////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1315
SUBJECT: GRB020331(=H1963): The "Easter" Burst Detected by HETE
DATE:    02/03/31 21:05:38 GMT
FROM:    George Ricker at MIT  <grr@space.mit.edu>

GRB020331(=H1963): The "Easter" Burst Detected by HETE

G. Ricker, J-L Atteia, N. Kawai, D. Lamb, and S. Woosley on behalf of 
the HETE Science Team;

R. Vanderspek, J. Villasenor, G. Crew, J. Doty, G. Monnelly, N. 
Butler, T. Cline, J.G. Jernigan, A. Levine, F. Martel, E. Morgan, G. 
Prigozhin, J. Braga, R. Manchanda, and G. Pizzichini, on behalf of 
the HETE Operations and HETE Optical-SXC Teams;

Y. Shirasaki, M. Matsuoka, T. Tamagawa, K. Torii, T. Sakamoto, A. 
Yoshida, E. Fenimore, M. Galassi, T. Tavenner, T. Donaghy, and C. 
Graziani, on behalf of the HETE WXM Team;

M. Boer, J-F Olive, J-P Dezalay, and K. Hurley on behalf of the HETE 
FREGATE Team;

write:


At 16:32:28.76 UTC (59548.76 s UT) on 31 March 2002, the HETE FREGATE 
and WXM instruments detected event H1963, a long (~50 sec) GRB. A GCN 
Alert Notice was issued at 16:39:31 UT. A preliminary localization 
was reported as a GCN Position Notice at 17:12:51 UT, ~40 min after 
the burst. The ground analysis has produced a refined location which 
can be expressed as a circle with a 90% confidence radius of 8 
arcminutes centered at:

RA = 13h 16m 22s.7, Dec = -17o 55' 23" (J2000)

In the FREGATE 8-40 keV band, H1963 had a duration of ~20 seconds.  A 
total of 2320 net counts were detected during that interval, 
corresponding to a fluence of ~4 x 10-7 ergs cm-2. The peak flux 
averaged over 0.85 s was ~1 x 10-7 ergs cm-2 s-1 (ie 4 x Crab flux). 
In the WXM 2-25 keV band, the localization SNR was >9.

Further information (including a light curve) for GRB020331is 
provided at the following URL:

http://space.mit.edu/HETE/Bursts/

This message is citable.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1316
SUBJECT: GRB 020331: Optical observations
DATE:    02/03/31 22:51:51 GMT
FROM:    Paul Price at RSAA, ANU at CIT  <pap@srl.caltech.edu>

P.A. Price and M.C. Begam (RSAA, ANU) report:

We have imaged the error-circle of GRB 020331 with the SSO
40-inch telescope + direct imager at 2002 Mar 31.79 UT
(approximately 2.5 hours after the burst).  Our images consisted
of individual 600 sec exposures and covered approximately 60%
of the refined HETE error circle (Ricker et al., GCN #1315) down
to approximately R ~ 19.3 mag.  We do not find any afterglow
candidate from visual comparison of our images with the Digitised
Sky Survey.

Further observations are planned.

This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1317
SUBJECT: GRB 020331, NIR observations
DATE:    02/04/01 16:27:37 GMT
FROM:    Sylvio Klose at TLS Tautenburg  <klose@tls-tautenburg.de>

S. Klose (Thueringer Landessternwarte Tautenburg),
H. Dannerbauer, J. Greiner (MPE Garching, AIP Potsdam), 
F. J. Vrba (USNO), A. Henden (USRA/USNO),
D. H. Hartmann (Clemson University),
J. Snigula (Universitaetssternwarte Muenchen),
U. Thiele (MPIA Heidelberg, Calar Alto), 
A.J. Castro-Tirado, J. Gorosabel (LAEFF-INTA, Madrid, and IAA-CSIC, Granada), 
J.M. Castro Ceron (ROA San Fernando),
and 
E. Pian (INAF, Astr. Obs. Trieste), 

on behalf of an even larger GRB team

report:


The r=8 arcmin error circle of the HETE burst GRB 020331 (Ricker et al., 
GCN #1315) was imaged in the K' band on April 1, 0:02 UT - 1:22 UT, 
using the Calar Alto 3.5-m telescope equipped with the Omega Prime
near-infrared camera (1k x 1k; fov about 6.7 x 6.7 arcmin). A mosaic
was taken to cover the whole error box. The integration time per field was
10 min. The limiting magnitude is about K'=19. Because of unstable
weather conditions about 10% of the error box have not been imaged.
About 20% of the frames are affected by a bad sky.

Based  on a visual comparison with the corresponding DSS2 red images we 
find a best afterglow candidate at coordinates  

        RA, DEC (J2000) = 13:16:15.0, -17:55:04   +/- 2 arcsec

very close to the bulge of an extended galaxy. 

The only reason why we prefer this object at the moment is a) it
seems that it has no counterpart on the DSS2 red survey and b) it is
relatively bright in K'. At the moment we can only provide a rough
estimate of its magnitude: K' = 17 +/- 1. We stress that this
is not based on second epoch imaging, i.e. no fading behavior has yet 
been found.

Further observations are in progress.


This message is quotable.

[GCN OPS NOTE (03apr02):  J.M. Castro Ceron was added to the author list.]

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1318
SUBJECT: GRB 020331 Optical Observations
DATE:    02/04/01 19:27:42 GMT
FROM:    Dieter Hartmann at Clemson.U  <hartmann@grb.phys.clemson.edu>

D. H. Hartmann (Clemson University)

reports on behalf of the SARA consortium GRB Team: 

We imaged the error-circle of GRB020331 (Ricker et al., GCN1315)
with the SARA 0.9m telescope at KPNO, starting at 02/04/01-05:25UT.
Two sets of ten R-band and ten I-band images were taken with 3 min
exposure centered on two positions:

RA, DEC (J2000) = 13:16:22.7, -17:55:23
RA, DEC (J2000) = 13:16:42.4, -17:55:23

Comparison with the Digitised Sky Survey red plates suggests a limiting
magnitude of R ~ 19 for each of the individual exposures. 

This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1319
SUBJECT: GRB020331 field photometry
DATE:    02/04/01 22:53:06 GMT
FROM:    Arne A. Henden at USNO/USRA  <aah@nofs.navy.mil>

A. Henden (USRA/USNO) reports on behalf of the USNO GRB team:

We have acquired BVRcIc all-sky photometry for
an 11x11 arcmin field centered at the HETE coordinates
for GRB020331 (Ricker et al. GCN 1315) with the USNOFS
1.0-m telescope on one photometric night.  Stars
brighter than V=14.0 are saturated and should be used with care.
We have placed the photometric data on our anonymous ftp site:
ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb020331.dat
The astrometry in this file is based on linear plate solutions
with respect to USNO-A2.0.  The internal errors are less than 100mas.

If an afterglow is detected, we will update this file
with additional photometric nights.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1320
SUBJECT: GRB02033 NIR observation at KPNO
DATE:    02/04/02 01:50:29 GMT
FROM:    Atsumasa Yoshida at Inst.Phys/Chem Research  <ayoshida@postman.riken.go.jp>

K. Ohta (Kyoto Univ.) and M. Akiyama (Subaru) report:

We have imaged the central region of the error circle of
GRB 020331 with the SQIID equipped to KPNO 2.1m telescope.
The field is centered on 13h16m22.7s and -17d55'23" (J2000)
with a field of view of about 5'x5'.
The J-, H-, and K-band images were taken simultaneously
at 7:06 (Apr 1st) (UT).  A total integration time is 15min 
for each band.
We have found the following two NIR objects that are not seen 
in the Digitized Sky Survey, APM catalog, and 2MASS images.
 
#1 13h16m29.5s -17d55'08" (J2000), J=17.7, H not measurable, K=16.8 
#2 13h16m23.2s -17d56'11" (J2000), J=17.6, H=17.2, K=16.8 
 
Accuracy of the coordinates is about 0.5". 
Photometry was roughly made using 2MASS objects   
exposed in the same frame; accuracy seems to be less than
0.1 mag (J-band), 0.3 mag (H-band), and 0.5 mag (K-band).
There is a possibility that these objects are not seen in
the POSS merely because they are red objects. 
If one of them will fade, it should be a candidate of the
afterglow of the GRB.  Further NIR observations are desirable. 
 
This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1321
SUBJECT: GRB020331 NIR observation at KPNO (re-submission)
DATE:    02/04/02 02:50:44 GMT
FROM:    Atsumasa Yoshida at Inst.Phys/Chem Research  <ayoshida@postman.riken.go.jp>

In the previous submission (GCN1320), there was an error in
the subject-line.  
This is the revised version but contains the same information 
about the obseration as in GCN1320. 

-------------------------------------------------------

K. Ohta (Kyoto Univ.) and M. Akiyama (Subaru) report:

We have imaged the central region of the error circle of
GRB 020331 with the SQIID equipped to KPNO 2.1m telescope.
The field is centered on 13h16m22.7s and -17d55'23" (J2000)
with a field of view of about 5'x5'.
The J-, H-, and K-band images were taken simultaneously
at 7:06 (Apr 1st) (UT).  A total integration time is 15min 
for each band.
We have found the following two NIR objects that are not seen 
in the Digitized Sky Survey, APM catalog, and 2MASS images.
 
#1 13h16m29.5s -17d55'08" (J2000), J=17.7, H not measurable, K=16.8 
#2 13h16m23.2s -17d56'11" (J2000), J=17.6, H=17.2, K=16.8 
 
Accuracy of the coordinates is about 0.5". 
Photometry was roughly made using 2MASS objects   
exposed in the same frame; accuracy seems to be less than
0.1 mag (J-band), 0.3 mag (H-band), and 0.5 mag (K-band).
There is a possibility that these objects are not seen in
the POSS merely because they are red objects. 
If one of them will fade, it should be a candidate of the
afterglow of the GRB.  Further NIR observations are desirable. 
 
This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1322
SUBJECT: GRB 020331: NIR Observations
DATE:    02/04/02 03:19:48 GMT
FROM:    Paul Price at RSAA, ANU at CIT  <pap@srl.caltech.edu>

P.A. Price (RSAA, ANU), C.G. Tinney (AAO) and B.P. Schmidt (RSAA, ANU)
report:

We observed the northern half of the error-circle of GRB 020331
with the Anglo-Australian Telescope + IRIS2 at approximately 2002 Mar
31.79 UT in Ks.  The afterglow candidates of Ohta & Akiyama (GCN #1320)  
are contained within the region covered by these observations.  Each of
these candidates appear to have a constant flux, within the errors.
Specifically, we find that sources 1 and 2 of Ohta & Akiyama are
approximately 3.53 and 3.65 magnitudes fainter than a reference star at
13:16:30.08 -17:55:48.0 J2000 (+/- 0.5 arcsec), which from 2MASS has
Ks = 12.99 +/- 0.05 mag.  Given the large log(time) difference between the
observations, it is likely that neither of these sources is the afterglow
of GRB 020331.

This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1323
SUBJECT: GRB 020331: NIR Observations
DATE:    02/04/02 06:27:32 GMT
FROM:    Paul Price at RSAA, ANU at CIT  <pap@srl.caltech.edu>

S. Klose (Thueringer Landessternwarte Tautenburg) and
P.A. Price (RSAA, ANU) report:

We have compared images obtained from the CAHA 3.5-m telescope (GCN #1317)
with images from the AAT 3.9-m telescope (GCN #1322) at the position of
the candidate afterglow (GCN #1317).  While the candidate is not clearly
resolved from the nearby galaxy in the images from the AAT, it is of a
similar brightness in each of the two observations.  Subtraction of the
two images demonstrates that the candidate is not strongly variable
between these two observations.  The candidate is therefore not likely the
afterglow of GRB 020331.

This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1334
SUBJECT: GRB 020331: Candidate Optical Afterglow
DATE:    02/04/07 06:37:50 GMT
FROM:    Derek Fox at CIT  <derekfox@astro.caltech.edu>

D.W. Fox, P.A. Price, and S.A. Yost (Caltech), with R. Burruss
(Palomar Observatory), C.G. Tinney (AAO), and M. Begam and
B.P. Schmidt (RSAA, ANU) report:

"We have observed the error box of GRB 020331 (GCN #1315) with the
Palomar Hale 200-inch telescope + LFC at 2002 Apr 1.40 and 2.38 UT in
Sloan i'.  Our observations cover the full burst localization to a
limiting equivalent R-band magnitude (derived by reference to a single
USNO star) of R ~ 23 mag.  Visual inspection of the difference image
reveals one afterglow candidate at coordinates

	RA: 13:16:09.54   Dec: -17:55:15.9   J2000

with an estimated uncertainty of 0.5 arcsec in each coordinate.  The
candidate faded by 0.6 mag between the two observations, implying a
power-law decay index of alpha ~ 0.6, which would be unusual for a
normal afterglow.  The candidate was R ~ 21 mag at the epoch of our
first observation, 17 hours after the burst trigger time of Mar 31.689
UT (GCN #1315).

The candidate is weakly detected on earlier images from the SSO
40-inch telescope, obtained Mar 31.78, which have a limiting magnitude
of R ~ 19.5 mag.  The source is also detected on Mar 31.79 Ks-band
images from the AAT (c.f. GCN #1322).  The candidate is not visible on
the second Digitized Sky Survey.

A finding chart for the candidate may be found at:

	http://darkalf.caltech.edu/~pap/grb020331finder.ps

This message may be cited."

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1339
SUBJECT: GRB020331: Optical Observations of Afterglow Candidate
DATE:    02/04/08 17:15:16 GMT
FROM:    George Ricker at MIT  <grr@space.mit.edu>

GRB020331: Optical Observations of Afterglow Candidate

G. Monnelly, A. Dullighan, N. Butler, R. Vanderspek, G. Ricker (MIT)

write:

We observed the HETE error circle of GRB020331 (Ricker et al., GCN
#1315) with the Baade 6.5m telescope at Magellan on 2002 April 1.22 UT
using LDSS-2.  The observations took place 12.7 hours after the burst.
Seven 90s R-band exposures were used to mosaic the entire HETE error
circle. The limiting magnitude was R = 23.5, with 0.6" seeing.

We detect the afterglow candidate reported by Fox et. al. (GCN #1334)
at R = 21.05 +/- 0.11.  In comparison to their finding chart, the OT
is clearly separated in our image from the stellar object 3.9 arcsec
to the southeast, and we detect the reference star at R = 18.52 +/-
0.11.  Magnitudes are calibrated against star G020331 (R = 18.945)
from the photometry of Henden et. al. (GCN #1319).

Further, Fox et. al. (GCN #1334) report a weak detection of the
candidate on Mar 31.78, in observations having a limiting magnitude
of R ~ 19.5 mag.  If we take R = 19.5 as an upper limit on the magnitude
at this epoch, then our observations constrain the power law decay
index to be steeper than alpha = 0.8.

This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1344
SUBJECT: GRB020331 optical observations with RIMOTS
DATE:    02/04/09 03:28:11 GMT
FROM:    Yuji Urata at RIKEN  <urata@crab.riken.go.jp>

 N. Kawai, Y. Urata (Titech/RIKEN), M. Kohama, K. Torii (RIKEN),
 A. Yoshida (AGU/RIKEN), K. Ayani, T. Kawabata (Bisei Astronomical
 Observatory), M. Chaya, H. Shibata, K. Sakamoto, M. Yamauchi (Miyazaki
 Univ.)  on behalf of the RIBOTS/RIMOTS team
 
  We have observed covering the entire error circle of GRB020331
 (Ricker et al. GCN 1315) field with the RIMOTS 30-cm telescope.  The
 observations started at an early epoch (+1.6 hours after the burst).
 All the images were taken with 15 sec exposure and stacked for deeper
 inspection.
 
  From a comparison with the DSS-2 images we did not identify any new
 point source for the GRB.  We summarize the observing time and the
 R-band limiting magnitude (SN=3), which was estimated by the
 comparison of our non-filter data with the R band field photometry by
 Henden (GCN 1319).
 
 Summary of observations on 2002/03/31
  Time(UT)     Limiting R mag
  start end    (SN=3)
  18:10 18:59  14.9          15s x 39 frames combined
  19:00 19:59  14.2          15s x 51 frames combined
  20:00 20:12  13.7          15s x 13 frames combined
 
 This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1346
SUBJECT: GRB020331: Confirmation of Afterglow Candidate with Magellan
DATE:    02/04/09 15:28:42 GMT
FROM:    George Ricker at MIT  <grr@space.mit.edu>

GRB020331: Confirmation of Afterglow Candidate with Magellan

A. Dullighan, G. Monnelly, N. Butler, R. Vanderspek, G. Ricker (MIT)

write:

We obtained second epoch observations of the HETE error circle of 
GRB020331 (Ricker et al., GCN #1315) with the Baade 6.5m telescope at 
Magellan on 2002 April 9.06 UT using LDSS-2. The observations took 
place 8.37 days after the burst, and 7.84 days after our first epoch 
observations (Monnelly et al., GCN #1339). Two 200s R-band exposures 
were used to image a 7.5 arcmin diameter region centered on the 
coordinates of the afterglow candidate first reported by Fox et. al. 
(GCN #1334).

In our second epoch observations, we detect the afterglow candidate 
at R = 22.9 +/- 0.14. In comparison to our first epoch measurement, 
with exactly the same instrument configuration, the afterglow 
candidate has declined by 1.8 +/- 0.2 magnitudes in R. As in our 
first epoch observations, magnitudes are calibrated against star 
G020331 (R = 18.945) from the photometry of Henden et. al. (GCN 
#1319).

Combining our first and second epoch observations, the power law 
decay index of the afterglow candidate is well-determined as alpha = 
0.62 +/- 0.1. We conclude that the Fox et al candidate is indeed the 
optical afterglow of GRB020331.

This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1363
SUBJECT: GRB 020331 Kyoto observation on March 31
DATE:    02/04/12 08:33:28 GMT
FROM:    Taichi Kato at Kyoto U  <tkato@kusastro.kyoto-u.ac.jp>

T. Kato (Kyoto U.), H. Yamaoka (Kyushu U.), R. Ishioka, M. Uemura
(Kyoto U.) report on behalf of the VSNET GRB team:

   We observed GRB 020331 (=H1963, the "Easter" burst detected by HETE,
GCN 1315) using unfiltered ST-7E CCD cameras on 25-cm and 30-cm telescopes
located at Kyoto University.

   The initial exposure started at 17h 19m 42s (7 min after the burst
localization, 47 min after the burst detection).  PSF photometry of
measurable 24 images yielded 2.0-sigma detection at the reported
afterglow (GCN 1339).  The object was found to be 6.4 mag (on 31.734 UT,
average of exposures) fainter than GSC 6166.129.  After a link with field
photometry by Henden (GCN 1319), we obtained a magnitude of 17.9 (system
close to Rc), with 1-sigma limits of 17.5-18.7.  The magnitude seems to be
marginally brighter than the extrapolation with the reported power index
(GCN 1346).

   The observation not only makes the earliest positive detection of
a GRB afterglow detected by HETE, but also makes the first evidence
that a GRB optical afterglow within ~1 hour of the burst can be at least
as bright as expected from the later power-law decay.

This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1382
SUBJECT: GRB020331: Third Epoch and Revised Second Epoch Optical
DATE:    02/04/24 21:11:54 GMT
FROM:    George Ricker at MIT  <grr@space.mit.edu>

GRB020331: Third Epoch and Revised Second Epoch Optical Observations 
with Magellan

A. Dullighan, G. Monnelly, N. Butler, R. Vanderspek, G. Ricker, Z. 
Wang (MIT); P. Challis, R. Kirshner (CfA)

write:

We obtained third epoch observations of the HETE error circle of 
GRB020331 (Ricker et al., GCN #1315) with the Baade 6.5m telescope at 
Magellan on 2002 April 13.21 UT using MagIC. The observations took 
place 12.53 days after the burst, and 12.00 days after our first 
epoch observations (Monnelly et al., GCN #1339). One 300s and three 
600s R-band exposures were stacked to image a 2 arcmin square region 
centered on the coordinates of the afterglow candidate first reported 
by Fox et. al. (GCN #1334).

Further calibration of the data from our second epoch observations 
has led to a revised magnitude estimate of R = 23.1 +/- 0.2 at 8.37 
days after the burst (cf. R = 22.9 initially reported in GCN #1346). 
We still place the magnitude of the first epoch observations at R = 
21.1 +/- 0.2 at 0.53 days after the burst.  This leads to a nominal, 
revised power law decay index of alpha = 0.67 +/- 0.1. However, the 
decay is likely to be significantly steeper than would be indicated 
by this nominal index, for the reasons given below.

In our third epoch observations, we measure an R magnitude of 23.2 
+/- 0.3 using aperture photometry at the position of the counterpart, 
consistent with the brightness at epoch 2. As in our first epoch 
observations, magnitudes are calibrated against star G020331 (R = 
18.945) from the photometry of Henden et. al. (GCN #1319).

Furthermore, we find that the emission centroid of the third epoch 
image is offset by  0.8" +/- 0.1" to the east. Our image reveals a 
source extended E-W through the position of the counterpart. We 
interpret the extended source to be the host galaxy of the optical 
counterpart: the GRB optical counterpart has faded below the 
directly-detectable limit, and our aperture photometry at all epochs 
includes the centroid of the host galaxy. In the third epoch image, 
we estimate that almost all of the detected light originates in the 
putative host galaxy. PSF subtraction of a 23.2 magnitude point 
source at the centroid of the galaxy leaves a faint residual source 
at the position of the counterpart, with an R magnitude of ~25. Due 
to the contamination by the putative host galaxy at the earlier 
epochs, the power law decay of the counterpart is likely to be 
steeper than we reported in GCN #1339 and GCN #1346.

This message may be cited.

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1459
SUBJECT: GRB020331: Late-time Optical Light Curve
DATE:    02/07/24 16:15:14 GMT
FROM:    Alicia Soderberg at Caltech  <ams@astro.caltech.edu>

A. M. Soderberg, D. W. Fox, and S. R. Kulkarni (Caltech) report
on behalf of the larger Caltech-NRAO-CARA GRB collaboration.

"We have observed the optical afterglow associated with GRB 020331
(GCN 1334) with HST+STIS (Clear) at four epochs spanning the period
25-50 days following the burst (one orbit per epoch).

Registration of the STIS data against ground-based images allows us to
identify the afterglow amidst a complex of at least three galaxies,
including the presumed host galaxy which lies under the afterglow
itself.  Aperture photometry on the optical transient + host yields
the following R-equivalent magnitudes for the first three epochs:

    HST Epoch   T (days since burst)     R (mag)
       1        23.9                     24.54 +/- 0.07
       2        36.6                     25.01 +/- 0.10
       3        42.7                     24.76 +/- 0.09

We have derived our R-equivalent magnitudes by assuming
(R-Clear)=-0.67 as given by the STIS Exposure Time Calculator for
a source with power-law spectrum (index=-1).
These values imply a power-law flux decay index over this interval with
index alpha=0.75, compatible with previous ground-based estimates
(Ricker et al., GCN 1382).

Preliminary analysis of the fourth epoch, T=50 days, indicates a
rebrightening of the optical afterglow by 0.2 +/- 0.1 mag as compared
with our Epoch 3.  We have requested additional HST observations to
help us clarify whether this rebrightening is statistically significant.

A finding chart of the field can be found at:

	http://www.astro.caltech.edu/~ams/grb020331.html

This message may be cited."

////////////////////////////////////////////////////////////////////////
TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1460
SUBJECT: GRB020331: Late-time Optical Light Curve (re-submission)
DATE:    02/07/24 19:13:51 GMT
FROM:    Alicia Soderberg at Caltech  <ams@astro.caltech.edu>

In the previous submission (GCN 1459), there is a misprint
in the table of magnitudes.  We report the correct values below.
The revised version of the GCN follows:

    HST Epoch   T (days since burst)     R (mag)
       1        23.9                     24.54 +/- 0.07
       2        36.6                     24.86 +/- 0.10
       3        42.7                     25.01 +/- 0.09
       4        49.3                     24.76 +/- 0.11
--------------------------------------------------------------------
A. M. Soderberg, D. W. Fox, and S. R. Kulkarni (Caltech) report
on behalf of the larger Caltech-NRAO-CARA GRB collaboration.

"We have observed the optical afterglow associated with GRB 020331
(GCN 1334) with HST+STIS (Clear) at four epochs spanning the period
25-50 days following the burst (one orbit per epoch).

Registration of the STIS data against ground-based images allows us to
identify the afterglow amidst a complex of at least three galaxies,
including the presumed host galaxy which lies under the afterglow
itself.  Aperture photometry on the optical transient + host yields
the following R-equivalent magnitudes for the four epochs:

    HST Epoch   T (days since burst)     R (mag)
       1        23.9                     24.54 +/- 0.07
       2        36.6                     24.86 +/- 0.10
       3        42.7                     25.01 +/- 0.09
       4        49.3			 24.76 +/- 0.11

We have derived our R-equivalent magnitudes by assuming
(R-Clear)=-0.67 as given by the STIS Exposure Time Calculator for
a source with power-law spectrum (index=-1).
The first three epochs imply a power-law flux decay index over this
interval with index alpha=0.75, compatible with previous ground-based
estimates (Ricker et al., GCN 1382).

Preliminary analysis of the fourth epoch, T=50 days, indicates a
rebrightening of the optical afterglow by 0.2 +/- 0.1 mag as compared
with our Epoch 3.  We have requested additional HST observations to
help us clarify whether this rebrightening is statistically significant.

A finding chart of the field can be found at:
http://www.astro.caltech.edu/~ams/grb020331.html

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