GRB020405 - VLT observations

GRB020405

R-band image taken with VLT-UT3 (Melipal)

2002 April 15.244: Melipal + FORS1

Melipal+FORS1 R image

The field of GRB020405 imaged in the R band on 2002 April 15.244. The tick marks indicate the OT. North is at top, East is to the left; the field size is about 25 x 25 arcsec. At least four extended objects around the OT (one to the East, one to the Northwest, one below and extending to the South, and one to the Southwest) appear to form a complex behaviour for this GRB.

GCN Circular no. 1375

GRB020405: VLT observations of the OT environment

N. Masetti, E. Palazzi (IASF/CNR, Bologna), E. Maiorano, A. Simoncelli (U. Bologna), E. Pian (INAF, OA Trieste), A. Castro-Tirado (IAA-CSIC, Granada), A. Fruchter (STScI, Baltimore), J. Greiner (MPE Garching and AI Potsdam), J. Hjorth (U. Copenhagen), L. Kaper, E. van den Heuvel (U. Amsterdam), R. Cabanac, A. Kaufer (ESO), on behalf of the GRACE Collaboration, report:

"We have obtained an R-band image (2 x 3 minutes integration) of GRB020405 from VLT-UT3 (Melipal) plus FORS1 on 2002 Apr. 15.244 under a seeing of 0.65 arcsec.

We find that the OT is located within a complex environment composed of at least four extended objects, one of which is underlying the OT and showing a bright knot (possibly a star-forming region, or alternatively the host nucleus) ~1 arcsec south of the OT itself.

Also, the presumed host galaxy indicated by Hjorth et al. (GCN #1329) and located ~2 arcsec southwest of the OT seems not to be the actual host but a galaxy which is likely interacting with it. Indeed, a spectrum of this galaxy taken with Melipal+FORS1 on 2002 April 7.310 shows that it is at the same redshift of the OT (GCNs #1330, #1340).

This finding strengthens the suggestion that GRBs are sometimes associated with interacting galaxies possibly displaying substantial star formation, as seen e.g. for GRB001007 (Castro Cerón et al. 2002, A&A, in press [astro-ph/0110049]).

No suggestion of a break in the light curve (see GCN #1369) is apparent up to ~10 days after the GRB. However, in the VLT image reported above, the OT brightness is already substantially contamined by the host emission. For this reason it would be quite difficult to see any future possible break in the OT light curve with ground-based observations.

A close-up of the VLT R-band image around the OT can be found at:

http://tonno.tesre.bo.cnr.it/~masetti/grb020405.html

This message can be cited.".

The BeppoSAX-GRB team in Bologna
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