Gamma-ray Burst 100401A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #10567
  J. R. Cummings (GSFC/UMBC), N. Gehrels (NASA/GSFC), F. E. Marshall (NASA/GSFC) on behalf of the Swift team
  At 2010-04-01T07:07:31.9 BAT detected a rate increase (trigger# 417974). The source was found with insufficient significance onboard to trigger an automated burst response. A significant source was found in ground analysis at RA, Dec 290.813, -8.257, which is:

  RA (J2000)   19h 23m 15.5s
  Dec (J2000) -08d 15' 25"
  

  with an estimated uncertainty of 2 arcmin radius (90% containment). The source was 10% coded in the BAT field of view.
  As seen in BAT, the burst had a single square-shaped pulse of about 2 seconds duration.
  The spectrum from 15 to 150 keV is best fit by a simple power law function with a photon index of 1.7 +- 0.2. We note that this is softer than is typical for "short, hard" GRBs. The fluence was (3.6 +- 1.2) erg/cm2. The 1-second peak flux was 2.4 photons/cm2.
  Since this burst was not detected with sufficient significance onboard, there are no automated data products. A Swift TOO is in progress.
• GCN Circular #10568
  A. Goldstein (UAH) and D. Gruber (MPE) report on behalf of the Fermi GBM Team:
  "At 07:07:32.24 UT on 1 April 2010, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 100401A (trigger 291798454 / 100401297) which was also detected by the Swift-BAT (J.R. Cummings et al. 2010, GCN 10567). The GBM on-ground location is consistent with the Swift-BAT position. The angle from the Fermi LAT boresight is 45 degrees.
  The GBM light curve consists of an initial bright pulse at trigger time lasting ~4 s followed by a second, much softer pulse of ~30 s in duration, approximately 65 s after trigger time. The total duration (T90) is estimated to be about 100 s (8-1000 keV). The time-averaged spectrum of the first pulse from T0-1.9 s to T0+3.2 s is best fit by a power law function with an exponential high energy cutoff. The power law index is -1.49 +/- 0.17 and the cutoff energy, parameterized as Epeak, is 144.90 +/- 62.20 keV (chi squared 439 for 483 d.o.f.). The first pulse is equally well fit by a simple power law with index -1.77 +/- 0.06 (chi squared 444 for 484 d.o.f.). The time-averaged spectrum of the second pulse from T0+74.9 s to T0+98.4 s is well fit by a power law function with an exponential high energy cutoff. The power law index is -1.52 +/- 0.39 and the cutoff energy, parameterized as Epeak, is 29.34 +/- 8.96 keV (chi squared 511 for 483 d.o.f.). The second pulse is equally well fit by a simple power law with index -2.16 +/- 0.11 (chi squared 514 for 484 d.o.f.).
  The event fluence (8-1000 keV) over the entire emission is (2.39 +/- 0.05)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0-1.4 s in the 8-1000 keV band is 3.61 +/- 0.16 ph/s/cm^2.
  The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
• GCN Circular #10569
  G. Stratta and V. D'Elia (ASDC) report on behalf of the Swift Team:
  Swift began a target of opportunity observation of GRB 100401A detected on ground (Cummings et al., GCN #10567) and by the Fermi/GBM (Goldstein and Gruber, GCN #10568), at 19:33:04 UT on April 2nd, 2010, approximately 36.4 hours after the Swift/BAT trigger. In about 2 ks of Photon Counting mode data, no X-ray source is detected inside the BAT error circle.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #10570
  M.M. Chester (PSU) and G. Stratta (ASDC) report on behalf of the Swift/UVOT team:
  Swift began a Target of Opportunity observation of GRB 100401A, detected by Swift/BAT (Cummings et al., GCN Circ. 10567) and by Fermi/GBM (Goldstein and Gruber, GCN Circ. 10568), on April 2nd, 2010 at 19:33:04 UT, approximately 36 hours after the Swift/BAT trigger.
  No optical afterglow consistent with the BAT position is detected in the UVOT exposure. The 3-sigma upper limit using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) is:

  Filter     T_start(s)   T_stop(s)      Exp(s)      3-sig UL (mag)
  
  u          131128       133123         1963         >20.8
  

  The value quoted above is not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.29 in the direction of the burst (Schlegel et al. 1998).
• GCN Circular #10577
  SUBJECT: GRB100401A, GROND Upper Limits
  A. Updike (Clemson University), A. Rau, P. Afonso and J. Greiner (all MPE Garching) report on behalf of the GROND team:
  We observed the field of GRB 100401A (Cummings et al., GCN #10567, Goldstein and Gruber, #GCN 10568) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,PASP 120, 405), mounted at the 2.2m ESO/MPI telescope at La Silla Observatory (Chile).
  Observations started on 2010, April 3, at 09:21 UT, 2.09 days after the burst, and consisted of 20 min in JHK and 24.6 min in g'r'i'z'. A second epoch was obtained on 2010, April 4, at 09:09 UT, 2.99 days after the burst.
  Image subtraction of the two epochs does not reveal a variable source, down to the following 1st epoch limiting magnitudes (all in AB system):

  g' > 23.7
  r' > 23.9
  i' > 23.4
  z' > 23.4
  J  > 21.8
  H  > 21.4
  K  > 20.3
  

  These magnitudes were obtained using 2MASS field stars and GROND zero-points as reference, and are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.29 mag in the direction of the burst (Schlegel et al. 1998).