GRB 060904B

I. Asfandyarov,  M. Ibrahimov (MAO),  A. Pozanenko (IKI), on behalf of
larger GRB follow up collaboration report:

We observed  the  error box of GRB060904b (Grupe et al., GCN 5505
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 )  with 1.5
m telescope of Maidanak Astronomical Observatory (MAO)  on September 4 and
5. A set of R images were taken under good weaher conditions.  The afterglow
(Rykoff  et al., GCN 5504
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 ; Grupe et al., GCN 5505
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 ) is clearly detected in
combined images of each epochs. A photometry of the afterglow based on USNO
A2.0 is following:

Mid time (UT), Exposure (s), R_ mag.,     Seeing

Sep. 04.999    4x360        21.63 +/-0.18  1.4"
Sep. 05.993    4x300        22.40 +/-0.30  1.1"

The message may be cited

K.Y. Huang, W.H. Ip, Y.S. Lee (NCU) and Y. Urata (Saitama Univ.)
on behalf of EAFON report:

"The NIR afterglow observations of GRB 060904B (Grup et al.; Rykoff et
al; Fugazza et al.) with CFHT/WICam started from 9.40 hours after the
GRB occurred. Our J and Ks images show the magnitude of the afterglow
are J~ 19 at 10.8 hours and Ks~ 17 at 9.4 hours (compare with 2MASS
stars).

  Refer to the SMART observations (Cobb et al., GCN 5515
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 ), our J band
result indicates the decay rate (Flux ~ t^alpha) may change form ~-
0.65 to ~ -1.37. However, we do not find the decay rate change from
our Ks band results.

We would like to thank CFHT/WIRCam staff, especially A. Loic and
P. Martin for their assistance.

This message may be cited."

T. Soyano, H. Mito (Tokyo Univ), and Y. Urata (Saitama Univ)
on behalf of EAFON report:

" We have made R-band follow-up observation of GRB 060904B afterglow
(Grup et al.; Rykoff et al; Fugazza et al.) using Kiso 1.05m Schmidt
telescope. The observation was started at 15:27 UT September 4, 2006
and lasted till 19:30. The preliminary analysis shows the optical
afterglow with 21.4+/-0.2 mag at 15.72 hours after the burst.
Further analysis is in progress. 

This message may be sited."

N.Prymak, G. Kanbach, H. Steinle, A. Stefanescu, S. Duscha, F. Schrey, 
M. Muehlegger (MPE Garching) of the
OPTIMA-Burst Team report on optical observations of GRB060904b (BAT 
trigger Nr. : 228006; Circ.Nr. 5505, Grupe et al.):

OPTIMA-Burst at the 1.3m Skinakas Observatory, of the University of
Crete, Greece, observed the Swift/UVOT 0.5"-errorcircle of GRB060904b 
(GCN Circ. 5519
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 , Oats et al.) on 2006 Sept. 04.
Relative photometry to several close-by USNO catalog stars (referenced 
by their R magnitude) was performed for the
detected optical transient in our unfiltered images of 25 second 
exposure each. Results are listed:

2006/Sept/04  post-BAT
 
start time(UT)  time(s)   R magnitude

02:39:25             502   16.90+-0.12
02:41:56             653   17.09+-0.16
02:44:00             777   17.24+-0.19
02:45:52             889   17.36+-0.17
02:47:47            1004   17.44+-0.14
02:48:56            1073   17.58+-0.14
02:55:29            1466   17.70+-0.22
02:56:01            1505   17.75+-0.20
02:58:52            1669   17.94+-0.18
03:00:14            1751   17.79+-0.21
03:01:05            1802   17.89+-0.14

Sorry for the delay, we didn't have Internet connection from Sept 2.5 to 
6.7.

G. Greco (Bologna University), F. Terra (Second University of
Roma "Tor Vergata"), C. Bartolini, A. Guarnieri, A. Piccioni
(Bologna University), D. Nanni (INAF/OAR and Second University
of Rome "Tor Vergata"), S. Bernabei (Bologna Observatory),
S. Sclavi(University of Rome "La Sapienza") and G. Pizzichini
(INAF/IASF Bologna) report:

On Sept. 5 we observed the field of GRB 060904b (Grupe et. al.,
GCN 5165
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 ) with the 152 cm Cassini Telescope located in Loiano,
equipped with BFOSC (seeing 1".5).
The photometry is based on the SDSS stars (J035252.20  -004344.1,
J035249.70  -004345.8 , also quoted in GCN 5507
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  by Cool et al.)
and the trasformation derived from Lupton (2005).
For the OT detected by Klotz et al. (GCN 5508
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 ) we find the
following magnitudes:
..Mean..UT .......Filter........Exptime (s).......magnitude
Sept...5.111........Rc............900............21.75+/-0.11
Sept...5.123........Rc............900............21.74+/-0.12
Sept...5.145........Rc............900............21.8 +/-0.2

One of our images is available in a public directory from where
it can be retrieved by sftp by using:
hostname: ermione.bo.astro.it
username: publicGRB
password: GRB_bo
directory: GRB060904b

B. E. Cobb and C. D. Bailyn (Yale), part of the larger SMARTS
consortium, report:

Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
obtained optical/IR imaging of the error region of GRB 060904b
(GCN 5505
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 , Grupe et al.) with a mid-exposure time of
2006-09-04 06:28 UT (~4 hrs post-burst ) and again
at 2006-09-04 08:28 UT (~6 hrs post-burst).  For each
set of observations, total summed exposure times amounted
to 15 minutes in I and V and 12 minutes in J and K.
(Imaging was carried out in a symmetrical manner so that the mid-exposure
time is the same for all final combined images in a given
set of observations.)

The afterglow of GRB 060904b (GRB 5505, Grupe et al.) is detected in
each combined image.

filter  magnitude at            change in magnitude
        4hrs post-burst         between 4 and 6hrs post-burst
--------------------------------------------------------
V       -                       0.56 +/- 0.06
I       19.04 +/- 0.03          0.63 +/- 0.04
J       17.84 +/- 0.08          0.29 +/- 0.10
K       15.99 +/- 0.06          0.46 +/- 0.07

Unfortunately, imaging was done under non-photometric conditions so
no Landolt or Persson standard stars are available with which
to determine the offset between instrumental and apparent
magnitude.  Therefore, the above values are determined using "on-chip"
standards with USNO-B1.0 stars in the optical and 2MASS stars in the IR.
The errors on the photometric calibration are ~0.3 in I and ~0.1
in J and K; these errors are in addition to the statistical errors listed
above. No USNO-B1.0 V-band values are available to calibrate
our V-band observations, so we can only report the change in magnitude
between epochs. These values have not been corrected for galactic 
extinction.

The average optical decay rate (afterglow flux proportional to t^-alpha)
between 4 and 6 hours post-burst is alpha ~ 1.4, and the average IR
decay rate is alpha ~ 0.9.

After correcting for a galactic extinction of E(B-V) = 0.173,
the spectral index of the afterglow at 4 hrs post burst is found to be
beta ~ -1.3 (flux proportional to wavelength^-beta).

A. Mescheryakov, R. Burenin, M. Pavlinsky, R. Sunyaev (IKI), 
 I. Khamitov, Z. Aslan (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.), 
 I. Bikmaev, N. Sakhibullin (KSU/AST)
 
 report:
 
 We observed the optical counterpart of GRB 060904B (Grupe et al., GCN
 5505
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 ; Rykoff et al., GCN 5504
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 ; D. Fugazza et al., GCN 5513
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 ) with
 Russian-Turkish 1.5-m telescope (RTT150, Bakirlitepe, TUBITAK National
 Observatory, Turkey). The observations were started at 02:39:35 UT,
 i.e. 8.21 min after the trigger and were ended approximately 20 min 
 later due to sunrize. We made series of 30 s exposures in R and also 
 few exposures in B and V.
 
 We estimate the following magnitudes for the OT:
 
 UT        t-t0    Rc      err
 --------------------------------------------------------- 
 2:39:50   8:46    16.75   0.02
   41:00   9:58    16.86   0.03
   42:09  11:05    16.99   0.03
   43:19  12:15    17.05   0.04
   44:29  13:05    17.22   0.05
   45:39  14:35    17.34   0.06
   47:58  16:54    17.48   0.09
   49:07  18:03    17.50   0.09
   50:17  19:13    17.64   0.10
 
 The magnitudes are derived using comparison stars from the USNO-B1
 catalog.
 
 This message can be cited.

C. Markwardt (GSFC/UMD), L. Barbier (GSFC), S. D. Barthelmy (GSFC),
J. Cummings (GSFC/UMD), E. Fenimore (LANL), N. Gehrels (GSFC),
D. Grupe (PSU), D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU),
G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC)
on behalf of the Swift-BAT team:
 
Using the data set from T-239 to T+807 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 060904B (trigger #228006)
(Grupe, et al., GCN Circ. 5505
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 ).  The BAT ground-calculated position is
RA,Dec = 58.218, -0.729 deg {3h 52m 52.3s, 0d 43' 45.0"} (J2000) +- 0.9 arcmin,
(radius, sys+stat, 90% containment).  The partial coding was 50%.
 
The mask-weighted lightcurve shows the burst starting at ~T-2 sec
with a FRED peak shape (halfwidth ~9 sec) with a return to background level
at ~T+50 sec.  Then a second, weaker peak starts at ~T+120 sec, peaks 
at ~T+155 sec and is done by ~T+220 sec.  T90 (15-350 keV) is 192 +- 5 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-0.9 to T+212.8 is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.70 +- 0.14.  The fluence in the 15-150 keV band is 1.7 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+1.16 sec in the 15-150 keV band
is 2.5 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence level.

S. R. Oates (UCL-MSSL), D. Grupe (PSU) on behalf of the Swift UVOT team

The Swift Ultra-Violet/Optical Telescope (UVOT) began observations of 
GRB060904b at 02:32:14 UT, ~71 seconds after the initial Swift BAT trigger
(Grupe et al, GCN 5505
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 ). An optical counterpart was detected with the
V filter at a position RA(J2000)= (03h,52m,50.54s, -00o43'31.1'') to within 0.5''.
An optical afterglow was detected in V, B, U, UVW1, UVM2 and UVW2 filters.

The photometery results are given for the 6 filters below:

Filter      Tstart  Tstop   Magnitudes and UL
---------------------------------------------
V             71    316      18.64 +/-  0.33
              4732   4931     19.16 +/-  0.36
              5960   6100     18.25 3 sigma UL

B            4322   4521     18.98 +/-  0.15
              5550   5749     19.56 +/-  0.28

U            4117   4316     18.32 +/-  0.19
              5346   5545     18.65 +/-  0.23

UVW1         3913   4112     18.78 +/-  0.31
              5141   5340     19.11 +/-  0.36

UVM2         3708   3907     18.88 +/-  0.36
              4936   5135     19.66 +/-  0.55

UVW2         4528   4727     18.96 +/-  0.33
              5756   5955     19.32 +/-  0.41
---------------------------------------------

The values quoted above are not corrected for the expected
Galactic extinction of E_{B-V}=0.173.

D. Grupe (PSU), O. Godet (U Leicester), and S. Barthelmy (GSFC)
report on behalf of the Swift/XRT team


We have analyzed the first 3 orbits with a total observing
time of 5.3 ks of Swift XRT data of GRB 060904B
(Grupe et al., GCN 5505
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 ), with 4.9 ks in photon counting mode
(pc) and 427s in Windowed Timing mode (WT).

The Photon Counting mode image
provides a refined XRT position:

RA(J2000) = 03h 52m 50.26s,
Dec(J2000) = -00d 43' 32.5"

with an error of 3.6" (90% confidence). This position is 3.9"
away from the preliminary XRT position reported in GCN 5505
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 .


After the start of the XRT observation in pc mode, a giant
flare started at 86s after the trigger and lasted to 490s
after the trigger. This flare has a total 0.3-10.0 keV flux
of 2.2e-9 ergs/s/cm2 and a fluence of 8.8e-7 ergs/cm2.
The underlying afterglow decay slope is 1.11+/-0.25. The
predicted flux 24h after the burst is 3e-13 ergs/cm2/s.


Spectral fits to the Windowed Timing mode data during the
flare suggest a significant absorption column density in
excess of the Galactic value (1.21e21 cm**-2). The spectrum
can be fitted by a single power law with a photon index
Gamma=2.16+/-0.04 and an absorption column density
NH=4.09+/-0.13 e21. Using the redshift z=0.703 as reported by
Fugazza et al. (GCN 5513
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 ) the intrinsic absorption column density
is NH,intr=7.6+/-0.4 e21 cm-2.
The spectrum of the pc mode data agrees
within the errors with this result.




This circular is an official product of the Swift XRT Team.

D. Fugazza, P. D'Avanzo (INAF/OABr), D. Malesani (SISSA), G. Tagliaferri 
(INAF/OABr), G. Chincarini (Univ. Milano-Bicocca), L. Stella (INAF-OAR), 
J.P.U. Fynbo (DARK/NBI), C. Lidman, H. Sana (ESO), report on behalf of 
the MISTICI collaboration.

We observed the optical counterpart of GRB 060904B (Grupe et al., GCN 
5505
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 ; Rykoff et al., GCN 5504
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 ). Spectroscopy was performed with VLT + 
FORS1, with mean time Sep 4.318 UT (5.15 hr after the burst).

Several absorption features were clearly identified, among which FeII 
2586, FeII 2600, Mg II 2795,2803, Mg I 2852, Ca H&K 3933,3968. The 
inferred redshift is z = 0.703.

We acknowledge excellent support from the ESO staff.

This message can be cited.

J. Skvarc on behalf of PIKA observing program at Crni vrh Observatory
reports:

We observed optical counterpart of GRB060904B (Swift trigger 228006)
using 60 cm robotic telescope at Crni Vrh Observatory, Slovenia.  A
variable object was detected at  ra=03:52:50.52, dec=-0:43:30.9.
The coordinates are derived using UCAC-2 catalog. 1-sigma accuracy of
these coordinates is about 0.2 arcseconds.

Alternating exposures using R and B filters were taken, starting 45 s
after the trigger was received. The following table contains start of
exposure (2006-09-04 UT), exposure duration in seconds and magnitude:

R filter:
2:32:02  90 18.21
2:37:32  90 17.01
2:43:03  90 17.11
2:48:33  90 17.79
2:54:03  90 18.19
2:59:37  90 17.66
3:08:27 180 17.78
3:13:23 180 17.79
3:17:50 180 17.99

B filter:
02:34:02 180 18.32
02:39:32 180 17.51
02:45:03 180 18.56
02:50:33 180 18.81

The magnitudes are derived using comparison stars from the USNO A2
catalog.  Estimated 1-sigma statistical uncertainty is 0.02 for R and
0.04 for B filter.



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A. de Ugarte Postigo (IAA-CSIC Granada), J.French (UCD Dublin) and
P.Kubanek (AsU AV CR Ondrejov & ISDC Versoix) reports on behalf of the
Watcher collaboration:

The 0.4m Watcher telescope, located at Boyden Observatory, South Africa,
observed the SWIFT error box for GRB 060904B (Grupe et al. GCN 5505
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 )
starting at 02:32:05 UT observing in R, V, I bands + unfiltered. We
detect the optical counterpart at coordinates reported by Rykoff et al.
(GCN 5504
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 ), with peak brightness unfiltered 17.1+/-0.3 at 02:39:30 UT,
consistent with Tarot peak detection (Klotz et al. GCN 5508
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 ).

This message is quotable.

A. de Ugarte Postigo, F. Aceituno, A.J. Castro-Tirado
(IAA-CSIC Granada), P. Kubanek (ASU AV CR ndrejov & 
ISDC Versoix) on behalf of a larger collaboration report:

"The 0.6m BOOTES-IR and 1.5m telescope, located at IAA-CSIC 
Observatorio de Sierra  Nevada in Granada (Spain), observed the 
SWIFT error box for GRB 060904B (Grupe et al. GCN 5505
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 ) starting at
02:38:30 UT observing in I & R-bands. We clearly detect the optical
counterpart reported by Rykoff et al. (GCN 5504
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 ), at coordinates J2000
(+/-0.5"):

03:52:50.54 -00:43:30.5

>From 02:38:30 to 02:48:35 UT the object has declined in 0.66 +/- 0.17 
magnitudes.

This message is quotable."

[GCN OPS NOTE(04sep06): Per author's request, the 'B' was added.]

Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report:

We imaged the field of GRB 060904B detected by SWIFT
(trigger 228006) with the TAROT robotic telescope (D=25cm)
located at the Calern observatory, France.

First image was acquired 23.1s after the GRB trigger
(10.4s after the notice). The field elevation increased from
37 degrees above horizon and weather conditions
were excellents. Images were taken during the
prompt phase.

Date of trigger : t0 = 2006-09-04T02:31:04.224

First image is a 60.0s exposure trailed from t0+23.1s
to t0+83.1s. The OT noticed by Rykoff et al.
(GCNC5504) is visible as a short flash of
magnitude R=15.8 during few seconds near t0+50s.

Second image is 30.0s exposure. OT is marginally
detected at R~18.5.

In the following images the OT becomes brighter.
A first visual inspection seems to show that
the peak of brightness (R~17) was reached
near t0+~400s.

The OT was still well detected on individual
images at t0+40min (R~17.7).

OT position (+/- 2 arcsec):

RA(J2000.0) = 03h 52m 50.62s
DEC(J2000.0) -00d 43' 29.4"

Magnitudes were estimated with the nearby USNO-B1 stars
and are not corrected for galactic dust extinction.

N.B. Galactic coordinates are lon=189.4387 lat=-39.1315
and the galactic extinction in R band is 0.1 magnitudes
estimated from D. Schlegel et al. 1998ApJ...500..525S.

This message may be cited.

Richard J. Cool (Arizona), Daniel J. Eisenstein (Arizona), David
W. Hogg (NYU), Michael R. Blanton (NYU), David J. Schlegel (LBNL),
J. Brinkmann (APO), Donald Q. Lamb (Chicago), Donald P. Schneider
(PSU), and Daniel E. Vanden Berk (PSU) report:

The Sloan Digital Sky Survey (SDSS) imaged the field of burst
GRB060904B prior to the burst.  As these data should be useful
as a pre-burst comparison and for calibrating photometry, we are
supplying the images and photometry measurements for this GRB field
to the community.

Data from the SDSS, including 5 FITS images, 3 JPGS, and
3 files of photometry and astrometry, are being placed at
http://mizar.as.arizona.edu/~grb/public/GRB060904B

We supply FITS images in each of the 5 SDSS bands of a 8'x8'
region centered on the GRB position (ra=58.2130 (03:52:51.1),
dec=-0.720000 (-00:43:12.0); Swift-BAT TRIGGER 228006), as well as
3 gri color-composite JPGs (with different stretches). The units in
the FITS images are nanomaggies per pixel.  A pixel is 0.396 arcsec
on a side. A nanomaggie is a flux-density unit equal to 10^-9 of
a magnitude 0 source or, to the extent that SDSS is an AB system,
3.631e-6 Jy.  The FITS images have WCS astrometric information.

In the file GRB060904B_sdss.calstar.dat, we report photometry
and astrometry of 299 bright stars (r<20.5) within 15' of the
burst location.  The magnitudes presented in this file are asinh
magnitudes as are standard in the SDSS (Lupton 1999, AJ, 118,
1406). Beware that some of these stars are not well-detected in
the u-band; use the errors and object flags to monitor data quality.

In the files GRB060904B_sdss.objects_flux.dat and
GRB060904B_sdss.objects_magnitudes.dat, we report photometry
of 1078 objects detected within 6' of the GRB position.
We have removed saturated objects and objects with model
magnitudes fainter than 23.0 in the r-band.  The fluxes listed
in GRB060904B_sdss.objects_flux.dat are in nanomaggies while the
magnitudes listed in GRB060904B_sdss.objects_magnitudes.dat are
asinh magnitudes.

All quantities reported are standard SDSS photometry, meaning that
they are very close to AB zeropoints and magnitudes are quoted
in asinh magnitudes.  Photometric zeropoints are known to about
2% rms.  None of the photometry is corrected for dust extinction.
The Schlegel, Finkbeiner, and Davis (1998) predictions for this
region are A_U=0.899 mag, A_g=0.661 mag, A_r = 0.480 mag, A_i=0.364
mag, and A_z=0.258 mag.

The file GRB060904B_sdss.spectro.dat contains a list of the 18
objects with SDSS spectroscopy within 6 arcminutes of the GRB
position.  In addition to the redshift and 1-sigma error for each
object, this file also lists the object spectroscopic classification.

SDSS astrometry is generally better than 0.1 arcsecond per
coordinate.  Users requiring high precision astrometry should take
note that the SDSS astrometric system can differ from other systems
such as those used in other notices; we have not checked the offsets
in this region.

More detailed information pertaining to our SDSS GRB releases
can be found in our initial data release paper (Cool et al. 2006,
astro-ph/0601218).  See the SDSS DR4 documentation for more details:
http://www.sdss.org/dr5.

These data have been reduced using a slightly different pipeline
than that used for SDSS public data releases.  We cannot guarantee
that the values here will exactly match those in the data release
in which these data are included.  In particular, we expect the
photometric calibrations to differ by of order 0.01 mag.

This note may be cited, but please also cite the SDSS data release
paper, Adelman-McCarthy et al. (2006, ApJS, 162, 38), when using
the data or referring to the technical documentation.

D. Grupe (PSU), S. D. Barthelmy (GSFC), M. M. Chester (PSU),
J. R. Cummings (NASA/UMD), S. T. Holland (GSFC/USRA),
S. D. Hunsberger (PSU), J. A. Kennea (PSU), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC/UMD), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL), M. Stamatikos (NASA/ORAU) and M. C. Stroh (PSU)
report on behalf of the Swift Team:

At 02:31:03 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060904B (trigger=228006).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA,Dec 58.213, -0.720 {03h 52m 51s, -00d 43' 11"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows an initial 5-sec wide
peak at T+1 sec followed by an ~30-sec wide weaker peak at T+150 sec. 
The total duration is about 180 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 02:32:12 UT, 69 seconds after the
BAT trigger. XRT found a variable, uncatalogued X-ray source located
at RA(J2000) = 03h 52m 50.0s, Dec(J2000) = -00d 43' 32.8", with an
estimated uncertainty of 6.5 arcseconds (90% confidence radius). This
location is 26 arcseconds from the BAT on-board position, within the
BAT error circle. The initial flux in the 2.5s image was 4.3e-10
erg/cm2/s (0.2-10 keV). The source shows a rapid increase in count
rate indicating a bright flare that is possibly correlated with the 
second bright peak in the BAT. 

UVOT took a finding chart exposure of 246 seconds with the V filter
starting 70 seconds after the BAT trigger. There is a candidate afterglow in the
rapidly available 2.7'x2.7' sub-image at (RA,DEC) (J2000) of
(58.2106,-0.7253) or (03h52m50.54s,-00o43'31.1")  with a 1-sigma
error radius of about 0.7 arc sec. This position is 7.7 arc sec. from
the center of the XRT error circle. The estimated magnitude is 18.6
with a 1-sigma error of about 0.5 mag. No correction has been made
for the expected extinction of about 0.6 magnitudes.

E.S. Rykoff (U Mich), W. Rujopakarn (U Mich), F. Yuan (U Mich), report 
on behalf of the ROTSE collaboration:

ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia, 
responded to GRB 060904B (Swift trigger 228006). The first image was at 
02:31:22.4 UT, 18.5 s after the burst (5.3 s after the GCN notice time). 
The unfiltered images are calibrated relative to USNO A2.0. We detect a 
17.3 magnitude, brightening source with coordinates:

      03:52:50.52      -00:43:30.85    (J2000)

start UT    	mag     mlim(of image)
----------------------------------
02:31:22.4     17.3     18.1

A jpeg image is available at 
http://www.rotse.net/images/gsb228006_3c011-020_key.jpg

Continuing observations are in progress.

[GCN OPS NOTE(04sep06): Per author's request the 060904A was changed to B.]