//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22558 SUBJECT: GRB 180329B: Swift detection of a burst with an optical afterglow DATE: 18/03/29 14:21:48 GMT FROM: David Palmer at LANL J. L. Racusin (NASA/GSFC), A. Deich (PSU), J.D. Gropp (PSU), J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL), B. Sbarufatti (PSU) and A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 14:08:23 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 180329B (trigger=819490). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 82.916, -23.708 which is RA(J2000) = 05h 31m 40s Dec(J2000) = -23d 42' 27" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a small complex peak from T-10 to T+20 s (peak of 800 counts/s) with a stronger peak from T+140 to T+160 (the limit of currently available data). The peak count rate was ~1400 counts/sec (15-350 keV), at ~147 sec after the trigger. The XRT began observing the field at 14:10:07.5 UT, 103.6 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 82.9031, -23.6889 which is equivalent to: RA(J2000) = +05h 31m 36.74s Dec(J2000) = -23d 41' 20.0" with an uncertainty of 6.5 arcseconds (radius, 90% containment). This location is 80 arcseconds from the BAT onboard position, within the BAT error circle. The initial flux in the 2.5 s image was 4.57e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 111 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 05:31:36.90 = 82.90376 DEC(J2000) = -23:41:25.9 = -23.69052 with a 90%-confidence error radius of about 0.62 arc sec. This position is 6.2 arc sec. from the center of the XRT error circle. The estimated magnitude is 17.65 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.04. The brighter, second, peak of this GRB occurs during the time that XRT and UVOT were taking data, so the early observations sample the prompt burst emission. Burst Advocate for this burst is J. L. Racusin (judith.racusin 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: 22559 SUBJECT: GRB 180329B: Enhanced Swift-XRT position DATE: 18/03/29 19:45:14 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 3233 s of XRT Photon Counting mode data and 6 UVOT images for GRB 180329B, 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 = 82.90376, -23.69085 which is equivalent to: RA (J2000): 05h 31m 36.90s Dec (J2000): -23d 41' 27.1" 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: 22560 SUBJECT: GRB 180329B: Swift-XRT refined Analysis DATE: 18/03/29 21:14:48 GMT FROM: Phil Evans at U of Leicester A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), S. J. LaPorte (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), S.L. Gibson (U. Leicester) and J.L. Racusin report on behalf of the Swift-XRT team: We have analysed 7.4 ks of XRT data for GRB 180329B (Racusin et al. GCN Circ. 22558), from 109 s to 17.7 ks after the BAT trigger. The data comprise 260 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN Circ. 22559). The late-time light curve (from T0+4.6 ks) can be modelled with a power-law decay with a decay index of alpha=1.14 (+/-0.12). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.54 (+/-0.04). The best-fitting absorption column is 7.5 (+1.4, -1.3) x 10^20 cm^-2, in excess of the Galactic value of 2.5 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.86 (+/-0.11) and a best-fitting absorption column of 6.5 (+2.8, -2.6) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (4.0 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 6.5 (+2.8, -2.6) x 10^20 cm^-2 Galactic foreground: 2.5 x 10^20 cm^-2 Excess significance: 2.6 sigma Photon index: 1.86 (+/-0.11) If the light curve continues to decay with a power-law decay index of 1.14, the count rate at T+24 hours will be 0.012 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.4 x 10^-13 (5.0 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00819490. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22562 SUBJECT: GRB 180329B: NOT optical afterglow detection DATE: 18/03/29 23:19:12 GMT FROM: Daniel Perley at Liverpool JMU D. A. Perley (LJMU), K. E. Heintz (Univ. of Iceland and DAWN/NBI), and D. Malesani (DAWN/NBI and DARK/NBI) report: We observed the location of GRB 180329B (Racusin et al., GCN 22558) using the Nordic Optical Telescope (NOT) equipped with the AlFOSC imaging camera. Three exposures of 300 s each were obtained in the SDSS r filter. Observations were taken during twilight at low elevation, and the field was partially vignetted due to the dome shutter. A weak source is detected in each exposure at a position coincident with the Swift UVOT and XRT error circles. We estimate a magnitude of m(r) = 19.4 +/- 0.2 mag at the time of our observations (midpoint UT 20:27:14), corresponding to 6.32 hr after trigger. The position of the afterglow (J2000) is: RA = 05:31:36.90 Dec = -23:41:26.3 (+/- 0.4") We thank the NOT staff (J. Telting) and the observer (L. Siltala) for acquiring these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22564 SUBJECT: GRB 180329B: RATIR Optical Observations DATE: 18/03/30 06:41:22 GMT FROM: Alan M. Watson at Instituto de Astronomia UNAM Alan M. Watson (UNAM), Nat Butler (ASU), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UVI), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (U. Wash.), and Vicki Toy (UMD) report: We observed the field of GRB 180329B (Racusin et al., GCN 22558) with the Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir from 2018/03 30.13 to 2018/03 30.18 UTC (12.92 to 14.22 hours after the BAT trigger), obtaining a total of 0.96 hours exposure in the r and i bands. For a source within the Swift-XRT error circle, in comparison with the USNO-B1 catalog, we obtain the following detections: r = 20.29 +/- 0.09 i = 20.32 +/- 0.10 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. The source has faded in r at the 4-sigma level when compared to the earlier NOT observation of Perley et al. (GCN 22562). We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22565 SUBJECT: GRB 180329B: Swift/UVOT Detection DATE: 18/03/30 11:38:14 GMT FROM: Sam Emery at MSSL-UCL S.W.K. Emery (UCL-MSSL) and J. L. Racusin (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 180329B 113 s after the BAT trigger (Racusin et al., GCN Circ. 22558). A fading source consistent with the XRT position (Beardmore et al. GCN Circ. 22559) also detected by the NOT (Perley et al. GCN Circ. 22562) and RATIR (Watson et al. GCN Circ. 22564) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 05:31:36.91 = 82.90381 (deg.) Dec (J2000) = -23:41:25.8 = -23.69051 (deg.) with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 113 263 147 17.69 +/- 0.04 white 550 6892 599 17.64 +/- 0.03 v 601 5867 274 17.25 +/- 0.07 b 526 6687 452 17.94 +/- 0.05 u 271 6482 697 17.00 +/- 0.04 u 16039 39219 1961 18.74 +/- 0.07 w1 650 6277 452 18.72 +/- 0.14 m2 626 6073 274 >19.8 w2 577 7017 390 >20.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.04 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22566 SUBJECT: GRB 180329B: Swift-BAT refined analysis DATE: 18/03/30 13:57:48 GMT FROM: Amy Lien at GSFC D. M. Palmer (LANL), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), J. L. Racusin (NASA/GSFC), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (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 180329B (trigger #819490) (Racusin et al., GCN Circ. 22558). The BAT ground-calculated position is RA, Dec = 82.905, -23.694 deg which is RA(J2000) = 05h 31m 37.2s Dec(J2000) = -23d 41' 39.8" with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 15%. The mask-weighted light curve shows a triple-peaked structure, with the first peak running from T-10 to T+40 sec, and the second peak from T+130 to T+160 sec. This is followed by a much weaker, softer peak from T+160 to T+280 sec. T90 (15-350 keV) is 210.0 +- 44.0 sec (estimated error including systematics). The time-averaged spectrum from T-9.91 to T+230.39 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.97 +- 0.56, and Epeak of 48.6 +- 9.1 keV (chi squared 54.64 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 3.3 +- 0.3 x 10^-6 erg/cm2 and the 1-sec peak flux measured from T+1.56 sec in the 15-150 keV band is 1.4 +- 0.4 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.93 +- 0.12 (chi squared 65.32 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/819490/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22567 SUBJECT: GRB 180329B: VLT/X-shooter spectroscopic observations DATE: 18/03/30 14:21:00 GMT FROM: Luca Izzo at IAA-CSIC L. Izzo (HETH/IAA-CSIC), K. E. Heintz (Univ. Iceland and DAWN/NBI), D. Malesani (DAWN/NBI and DARK/NBI), B. Milvang-Jensen (DAWN/NBI), N.R. Tanvir (Univ. Leicester), D.A. Perley (LJMU), A. de Ugarte Postigo (HETH/IAA-CSIC and DARK/NBI), J.P.U. Fynbo (DAWN/NBI), D.A. Kann (HETH/IAA-CSIC) report on behalf of the Stargate Consortium: We observed the optical afterglow of GRB 180329B (Racusin et al. GCN 22558, Perley et al. GCN 22562) with the ESO VLT/X-shooter spectrograph, covering the wavelength range 3000-21000 AA. Spectroscopy started at 00:10:12 UT on 2018-03-30 (~10 hours after the GRB trigger) and consisted of 2 exposures of 600 s. Preliminary analysis of the spectrum reveals absorption lines of O I 1302, C IV 1548/50, Al II 1670, Fe II 2344, 2374, 2382, 2586, 2600, Mg II 2796/2803 and Mg I 2853 at a common redshift of z=1.998. This is consistent with a broad absorption seen in the UVB arm spectrum at ~3635 AA, due to a damped Lyman-alpha feature. We therefore propose this to be the redshift of the GRB. We acknowledge the excellent support from the ESO staff, particularly Marcela Espinoza, Luca Sbordone, Eleonora Sani and Pascale Hibon in obtaining these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22571 SUBJECT: GRB 180329B: LCO FTS observations DATE: 18/03/31 11:57:19 GMT FROM: Cristiano Guidorzi at Ferrara U,Italy C. Guidorzi, R. Martone (U. Ferrara), S. Kobayashi (LJMU), C.G. Mundell (U. Bath), A. Gomboc (U. Nova Gorica), I.A. Steele (LJMU) on behalf of a large collaboration report: The LCO 2-m unit Faulkes Telescope South in Siding Springs began observing Swift GRB 180329B (Racusin et al. GCN 22558) on March 30, 08:56 UT (0.78 days since the GRB) with the SDSS-R filter. We detect the optical afterglow (Racusin et al.; Perley et al. GCN 22562) with the following magnitude: Mid Time from GRB  Exposure       Filter       Magnitude (AB) (days)             (s) ------------------------------------------------------------- 0.79               5x120          SDSS-R       20.14 +- 0.21 ------------------------------------------------------------- as calibrated against nearby Pan-STARRS objects.