XRF 030723

N. Kawai, G. Kosugi, Y. Komiyama, H. Furusawa, Y. Urata, and T. Yamada
on behalf of the Subaru GRB team report:

"We have observed the field of XRF030723 (=H2777, GCN 2320
Loading...
 
 ) with the
Subaru Prime Focus Camera on 2003 September 29 - October 3 UT in V,
Rc, Ic, and z' bands.  We detected an unresolved source at the
position of the proposed host galaxy (Fynbo et al. GCN 2403
Loading...
 
 ) in
Rc, Ic and z' bands.

With the preliminary analysis, the magnitude of the source was 
R=27.6 +/- 0.4 (2.4 hour exposure, mean seeing 0.7 arcsec).  
It has a red color, and we were not able to obtain significant
detection of the source with the 1.7 hour exposure in V band.

The images are posted at

http://www.naoj.org/staff/george/Distribute/XRF030723/XRF030723.html."

Johan P. U. Fynbo (U. of Aarhus), Jens Hjorth, Brian L. Jensen 
(U. of Copenhagen), Jesper Sollerman (U. of Stockholm),
Michael I. Andersen (AIP, Potsdam), Javier Gorosabel (STScI)
report on behalf of the GRACE collaboration:

"We have observed the field of XRF 030723 (=HETE trigger 2777,
GCN 2320
Loading...
 
 ) with the FORS1 optical camera on the ESO VLT on 
September 24. In a deep (about 1 hr) R-band image with a mean 
seeing of 0.68 arcsec we detect a very faint, extended source
at the position of the optical afterglow (GCN 2323
Loading...
 
 ). The
galaxy has a position angle of about 90 degrees EofN. We 
interpret this as the likely host galaxy of XRF 030723. The 
magnitude of the galaxy is about R=26.8+/-0.4. An image of the
galaxy can be seen at: 
http://www.astro.ku.dk/~brian_j/xrf/xrf030723.

We acknowledge excellent support from the Paranal staff, in 
particular Poshak Gandhi."


-- 
Johan Fynbo <jfynbo@phys.au.dk>

XRF030723(=H2777): Chandra Fading X-ray Afterglow Confirmed

N. Butler, P. Ford, G. Ricker, R. Vanderspek, J. Villasenor (MIT); D. 
Lamb (U. Chicago); G. Garmire (PSU); L. Piro (CNR); and J.G. Jernigan 
(UCB), on behalf of a Chandra GRB ToO Team,

write:

On 4 August 2003, the Chandra Observatory targeted the field of 
XRF030723, an X-ray flash localized by the HETE satellite (=H2777; 
Prigozhin et al, GCN 2313
Loading...
 
 ). The duration of the observation was 85 
ksec, and it was a followup to the 25 ksec observation reported by 
Butler et al.  in GCN 2328
Loading...
 
 .  The observation spanned the interval 4 
August 22:22 UT to 5 August 22:27 UT, 12.66 to 13.67 days after the 
burst. The SXC error circle from Prigozhin et al. was completely 
contained within the field-of-view of the Chandra ACIS-S3 chip.

Within the SXC error circle, the three X-ray sources from GCN 2328
Loading...
 
  
are detected.  Only source #1 is observed to vary in flux at a 
significance level of >1 sigma.  We detect 74 counts in the 0.5-8.0 
keV band, corresponding to a >7-sigma significance decrease (i.e. 
factor of ~6) in flux since the first epoch observation.  We are thus 
extremely confident that source #1 is the X-ray counterpart to 
XRF030723 and is the counterpart to the optical source discovered by 
Fox et al. (GCN 2323
Loading...
 
 ).

If we jointly fit the counts from the first and second Chandra 
epochs, we find that the data are well described by a power-law with 
absorption fixed at the Galactic value in the source direction (chi^2 
= 8.9 for 9 [12-3] degrees of freedom).  The best fit photon number 
index (for both epochs) is gamma = 1.9 +/- 0.3, which is a typical 
value for the X-ray afterglows of long duration GRBs.  Using this 
model, we find that the first epoch flux is ( 2.2 +/- 0.3 ) x 10-14 
erg cm-2 s-1 (0.5-8.0 keV band), while the second epoch flux is ( 3.5 
+/- 0.5 ) x 10-15 erg cm-2 s-1 (0.5-8.0 keV band).  The decrease in 
flux between the two epochs can be described by a power-law with a 
decay index of alpha= -1.0 +/- 0.1.  This value of alpha is 
consistent with the power-law decline reported in the optical by 
Dullighan et al. (GCN 2336
Loading...
 
 ) for <~1.5 day after the GRB; however, the 
index is considerably flatter than the index at t>1.5 days reported 
by Dullighan et al. This flatter X-ray decay may possibly be related 
to the rebrightening of the optical afterglow reported by Fynbo et 
al. (GCN 2345
Loading...
 
 ).

We gratefully acknowledge the timely assistance of the observatory 
staff at the Chandra Science Center in arranging for the acquisition 
and preliminary processing of these data.

This message may be cited.

J. P. U. Fynbo (U. Aarhus), J. Hjorth (U. Copenhagen), J. Gorosabel 
(IAA-CSIC/STScI), B. L. Jensen (U. Copenhagen), M. I. Andersen (AIP), 
R. A. M. J. Wijers (U. Amsterdam), C. Kouveliotou (NASA/MSFC), on behalf 
of GRACE, report:

"We have monitored the afterglow of XRF 030723 (Prigozhin et al. GCN #2313
Loading...
 
 ; 
Fox et al. GCN #2323
Loading...
 
 ; Butler et al. GCN #2328
Loading...
 
 ) with the ESO VLT. Between 
Aug 3.2 UT and Aug 6.3 2003 UT the optical afterglow brightened by 1.0 mag 
to R ~ 24.3. If this is due to the emergence of a supernova it would 
strengthen the link between GRBs and XRFs. It would also indicate a fast rise 
for the supernova and a relatively low redshift for XRF 030723, z < 1, 
consistent with the earlier spectroscopic constraints (Fynbo et al. 
GCN #2327
Loading...
 
 ). Alternatively, we may be seeing a rebrightening due to late 
energy injection (refreshed shock). Continued spectroscopic and photometric 
monitoring is planned. 

Images are posted at http://www.astro.ku.dk/~brian_j/grb/grb030723

We thank the Paranal Observatory staff for efficiently conducting the
reported service-mode observations."

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

Because an optical afterglow (Fox et al., GCN 2323
Loading...
 
 ) has been
discovered for the HETE XRF030723 (Prigozhin et al., GCN 2313
Loading...
 
 ),
we have updated our field photometry file (Henden GCN 2317
Loading...
 
 )
to include a total of 3 photometric nights.  The last two
nights were repositioned so that the field center corresponds
to the SXC error circle center, with the OT therefore only
a couple of arcmin from the calibration field center.

This file can be found at:
ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb030723.dat
Mean photometric errors are under 0.02mag and mean coordinate
errors (UCAC2) are less than 100mas.

No changes are expected beyond this point.

D. A. Smith, C. W. Akerlof (U. of Michigan) and R. Quimby (U of Texas Austin)
report on behalf of the ROTSE collaboration:

We have re-analyzed the ROTSE-III early observations of event 030723 (See Smith
& Quimby, GCN Circ. #2318
Loading...
 
  for details on the ROTSE observations) after the
report of the counterpart candidate discovered by Fox et al. (GCN Circ. #2323
Loading...
 
 ).
We performed a fit to a template PSF placed at a list of targets selected from
Henden's photometry report (GCN Circ. #2317
Loading...
 
 ).  We find no convincing evidence
for a detection of the OT in the first four of our images, but the last two
images do yield marginal possible detections.  We derive 19.5+-0.4 for the
fifth image (S/N=2.7) and 19.3+-0.4 for the sixth (S/N=3.1).  We derive the
following 2-sigma upper limits on the OT magnitude for each image, as
calibrated to the R band values given by Henden:

Time from burst (min):  0.79    3.2    8.1    19.7   31.3   42.9
R band magnitude     : >19.0   >19.7  >19.1  >19.5  >18.9  >18.8

Note that these numbers are not limiting magnitudes for each image but upper
limits to the brightness of an object at the OT location.  Also, the ROTSE
images are unfiltered, and since no color information is available for the
early afterglow, we have not applied any color correction to this calibration.

Second Epoch Magellan Observations of XRF030723 (=H2777)

A. Dullighan, N. Butler, R. Vanderspek, J. Villasenor,  and G. Ricker
(MIT)

write:

We have observed the SXC error circle for the HETE-discovered X-ray
flash XRF030723 (=H2777; Prigozhin et al, GCN 2313
Loading...
 
 ) with the MagIC
instrument on the 6.5m Magellan Clay telescope at Las Campanas
Observatory in Chile. Two 200 second, Harris R-band exposures were taken
in an interval centered on July 28.385 UT, at 5.13 days after the
burst.  The seeing was ~0.8 arcsec. Coaddition of the images gives a
limiting magnitude of R = 24.3.

We detect the optical counterpart (Fox et al., GCN 2323
Loading...
 
 ) of GRB 030723
at R = 24.2 +/- 0.3.  Combining our photometry with that available from
the GCN Circulars (Bond, GCN 2329
Loading...
 
 ; Dullighan et al., GCN 2326
Loading...
 
 ; Fox et al.,
GCN 2323
Loading...
 
 ), we estimate a late time power law decay index of ~2, and an
early power law decay of 0.9.  The break in the light curve is between
30-50 hours after the burst.  Our measurements have been calibrated
against the USNO photometry data reported by Henden in GCN 2317
Loading...
 
 .

A plot of this light curve can be seen at:

  http://space.mit.edu/HETE/Bursts/GRB030723/

We gratefully acknowledge observational assistance by Matthew J. Holman
and Jeff McClintock.

This message may be cited.

A. M. Soderberg and E. Berger (Caltech) with D. A. Frail (NRAO)
report on behalf of the Caltech-NRAO GRB Collaboration:

"We have observed the field of XRF030723 with the Very Large Array on
July 26.42 UT at 8.46 GHz.  We do not detect a radio counterpart
to the optical transient reported by Fox et al. (GCN #2323
Loading...
 
 ). The 3 sigma
detection limit at the position of the optical afterglow is 180 microJy."

Howard E. Bond (Space Telescope Science Institute) reports:

As noted in (GCN #2316
Loading...
 
 ) the error circle of XRF 030723 was imaged with the
SMARTS Consortium 1.3m reflector at Cerro Tololo on UT 2003 July 24.080,
24.173, and 24.281.  An additional observation was obtained at UT 2003 July
25.414.  R-band exposures of 3x300 sec were taken at each epoch  

The fading of the optical transient reported by Fox et al. (GCN #2323
Loading...
 
 ) is
confirmed, albeit at low S/N.  At July 24.080 the source was unfortunately
located on a low-sensitivity region of the CCD.  On July 24.173 and 24.281 it
had R magnitudes of 21.0 and 20.9 (calibrated against a Landolt standard
field, but with uncertainties of at least 0.1 mag).  On July 25.414 the
transient had faded below detectability and was at least 1 mag fainter than on
the previous night.

I thank Rebeccah Winnick, David Gonzalez, and Juan Espinoza for arranging and
executing the observations on very short notice.

XRF030723(=H2777): Observations with the Chandra X-ray Observatory

N. Butler, P. Ford, G. Ricker, R. Vanderspek, J. Villasenor (MIT); D.
Lamb (U. Chicago); G. Garmire (PSU); L. Piro (CNR); and J.G. Jernigan
(UCB), on behalf of a Chandra GRB ToO Team,

write:

On 25 July 2003, the Chandra Observatory targeted the field of 
XRF030723, an X-ray flash localized by the HETE satellite (=H2777; 
Prigozhin et al, GCN 2313
Loading...
 
 ). The 25 ksec observation spanned the 
interval 09:52-17:05 UT on 25 July, 51.4 - 59.0 hours after the 
burst. The SXC error circle from Prigozhin et al. was completely 
contained within the field-of-view of the Chandra ACIS-I array.

Within the SXC error circle, we detect 3 sources in the 0.5-8 keV band:

#      Chandra Name           RA           DEC         Cts
1 CXOU J214924.4-274248   21 49 24.421  -27 42 48.00   78
3 CXOU J214926.9-274146   21 49 26.891  -27 41 45.92   19
4 CXOU J214928.7-274211   21 49 28.724  -27 42 11.47   16

The brightest object within the SXC error circle, Chandra Source #1, 
lies 62" from the center of the SXC error circle, and is within 0.7" 
of the optical transient reported by Fox et al. (GCN 2323
Loading...
 
 ). We 
estimate a position uncertainty of 1.4" for the Chandra sources. 
Astrometry was performed using six stars from the USNO-A2 catalog.

The Chandra results provide further evidence that the optical 
transient reported by Fox et al. (GCN 2323
Loading...
 
 ; see also Wood-Vasey et 
al., GCN 2325
Loading...
 
 ) and confirmed by Dullighan et al. (GCN 2326
Loading...
 
 ) is indeed 
the counterpart and afterglow of XRF030723.

We gratefully acknowledge the timely assistance of Roger Brissenden 
and the observatory staff at the Chandra Science Center in arranging 
for the acquisition and preliminary processing of these data.

This message may be cited.

J. P. U. Fynbo (U. Aarhus), J. Hjorth (U. Copenhagen), J. Gorosabel
(IAA-CSIC/STScI), P. M. Vreeswijk (ESO Chile), J. E. Rhoads (STScI),
on behalf of GRACE, report:

"We have obtained VLT spectra of the candidate afterglow of XRF 030723
(Fox et al. GCN #2323
Loading...
 
 ). 22 600-sec spectra covering 3650 - 7500 A at
13 A resolution were obtained with FORS1/UT1 starting on July 26.25
2003 UT. A preliminary reduction of the spectra indicates a blue,
featureless continuum with no obvious absorption or emission features.
The apparent absence of absorption lines may indicate a low redshift or
a low-density environment. The absence of a Lyman Forest suggests a 
redshift below 2.1. A detailed analysis is in progress.

We thank the Paranal Observatory staff for efficiently conducting the
reported service-mode observations."

Magellan Observations of XRF030723 (=H2777)

A. Dullighan, N. Butler, R. Vanderspek, J. Villasenor,  and G. Ricker (MIT)

write:

We have observed the SXC error circle for the HETE-discovered X-ray 
flash XRF030723(=H2777; Prigozhin et al, GCN 2313
Loading...
 
 ) with the LDSS2 
instrument on the 6.5m Magellan Clay telescope at Las Campanas 
Observatory in Chile. Four 6 minute Harris R-band exposures were 
taken in an interval centered on July 24.31 UT, extending from 24.8 h 
to 25.2 hours after the burst.  The seeing was ~0.6 arcsec. 
Coaddition of the images gives a limiting magnitude of R = 24.5 
magnitudes.

We detect the suggested optical counterpart (Fox et al., GCN 2323
Loading...
 
 ) of 
GRB 030723 at R = 21.13 +/- 0.05 magnitudes.  Combining our 
photometry with that of Fox et al, we estimate a power law decay 
index of 1.6. Our measurements have been calibrated against the 
recent USNO photometry data reported by Henden in GCN 2317
Loading...
 
 .

We gratefully acknowledge observational assistance by A. McWilliam and D. Osip.

This message may be cited.

D.B. Fox, D.L. Kaplan, B. Cenko, and S.R. Kulkarni (Caltech), with
A. Nechita (Harvard), report on behalf of the Caltech-NRAO GRB
Collaboration:

"We have observed the HETE-2 SXC localization region for XRF030723
(Prigozhin et al., GCN #2313
Loading...
 
 ) with the 60-inch and 200-inch (Hale)
telescopes on Mt. Palomar, on two successive nights commencing at
approximately July 24.4 UT and July 25.4 UT.  60-inch observations
were made in R-band with CCD13; 200-inch observations were made in
Ks-band with WIRC.  We have photometered these data against the USNO
and 2MASS catalogs; limiting magnitudes for our exposures are
approximately R~22.8 and Ks~19.4 on July 24.5 UT (mean epoch), and
R~22.5 and Ks~19.0 on July 25.5 UT, respectively.

"Comparison of the two epochs of R-band imaging reveals a stationary,
point-like, fading source with magnitudes R~21.3 on July 24.5 and
R~22.4 (near the limit of detection) on July 25.5.  This source is
also detected in our July 24.5 Ks-band image with Ks~18.65; it is not
detected in our July 25.5 Ks-band image to the Ks~19.0 limit.  The
coordinates of the source, referenced to the GSC 2.2, are:

    RA 21:49:24.40,  Dec -27:42:47.4 (J2000)

with an uncertainty of less than 0.5" in each coordinate.  

Given the pronounced fading of the source we suggest that it is likely
to be the optical counterpart of XRF030723.  

Images of the field and proposed counterpart will be provided soon at
the webpage: 

    http://www.astro.caltech.edu/~derekfox/xrf030723/

B. L. Jensen (U. Copenhagen), J. Gorosabel (IAA-CSIC/STScI), J. Hjorth,
C. Vinter (U. Copenhagen), J. P. U. Fynbo (U. Aarhus), P. M. Vreeswijk
(ESO Chile) report:

"R-band exposures covering the 2' radius HETE-2 SXC error circle of XRF 030723
(Prigozhin et al., GCN #2313
Loading...
 
 ) were obtained at the Danish 1.5-m telescope
(ESO La Silla) on July 24.3 and July 25.3 2003 UT. In the combined images,
reaching limiting magnitudes of R ~ 24, no counterpart to the first ROTSE-III
source (Smith & Quimby, GCN #2318
Loading...
 
 ) is apparent. At RA(J2000.0) = 21 49 24.54,
Dec (J2000.0) = -27 40 35.0, 2.1" from the reported location of the second
ROTSE-III source, an object with R = 23.2 +- 0.3 is detected (photometry based
on the calibration provided by Henden (GCN #2317
Loading...
 
 )). The object is unresolved
in 1.3" seeing and appears to be constant in brightness between the two
epochs. Images are posted at
http://www.astro.ku.dk/~brian_j/grb/grb030723 "

XRF030723 (= H2777): Chandra Observations Scheduled

G. Ricker, P. Ford, N. Butler, R. Vanderspek, J. Villasenor (MIT); D. 
Lamb (U. Chicago); G. Garmire (PSU); L. Piro (CNR); and J.G. Jernigan 
(UCB), on behalf of a Chandra GRB ToO Team,

write:

Chandra target-of-opportunity observations of the HETE SXC error 
circle for XRF030723 (= H2777: Prigozhin et al, GCN 2313
Loading...
 
 ) have been 
approved and scheduled. The first epoch observation will commence at 
10h UT on 25 July, with a second epoch observation ~1 week later.

The scheduling of contemporaneous observations at other wavelengths, 
especially deep initial epoch optical and IR observations, is 
strongly encouraged.

After reinspection of the data, it was found that the photometric
calibration field center is not at the SXC coordinates, but rather
20 timesec (=267 arcsec) to the east due to operator error.
The SXC localization center is present in the dataset, but the
western part of the error circle was missed.  We apologize for
the miscentering.

D. A. Smith (U. of Michigan) & R. Quimby (U. of Texas) report on behalf of the
ROTSE collaboration:

The ROTSE-IIIb instrument at McDonald Observatory, Texas, responded
automatically to HETE-2 alert 2777, and began taking images within 5 s of when
the alert was distributed.  The first exposure began 47 seconds after the burst
trigger time.  All objects in the SXC 2' (radius) error circle that appear in
more than four individual ROTSE images match to sources in the USNO 2.0
catalog.  Unfiltered limiting magnitudes, calibrated to USNO R-band, for the
first ten (5-s) images were around 16.5, for the second ten (20-s) images
around 17.5, and for the next 40 (60-s) images around 18.0.  We then co-added
sets of ten frames each to drive the limiting magnitudes down to 18.1, 18.7,
and 19.1, respectively.  We also co-added the first twenty frames as a check
against false positives in the first two co-added images.

Only two non-USNO sources within the error circle appear in more than the first
of the co-added, composite images.  We find no sources that appear in the five
later co-adds that are not in the first one.  Both of the non-USNO sources in
the first image are dimmer in the second and third images, and both vanish by
the fourth image.  Neither source appears to be in the DSS or the 2MASS J and K
archival images of this field, and neither source appears in images taken the
following night (to a limiting magnitude of 18.6) at 0.95 d after the burst.

One of the sources is too close to a USNO-cataloged star for SExtractor to
de-blend the two.  The star is at coordinates 21h 49m 24s.8, -27o 40' 10".16
(J2000.0), and its derived ROTSE magnitude (which would contain emission from
both sources) fades by 1.6 mag from 17.3+-0.1 to 18.9+-0.2 as the nearby source
(which is about 7.5" East and 3" South) disappears.  The following night, this
star was measured at 18.9+-0.2.
 
The second source was isolated, and we derive the following light curve:
R.A.            Dec.  (J2000.0)  Magnitude
21h 49m 24s.379 -27o 40' 35".04  17.9+-0.2  18.2+-0.2 18.2+-0.1  > 19.1   > 19.1   > 19.1
(Time from burst)                (47.3 s)   (191.9 s) (8.1 m)    (19.7 m) (31.3 m) (42.9 m)

We cannot at this time determine if either of these sources is related to the
HETE-2 event.  Images and finding charts can be found at
http://grad40.as.utexas.edu/~quimby/HETE2777

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 SXC error box for the HETE burst XRF030723 (Prigozhin
et al., GCN 2313
Loading...
 
 ) with the USNOFS 1.0-m telescope on one
photometric 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/grb030723.dat
The astrometry in this file is based on linear plate solutions
with respect to UCAC2.  The external errors are less than 100mas.
However, this field was observed at high airmass and with
incoming clouds, so the photometric zeropoint accuracy is
about 0.03mag with the potential of a larger systematic error.

We do not intend to reobserve this field unless an optical
transient is discovered.  As always, however, you should check
the dates on the .dat file prior to final publication in case
further observations are made.

Howard E. Bond (Space Telescope Science Institute) reports:

The SXC error circle of XRF 030723 (HETE Burst H2777) was imaged with the
SMARTS Consortium 1.3m reflector at Cerro Tololo on 2003 July 24.080, 24.173,
and 24.281.  The 6'x6' CCD field was centered at RA= 21h 49m 27.4s, Dec= -27d
42' 01" (J2000), and R-band exposures of 3x300 sec were taken at each epoch.

Visual inspection of the images shows no new sources compared to the
second-epoch Digitized Sky Survey red images, nor any obviously variable fainter
objects.

W. Li, R. Chornock, A. V. Filippenko, and S. Jha (UC Berkeley) report:

The Katzman Automatic Imaging Telescope (KAIT) responded to GRB 030723
(HETE Trigger #2777) automatically. The first four alerts issued via
GCN at 6:29 UT, 6:37 UT, 6:43 UT, and 6:45 UT were not observed due to
altitude limits, and we remotely (but manually) obtained 8 images starting
at 7:38 UT (about 1.2 hours after the burst), covering a 12'.5 x 12'.5
region centered on R.A. = 21:49:41, Decl. = -27:48:29 (J2000). KAIT
responded to the alert issued via GCN at 9:47 UT (3.3 hours after the
burst) automatically, and obtained 9 images covering a 12'.5 x 12'.5
region centered on R.A. = 21:48:51, Decl. = -27:41:16 (J2000). The alert
issued at 13:38 UT was not observed due to bright dawn. 

Visual inspection of the images reveals no obvious new source compared
with the DSS II (red) to a limiting magnitude of 19.0 - 20.0 (the images
have different exposure times). Specifically, the images taken around
7:38 UT covered about 50% of the error circle of the ground analysis burst
position issued at 13:38 UT via GCN.

XRF 030723, optical observations
-------------------------
 
A. de Ugarte (IAA-CSIC, Granada), P. Tristram (Univ. of
Auckland), T. Sekiguchi (Univ. of Nagoya), M. Jelinek
(ASU-CAS, Obs. Ondrejov), J. Gorosabel (IAA-CSIC and
STScI, Baltimore), S. Guziy (IAA-CSIC), J. M. Castro
Cer�n (STScI), P. Kilmartin (Mt. John Obs.), Ph. Yock
(Univ. of Auckland) and A. J. Castro-Tirado (IAA-CSIC)
 
communicate:
 
"Following the detection of the X-ray flash 030723 by
HETE-2, we have imaged the entire error box with the
0.6-m telescope (+MOA camera) at Mt. John Observatory
in wide R- and B-band filters (3 x 300-s each) starting
on July 23.59 UT (i.e. 7.6 hr after the event).
Comparison of a single R-band frame with the DSS-2 (R-
-band) reveals no optical transient down to the DSS-2
limiting magnitude."

XRF030723 (=H2777): An X-ray Flash Localized by the HETE WXM and SXC

G. Prigozhin, N. Butler, G. Crew, J. Doty, A. Dullighan, R.
Vanderspek, J. Villasenor, T. Cline, J. G. Jernigan, A. Levine, F.
Martel, E. Morgan, G. Monnelly, 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;

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

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

write:

At 06:28:17.45 UTC (23297.45 s UT) on 23 July 2003, the HETE FREGATE, 
WXM, and SXC instruments detected an X-ray flash, designated 
XRF030723 (=H2777), located at high galactic latitude (b = 50 
degrees).

The burst triggered the WXM in the 2-25 keV energy band. The burst 
signal-to-noise was ~9.  A GCN burst alert was issued 42s later, 
reporting a flight-derived WXM localization with a 30 arcmin radius 
(90% confidence). Ground analysis of the WXM data produced a 
localization that was reported in a GCN Notice at 09:47:25 UT. The 
WXM data provided a localization that can be expressed as a 90% 
confidence circle that is 9.4 arcminutes in radius and is centered 
at--

WXM-ground:   RA= +21h 48m 52s,  Dec= -27d 41' 16"  (J2000)

Ground analysis of the SXC data provided an initial localization that 
was disseminated as a GCN Notice at 13:38:19 UT. A refined SXC 
localization can be expressed as a 90% confidence circle that is 2 
arcmin in radius and is centered at--

SXC-Ground:   RA= +21h 49m 27.4s, Dec= -27d 42' 01"  (J2000)


The burst duration (t90) in the 7-30 keV band was ~23 s. A total of 
1210 counts were detected by Fregate during that interval, 
corresponding to a fluence of ~2 x 10-7 ergs cm-2. The peak flux in a 
1.2 s bin was >3 x 10-8 ergs cm-2 s-1 (ie >0.9 x Crab flux) in the 
same energy band.

In the 30-400 keV band, the fluence was < 0.7 x 10-7 ergs cm-2, which 
is  < 0.4 times the fluence in the 7-30 keV band; thus we conclude 
that H2777 is an X-ray flash.

A light curve and finding chart for XRF030723 is provided at the following URL:

http://space.mit.edu/HETE/Bursts/GRB030723

This message may be cited.