Gamma-ray Burst 110428A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #11982
  V. Vasileiou (CNRS/IN2P3/LUPM), N. Omodei (Stanford University), D. Kocevski (SLAC), F. Piron (CNRS/IN2P3/LUPM), on behalf of the Fermi Large Area Telescope collaboration.
  Based on an on-ground analysis, the Large Area Telescope (LAT), on-board the Fermi Gamma-ray Space Telescope, detected high energy emission extending up to ~3 GeV from the GBM-detected GRB 110428A (trigger 325675112). The detected emission lasts up to ~200 seconds.
  We obtain a localization of RA, DEC (J2000 deg) = 5.30, 64.80 (00h 21m 12s, 64d 47' 42.0"), (galactic l=119.71 deg, b=2.11 deg), with a statistical error of 0.15 deg (68% CL), compatible with the GBM localization. The burst was initially at an angle of ~34 degrees to the LAT boresight and triggered an autonomous repoint of the spacecraft. According to preliminary spectral fits, the spectral index of the detected emission is -1.5+-0.1 (68% CL) at E>100MeV energies.
  Further analysis is ongoing.
  The Fermi LAT point of contact for this burst is Vlasios Vasileiou (vlasios.vasileiou@lupm.in2p3.fr).
  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 #11983
  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 bright GRB 110428A localized by Fermi-LAT (Vasileiou et al., GCN 11982) triggered Konus-Wind at T0=33509.450 s UT (09:18:29.450). The burst light curve shows two pulses started at ~T0-9 s with a total duration of ~15 s.
  As observed by Konus-Wind the burst had a fluence of 2.70(-0.16, +0.15)x10^-5 erg/cm2, and a 64-ms peak flux measured from T0+1.296 s of 8.47(-1.17, +1.18)x10^-6 erg/cm2/s (both in the 20 keV - 2 MeV energy range).
  The time-integrated spectrum of the burst (from T0 to T0+13.568 s) can be fitted (in the 20 keV - 2 MeV range) by the GRB (Band) model for which: the low-energy photon index is alpha = -0.30(-0.11, +0.12), the high energy photon index beta = -3.00(-0.58, +0.27), the peak energy Ep = 184(-10, +12) keV (chi2 = 78.2/59 dof). The spectrum at the maximum count rate (measured from T0+0.256 to T0+1.536 s) can be fitted (in the 20 keV - 2 MeV range) by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.19(-0.13, +0.14), and Ep = 257(-16, +17) keV (chi2 = 63.1/52 dof). Fitting by GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.5 (chi2 = 63.1/51 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/GRB110428_T33509/
• GCN Circular #11984
  A. Melandri, P. D'Avanzo, R. Margutti (INAF-OAB), B. Sbarufatti (INAF- OAB/IASFPA) and M. Stamatikos (OSU/NASA/GSFC) report on behalf of the Swift Team:
  At 00:47 UT, April 29th, 2011, Swift began a Target of Opportunity observation of the Fermi GBM/LAT discovered burst GRB 110428A (Vasileiou et al. GCN 11982), ~55.6 ks after the Fermi detection.
  In 4.8 ks of Photon Counting mode data, we detect two sources within the Fermi-LAT error circle (0.15 deg radius, 68% CL) at the following positions:

  Source 1:
  RA(J2000):   00 21 50.47
  Dec(J2000): +64 48 52.4
  with an uncertainty of 4.6 arcsec.
  
  Source 2:
  RA(J2000):   00 22 22.22
  Dec(J2000): +64:50:57.1
  with an uncertainty of 7.1 arcsec.
  

  Uncertainty radii are given at 90% containment.
  We note that the position of Source 1 is consistent with a known ROSAT source (1RXS J002150.5+644850) also present in the DSS. Source 2 is an uncatalogued object.
  The two sources have a count rate of about (1.2e-2 +/- 1.8e-3) and (2.9e-3 +/- 9.1e-4) cts/s, respectively. It is not possible to determine whether these sources are fading given the current statistics. Further Swift-XRT observations of the field are planned. We encourage ground-based follow-up observations.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #11988
  W. Iwakiri, Y. Terada, M. Tashiro, K. Takahara, T. Yasuda (Saitama U.), T. Uehara, Y. Hanabata, T. Takahashi, Y. Fukazawa (Hiroshima U.), N. Vasquez (Tokyo Tech.) K. Yamaoka (Aoyama Gakuin U.), M. Ohno, M. Kokubun, T. Takahashi (ISAS/JAXA), S. Sugita (Nagoya U.), Y. E. Nakagawa (Waseda U.), N. Ohmori, M. Akiyama, M. Yamauchi (Univ. of Miyazaki), Y. Urata, P. Tsai (NCU), K. Nakazawa, K. Makishima (Univ. of Tokyo), on behalf of the Suzaku WAM team, report:
  The long bright GRB 110428A localized by Fermi-LAT (Vasileiou et al., GCN 11982) was observed the Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV at 09:18:30 UT (=T0).
  The observed light curve shows double-peaked structure starting at T0-2s, ending at T0+10 s with a duration (T90) of about 5 seconds. The fluence in 100 - 1000 keV was 1.31 (-0.43, +2.03) x 10^-5 erg/cm^2. The 1-s peak flux measured from T0+4 s was 9.91 (-0.34, +1.19) photons/cm^2/s in the same energy range.
  Preliminary result shows that the time-averaged spectrum from T0-2s to T0+10s is well fitted by a power-law with exponential cutoff model : dN/dE ~ E^{-alpha} * exp(-(2-alpha)*E/Epeak) with alpha 1.11 (-0.22, +0.19), and Epeak 195.5 (-14.4, +15.9) keV (chi2/d.o.f. = 15.8/20). All the quoted errors are at statistical 90% confidence level.
• GCN Circular #11989
  A. Melandri, P. D'Avanzo, R. Margutti (INAF-OAB), B. Sbarufatti (INAF- OAB/IASFPA) report on behalf of the Swift Team:
  Swift continued to monitor the field of GRB 110428A (Vasileiou et al., GCN 11982) in two different observations carried out on April 29th and May 1st, 2011.
  In the final 18.49 ks of data (at a mean T-T0 = 2.07 days after the burst event) we still detect Source #1 reported by Melandri et al. (GCN 11984) with count rate of (1.6e-2 +/- 1.1e-3) cts/s, consistent with a constant flux for this source.
  Source #2 is no longer detected with a 3 sigma upper limit of 1.4e-3 cts/s. The probability for this source of having a constant flux is 8e-6. This is evidence of the fading of Source #2 with respect to the XRT observation reported in Melandri et al. (GCN 11984). Therefore we consider Source #2 as the X-ray afterglow of GRB 110428A.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #12012
  D. Tierney (UCD) and G. Fitzpatrick (UCD) report on behalf of the Fermi GBM Team:
  "At 09:18:30.41 UT on 28 April 2011, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 110428A (trigger 325675112 / 110428388) which was also detected by the Fermi-LAT (V. Vasileiou et al. 2011, GCN 11982), Konus-Wind (S. Golenetskii et al. 2011, GCN 11983), and Suzaku WAM (W. Iwakiri et al. 2011, GCN 11988). The GBM on-ground location is consistent with the Swift-XRT position (A. Melandri et al. 2011, GCN 11984).
  The GBM light curve consists of a single pulse with a duration (T90) of 5.6 +/- 0.2 s (50-300 keV). The time-averaged spectrum from T0+1.8 s to T0+9 s is best fit by a Band function with Epeak = 175.60 (+3.95/-3.82) keV, alpha = -0.20 (+0.03/-0.03), and beta = -2.88 (+0.10/-0.12) (C-Stat 559.66 for 482 d.o.f.).
  The event fluence (10-1000 keV) in this time interval is (2.27 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+7 s in the 10-1000 keV band is 26.8 +/- 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 #12017
  "Poonam Chandra (RMC), Dale A. Frail (NRAO), S. Bradley Cenko (Berkeley), Fiona Harrison (Caltech) and Srinivas Kulkarni (Caltech) report:
  We observed the Fermi burst GRB 110428A (Vasileiou et al. GCN 11982) with the Expanded Very Large Array (EVLA) at various radio frequencies between April 30 and May 13. We did not detect any significant radio source within the 7.1" error circle of source 2 (Melandri et al. GCN 11984). Below are the details and 3-sigma upper limits from our observations:

  Epoch                   Frequency            3-sigma upper limit          
  Apr 30.45 UT        4.5 GHz                93 
  uJy                                
  Apr 30.45 UT        7.9 GHz                66 
  uJy                                
  May 3.50 UT         4.5 GHz                66 
  uJy                                
  May 3.50 UT         7.9 GHz                54 
  uJy                               
  May 6.74 UT         4.5 GHz                87 
  uJy                                
  May 6.74 UT         7.9 GHz                60 
  uJy                                
  May 10.48 UT       22.45 GHz            240 
  uJy                               
  May 13.41 UT       8.33 GHz              35 
  uJy                                
  

  We thank the EVLA staff for scheduling our observations so promptly. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc."