GCN Circular 1002
Subject
GRB 010222, Optical Observations
Date
2001-03-02T21:19:06Z (23 years ago)
From
Stephen Holland at U. of Notre Dame <sholland@nd.edu>
An Early Break in the Optical Light Curve of GRB 010222
Stephen Holland (Notre Dame)
Johan Fynbo (ESO)
Javier Gorosabel (DSRI)
Arne Henden (USNO)
Jens Hjorth (Copenhagen)
Brian Jensen (Copenhagen)
Holger Pedersen (Copenhagen)
We have obtained deep Cousins R-band images of the optical
afterglow associated with GRB 010222 using the 2.5m Nordic Optical
Telescope (NOT) at La Palma and the USNO 1.0m telescope at Flagstaff
Station. Preliminary magnitudes, using Rc = 17.175 for Stanek's
(2001a, GCN 970) Star "A", as calibrated by Henden (2001, GCN 987),
are:
UT(middle) Rc err Telescope
-----------------------------------------------
2001:02:23.0102 19.733 0.014 NOT
2001:02:23.0171 19.707 0.013 NOT
2001:02:23.0216 19.739 0.012 NOT
2001:02:23.0844 19.829 0.011 NOT
2001:02:23.0889 19.852 0.010 NOT
2001:02:23.1463 19.933 0.009 NOT
2001:02:23.1661 19.960 0.014 NOT
2001:02:23.2116 20.031 0.009 NOT
2001:02:23.2858 20.126 0.018 NOT
2001:02:24.0701 20.950 0.024 NOT
2001:02:24.1313 20.975 0.024 NOT
2001:02:24.1358 21.012 0.025 NOT
2001:02:24.1410 21.052 0.025 NOT
2001:02:24.1579 21.006 0.023 NOT
2001:02:24.1750 21.043 0.025 NOT
2001:02:24.1863 21.000 0.023 NOT
2001:02:24.2469 21.035 0.022 NOT
2001:02:25.0534 21.536 0.057 NOT
2001:02:25.0579 21.426 0.058 NOT
2001:02:25.2535 21.638 0.044 NOT
2001:02:25.2583 21.667 0.041 NOT
2001:02:22.4874 18.39 0.05 USNO
2001:02:22.5241 18.51 0.05 USNO
2001:02:22.5236 18.67 0.06 USNO
2001:02:22.5385 18.66 0.06 USNO
2001:02:24.4632 21.23 0.06 USNO
-----------------------------------------------
In order to maintain as much uniformity as possible in the
photometry we first restrict ourselves to data taken with the NOT.
This data extends from 0.70 to 2.95 days after the burst and is
consistent with a single power law with a slope of -1.24 +/- 0.02 (Q <
99.954%).
We supplemented this data with R-band photometry of GRB 010222
from Stanek et al. (2001a, GCN 970), Price et al. (2001, GCN 973),
Orosz (2001, GCN 976), Stanek et al. (2001b, GCN 983), Masetti et
al. (2001, GCN 985), Oksanen et al. (2001, GCN 990), Stanek & Falco
(2001, GCN 991), Velentini et al. (2001, GCN 992), Watanabe et
al. (2001, GCN 993), and Veillet (2001, GCN 1000). All the photometry
was adjusted to the photometric zero points of Henden (2001a, GCN
987), except for that of Veillet (2001, GCN 1000), which was used "as
is". The photometry was corrected for Galactic extinction assuming a
reddening of E(B-V) = 0.023 and an R-band extinction of A_R = 0.061.
The complete data set is not consistent with a single power law
(Q < 0.001%). Photometry earlier than 0.33 days after the burst is
weakly consistent with a single power law with a slope of -0.71 +/-
0.13 (Q = 77.969%), and the photometry later than 0.57 days after the
burst is consistent with a single power law with a slope of -1.24 +/-
0.02 (Q = 99.990%). Fitting a broken power law (see Holland et al.,
2000, A&A, 364, 467 for the method) to the light curve yields a break
at 0.48 +/- 0.11 days (11.5 +/- 2.6 hours) after the burst, and slopes
of -0.72 +/- 0.13 before the break and -1.24 +/- 0.02 after the break
(Q = 99.991%). The smooth function of Beuermann et al. (1999, A&A,
352, L26) with slopes of -0.67 +/- 0.34 before the break, -1.29 +/-
0.06 after the break, and an exponent of 1.8 +/- 4.4 provides a
slightly better fit (Q = 99.998%) to the data than the broken power
law does. Our fits suggest that the break occurred rapidly between
0.33 and 0.57 days (8 and 14 hours) after the burst. A plot of the
light curve and the two fits, along with a deep composite image of the
field containing the GRB, is available at
"http://www.nd.edu/~sholland/grb/grb010222/index.html".
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