Gamma-ray Burst 120226A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #12989
  V. Vasileiou (CNRS/IN2P3/LUPM) and J. L. Racusin (NASA/GSFC) report on behalf of the Fermi-LAT team:
  Fermi-LAT has detected high energy emission from GRB 120226A in ground analysis. The GRB was triggered on by Fermi-GBM at 20:54:17.03 on Febuary 26, 2012 (trigger 351982459).
  The GRB was significantly detected during the prompt phase only using a non-standard LAT data selection most sensitive in the tens-of-MeV energy range, with which over ~50 counts above background were detected within a 60 s interval coinciding with the time of the GBM emission. This data selection has insufficient spatial resolution to provide a reliable LAT localization.
  However, the GRB became detectable with the standard LAT analysis techniques only after data of longer time scales were accumulated. A preliminary maximum-likelihood analysis of the E>100MeV P7SOURCE_V6 LAT data generated during the first 1.9 ks after the GBM trigger (until the GRB became occulted by the Earth) revealed a source with a ~4 sigma statistical significance, corresponding to ~14 excess events. The source spectrum is best fit with a power law of index -1.6+-0.3. Using this analysis, we obtained the best LAT on-ground localization of:

  RA(J2000) = 305.30 deg
  Dec(J2000) = 40.75 deg
  

  with an error radius 0.36 deg (90% containment, statistical error only), which is 4 deg from the best GBM localization and ~37 deg with respect to the LAT boresight at the time of the trigger. The GRB triggered an autonomous repoint of the Fermi spacecraft bringing our best localization to ~12 deg from the LAT boresight for 1.9 ks after the trigger. The burst position is close to the Galactic plane at (l,b) = 78.5, 2.3 deg.
  A Swift TOO has been requested.
  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 #12993
  K. Hurley on behalf of the Mars Odyssey and MESSENGER GRB teams,
  J. Goldsten on behalf of the MESSENGER GRNS GRB team,
  I. G. Mitrofanov, D. Golovin, M. L. Litvak, and A. B. Sanin, on behalf of the HEND-Odyssey GRB team,
  S. Golenetskii, R. Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, D. Svinkin, and T. Cline on behalf of the Konus-Wind team,
  V. Connaughton, M. Briggs, and C. Meegan, on behalf of the Fermi GBM team,
  A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo, and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,
  S. Barthelmy, J. Cummings, N. Gehrels, H. Krimm, and D. Palmer, on behalf of the Swift-BAT team,
  K. Yamaoka, M. Ohno, Y. Hanabata, Y. Fukazawa, T. Takahashi, M. Tashiro, Y. Terada, T. Murakami, and K. Makishima on behalf of the Suzaku WAM team, and
  D. M. Smith, J. McTiernan, and W. Hajdas, on behalf of the RHESSI team, report:
  The long-duration, bright GRB 120226A was observed by Fermi (GBM: trigger 351982459), INTEGRAL (SPI-ACS), Konus-Wind, MESSENGER (GRNS), Mars Odyssey (HEND), Swift (BAT), RHESSI, and Suzaku (WAM) at about 75257 s UT (20:54:17). The burst was outside the coded field of view of the BAT.
  We have triangulated it to a preliminary, 3 sigma error box whose coordinates are:

    ---------------------------------------------
     RA(2000), deg                 Dec(2000), deg
    ---------------------------------------------
    Center:
     302.930 (20h 11m 43s) +48.665 (+48d 39' 55")
    Corners:
     300.395 (20h 01m 35s) +46.181 (+46d 10' 53")
     303.595 (20h 14m 23s) +49.580 (+49d 34' 48")
     305.877 (20h 23m 30s) +51.105 (+51d 06' 19")
     302.306 (20h 09m 13s) +47.751 (+47d 45' 04")
    ---------------------------------------------
  

  The error box area is 1.2 sq. deg, and its maximum dimension is 6.1 deg.
  This box can be improved.
  The center of the LAT position reported by Vasileiou & Racusin (GCN 12989) is 9.1 deg from the center of the error box (6.5 deg from the nearest corner). Further analysis of the LAT data will be presented in a forthcoming GCN Circular.
  The time history and spectrum will be given in forthcoming GCN Circulars.
  A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB120226_T75259/IPN/
• GCN Circular #12994
  Weikang Zheng and Carl Akerlof report on behalf of the ROTSE collaboration:
  We analyzed the high energy LAT data of GRB 120226A (Vasileiou and Racusin, GCN 12989) using the matched filter technique (Akerlof et al, 2010, ApJ, 725, L15; 2011 ApJ, 726, 22; Zheng et al. 2012, ApJ 745,72, GCN 12822). We only selected the photons with energy above 100 MeV in our pipeline analysis. Our localization result gives the coordinate of Ra = 300.05, Dec=48.81 (J2000) with uncertainty ~0.5 degree. This location is about 7 degrees away from GBM trigger (Ra = 304.29,Dec = 42.1) and about 9 degrees away from the LAT location (Ra = 305.30, Dec = 40.75) given in GCN 12989. Our localization is much closer to the center of IPN location (Ra = 302.930, Dec = 48.665, K. Hurley et al. GCN 12993), about 2 degrees away.
  The LAT data signal is weak, too low to claim a firm detection. Only four photons were identified near the estimated coordinate within a 50s time window following the GBM trigger but by extending the duration to 250s, the number of photons increases to about 10. We encourage X-ray follow-up observations of the new location.
  All the pipeline results including the skymap can be found at the following link: http://www.rotse.net/LAT/GBMTriggers/351982459/351982459_res.html
• GCN Circular #12995
  N. Omodei (SU), V. Pelassa (UAH), V. Vasileiou (CNRS/IN2P3/LUPM) and J. L. Racusin (NASA/GSFC) report on behalf of the Fermi LAT and GBM teams:
  "At 20:54:17.03 UT on February 26, GRB 120226A triggered Fermi-GBM (trigger 351982459 / 120226871) and was detected by the Fermi-LAT during the prompt phase using a non-standard LAT data selection technique, as reported by Vasileiou and Racusin (GCN Circular 12989). It was also triangulated by the IPN (Hurley et al, GCN 12993).
  The GBM light curve consists of several peaks with a duration (T90) of 57 +/- 2s (50-300 keV). The time-averaged spectrum for the GBM observation, from T0+0.004 s to T0+75.778 s, is well fit by a Band function with Epeak = 296.70 +/- 13.60 keV, alpha = -1.00 +/- 0.02 , and beta = -2.28 +/- 0.10 (Castor stat 742.54 for 487 d.o.f.). The event fluence (10-1000 keV) in this time interval is (6.125 +/- 0.064)E-05 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+17.216 s in the 10-1000 keV band is 12.0 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog.
  The significance of this burst in the LAT at low energies (above 20 MeV) is above 6 sigma using a class of non-standard events. The structure of the light curve is consistent with the GBM observation. However, the re-analysis of P7SOURCE_V6 events shows that the temporally extended emission reported by Vasileiou and Racusin (GCN Circular 12989) is likely due to the bright pulsar PSR J2021+4026 in the field-of-view. This source is 0.31 degrees away from the position reported in GCN Circular 12989, and the measured flux (>100 MeV) of (1.32+/-0.02)E-06 ph/s/cm^2 (Nolan et al. 2012, in press. http://arxiv.org/abs/1108.1435) is also compatible with the observed number of gamma rays.
  The IPN localization reported by Hurley et al. (RA=302.930, Dec=48.665; GCN Circular 12993) is not compatible with the original LAT localization and suggests that the analysis of GRB 120226A by Vasileiou and Racusin (GCN Circular 12989) was affected by the bright foreground pulsar.
  GRB 120226A is not detected at high energy by the LAT and therefore any localization using Fermi LAT data should be regarded with caution.
  The Fermi LAT point of contact for this burst is Nicola Omodei (nicola.omodei@stanford.edu).
  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 #12996
  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 GRB 120226A (GBM trigger 351982459; IPN localization: Hurley at al., GCN 12993; Fermi/LAT & Fermi/GBM detection: Omodei et al., GCN 12995) triggered Konus-Wind at T0=75259.724s UT (20:54:19.724)
  The light curve shows multiple partly overlapped pulses. A total duration of the burst is ~80 s. The emission is seen up to ~4 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB120226_T75259/
  As observed by Konus-Wind the burst had a fluence of 7.5(-1.2,+0.9)x10-5 erg/cm2, and a 256-ms peak flux, measured from T0+25.600 s, of 2.5(-0.3,+0.3)x10-6 erg/cm2/s (both in the 20 keV - 5 MeV energy range).
  The time-integrated spectrum of the burst (measured from T0 to T0+78.086 s) is best fit in the 20 keV - 5 MeV range with the GRB (Band) model, for which: the low-energy photon index alpha = -1.01 (-0.07, +0.07), the high energy photon index beta = -2.5 (-0.9, +0.2), the peak energy Ep = 279(-28, +39) keV, chi2 = 88.6/75 dof.
  The spectrum at the maximum count rate (measured from T0+20.992 to T0+28.928 s) is best fit in the 20 keV - 5 MeV range by a power law with exponential cutoff model, for which alpha = -0.96 (-0.09, +0.10), and Ep = 317(-42, +54) keV, chi2 = 79.0/76 dof.
  All the quoted results are preliminary. All the quoted errors are at the 90% confidence level.