Gamma-ray Burst 090418B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN/BACODINE POSITION NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Sat 18 Apr 09 21:55:34 UT
  NOTICE_TYPE:     Swift-BAT Slew GRB Position
  ID_NUM:          27
  GRB_RA:          225.910d {+15h 03m 38s} (J2000),
                   226.017d {+15h 04m 04s} (current),
                   225.331d {+15h 01m 20s} (1950)
  GRB_DEC:         +17.220d {+17d 13' 12"} (J2000),
                   +17.184d {+17d 11' 02"} (current),
                   +17.415d {+17d 24' 53"} (1950)
  GRB_ERROR:       0.38 [arcmin radius, statistical only]
  GRB_INTEN:       1541810 [cnts]    Image_Peak=0 [image_cnts]
  TRIGGER_DUR:     104.400 [sec] 
  TRIGGER_INDEX:   10     Criteria: S(15-50) > 4.0 sigma  AND  H(50-150) > 4.0 sigma
  ENERGY_RANGE:    15-150 keV
  BKG_INTEN:       0 [cnts]
  BKG_TIME:        0.00 SOD {00:00:00.00} UT
  BKG_DUR:         0 [sec]
  GRB_DATE:        14939 TJD;   108 DOY;   09/04/18
  GRB_TIME:        32421.18 SOD {09:00:21.18} UT
  SOLN_STATUS:     0x13
  RATE_SIGNIF:     0.00 [sigma]
  IMAGE_SIGNIF:    0.00 [sigma]
  SUN_POSTN:        26.95d {+01h 47m 47s}  +11.11d {+11d 06' 51"}
  SUN_DIST:        146.00 [deg]   Sun_angle= 10.7 [hr] (West of Sun)
  MOON_POSTN:      315.85d {+21h 03m 23s}  -16.07d {-16d 04' 27"}
  MOON_DIST:        94.54 [deg]
  MOON_ILLUM:      37 [%]
  GAL_COORDS:       21.90, 57.94 [deg] galactic lon,lat of the burst (or transient)
  ECL_COORDS:      217.59, 32.99 [deg] ecliptic lon,lat of the burst (or transient)
  COMMENTS:        SWIFT-BAT Slew GRB Coordinates.  
  COMMENTS:        A point_source was found.  
  COMMENTS:        This does not match any source in the ground catalog.  
  COMMENTS:        This is a GRB.  
  COMMENTS:        Extremely high confidence of reality (gold-plated).  
  COMMENTS:        This Notice was ground-processed from flight-data.  
  COMMENTS:          
  

• red DSS finding chart ps-file
  
  
• GCN Circular #9159
  A. Copete, J. Grindlay (Harvard) S. Barthelmy, C. Markwardt, N. Gehrels (NASA/GSFC)
  We report the detection of a bright GRB by the BAT Slew Survey (BATSS) in the slew that started at 08:59:02 and lasted 151 sec. The ground- calculated position is RA, Dec = 225.910, +17.224 deg, which is

  RA (J2000) = 15h 03m 38s
  Dec(J2000) = +17d 13' 26"
  

  with an uncertainty of 1.91 arcmin (90% confidence, including systematics). The detection was triggered by simultaneous independent detections of 86.0 sigma and 41.8 sigma from imaging in the 15-50 keV and 50-150 keV energy bands, respectively. The burst mask-tagged lightcurve lightcurve in the 15-150 keV band shows a strong and broad multi-peaked emission structure starting at T+25sec as the burst enters the BAT field-of-view, lasting 48 sec, and peaking 6 times at T +29, T+35, T+38, T+47, T+58 and T+62sec. This is followed by a weaker broad peak starting at T+87sec, lasting 28sec and peaking at T+100sec. T90 = 65.0sec and T50 = 17.0sec.
  The time-averaged spectrum over the 120 sec exposure time of the source is best fit by a power law with an exponential cutoff, with photon index 1.42 and high-energy cut at 319 keV. The fluence in the 15-150 keV band is 1.6 x 10^-5 erg/cm^2, and the peak 1-sec flux is 6.5 x 10^-7 erg/cm^2/sec at T+38sec. A follow-up Swift ToO observation for this burst has been scheduled.
• GCN Circular #9171
  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 Swift-BATSS GRB 090418B (Copete et al., GCN 9159) triggered Konus-Wind at T0=32366.325 s UT (08:59:26.325).
  The burst light curve shows a soft weak precursor at ~T0-20 s, the main multipeaked pulse at T0 with a duration of ~45 s, and a weak soft pulse at ~T0+70 with a duration of ~30 s (the same lc structure was seen by BAT: Copete et al., GCN 9159).
  As observed by Konus-Wind the burst had a fluence of (2.31 +/- 0.09)x10^-5 erg/cm2, and a 256-ms peak flux measured from T0+15.840 s of (1.54 +/- 0.20)x10^-6 erg/cm2/s (both in the 20 keV - 1 MeV energy range).
  The time-integrated spectrum of the burst (from T0 to T0+40.704 s) can be fitted (in the 20 keV-1 MeV range) by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.23(-0.09, +0.010), and Ep = 117(-7, +8) keV (chi2 = 62.0/56 dof). Fitting by GRB (Band) model yields the same alpha and Ep, and only an upper limit on the high energy photon index: beta < -3.18 (chi2 = 62.0/55 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/GRB090418_T32366/
• GCN Circular #9176
  C. Guidorzi (U. Ferrara), R.J. Smith, I.A. Steele, C.G. Mundell, D. Bersier (Liverpool JMU), A. Gomboc (U. Ljubljana), P. O'Brien, N. Tanvir (U. Leicester) on behalf of a large collaboration report:
  On 2009 April 19 at 12:53:50 UT we observed the Swift-BAT Slew Survey GRB 090418B (Copete et al., GCN Circ. 9159) with the 2-m Faulkes Telescope North using the i' and R filters.
  From a set of 6x300 s frames in each filter, we could not find any uncatalogued object inside the BAT error circle with respect to the SDSS field stars, down to the following limiting magnitudes:

  Mid Time   Exposure  Filter   Limit
  (days)      (s)               (mag)
  -------------------------------------
  1.17        6x300      i'      > 21
  1.20        6x300      R       > 21.5
  -------------------------------------
  

• GCN Circular #9178
  P. Afonso (MPE), S. Klose (Tautenburg), T. Kruehler and J. Greiner (both MPE Garching), report on behalf of the GROND team:
  GROND (Greiner et al. 2008, PASP 120, 405), mounted at the 2.2m ESO/MPI telescope at La Silla Observatory (Chile) started follow-up observations of GRB 090418B (Copete et al., GCN #9150) on April 19, at 03:00 UTC (18.0 h after the burst). In addition, a second epoch of imaging was obtained, which started on April 20, 04:05 UTC.
  Similar to Guidorzi et al. (2009, GCN #9176) we do not detect any new object with respect to SDSS/2MASS inside the BAT error circle. Image subtraction between the two epochs does not reveal any obvious variable source. Upper limits from the first observation are as follows (all in the AB system):

  g' > 23.8 mag
  r' > 24.0 mag
  i' > 23.2 mag
  z' > 23.0 mag
  J > 22.0 mag
  H > 21.4 mag
  K > 20.8 mag
  

  Quoted upper limits have been derived using SDSS and 2MASS field stars as reference.
• GCN Circular #9181
  Markku Nissinen (Taurus Hill Observatory) and Veli-Pekka Hentunen (Taurus
  Hill Observatory) report:
  Global-rent-a-scope GRAS002 Tak Mewlon 0.30m telescope with SBIG ST-8E
  CCD at Mayhill (New Mexico, USA) was used for follow-up observations of
  GRB090418B. The observations were started on April 19, at 03:55 UTC (19 hours
  after the burst) and stopped at 05:35 UTC. Four unfiltered 600 seconds images
  were taken. We do not detect any new object with respect to POSSII F/USNO-B1.0
  inside the BAT error circle. Upper limit for the observations is > 20.5 mag (3UL). Quoted upper limit has been derived using POSSII F and USNO-B1.0 field stars as reference.
  Quoted upper limit has been derived using POSSII F and USNO-B1.0 field stars as reference.
• GCN Circular #9186
  K. Kono, E. Sonoda, M. Yamauchi, N. Ohmori, H. Hayashi, K. Noda, A. Daikyuji, Y. Nishioka (Univ. of Miyazaki), M. Ohno, M. Suzuki, M. Kokubun, T. Takahashi (ISAS/JAXA), W. Iwakiri, M. Tashiro, Y. Terada, A. Endo, K. Onda, T. Sugasahara (Saitama U.), Y. Urata (NCU), T. Enoto, K. Nakazawa, K. Makishima (Univ. of Tokyo), K. Yamaoka, S. Sugita (Aoyama Gakuin U.), Y. E. Nakagawa, T. Tamagawa (RIKEN), T. Uehara, T. Takahashi, Y. Fukazawa, Y. Hanabata (Hiroshima U.), S. Hong (Nihon U.), N. Vasquez (Tokyo Tech.), on behalf of the Suzaku WAM team, report:
  The long GRB 090418B was detected by the Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV at 08:54:21.299 UT (=T0). The observed light curve shows a multi-peaked structure starting at T0-3 s, ending at T0+35 s, with a duration (T90) of about 29 seconds.
  The fluence in 100 - 1000 keV was 1.22 (-0.14, +0.06) x10-5 erg/cm2. The 1-s peak flux measured from T0+32 s was 2.13 (-0.58, +0.35) photons/cm2/s in the same energy range.
  Preliminary result shows that the time-averaged spectrum from T0+14 s to T0+52 s is well fitted by a single power-law with a photon index of 2.09 (-0.20, +0.22) (chi2/d.o.f = 13/17).
  All the quoted errors are at statistical 90% confidence level, in which the systematic uncertainties are not included.
  The light curves for this burst will be available at: http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/untrig/grb_table.html
• GCN Circular #9191
  I. Bikmaev, R.Zhuchkov, N. Sakhibullin (KSU/AST), I. Khamitov, Z. Eker (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.), R. Burenin, M. Pavlinsky, R. Sunyaev (IKI)
  report:
  The field of GRB 090418B (Copete et al., GCN 9159) was observed with Russian-Turkish 1.5-m telescope (RTT150, Bakirlitepe, TUBITAK National Observatory, Turkey). We obtained series of 3x300s exposures in Rc filter, centered on April 19, 01:04 UT, i.e. 16 hours after the burst. In addition, a second epoch of 4x300 sec exposures was obtained in Rc filter on April 20, 0:17 UT.
  Similarly to Guidorzi et al. (GCN 9176), Afonso et al. (GCN 9178), Nissinen et al. (GCN 9181) we do not detect any obvious fading optical source inside the BAT error circle. The upper limit for the first epoch of our observations is Rc > 22.7 mag.