GCN Circular 4913

D. A. Kann (TLS Tautenburg), S. Covino (INAF/OABr) and D. Malesani (SISSA)
report:

We concur that the candidate afterglow of GRB 060323 reported by Kann & 
Stecklum (GCN 4909
Not found
 
 
) is faintly visible in the SDSS. The astrometry reported by
Kann & Stecklum (with errors of 0."7) is correct, but the object was misidentified.

The afterglow candidate reported by Covino et al. (GCN 4911
Not found
 
 
) is visible on the TLS Ic 
and Rc image and possibly on the V band image.

Photometry of the OT candidate by Covino et al. using the comparison star given
by Kann & Stecklum shows marginal evidence for fading, but the low S/N
makes it difficult to assess this with certainty.

Assuming the magnitude of 23.1 at 0.37 days after the GRB to be correct, this is 
one of the faintest afterglows ever discovered. The extinction along the line of sight 
is negligible (E(B-V)=0.015, Schlegel et al., 1998) and there are no indications of 
excess hydrogen column density in the X-ray afterglow (Vetere et al., GCN 4910
Not found
 
 
). This 
seems to exclude a large extinction within the GRB host galaxy. The afterglow is 
fainter at this epoch than all afterglows in the sample of Kann, Klose & Zeh (ApJ, in 
press, astro-ph/0512575), and also fainter than other faint OTs not in the sample.

Another explanation for the faintness may be that this is a high-redshift event, even 
though the BAT analysis (Parsons et al., GCN 4912
Not found
 
 
) shows no signs of extended 
low-level emission often seen in high-redshift events (e.g., GRB 050904).

We highly encourage NIR observations of the Covino et al. afterglow candidate to 
determine the colors and look for a possible Lyman dropout. Spectroscopy is also 
encouraged, but very large facilities will be needed.

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