Gamma-ray Burst 090427

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN Circular #9277
```
TITLE:   GCN CIRCULAR
NUMBER:  9277
SUBJECT: IPN triangulation of very bright GRB 090427
DATE:    09/04/28 11:00:20 GMT
FROM:    Valentin Pal'shin at Ioffe Inst  
```
V. Pal'shin, S. Golenetskii, R.Aptekar, D. Frederiks, E. Mazets, P. Oleynik, D. Svinkin, M. Ulanov on behalf of the Konus-Wind and Konus-RF teams,
K. Hurley and T. Cline, on behalf of the Mars Odyssey and Konus GRB teams,
W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr, on behalf of the GRS-Odyssey GRB team,
I. G. Mitrofanov, D. Golovin, M. L. Litvak, and A. B. Sanin, on behalf of the HEND-Odyssey GRB team,
M. Marisaldi, G. Di Cocco, F. Fuschino, M. Galli, C. Labanti, on behalf of the AGILE MCAL team,
E. Del Monte, E. Costa, I. Donnarumma, Y. Evangelista, M. Feroci, I. Lapshov, F. Lazzarotto, L. Pacciani, M. Rapisarda, P. Soffitta, on behalf the SuperAGILE team,
A. von Kienlin, G. Lichti, and A. Rau, and K. Hurley on behalf of the INTEGRAL SPI-ACS team report:
Konus-Wind, Konus-RF, Mars-Odyssey (GRS and HEND), SuperAGILE, AGILE-MCAL, and INTEGRAL-SPI-ACS observed the bright GRB 090427 at about 84387 s UT (23:26:27). The burst was outside the coded field of view of the SuperAGILE.
The burst light curve shows a multipeaked structure with a duration of ~15 sec.
We have triangulated it to the following 3-sigma error box:
```
-----------------------------------------------
    RA(2000), deg              Dec(2000), deg
-----------------------------------------------
Center:
  235.931 (15h 43m 43s)   -13.498 (-13d 29' 53")
Corners:
  236.026 (15h 44m 06s)   -12.481 (-12d 28' 52")
  236.183 (15h 44m 44s)   -12.470 (-12d 28' 12")
  235.820 (15h 43m 17s)   -14.521 (-14d 31' 16")
  235.658 (15h 42m 38s)   -14.542 (-14d 32' 30")
-----------------------------------------------
```
The error box area is 0.313 sq. deg. This error box may be improved.
Preliminary analysis of the Konus-Wind data yields a burst fluence of ~1x10^-4 erg/cm2 (in the 20 keV - 8 MeV range), and an Epeak of the time-integrated spectrum of ~750 keV.
IPN triangulation map is available at http://www.ioffe.ru/LEA/GRBs/GRB090427_T84392/IPN/
GCN Circular #9296
```
TITLE:   GCN CIRCULAR
NUMBER:  9296
SUBJECT: Konus-Wind observation of very bright GRB 090427
DATE:    09/04/29 16:16:22 GMT
FROM:    Valentin Pal'shin at Ioffe Inst  
```
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 very bright GRB 090427 localized by IPN (Pal'shin et al., GCN 9277) triggered Konus-Wind at T0=84392.051 s UT (23:26:32.051).
As observed by Konus-Wind the burst had a fluence of (1.03 +/- 0.05)x10^-4 erg/cm2, and a 16-ms peak flux measured from T0+9.200 s of (1.10 +/- 0.13)x10^-4 erg/cm2/s (both in the 20 keV - 8 MeV energy range).
The time-integrated spectrum of the burst (from T0 to T0+17.920 s) can be fitted (in the 20 keV - 8 MeV range) by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.31 +/- 0.04, and Ep = 751(-67, +78) keV (chi2 = 90.5/85 dof). Fitting by GRB (Band) model yields the same alpha and Ep, and only an upper limit on the high energy photon index: beta < -2.8 (chi2 = 90.4/84 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/GRB090427_T84392/
GCN Circular #9307
A. Pelangeon & J-L. Atteia (LATT-OMP) report:
We used the spectral parameters of GRB 090427 provided by Golenetskii et al. (GCNC 9296) to compute the spectral pseudo-redshift(**) of this burst localized by IPN (Pal'shin et al., GCNC 9277).
We find a pseudo-redshift pz= 1.48 +/- 0.20
** cf. http://www.ast.obs-mip.fr/grb/pz
GCN Circular #9317
ICSP VLF observation of GRB090427 from two receivers
Sushanta K. Mondal (ICSP), Sandip K. Chakrabarti (S. N. Bose Centre and ICSP), Narendra N. Patra (Univ. Pune) and D. Bhowmick (ICSP)
Two ICSP VLF receivers clearly observed the effects of GRB090427 (GCN#s 9277, 9296) on the ionosphere simultaneously. The subflare point (13.5d S, 28.2d E) being closer to western India the signal was prominent from our Pune receiver (18.5d N, 74d N) while it was weaker at our Kolkata (22.5N, 88.5d E) receiver in eastern India. These two stations were ~1000 miles apart.
Both the receivers detected the GRB right after triggering and the correlation of the signals were found excellent for about ~70 seconds. Before the triggering, the correlation was poor.
A comparison of the smoothed signals can be found in grb27GCN.jpg in http://www.bose.res.in/~chakraba/grb090427-1.html. This message may be cited.
GCN Circular #9319
F. Olivares, T. Kruehler, J. Greiner (all MPE Garching) report on behalf of the GROND team:
We observed the central area of the error box of GRB 090427 localized by the IPN (Pal'shin et al., GCN #9277) simultaneously in g'r'i'z'JHK with GROND mounted at the 2.2m ESO/MPI telescope at La Silla Observatory (Chile). Three adjacent pointings centered at
```
RA = 15,43,31.0  Decl. = -13,40,00
RA = 15,43,43.4  Decl. = -13,30,00 (center of IPN box)
RA = 15,43,55.0  Decl. = -13,20,00 
```
have been observed with our 10x10 arcmin (in JHK) and 5.4x5.4 arcmin (g'r'i'z') field-of-view, thus covering about 27% and 8% of the full error box respectively (see sketch at http://www.mpe.mpg.de/~jcg/grb090427.html).
Observations started on 29 Apr. 2009 at 06:20 UT, 30.9 h after the burst, and consisted, for each of the three fields, of a set of images with a total integration time of 8 min in JHK and 7.7 min in g'r'i'z'. A second epoch of all three fields was obtained on 30 Apr. 2009 starting at 05:18 UT.
Image subtraction of the two epochs does not reveal a variable source in any of the three fields, down to limiting magnitudes (all in AB system) of
```
g' > 23.9
r' > 23.8
i' > 23.5
z' > 23.2
J > 22.2
H > 21.7
K > 20.6 
```
These magnitudes have been obtained using 2MASS field stars and the GROND zeropoints as reference.

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Jochen Greiner, last update: 04-May-2009 [Disclaimer]