Gamma-ray Burst 130518A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #14674
  Shaolin Xiong (UAH) reports on behalf of the Fermi GBM Team:
  "At 13:54:37.53 UT on 18 May 2013, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 130518A (trigger 390578080 / 130518580).
  High peak flux from the GRB caused GBM to issue a repoint request, but the spacecraft did not slew to this burst due to the Solar TOO.
  The on-ground calculated location, using the GBM trigger data, is RA = 355.88, DEC = 46.05 (J2000 degrees, equivalent to 23 h 43 m, 46 d 03 '), with an uncertainty of 1 degrees (radius, 1-sigma containment, statistical only; there is additionally a systematic error which is currently estimated to be 2 to 3 degrees). The angle from the Fermi LAT boresight is 43 degrees.
  The GBM light curve consists of several pulses with a duration (T90) of about 48 s (50-300 keV). The time-averaged spectrum from T0+10 s to T0+60 s is adequately fit by a Band function with Epeak = 396 +/- 9 keV, alpha = -0.86 +/- 0.01, and beta = -2.27 +/- 0.04.
  The event fluence (10-1000 keV) in this time interval is (9.3 +/- 0.06)E-5 erg/cm^2. The 1-sec peak photon flux measured starting from T0+25.6 s in the 10-1000 keV band is 45.4 +/- 0.4 ph/s/cm^2.
  The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
• GCN Circular #14675
  Nicola Omodei (Stanford) and Julie McEnery (GSFC) report on behalf of the Fermi-LAT team:
  At 13:54:37.53 UT on 18 May 2013, Fermi LAT detected high energy emission from GRB 130518A, which was also detected by Fermi-GBM (trigger 390578080 /130518580, GCN 14674).
  The best LAT on-ground location is found to be RA=355.809, DEC=47.641 (J2000) with an error radius of 0.34 deg (68% containment, statistical error only).
  The burst was about 43 deg from the LAT boresight at the time of the trigger. The data from the Fermi LAT shows emission lasting approximately 100 seconds with a TS of 50. Multi-peaked emission lasting roughly 40 seconds can be seen using the non-standard LAT Low Energy (LLE) with a significance of ~15 sigma.
  A Swift TOO request has been submitted.
  The Fermi LAT point of contact for this burst is Sara Cutini (sara.cutini@asdc.asi.it).
  The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
• GCN Circular #14676
  J. R. Cummings (UMBC/CRESST/GSFC) reports on behalf of the BAT team
  At 13:55:07.4 UT, the Swift Burst Alert Telescope (BAT) triggered on the Fermi GBM and LAT GRB 130518A (Xiong, GCN # 14674 and Omodei et al., GCN# 14675) (BAT trigger=556113). No significant source was found onboard. In ground analysis, a significant source was found at RA, Dec 355.671, +47.478 which is:

      RA(J2000)  =23h 42m 41.1s 		
      Dec(J2000) = +47d 28' 41.5"
  

  with an uncertainty of 2.9 arcmin (radius, 90% containment, including systematic uncertainty). This position is 11 arcmin from the LAT position, within the LAT error circle. BAT partial coding was 5%. The unweighted lightcurve shows two overlapping peaks with a duration of about 14 sec. The peak count rate was ~9400 counts/sec (15-350 keV), at ~4 sec before the trigger.
• GCN Circular #14677
  S. Golenetskii, R.Aptekar, D. Frederiks, E. Mazets, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind team, report:
  The long-duration intense GRB 130518A (Fermi-GBM detection: Xiong, GCN 14674; Fermi-LAT detection: Omodei and Julie McEnery, GCN 14675; Swift-BAT trigger 556113: Cummings, GCN 14676) triggered Konus-Wind at T0=3D50097.501s UT (13:54:57.501) against very high and variable solar particles background.
  The light curve shows a bright hard pulse from ~T0-10 s to ~T0+20s, followed by a weaker count rate increase at ~T0+33s and a tail of soft extended emission, which is traceable out to ~T0+100s.
  The emission in the main pulse is seen up to 12 MeV.
  The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB130518_T50097/
  As observed by Konus-Wind, the burst had a fluence of (1.5 =B1 0.15)x10-4 erg/cm2, and a 64-ms peak flux, measured from T0+1.856s, of (2.1 =B1 0.2)x10-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
  The time-integrated spectrum (measured from T0 to T0+20.224 s) is best fit in the 20 keV - 15 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha =3D -0.92 =B1 0.08, the high energy photon index beta =3D -1.97 =B1 0.08, the peak energy Ep =3D 370 =B1 55 keV, chi2 =3D 85/94 dof.
  The spectrum at the maximum count rate (measured from T0+0.768 to T0+2.304 s) is best fit in the 20 keV - 15 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha =3D -0.80 =B1 0.09, the high energy photon index beta =3D -2.04 =B1 0.11, the peak energy Ep =3D 452 =B1 72 keV, chi2 =3D 95/97 dof.
  For both spectra, we note a hint of counts excess over the model flux in the spectral channels around ~10 MeV.
  All the quoted results are preliminary.
• GCN Circular #14678
  P.A. Evans (U.Leicester), M. de Pasquale (MSSL/UCL), M.C. Stroh (PSU) and M. H. Siegel (PSU) report on behalf of the Swift team:
  Swift conducted a series of observations, tiled on the sky, of the Fermi/LAT GRB 130518A. In these observations we find an uncatalogued source at RA,Dec =3D 355.6658, +47.4653 degrees (J2000.0) which is equivalent to:

  RA(J2000.0) =3D    23h 42m 39.79s
  Dec (J2000.0) =3D +47d 27' 55.2"
  

  with an uncertainty of 3.6 arcsec (radius, 90% confidence).
  This source shows weak evidence of fading: a power-law fit gives a decay index of 0.66 (+/- 0.80); at this level we therefore cannot confirm whether this is the afterglow of GRB 130518A.
  The spectrum of this source can be fitted with an absorbed power-law with a spectral index of 2.5 (+0.8, -0.6). The best-fitting absorption column is 2.4 (+2.2, -1.4) x 10^21 cm^-2, consistent with the Galactic value of 1.0 x 10^21 cm^-2 (Kalberla et al., 2005).
  UVOT observed the field of the XRT source in u filter between 30.5 ks and 59.9 ks after the trigger, for a total exposure time of 2.7 ks. We detect an optical object with magnitude u =3D 19.0 =B1 0.1 just outside = the 3.6 arcsec XRT error circle. The source shows weak indication of fading between the beginning and the end of observations.
  This circular is an official product of the Swift team.
• GCN Circular #14679
  Eleonora Troja (GSFC), Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM)= , Chris Klein (UCB), Ori Fox (UCB) J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UCSC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jos=E9 A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes=FAs Gonz=E1lez (UNAM), Carlos Rom=E1n-Z=FA=F1iga (UNAM), Neil Gehrels= (GSFC), and Harvey Moseley (GSFC) report:
  We observed the field of GRB 130518A (Xiong, et al., GCN 14674; Omodei, et al., GCN 14675) with the Reionization and Transients Infrared Camera (RATIR;www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astron=F3mico Nacional on Sierra San Pedro M=E1rtir from from 2013/05 19.44 to 2013/05 19.47 UTC (20.54 to 21.49 hours after the GBM trigger), obtaining a total of 0.64 hours exposure in the r' and i' bands, 0.27 hours exposure in the Z and Y bands, and 0.15 hours exposure in the J, and H bands.
  We detect a new, uncatalogued source at RA,Dec =3D 355.66781, +47.46493 (J2000) with an uncertainty of 0.5 arcsec. This position is 5 arcsec from the XRT localization, just outside the XRT error circle (Evans, et al., GCN 14678). In comparison with SDSS DR8 and 2MASS, we obtain the following detections:

       r'    19.38 =B1 0.02
       i'    19.10 =B1 0.02
       Z     18.83 =B1 0.04
       Y     18.65 =B1 0.04
       J     18.28 =B1 0.07
       H     18.47 =B1 0.11
  

  These magnitudes are in the AB system and not corrected for Galactic extinction in the direction of the GRB. We have evidence at the 2-3 sigma level of fading in r' and i' over the duration of our observations.
  Further observations are planned.
  We thank the staff of the Observatorio Astron=F3mico Nacional in San Pedr= o M=E1rtir.
• GCN Circular #14680
  S. B. Cenko (UC Berkeley) reports on behalf of a larger collaboration:
  We have imaged the location of the Fermi GBM (Xiong et al., GCN 14674), LAT (Omodei et al., GCN 14675), Swift BAT (Cummings et al., GCN 14676), and Konus-Wind (Golenetskii et al., GCN 14677) GRB 130518A with the robotic Palomar 60 inch telescope. Observations were obtained in the r' and i' filters beginning at 10:24 UT on 2013 May 19 (~ 0.85 d after the GBM trigger).
  We detect the optical afterglow (Evans et al., GCN 14678; Troja et al., GCN 14679) in both filters. Using several nearby point sources from SDSS for calibration, we measure a magnitude of r' = 19.3 at this time.
• GCN Circular #14681
  P.A. Evans (U.Leicester), M.C. Stroh (PSU) and M. H. Siegel (PSU) report on behalf of the Swift-XRT team:
  Swift has performed a second observation of GRB 130518A. We collected 1 ks of data, starting 122.5 ks after the Fermi trigger (Xiong, GCN Circ. 14674; Omodei & McEnery, GCN Circ. 14675). The XRT source reported by Evans et al. (GCN Circ. 14678) is detected at a level of 0.013 =C2=B1 0.005 ct/sec, significantly below the level in the previous observations, confirming that it has faded. The best-fitting power-law decay index is 1.1 (+0.5, -0.3).
  We therefore conclude that this object is the afterglow of GRB 130518A.
  
• GCN Circular #14684
  Eleonora Troja (GSFC), Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM)= , Chris Klein (UCB), Ori Fox (UCB) J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UCSC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jos=E9 A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes=FAs Gonz=E1lez (UNAM), Carlos Rom=E1n-Z=FA=F1iga (UNAM), Neil Gehrels= (GSFC), and Harvey Moseley (GSFC) report:
  We again observed the field of GRB 130518A (Xiong, et al., GCN 14674; Omodei, et al., GCN 14675) with the Reionization and Transients Infrared Camera (RATIR;www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astron=F3mico Nacional on Sierra San Pedro M=E1rtir from 2013/05 20.43 to 2013/05 20.46 UTC (44.41 to 45.24 hours after the GBM trigger), obtaining a total of 0.71 hours exposure in the r' and i' bands.
  In comparison with SDSS DR8, we obtain the following detections of the so= urce reported earlier (Troja, et al., GCN 14678; Cenko, GCN 14680):

  r'    20.47 =B1 0.04
  i'    20.19 =B1 0.04
  

  These magnitudes are in the AB system and not corrected for Galactic extinction in the direction of the GRB.
  In comparison with our earlier observations (Troja, et al., GCN 14678), t= he source has faded by slightly more than 1 magnitude in r' and i' between about 21= hours and 45 hours after the trigger. This confirms that the source corresponds= to the afterglow of GRB 130518A.
  We thank the staff of the Observatorio Astron=F3mico Nacional in San Pedr= o M=E1rtir.
• GCN Circular #14685
  R. S=E1nchez-Ram=EDrez (IAA-CSIC), J. Gorosabel (UPV-EHU, IAA-CSIC), A. J. Castro-Tirado (IAA-CSIC), J. Cepa and G. G=F3mez-Velarde (IAC), on behalf= of a larger collaboration, report:
  We observed the location of the Fermi GRB 130518A (Xiong et al. GCNC 14674, Omodei et al. GCNC 14675) -also detected by Swift and Konus (Cummings et al. GCNC 14676, Golenetskii et al. GCNC 14677)- with the OSIRIS spectrograph mounted at the 10.4m GTC located at Roque de los Muchachos Observatory (La Palma, Spain). Observations began on May 20.199= 5 UT (i.e. 40.9 hr post burst). The optical afterglow (Evans et al. GCNC 14678, Troja et al. GCNC 14579) is well detected with the blue (R1000B) grism and in the resulting spectrum we see a strong, broad damped-Lya absorption feature at ~4100A, combined with many metal lines including SII, SiII, CII, SiIV, CIV, FeII, AlII and AlIII at a common redshift of z=3D2.49.=94
  We thank E. Troja for providing the ID-chart.
• GCN Circular #14687
  A. Cucchiara (UCSC), S. B. Cenko (UC Berkeley) report on behalf of a larger collaboration:
  "We obtained spectroscopy of the afterglow of the LAT-GRB 130518A=20 (Xiong et al. GCN 14674, Omodei et al. GCN 14675, Evans et al.=20 GCN 14678) with Gemini-North / GMOS, beginning a May 20.60 UT=20 roughly 2.05 days after the burst.=20 Two different central wavelengths were observed giving a coverage=20 from ~3850-6730 A.=20 We identify several absorption features, including Lyman-alpha, SiIV(1394,1402), SiII1526, and CIV(1548,1550) at the common redshift of z=3D2.488.
  This result is consistent with the one reported by S=E1nchez-Ram=EDrez et al. (GCN 14685).
  We thank the Gemini-staff for their help in performing these observations."
• GCN Circular #14689
  A. J. Castro-Tirado (IAA-CSIC Granada), M. Bremer and J.-M. Winters (IRAM Grenoble), on behalf of a larger collaboration, report:
  "We conducted mm observations towards GRB 130518A (Xiong et al. GCNC 14674, Omodei et al. GCNC 14675) starting at 61 hr post burst with the PdBI at 86.7 GHz. At the position of the optical afterglow (Evans et al. GCNC 14678, Troja et al. GCNC 14579), we detect a ~2 mJy point source. Further mm observations are planned."
• GCN Circular #14725
  T. Kawano, M. Ohno, K. Takaki, R. Nakamura, S. Furui, Y. Fukazawa (Hiroshima U.), T. Yasuda, M. Tashiro, Y. Terada, Y. Ishida, H. Ueno, S. Sugimoto (Saitama U.), M. Yamauchi, N. Ohmori, M. Akiyama (Univ. of Miyazaki), K. Yamaoka (Nagoya U.), S. Sugita (Ehime U.), Y. E. Nakagawa, M. Kokubun, T. Takahashi (ISAS/JAXA), W. Iwakiri(RIKEN), Y. Hanabata (ICRR), Y. Urata (NCU), K. Nakazawa, K. Makishima (Univ. of Tokyo) on behalf of the Suzaku WAM team, report:
  The bright, long GRB 130518A (Fermi-GBM detection: Xiong, GCN 14674; Fermi-LAT detection: Omodei and Julie McEnery, GCN 14675; Swift-BAT trigger 556113: Cummings, GCN 14676) triggered the Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV at UT 13:54:50.635(=T0).
  The observed light curve shows a bright peak followed by a weaker emission seen up to T0+24 s with a duration (T90) of about 22 seconds. The fluence in 100 - 1000 keV was 7.05 (-0.34, +0.20) x10^-5 erg/cm^2. The 1-s peak flux measured from T0+11 s was 15.9 (-0.89, +0.61) photons/cm^2/s in the same energy range.
  Preliminary result shows that the time-averaged spectrum from T0-5 s to T0+30 s is well fitted by a GRB Band model as follows. the low-energy photon index alpha: -1.42 (-0.18, +0.26), the high-energy photon index beta: -2.27 (-0.22, +0.12), and the peak energy Epeak: 550 (-91, +99) keV, (chi^2/d.o.f = 74.0/68).
  Due to the brightness of this burst, a 5% systematic error was added for low energy channels. All the quoted errors are at statistical 90% confidence level.
  The light curves for this burst are available at: http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html