GRB 020418

K. Hurley, on behalf of the Ulysses GRB team;

F. Frontera, C. Guidorzi, and E. Montanari, on behalf of the BeppoSAX GRBM team;

I. Mitrofanov, D. Anfimov, A. Kozyrev, M. Litvak, and A. Sanin,
on behalf of the HEND/Odyssey GRB team;

T. Cline, on behalf of the Ulysses and Mars Odyssey GRB teams; 

W. Boynton, C. Fellows, K. Harshman, C. Shinohara, and R. Starr, on
behalf of the GRS/Odyssey GRB team, report:

Ulysses, Mars Odyssey - HEND, and BeppoSAX observed this
GRB at 31110 s.  As observed by Ulysses, it had a duration of ~15
seconds, a 25-100 keV fluence of ~10^-5 erg/cm2, and a peak flux of
~10^-6 erg/cm2 s over 0.25 s.

We have triangulated it to a preliminary, 3 sigma error box
with approximate area 20 square arcminutes whose coordinates
are:

                     RA(2000)                 DEC(2000)
 ERROR BOX CENTER:  08 h 00 m 17.58 s    -48 o 38 '  43.64 " 
 ERROR BOX CORNER 1: 08 h 00 m 43.70 s    -48 o 38 '  11.00 " 
 ERROR BOX CORNER 2: 07 h 59 m 43.77 s    -48 o 36 '  59.65 " 
 ERROR BOX CORNER 3: 08 h 00 m 51.42 s    -48 o 40 '  27.43 " 
 ERROR BOX CORNER 4: 07 h 59 m 51.46 s    -48 o 39 '  16.15 " 



This error box can be improved.

P.A. Price, B.P. Schmidt (RSAA, ANU) and T.S. Axelrod (Arizona) report:

We have observed the error box of GRB 020418 (GCN #1376
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 ) with the robotic
MSO 50-inch telescope + MACHO imager at 2002 Apr 19.42 UT (approximately
25.5 hours after the GRB) with 3 x 300 sec exposures.  The combined image
covers the entire error box down to a limiting magnitude of R ~ 21.1 mag,
based on comparison with USNO-A2.0 magnitudes.  We do not find any
convincing afterglow candidate upon visual comparison with the second
Digitised Sky Survey down to the plate limit, R ~ 20.5 mag.

Further observations are planned.

This message may be cited.

P.A. Price, B.P. Schmidt (RSAA, ANU) and T.S. Axelrod (Arizona) report:

We have re-observed the error box of GRB 020418 (GCN #1376
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 ) with the
robotic MSO 50-inch telescope + MACHO imager at 2002 Apr 20.41 UT to
search for variable sources that might be the afterglow.  On PSF-matched
image subtraction from our first epoch image (GCN #1377
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 ), we do not find
any afterglow candidate to the limiting magnitude of our first epoch
images (R ~ 21.2 mag).

This message may be cited.

J. Gorosabel* (IAA-CSIC Granada), J. Hjorth, P. Jakobsson, J. Rasmussen, 
B. L. Jensen, H. Pedersen (Univ. of Copenhagen), J. M. Castro Ceron* 
(ROA San Fernando), A. Hornstrup (DSRI Copenhagen), A.O. Jaunsen (ESO Paranal),
M. Weidinger, J. Fynbo* (IFA Aarhus), M. I. Andersen (Univ. of Oulu),
P. Moller  (ESO Garching), S. Holland (Univ. of Notre Dame),
A. J. Castro-Tirado (IAA-CSIC Granada), E. Pian (INAF, OA Trieste),
A. Fruchter (STScI, Baltimore), J. Greiner (MPE Garching and AI Potsdam),
L. Kaper, E. van den Heuvel (Univ. of Amsterdam), on behalf of the GRACE 
collaboration, report:

We summarise the results of an optical and near-infrared search for the
afterglow of GRB 020418 carried out with the 1.54-m Danish Telescope and 
the 3.58-m New Technology Telescope, both at ESO's La Silla observatory.

The log of the observations is displayed in the following table:

 =========================================================================
       Date UT       Filter ExpTime Telescope   Seeing Time since Error box
       2002                   (s)  (+Instrument) (")   GRB (days) Coverage (%)
 --------------------------------------------------------------------------
 April 19.9435--20.0066 Ks  45x60 3.58NTT(+SOFI) 0.65    1.6150    60**
 April 19.9445--19.9935 J   20x60 3.58NTT(+SOFI) 0.65    1.6089    60**
 April 19.9760--20.0507 R  10x420 1.54D(+DFOSC)  1.05    1.6532    100
 April 20.9541--21.0177 Ks  45x60 3.58NTT(+SOFI) 0.70    2.6258    60**
 April 20.9551--21.0052 J   20x60 3.58NTT(+SOFI) 0.70    2.6200    60**
 April 20.9720--21.0340 R   6x500 1.54D(+DFOSC)  0.90    2.6429    100
 June  01.9642--02.0267 R   9x500 1.54D(+DFOSC)  1.90   44.6353    100
 June  02.9592--03.0155 R   8x500 1.54D(+DFOSC)  1.40   45.6273    100
 --------------------------------------------------------------------------
 ** Central part
 ==========================================================================

Comparison of the images reveals no variable source contained in the error
box brighter than R = 23.0. Correcting for the effect of the Galactic 
extinction, the R-band upper limit corresponds to R = 22.3. 

For the central part of the error box (the 60% of the error box covered for 
SOFI) we can set limits of Ks >= 21.0, J >= 22.6 and R >= 22.3 for any 
variable source (magnitudes corrected for Galactic reddening).

We acknowledge the assistance of L. Vanzi at La Silla.

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* Visiting the Astronomical Observatory of the University of Copenhagen.