GRB 080623

T. N. Ukwatta (GSFC/GWU), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), O. Godet (U Leicester),
S. T. Holland (CRESST/USRA/GSFC), S. D. Hunsberger (PSU),
J. A. Kennea (PSU), A. Moretti (INAF-OAB), K. L. Page (U Leicester),
D. M. Palmer (LANL), D. Perez (U Leicester), M. Perri (ASDC) and
G. Stratta (ASDC) report on behalf of the Swift Team:

At 10:25:28 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080623 (trigger=315080).  Swift did not immediately slew
because of an Earth observing constraint. 
The BAT on-board calculated location is 
RA, Dec 237.660, -62.038, which is 
   RA(J2000)  =  15h 50m 38s
   Dec(J2000) = -62d 02' 16"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showes several overlapping peaks
with a duration of about 25 sec.  The peak count rate
was ~2500 counts/sec (15-350 keV), at ~7 sec after the trigger. 

XRT and UVOT observations will begin when the source comes out of 
Earth constraint near T+21 minutes. 

Burst Advocate for this burst is T. N. Ukwatta (tilan.ukwatta AT gmail.com). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)

D. Perez (U. Leicester-U. Jaen), K. Page, P. Evans, A. Beardmore (U. 
Leicester) report on behalf of the Swift XRT Team

The XRT began observing the field at 10:47:31.4 UT, 22.0 minutes after the 
BAT trigger. Using promptly downlinked data we find a fading, uncatalogued 
X-ray source located at RA, Dec 237.66083, -62.04897 which is equivalent 
to:
   RA(J2000)  = 15h 50m 38.60s
   Dec(J2000) = -62d 02' 56.3"
with an uncertainty of 3.0 arcseconds (radius, 90% containment). This
location is 39 arcseconds from the BAT onboard position, within the BAT
error circle.

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
2.59e+21 cm^-2 (Kalberla et al. 2005).

S. T. Holland (CRESST/USRA/GSFC) reports on behalf of the Swift/UVOT
Team:

    UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 1331 seconds after the BAT trigger. No
afterglow candidate has been found in the initial data products. The
2.7'x2.7' sub-image covers 100% of the XRT error circle (Perez, et
al., 2008, GCN Circ. 7895
Loading...
 
 ). The 3-sigma upper limit is 21.1 mag.  No
correction has been made for the large expected extinction
corresponding to E(B-V) of 0.35 mag.  The USNO B1.0 star 279-072176 is
located 2.07 arcsec from the centre of the XRT error circle.

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

We imaged the field of GRB 080623 detected by SWIFT
(trigger 315080) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 425.1s after the GRB trigger
(14.8s after the notice). The elevation of the field
decreased from 12 degrees above horizon and weather
conditions were good but only four images of 90s were
taken due to the end of the night.

The date of trigger : t0 = 2008-06-23T10:25:28.44

We do not detect any optical transient
at the XRT position (Ukwatta et al. GCNC 7894)
with the following limiting magnitudes:

The first image is 90.0s exposure:
t0+425s to t0+515s : R > 16.2

We co-added the four exposures:
t0+425s to t0+802.0s : R > 17.0

This last value is conservative because
the star density is high and the spatial
sampling of TAROT (i.e. 3.3 arcsec/pix) is not
adapted to separate close sources fainter than
mag 17.0 at the XRT position.

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

N.B. Galactic coordinates are lon=322.3398 lat= -6.1221
and the galactic extinction in R band is 0.94 magnitudes
estimated from D. Schlegel et al. 1998ApJ...500..525S.

This message may be cited.

A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 199 s of overlapping XRT Photon Counting mode and UVOT
data for GRB 080623, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 237.66166, -62.04919 which is equivalent
to:

RA (J2000): 15h 50m 38.80s
Dec (J2000): -62d 02' 57.1"

with an uncertainty of 2.4 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest position
can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is
described by Goad et al. (2007, A&A, 476, 1401
http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an
extension of this method.

This circular was automatically generated, and is an official product of the
Swift-XRT team.

W. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC),
E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD), D. Palmer (LANL),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+1390 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 080623 (trigger #315080)
(Ukwatta, et al., GCN Circ. 7894
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 237.667, -62.044 deg which is 
   RA(J2000)  =  15h 50m 40.1s 
   Dec(J2000) = -62d 02' 36.7" 
with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 33%.
 
The mask-weighted light curve shows four overlapping peaks starting
at ~T-1 sec and ending at ~T+18 sec.  T90 (15-350 keV) is 15.2 +- 5 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-0.7 to T+16.0 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.35 +- 0.15.  The fluence in the 15-150 keV band is 1.0 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+7.23 sec in the 15-150 keV band
is 2.0 +- 0.3 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/315080/BA/

D. Perez (U. Leicester-U. Jaen), K.L. Page (U. Leicester), T. N. Ukwatta
(GSFC/GWU), report on behalf of the Swift-XRT team:


We have analysed the first three orbits of data obtained for GRB 080623
(Ukwatta et al., GCN Circ. 7894
Loading...
 
 ), covering 4.3ks of Photon Counting (PC)
mode data. The UVOT-enhanced XRT position was given by Beardmore et al.
in GCN Circ. 7898
Loading...
 
 .

The light-curve can be fitted with a single powerlaw with a decay of
alpha ~1.0 +/- 0.1.


The first three orbits of PC data can be modelled with an absorbed
powerlaw, with Gamma = 2.03 +/- 0.14 and total NH = (0.37 +/-
0.05)x10^22 cm^-2, in excess of the Galactic value of 0.26x10^22 cm^-2.

The observed (unabsorbed) flux over this time interval is 8.05 x10^-12
(1.34x10^-11) erg cm^-2 s^-1.  The counts to observed flux conversion is
5.3x10^-11 erg cm^-2 count^-1.

If the light-curve continues to decay at alpha ~ 1.0, the count rate at
24 hours is predicted to be 0.0086 count s^-1, corresponding to an
observed flux of 4.5x10^-13 erg cm^-2 s^-1.

This is an official product of the Swift-XRT team.

A. A. Breeveld (MSSL/UCL) and T. N. Ukwatta (GSFC/GWU) report on behalf
of the Swift/UVOT team.

The Swift Ultra-Violet/Optical Telescope (UVOT) began settled
observations of GRB 080623 (Ukwatta et al., GCN Circ. 7894
Loading...
 
 ) 22.15 
minutes after the trigger, as reported in Holland, GCN Circ. 7896
Loading...
 
 .  We 
confirm that no afterglow is detected at the position of the enhanced 
XRT position (Beardmore et al., GCN Circ. 7898
Loading...
 
 ) in the initial finding 
chart or subsequent summed images.

The following table gives the 3 sigma upper limits in all filters.

Filter  T_start(s)  T_stop(s)  Exp(s)  Mag UL (3sig)

white   1329        1428       98.1    >20.4
white   1559        2713       76.9    >20.3
white   8133        8332      196.6    >20.8
v       1436        2598      155.6    >19.0
b       1535        2698      155.5    >19.9
u       1510        2673      155.4    >19.7
uvw1    1486        2648      155.5    >19.4
uvm2    1460        2623      155.6    >19.1
uvw2    1575        2573      136.1    >19.3

The values quoted above are in the UVOT photometric system (Poole et al.
2008, MNRAS, 383, 627).  No correction has been made for the large 
expected extinction corresponding to E(B-V) of 0.35 mag in
the direction of the burst (Schlegel et al. 1998).

A. Updike (Clemson Univ.), S. Loew, J. Greiner, T. Kruehler,
A. Kuepcue Yoldas, A. Yoldas,  (all MPE Garching),
G. Szokoly (Eoetvoes Univ., Budapest and MPE Garching),
report for the GROND team:

We observed the field of GRB 080623 detected by Swift/BAT (Ukwatta et al.
2008, GCN 7894
Loading...
 
 ) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405), mounted at the 2.2m MPI/ESO telescope at La Silla
(Chile). A first epoch started on Jun. 23 at 22:50 UT (12.3 hrs after the
GRB) and continued for 2.5 hours; the second epoch was obtained on Jun. 24
at 23:50 UT (mid-time).

We do not detect any new source within the astrometrically corrected XRT
position (Beardmore et al. 2008, GCN 7898
Loading...
 
 ).

We note that there is a bright star at the border of the XRT error circle
and a fainter one just outside the XRT error circle.  A finding chart can
be found at http://www.mpe.mpg.de/~jcg/grb080623.html .  Both objects are
visible in DSS2-R and are constant between our two epochs.  Image
subtraction revealed no hidden sources.

Limiting magnitudes inside the XRT error circle are g'>24.3, r'>23.5,
i'>21.8, z'>21.7, J>20.2, H>19.4, K>17.5, calibrated against USNO-B1 and
2MASS stars.

Y. Terada, M. Tashiro, Y. Urata, K. Onda, A. Endo, N. Kodaka, K. Morigami, 
T. Sugasahara, W. Iwakiri (Saitama U.),
M. Ohno, M. Kokubun, M. Suzuki, T. Takahashi (ISAS/JAXA),
Y. Fukazawa, T. Takahashi, T. Uehara, C. Kira, Y. Hanabata (Hiroshima U.), 
K. Yamaoka, S. Sugita (Aoyama Gakuin U.),
Y. E. Nakagawa, T. Tamagawa (RIKEN), 
T. Enoto, K. Nakazawa, K. Makishima (Univ. of Tokyo), 
E. Sonoda, M. Yamauchi, H. Tanaka, R. Hara (Univ. of Miyazaki), 
S. Hong (Nihon U.), on behalf of the Suzaku WAM team, report:

The long GRB 080623 (Swift/BAT trigger #315080 ; Ukwatta et al., GCN 7894
Loading...
 
 ) 
was detected by the Suzaku Wide-band  All-sky Monitor (WAM) which covers 
an energy range of 50 keV - 5 MeV at 10:25:28 UT on 23 July 2008 (=T0). 
The observed light curve shows a multi-peaked structure starting at T0, 
ending at T0+10 s with a duration (T90) of about 7 seconds. The fluence in 
100 - 1000 keV was (1.6 +/- 0.4) E-6 erg/cm^2. The 1-s peak flux measured 
from T0+ 8 s was 0.5 +/- 0.4 photons/cm^2/s in the same energy range.

Preliminary result shows that the time-averaged spectrum from T0 to T0+10 s
is well fitted by a single power-law with a photon index of 2.0 -0.9+1.0
(chi^2/d.o.f =  5.6 / 8) at the 150 - 600 keV bandpass.
----

All the quoted errors are at statistical 90% confidence level,
in which the systematic uncertainties are not included.

----
The light curves with 1-sec time resolution for this burst will be 
appeared at the following URL.
 http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/untrig/grb_table.html

[GCN OPS NOTE(30jun08): Per author's request, the Subject was changed
from "080523" to "080623".]