmy at NASA/GSFC J. Cummings (GSFC/UMBC), L. Barbier (GSFC), S. D. Barthelmy (GSFC), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), 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-120 to T+302 sec from recent telemetry downlinks, we report further analysis of BAT GRB 070318 (trigger #271019) (Cummings, et al., GCN Circ. 6210). The BAT ground-calculated position is RA, Dec = 48.486, -42.950 deg which is RA(J2000) = 03h 13m 56.6s Dec(J2000) = -42d 57' 1.1" with an uncertainty of 0.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 80%. The mask-weighted lightcurve is a single FRED peak starting at ~T-10sec, peaking at ~T+2 sec, and returning to background at around T+120 sec. There is the possibility of weak peaks at ~T+140 and T+170 sec at the ~3-sigma level. T90 (15-350 keV) is 63 +- 3 sec (estimated error including systematics). The time-averaged spectrum from T-1.0 to T+89.4 is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.44 +- 0.08. The fluence in the 15-150 keV band is 2.3 +- 0.1 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+1.94 sec in the 15-150 keV band is 1.6 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6213 SUBJECT: GRB 070318: Swift/UVOT Continued Observations DATE: 07/03/18 17:09:46 GMT FROM: Frank Marshall at GSFC F.E. Marshall (NASA/GSFC) and J.R. Cummings (NASA/UMBC) report on behalf of the Swift team: The bright optical afterglow of GRB 070318 (Cummings et al., GCN Circ. 6210) is following an approximately power-law decay. At 13,000 sec. after the trigger, the magnitude in the UVOT B filter is ~19.9 with a best-fit decay index of 1.16. If this rate of decay continues, the B magnitude will be 22.3 at one day after the trigger and 23.2 a day later. The afterglow has been detected in all 7 UVOT filters indicating that the redshift is less than ~2. Observations with ground-based telescopes are encouraged. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6214 SUBJECT: GRB070318: Swift-XRT refined analysis DATE: 07/03/18 17:16:54 GMT FROM: Teresa Mineo at INAF-IASFA V. La Parola, T. Mineo, B. Sbarufatti, V. Mangano, G. Cusumano (INAF-IASF Pa) report on behalf of the Swift XRT team: We have analysed the first two orbits of Swift-XRT data on GRB 070318 (Cummings, et al., GCN Circ. 6210), with a total exposure of 427 s seconds in Window Timing (WT) mode and 33.4 ks seconds in Photon Counting (PC) mode. This provides a refined XRT position at RA,Dec=48.4870,-42.9454 which is: RA (J2000) = 03h 13m 56.9s Dec(J2000) = -42d 56m 43.6s with an estimated error radius of 3.5 arcseconds (90% confidence). This position is 16.8 arcseconds from the BAT refined position (Cummings, et al., GCN 6212), 6.2 arcseconds from the initial XRT position, and 2.9 arcseconds from the UVOT optical candidate (Cummings, et al., GCN Circ. 6210). The 0.3-10 keV X-ray light curve presents a bright flare peaking at about 280 s from the trigger and a second fainter peak at 200 s. The underlying light curve between 70 s and 7.5 ks can be fit with a simple power-law with a decay slope of 1.11 ± 0.02. The X-ray spectrum from the XRT/WT data covering up to the beginning of the bright flare is well fit by an absorbed power-law with a photon index of 1.4±0.1 and column density of (1.5±0.7)E21 cm**-2, higher than the Galactic column density in the direction of the source (2.5E20 cm**-2). The unabsorbed 0.3-10 keV flux for this spectrum is 1.3E-9 erg/cm**2/s. The XRT/WT spectrum of the bright flare and the XRT/PC spectrum are modelled by an absorbed power law with photon index of 1.9±0.1 and column density of (1.3±0.3)E21 cm**-2. The unabsorbed 0.3-10 keV flux of the bright flare is 8.2E-10 erg/cm**2/s and the one relative to the PC spectrum is 1.0E-10 erg/cm**2/s. Assuming the X-ray emission continues to decline at the same rate, we predict a 0.3-10 keV XRT count rate of 5E-3 count/s at T+48hr, which corresponds to an observed 0.3-10 keV flux of 2.5e-13 erg/cm**2/s. This circular is an official product of the Swift XRT Team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6215 SUBJECT: GRB070318: Swift UVOT continuing observations DATE: 07/03/18 23:35:03 GMT FROM: Mat Page at MSSL/Swift M. Page (MSSL-UCL), M. Chester (PSU), J. R. Cummings (NASA/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT began taking data in the field of GRB070318 88s after the BAT trigger (Cummings et al., GCN 6210, Marshall et al., GCN 6213). The afterglow is detected in all UVOT filters. The photometry results are given for the 7 UVOT filters below. The first White exposure was affected by the star tracker loss of lock, so results from this exposure are not reported below. Filter T+(s) Exp(s) Mag White 706 10 15.53 +/- 0.08 White 6364 197 18.14 +/- 0.07 V 214 400 15.43 +/- 0.02 B 692 10 16.25 +/- 0.12 B 6159 197 18.91 +/- 0.13 U 667 19 15.89 +/- 0.09 U 5955 197 18.23 +/- 0.11 UVW1 644 19 16.89 +/- 0.18 UVW1 5750 197 19.62 +/- 0.30 UVM2 619 19 17.97 +/- 0.37 UVM2 5545 197 > 19.87 (3-sigma UL) UVW2 870 19 18.03 +/- 0.30 UVW2 6569 197 > 20.37 (3-sigma UL) T+ is the start time of the exposure since the BAT trigger. These magnitudes are not corrected for the expected extinction of E(B-V)=0.017. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6216 SUBJECT: GRB 070318: absorption-line redshift DATE: 07/03/19 07:28:15 GMT FROM: Andreas O. Jaunsen at ITA/U Oslo A.O. Jaunsen (Univ. Oslo), J.P.U. Fynbo (DARK/NBI), M.I. Andersen (AIP) and P. Vreeswijk (ESO) report on behalf of a larger collaboration. We observed the field of GRB 070318 (Cummings et al., GCN 6210, La Parola et al, GCN 6214 and Page et al. GCN 6215) with the ESO/VLT UT2 equipped with FORS1. Observations started on 2007 Mar 19.008 UT and an 1800-s spectra was acquired with the 300V grism covering a wavelength range of 3500-8500A. We identify several absorption lines from MgII, MgI, FeII, MnII of which the MgII doublet 2796,2804 is the most prominent at a redshift of z=0.836. We thank the excellent support from the ESO/Paranal staff. [GCN OPS NOTE(19mar07): Per author's request, the phrase "several emission lines" was changed to "several absorption lines" and "MI" was changed to "Mg I".] [GCN OPS NOTE(23may08): This time I actually changed the text!] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6217 SUBJECT: GRB 070318: Gemini + Magellan spectra DATE: 07/03/19 07:39:56 GMT FROM: Hsiao-Wen Chen at U Chicago H.-W. Chen (U Chicago), J. X. Prochaska (UCO/Lick Observatory), S. Herbert-Fort (Steward Observatory), D. Christlein (Universidad de Chile/Yale), and S. Cortes (Steward Observatory) report on behalf of a larger collaboration: "We obtained 2x1800 sec long-slit spectra of the optical transient of GRB070318 (Cummings et al., GCN 6210), using GMOS and an the R400 grating on the Gemini south telescope. The observations started at March 19.001 UT, ~ 16.5 hours after the initial Swift trigger. The spectra covered a wavelength range from 5930 Ang through 8750 Ang. We also obtained 2700 sec long-slit spectra, using IMACS and the 300 l/mm grism on the Magellan Baade telescope. The observations started at March 19.011 UT, and the spectra cover a wavelength range from 4200 Ang through 6500 Ang. We identify MgII 2796,2803, MgI 2852, FeII 2600, and TiII 3384 lines at z=0.840 +/- 0.002, but no other apparent MgII absorption doublet. We therefore confirm the redshift reported by Jaunsen et al. (GCN 6216) as the location of the afterglow. Further analysis is underway." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6220 SUBJECT: GRB070318: Swift UVOT indicates unusual optical/UV afterglow DATE: 07/03/21 21:08:42 GMT FROM: Mat Page at MSSL/Swift M.J. Page (MSSL-UCL), F.E. Marshall (NASA/GSFC) S. Immler (GSFC/USRA) S. T. Holland (CRESST/GSFC/USRA) and J.R. Cummings (GSFC/UMBC) report on behalf of the Swift/UVOT team: The optical/UV afterglow of GRB 070318 (Cummings et al, GCN 6210) decayed to magnitude of 21.5 in the UVOT white filter in the first 24 hours after the BAT trigger, and has remained at approximately constant brightness for at least 48 hours since that time. Examination of the Supercosmos scan of the UK Schmidt sky survey plate at this location reveals no evidence for a host galaxy (the plate limit is Bj>22 mag). For the flattening of the lightcurve to be due to the host galaxy, the host galaxy would have to be very luminous (Mb ~ -22) and have an unusually blue spectrum (e.g. peaking in the U band, observer frame). It therefore seems more likely that this is an afterglow with a very unusual lightcurve. Swift continues to monitor the afterglow. Further ground-based observations are encouraged. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6296 SUBJECT: GRB 070318, SMARTS optical/IR afterglow observations DATE: 07/04/14 20:03:36 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 070318 (GCN 6210, Cummings et al.) with a mid-exposure time of 2007-03-19 00:09 UT (~16.7 hrs post-burst) and again at 2007-03-21 00:07 UT (~64.6 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 070318 (GRB 6210, Cummings et al.) is detected in the first epoch images and is observed to fade between the first and second epochs. time-post bursts (hrs) I magnitude J magnitude ------------------------------------------------------ 16.7 19.82+/-0.07 18.29+/-0.11 64.6 20.28+/-0.12 > 18.6 (3 sigma limit) Magnitudes are calibrated using Landolt standard stars in the optical and 2MASS stars in the IR. The optical decay rate (afterglow flux proportional to t^-alpha) between 16.7 and 64.6 hours post-burst is alpha ~ 0.3 (and the IR decay is consistent with this value). This unusually shallow decay was also noted in the UVOT observations of this afterglow (GCN 6220, Page et al.). A third late-time epoch was obtained at 2007-04-06 23:46 UT (~20 days post-burst). No source or host galaxy is detected at the position of the optical afterglow to a limiting magnitude of I > 21.7 and J > 19.2. This indicates that the decay rate of the afterglow must have steepened sometime after our second epoch observation.