GRB 030418

P.A. Price, R. McNaught, G.J. Garradd, M.A. Verrender and T.M. Smith
(RSAA, ANU) report:

We have observed the error-circle of HETE trigger #2686 (GRB 030418) with
the Siding Spring Observatory 40-inch telescope + Direct Imager.  Our
observations consisted of 5x300 sec exposures in R-band, commencing at
April 18.51 UT.  We identify in our images a source not present on the
DSS2 F or N plates.  The source has no apparent proper motion between
our images, and is located at:

	RA: 10:54:33.69   Dec: -7:01:40.8   J2000

with an estimated error of 0.5 arcsec.  We estimate that the source was 
R ~ 18.8 mag at the time of our observations.

Further observations are planned.

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P.A. Price, R. McNaught, G.J. Garradd, M.A. Verrender and T.M. Smith
(RSAA, ANU) report:

A finding chart for the GRB 030418 optical afterglow candidate (GCN #2148
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 )
is available from:

	http://www.mso.anu.edu.au/~pap/grb030418finder.ps

The offset from star A (marked) to the optical afterglow candidate is
29.02" W, 22.05" S.

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P.A. Price, R. McNaught, G.J. Garradd, M.A. Verrender and T.M. Smith
(RSAA, ANU) report:

We have re-observed the GRB 030418 optical afterglow candidate (GCN #2148
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 )
with the Siding Spring Observatory 40-inch telescope + Direct Imager.  
Our observations consisted of another 5x300 sec exposures in R-band,
commencing at April 18.61 UT.  Comparison of our two epochs reveals that
the source faded by about 1 magnitude between the two observations, being
R ~ 19.8 mag in the second epoch.  We therefore believe this source is the
optical afterglow of GRB 030418.

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H. Mito, S. Nishiura and Y. Urata on behalf of the Kiso GRB team:

" We have observed the field of GRB030418(=H2686) using the Kiso
observatory 1.05 m Schmidt telescope with near infrared camera KONIC.
The KONIC has circular field of view with 8.5'radius. We started to
observe the center region of HETE S/C_Update (Seq_Num 2) with J, H, Ks
band at 21 min after the burst. The afterglow reported Price et
al. (GCN2148
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 ) is out of these images.
 
 We re-pointed to the field including the afterglow position at 69 min
after the burst, . We obtained five J-band images with 300 s
exposures.

 We could not identify the afterglow with the limiting magnitude J ~
13 (3 sigma) at the 69 min after the burst. We estimated it comparison
with 2MASS J1054356-070118.

The more accurate analysis are in progress."

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W. M. Wood-Vasey, Lawrence Berkeley National Laboratory, using images
obtained by R. Bambery, S. Pravdo, M. Hicks, and K. Lawrence
(Near-Earth Asteroid Tracking project, Jet Propulsion Laboratory),
reports historical upper limits for the optical transient for 
GRB 030418 of Price et. al (GCN #2148
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 ) from images taken with the
Haleakala MSSS 1.2-m and Palomar Oschin 1.2-m telescopes from 
2001 Apr 19 -- 2003 Mar 28.

A co-addition of these images (Haleakala: 2001 Apr 19, May 7, 2002 Jan
8, Jan 14, Feb 4; Palomar: 2002 Feb 7, Feb 17, Mar 9, Apr 8, Apr 19,
May 11, 2003 Mar 28) shows nothing at this location to a combined
limiting magnitude of 22.81 (S/N = 3).

The co-addition is available at:

http://supernova.lbl.gov/~wwoodvas/GRB/#GRB030418

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All dates UT.

Smith, D. A., Rykoff, E. S., McKay, T. A. report on behalf of the ROTSE
collaboration:

The ROTSE-IIIa robotic telescope at Siding Springs Observatory, NSW, responded
automatically to the two HETE alerts for this burst, in each case beginning a
~45 minute sequence of unfiltered observations within six seconds of the alert
time stamp, the first of which was 238 s after the burst.  Each image sequence
began with 10 5-s images and then continued with 90 20-s images.

The 20-s images reached typical limiting magnitudes of 17.5 calibrated against
the USNO A2.0 catalog in R band, while the 5-second images reached
16.9. Sensitivity was degraded by the full moon.  Automated software searched
these frames for variable sources not in the USNO catalog and failed to
identify any counterpart candidates.  In particular, no source was initially
detected at the location of the optical counterpart reported by Price et al.
(GCN Circ. 2148
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 ).

Co-addition of multiple frames, however, yielded significant detections of the
optical transient.  We co-added our 200 observations into groups of ten, and
found that from 10:05:23 to 10:50:05, and again from 11:43:07 to 12:20:42, we
measure the transient to vary irregularly between 18.7 and 17.4, with errors of
order 0.15 mag.  This means that from 360 s to 2.3 h after the burst, the
transient showed no evidence for decay, in marked contrast to other bursts that
have been observed at early times, such as 990123 and 021211.

V. Lipunov, A. Krylov, V. Kornilov, G. Borisov, A. Belinski, I. Chilingarian,
D. Kuvshinov, M.V. Kuznetsov,  S. Potanin, V. Vitrischak

Sternberg Astronomical Institute, Alexsandr Krylov Observatory, Moscow
report:


The error box of GRB030418 (HETE 2679) was
observed with MASTER system (280mm, http://observ.pereplet.ru). We
obtained 20 measurements in R filter. Our observations started at Apr 18,
21:00 UT (11 hours after the GRB) and  had been lasting for 2.5 hours
up to Apr 18   22:36 UT (12,5 hours after  the  GRB).

There is no OT brighter than 16.5  (R-band) in error box. Transparency was
quite poor due to low altitude of the field above the horizont.

Our  fits-images are available at:
http://observ.pereplet.ru/images/GRB030418/30S9.zip


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Optical Observations of GRB 030418 with Magellan

A. Dullighan, N. R. Butler, G. R. Ricker, J. L. Elliot, K. Clancy 
(MIT), and D. Osip (Las Campanas Observatory)

report:

On 2003 April 21.01 UT, we observed the optical afterglow (Price et 
al; GCN2148
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 ) of the HETE-localized GRB 030418 (=H2686) with the 
Magellan 6.5 meter Clay telescope at Las Campanas Observatory in 
Chile.  Our observations consisted of three 300s R-Band images and 
one 300s I-Band image, taken with the MagIC instrument.  The 
afterglow brightness had declined significantly since the 
measurement reported in GCN2148
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 , consistent with a power law decay 
index = 1.3+/-0.1. The afterglow was still point-like in our images, 
with a FWHM of 0.5 arcsec. Our results were as follows:

UT                 t-t0 (days)    Mag
2003-04-21.02      2.60           R=23.64 +/- 0.07
2003-04-21.03      2.61           I=22.60 +/- 0.05

The magnitudes reported above are relative to those of the USNO B1 
catalog star at RA = 10h 54m 32.71s, Dec = -07:02:16.4 (J2000), taken 
as having R=19.33 and I=18.31. Magnitude errors for the USNO star 
were not available, and so are not included in the errors we report 
here.  Possible errors in the magnitudes of the USNO catalog star 
should be taken into account when comparing our afterglow magnitudes 
to other measurements. Further observations are planned.

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

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

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

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

write:

At 09:59:18.85 UTC (35958.85 s UT) on 18 April 2003, the HETE FREGATE
and WXM instruments detected event H2686, a long, X-ray-rich GRB.

The burst triggered FREGATE in the 30-400 keV energy band.  The WXM
flight localization was correct and was reported in a GCN Notice at
10:02:54 UTC, 215 sec after the beginning of the burst.

Ground analysis of the WXM data produced a refined location, which was
reported in a GCN Notice at 11:43:01 UTC, 104 minutes after the
beginning of the burst.  The WXM ground localization SNR was 9.  The
WXM localization can be expressed as a 90% confidence circle that is 9
arcminutes in radius and is centered at:

R.A. = 10h 54m 53s, Dec. = -06d 59' 22" (J2000).

The SXC was off because of illumination by the full moon.

The T_90 duration of the burst in the 30-400 keV band was ~ 135 s.  The
fluence of the burst was ~ 1.2 x 10^-6 erg cm^-2 in the 2-25 keV energy
band and ~ 2.5 x 10^-6 erg cm^-2 in the 30-400 keV energy band; thus
S(2-25)/S(30-400 keV) ~ 0.5.  Therefore this burst is an X-ray-rich
GRB.

A light curve and skymap for GRB030418 is provided at the following
URL:

http://space.mit.edu/HETE/Bursts/GRB030418

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

We have acquired BVRcIc all-sky photometry for
a 11x11 arcmin field centered at the coordinates
of the optical transient (Price et al. GCN 2148
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 )
for the HETE burst GRB030418 (H2686; Shirasaki et al. GCN 2210
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 )
with the USNOFS 1.0-m telescope on one marginal night.
Stars brighter than V=13.5 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/grb030418.dat
The astrometry in this file is based on linear plate solutions
with respect to UCAC2.  The external errors are less than 100mas.
Due to drifting smoke from prescribed forest fires, the external
photometric error is potentially larger than normal.  We will
acquire additional photometry in the next week or so to
reduce the external error.

As always, you should check the dates on the .dat file prior to
final publication to get the latest photometry.  There is
a README file on the ftp directory to give you information
about the procedures used to calibrate these fields.

GRB 030418: Second Epoch Optical Observations with Magellan

A. Dullighan, N. R. Butler, G. R. Ricker, J. L. Elliot, K. Clancy
(MIT), and D. Osip (Las Campanas Observatory)

report:

On 2003 April 25.00 UT, we observed the optical afterglow (Price et 
al; GCN2148
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 ) of the HETE-localized GRB 030418 (Shirasaki et al; 
GCN2210
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 ) with the Magellan 6.5 meter Clay telescope at Las Campanas 
Observatory in Chile.  Our observations consisted of two 400s R-Band 
images, one 400s I-Band image, and one 400s V-Band image taken with 
the MagIC instrument.

The afterglow declined in brightness with respect to our previous 
measurements (Dullighan et al; GCN2168
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 ). The R band data is 
consistent with a revised power law decay index = 1.2 +/- 0.1, when 
the two data points from Price et al. (GCN2148
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  and GCN2150
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 ) are 
included.  The afterglow was still point-like, but very close to the 
limiting magnitudes of the images.  No evidence of a host galaxy is 
observed.  We can, however, place a limit on the redshift of the 
afterglow of z<~5, due to the small V-R color difference we observe 
(i.e., no evidence for a Lyman alpha break). Our second epoch results 
were as follows:

UT               t-t0 (days)   Mag
2003-04-25.00    6.58          R=24.9 +/- 0.4
2003-04-25.01    6.59          I>24 (limiting magnitude)
2003-04-25.02    6.60          V=25.1 +/- 0.5

The magnitudes reported above are referenced to the photometry 
reported by A. Henden (GCN2216
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 ).  We have also recalibrated the 
magnitudes we reported in GCN 2168
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  to A. Henden's photometry 
(GCN2216
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 ).  The errors in calculating relative magnitudes have now 
been taken into account. Our revised first epoch results are as 
follows:

UT               t-t0 (days)   Mag (Original)     Mag (Revised)
2003-04-21.02    2.60          R=23.64 +/- 0.07   R=23.3 +/- 0.1
2003-04-21.03    2.61          I=22.60 +/- 0.05   I=23.0 +/- 0.1


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P. Ferrero and G. Pizzichini (IASF-CNR, Bologna),
C. Bartolini, A. Guarnieri, A. Piccioni (Bologna University), 
 and A. De Blasi (Bologna Astronomical Observatory) report:

On 2003, April 18 we observed the optical afterglow of HETE GRB 
030418 (Shirasaki et al., GCN 2210
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 , Price et al., GCN 2148
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 ) with 
the 152 cm telescope in Loiano in V, Rc and I.

 Using the star at RA 163.623207 Dec -7.039357 , R = 19.852 +/- 0.245
reported by Henden (GCN 2216
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 ), in unfavorable conditions due to the  
moon,  we obtained the following R magnitudes:

     exp time              starting time (UT)          mag
 
(2 X 600 sec, co-added)   19:31:05 and 19:44:50   R = 20.50 +/- 0.30
 
(2 X 600 sec, co-added)   20:10:03 and 20:23:05   R = 20.65 +/- 0.29

 
Our images in .jpg form can be retrieved by sftp using
hostname: ermione.bo.astro.it
username: publicGRB
password: GRB_bo

where a log of our recent observations of GRBs error boxes and OTs in 
Loiano can also be found. We plan to update it by adding the list of
previous observations. 
   
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