GCN Circular 3064
Subject
GRB 050219b: candidate NIR afterglow
Date
2005-02-24T22:27:28Z (20 years ago)
From
Paolo D'Avanzo at INAF-OAB <davanzo@merate.mi.astro.it>
P. D'Avanzo, D. Fugazza, S. Covino, G. Tagliaferri, D. Malesani, L.A.
Antonelli, S. Campana, G. Chincarini, M. Della Valle, F. Fiore, L.
Stella, F.M. Zerbi, on behalf of the MISTICI collaboration report :
Optical and near-infrared monitoring of the field of GRB050219b
(Cummings et al., GCN 3044) was performed at the ESO-VLT, with the FORS2
and ISAAC instruments respectively. Observations were carried out under
a clear sky, starting 0.18 days after the GRB. The log is reported below.
Mean date (UT) t-t0 (days) filter seeing (")
----------------------------------------------
Feb 20.062 0.18 R 1.0
Feb 21.062 1.18 R 1.0
Feb 21.088 1.21 Ks 0.5
Feb 24.024 4.14 Ks 0.5
----------------------------------------------
t0 = Feb 19.879 UT (GRB trigger).
In the refined XRT position and error circle (Burrows et al., GCNs 3043;
Racusin et al., GCN 3049) we detect three sources in the Ks images:
1. RA: 05:25:15.99 Dec: -57:45:28.7
2. RA: 05:25:16.13 Dec: -57:45:30.5
3. RA: 05:25:15.59 Dec: -57:45:25.4
Source #2 and #3 do not exhibit significant variations (the latter being
also present in the 2MASS catalogue).
Source #1 is pointlike and is fading by 1.09 +- 0.19 mag in the Ks band
between 1.21 and 4.15 days after the burst. We therefore identify this
is the NIR afterglow of GRB050219b. The flux decay index (F =
K*t^-delta) is delta = 0.81 +- 0.14.
The candidate afterglow has a magnitude Ks = 21.47 +- 0.18 on Feb 24.02,
based upon field calibration with standard stars. We caution that we get
Ks = 16.45 +- 0.04 for the 2MASS star quoted above (source #3), which
has a tabulated magnitude K=15.345 in the 2MASS catalog.
In the R band, no source is detected at the position of the candidate
afterglow, down to a limiting magnitude R~23, based on calibration
against the USNO catalog.
Further observations are planned at the VLT.
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