GRB 080613B

C. B. Markwardt (CRESST/GSFC/UMD), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), G. Cusumano (INAF-IASFPA),
C. Gronwall (PSU), C. Guidorzi (INAF-OAB),
S. T. Holland (CRESST/USRA/GSFC), J. Mao (INAF-OAB),
F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),
J. P. Osborne (U Leicester), K. L. Page (U Leicester),
M. Stamatikos (NASA/ORAU), R. L. C. Starling (U Leicester),
G. Tagliaferri (INAF-OAB) and H. Ziaeepour (UCL-MSSL) report on
behalf of the Swift Team:

At 11:12:37 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080613B (trigger=313954).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is
RA, Dec 173.797, -7.098 which is
   RA(J2000) = 11h 35m 11s
   Dec(J2000) = -07d 05' 53"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty).  The BAT light curve shows multiple overlapping
peaks with a duration of about 50 sec.  The peak count rate
was ~10000 counts/sec (15-350 keV), at ~T+0 sec after the trigger. 

The XRT began observing the field at 11:13:47.4 UT, 69.5 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 173.79896, -7.10590 which
is equivalent to:
   RA(J2000)  = 11h 35m 11.75s
   Dec(J2000) = -07d 06' 21.2"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 29 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 3.83e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 79 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. The 3-sigma upper limit is 19.7 mag. The 8'x8' region for
the list of sources generated on-board covers 100% of the XRT error circle. The
list of sources is typically complete to about 18 mag. No correction has been
made for the expected extinction corresponding to E(B-V) of 0.04. 

Burst Advocate for this burst is C. B. Markwardt (Craig.Markwardt AT nasa.gov). 
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.)

J. Mao, C. Guidorzi, F. Pasotti (INAF-OAB) and C. B. Markwardt 
(CRESST/GSFC/UMD),
report on behalf of the Swift-XRT team:

The Swift-XRT began observing GRB 080613B (trigger=313954, Markwardt et
al., GCN Circ. 7873
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 ) in Windowed Timing (WT) mode, 76 s after the BAT
trigger. The data of the first orbit consist of 149 s in Windowed Timing
mode and 794 s in Photon Counting mode.

Using 757 s of overlapping XRT Photon Counting mode and UVOT data, 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 = 173.79773, -7.10501 which is equivalent to:

RA (J2000): 11 35 11.46
Dec (J2000): -07 06 18.0

with an uncertainty of 2.3 arcsec (radius, 90% confidence).

The light curve from 76 to 219 s can be modelled  as a power law with a 
photon index
of 2.15 +/- 0.11 (90%), followed by a sudden drop of about 2 orders of 
magnitudes up to ~400 s,
after which the decay resumes a value around 1.5.

The WT mode spectrum spanning from 76 to 219 s can be fit by a
power-law model, with a spectral photon index of 1.17 +/- 0.07 and an 
absorbing column
density of 3.7 (-2.0, +2.3)e20 cm^-2 , consistent with the average Galactic
one, 3.2e20 cm^-2.

The corresponding observed (unabsorbed) 0.3-10 keV flux is 1.05e-9 (1.09e-9)
erg cm^-2 s^-1.

If the burst continues to decay at the same rate, we predict an
XRT count rate of 6e-5 count/s at T+24 hours, which corresponds
to an observed 0.3-10 keV flux of approximately 3.5e-15 erg cm^-2 s^-1.
However, we caution about this prediction due to the presently large
uncertainty on the decay rate.

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

T. Ukwatta (GWU), S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC),
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)
(i.e. the Swift-BAT team):
 
Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 080613B (trigger #313954)
(Markwardt, et al., GCN Circ. 7873
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 ).  The BAT ground-calculated position is
RA, Dec = 173.806, -7.102 deg, which is 
   RA(J2000)  =  11h 35m 13.3s 
   Dec(J2000) = -07d 06' 06.5" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 89%.
 
The mask-weighted light curve shows several overlapping peaks in a FRED-like
envelope lasting out to ~T+180 sec.  T90 (15-350 keV) is 105 +- 35 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-5.3 to T+236.5 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.39 +- 0.06.  The fluence in the 15-150 keV band is 5.8 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+2.23 sec in the 15-150 keV band
is 2.7 +- 0.2 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/313954/BA/

W.Landsman (GSFC/Adnet) and C. Markwardt (CRESST/GSFC/UMD) , on behalf 
of the Swift/UVOT team.

The Swift Ultra-Violet/Optical Telescope (UVOT) began settled 
observations of GRB 080613B (trigger 313954) 79 seconds after the BAT 
trigger (Markwardt et al.,GCN Circ. 7873).  No afterglow is detected at 
the enhanced XRT position (Mao et al., GCN Circ.7875
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 ) in the initial 
white finding chart or subsequent summed images. The limiting 
magnitudes  (3-sigma in 5" radius apertures) in each of the UVOT filters 
are as follows:

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

white       79       180        98     >20.4
white       79      7227       627     >21.4
v          185      7566      1167     >20.1
b          665      7023       451     >20.5
u          640     13348       312     >20.1
uvw1       616     13323      1179     >20.8
uvm2       591     12415      1102     >21.2
uvw2       695     18103       936     >21.0

The values quoted above are in the UVOT photometric system (Poole et al. 
2008, MNRAS, 383, 627).  They are not corrected for the expected 
Galactic extinction corresponding to a reddening of E(B-V)=0.04 mag in 
the direction of the burst (Schlegel et al. 1998).

Christina C. Thoene, Daniele Malesani, Johan P. U. Fynbo (DARK), Lison Malo
(Universite de Montreal), Richardo J. Cardenes and Anlaug Amanda
Djupvik (NOT) report:

We observed the field of GRB 080613B (Markwardt et al., GCN 7873
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 ) on
June 13 with the NOT on La Palma using StanCam
and NOTCAM. Observations of 4x300s in R band were obtained with
StanCam starting at UT 21:57 and 5x270s with NOTCAM in the Ks band
starting UT 23:17.
In the stacked images of both filters we do not detect any optical
counterpart within the XRT error circle (Mao et al. GCN 7875
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 ). The
limiting magnitudes are about R=22 mag and Ks=17.6 based on USNO and
2MASS stars in the field respectively.

[GCN OPS NOTE(14jun08): Per author's request, the two references
were added and the author list order was chanegd.]

C. Clemens, A. Updike (Clemson University), T. Kruehler, J. Greiner, A. Kupcu 
Yoldas, A. Yoldas (all MPE Garching) and G. Szokoly (Eoetvoes Univ., Budapest 
and MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 080613B (Swift trigger 313954; Markwardt et al., 
GCN #7873
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 ) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, 
PASP 120, 405) mounted at the 2.2m ESO/MPI telescope at La Silla Observatory 
(Chile).

Observations started at 22:47 UT on June 13th, 2008, 11.6 hrs after the GRB 
trigger.

We do not detect any object within the refined 3.6'' Swift-XRT error circle 
reported by Mao et al. (GCN #7875
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 ) to the following 3-sigma upper limits:

g' > 24.4,
r' > 24.4,
i' > 23.5,
z' > 23.5 and
J > 22.4.

Given upper limits are calibrated against USNO-B1 as well as 2MASS field 
stars.

S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, P.
Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind 
team report:

The long GRB 080613B (Swift-BAT trigger
#313954: Markwardt et al., GCN 7873
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 , Ukwatta et al., GCN 7876
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 ) triggered 
Konus-Wind at T0=40358.636 s UT (11:12:38.636).

The burst light curve shows a multipeaked structure with a duration of ~30s.

As observed by Konus-Wind the burst
had a fluence of 2.21(-0.38, +0.44)x10^-5 erg/cm2,
and a 256-ms peak flux measured from T0-0.144 s
of 4.76(-1.24, +1.39)x10^-6 erg/cm2/s
(both in the 20 keV - 3 MeV energy range).

The time-integrated spectrum of the burst
(from T0 to T0+33.024 s) is well fitted (in the 20 keV-3 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -1.05 +/- 0.18
and Ep = 733(-200, +285) keV (chi2 = 56.6/65 dof).
Fitting by GRBM (Band) model yields the same alpha and Ep,
and only an upper limit on the high energy photon index: beta < -2.05
(chi2 = 56.5/64 dof).

All the quoted errors are at the 90% confidence level.

The Konus-Wind light curve of this GRB is available
at http://www.ioffe.rssi.ru/LEA/GRBs/GRB080613_T40358/

M. Yoshida, K. Yanagisawa, Kuroda, D., Y. Shimizu, S. Nagayama,
Toda, H. (OAO, NAOJ) and N. Kawai (Tokyo Tech) report on behalf
of the MITSuME collaboration:

We performed optical imaging observation (g', Rc, and Ic) of the
field of GRB 080613B (Markwardt et al. GCN 7873
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 ) with 50cm MITSuME
telescope at Okayama Astrophysical Observatory from 11:19:09 UT
(6m 31s after the trigger) to UT 12:43:30 on June 13 2008.

We could not identify any new source in the XRT error circle
(Mao et al. GCN7875
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 ). Three sigma limiting magnitudes of our
observation are listed below.


Observation date: 2008-06-13 UT

Start-UT   mid-UT    exp-T    g'      Rc      Ic
----------------------------------------------------
11:19:09   11:31:16  10min    >18.4   >18.3   >18.0
11:31:26   12:07:28  60min    >18.7   >18.4   >18.1
----------------------------------------------------