TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  2632
SUBJECT: GRB040624: optical monitoring at TNG
DATE:    04/07/26 14:25:43 GMT
FROM:    Stefano Covino at Brera Astronomical Observatory  <covino@merate.mi.astro.it>

P. D'Avanzo, D. Fugazza, A. Melandri, D. Malesani, G. Tagliaferri, L.A.
Antonelli, S. Campana, G. Chincarini, S. Covino, A. Cucchiara, M. Della
Valle., G.L. Israel, S. Kalogerakos, N. Masetti, E. Pian, L. Stella, L.
Di Fabrizio, M. Pedani, report on behalf of a larger collaboration:

We continued monitoring the field of the INTEGRAL GRB 040624 (Mereghetti
et al., GCN 2613), in order to look for a possible supernova (SN). Our
search was carried out to test the hypotesis that GRB 040624 exploded
inside the Abell cluster A1651 at z=0.0845, whose galaxies were detected
in our previous optical images (Fugazza et al., GCN 2617). Observations
were performed with the Italian Telescopio Nazionale Galileo (TNG),
equipped with the DOLORES camera, under good conditions. The observing
log is reported below:

UT start    t-t0 (d)  t_exp   seeing  filters  R_lim (10 sigma)
---------------------------------------------------------------
Jul  6.92   12.6      3x180s  1.4"    VRI      22.6
Jul 14.92   20.6      2x180s  1.3"    VRI      22.0
--------------------------------------------------------------- 
t0 = 2004 Jun 24.35 UT (burst onset)

No significantly varying sources were found by comparing the images
taken at these two epochs, nor by comparing these with our earlier
measurements (GCN 2617). PSF-matched image subtraction carried out with
the ISIS package also yielded no convincing candidates.

If GRB 040624 occurred inside a galaxy belonging to the cluster, its
peak luminosity would be L ~ 9x10^47 erg/s, intermediate between those
of GRB980425 at z=0.0085 and GRB 031203 at z=0.1055. A SN similar to
SN1998bw would reach a peak magnitude R ~ 18.5 and would be easily
detectable in our images even if spatially coincident with a relatively
bright host galaxy.  However, intrinsic obscuration may play a
significant role in depressing the SN flux. Moreover, an intrinsically
dimmer SN than SN1998bw cannot be excluded. 

Therefore, the lack of a SN detection in our images does not allow us to
draw conclusions about the distance of the GRB.


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