GRB 080411

F. E. Marshall (NASA/GSFC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), N. Gehrels (NASA/GSFC), O. Godet (U Leicester),
S. T. Holland (CRESST/USRA/GSFC), H. A. Krimm (CRESST/GSFC/USRA),
C. B. Markwardt (CRESST/GSFC/UMD), K. M. McLean (GSFC/UMD),
C. Pagani (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL),
M. Stamatikos (NASA/ORAU), R. L. C. Starling (U Leicester),
T. N. Ukwatta (GSFC/GWU), L. Vetere (PSU) and P. A. Ward (MSSL-UCL)
report on behalf of the Swift Team:

At 21:15:32 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080411 (trigger=309010).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 38.018, -71.342 which is 
   RA(J2000)  =  02h 32m 04s
   Dec(J2000) = -71d 20' 30"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The TDRSS BAT lightcurve shows the burst
starting with a fast rise from background to ~13,000 counts/sec in
approximately 0.5 sec.  There are several peaks after that with the
fourth peak (T+19 sec) at 75,000 cnts/sec.  There are several more peaks 
after that lasting out to at least T+70 sec. 

The XRT began observing the source at 21:16:42 UT (71 s after the 
trigger).  The XRT centroided on something very bright. 
We have lost most of our prompt diagnostic messages
because the spacecraft switched from TDRSS telemetry
to Malindi telemetry shortly after the burst, and our
prompt image does not include the source.  However,
the information within the header indicates that the
source is located near the center of the XRT field
of view, and is therefore probably real.  If real,
the position is 
GRB_RA:           37.9860d {+02h 31m 56.6s} (J2000),
GRB_DEC:         -71.3021d {-71d 18' 07.5"} (J2000),

with an uncertainty of 4.3 arcseconds (90% confidence 
radius), and the flux during this image was approximately
4.4e-7 cgs (~ 10 Crabs) in the 0.1 s image.  The XRT 
position is 148 arcseconds from the BAT position. 

No UVOT data for this burst are currently available. 

Burst Advocate for this burst is F. E. Marshall (marshall AT milkyway.gsfc.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.)

T. Kruehler, A. Kupcu Yoldas, J.Greiner, C. Clemens, 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 080411 detected by BAT (Marshall et al., GCN
#7584
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 ) simultaneously in g'r'i'z'JHK with GROND mounted at the 2.2m
ESO/MPI telescope at La Silla Observatory (Chile).

Observations started in twilight at 23:15 UT on April 11th, 2008, 2h after
the burst.

We detect a new bright point source just at the edge of the XRT error
circle (Marshall et al. GCN #7584
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 ) at

RA (J2000.0) = 02:31:55.20
DEC (J2000.0) = -71:18:07.6

with an uncertainty of 0.8".

The object is detected in all of the seven bands, implying a redshift
smaller than 3.5.

Preliminary photometry yields an r' band magnitudes of 16.5 calibrated
against USNO field stars.

The given magnitudes are not corrected for the Galactic foreground
reddening of E(B-V)=0.03 mag (Schlegel et al., 1998).

Christina C. Thoene (DARK/NBI), Annalisa De Cia (Univ. Iceland), Daniele 
Malesani, and Paul M. Vreeswijk (DARK/NBI), report:

We observed the optical afterglow of GRB 080411 (Marshall et al., GCN 
7584
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 ; Kruehler et al., GCN 7586
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 ) wih the ESO VLT equipped with FORS1 
with grism 300V. In a 600 s exposure taken at large airmass (average of 
2.45) the afterglow trace is clearly detected. The mean time of the 
observations is Apr 11.987 UT (2.4 hr after the trigger). In the 
acquisition image, we measure R = 17.25 based on archival zeropoints.

We detect very strong absorption lines from Mg II, Mg I, Fe II and 
several other ions at a redshift z = 1.03. Given the strength of the 
features, we consider this to be the redshift of the GRB. We caution 
that the wavelength calibration is based on archival data.

We acknowledge excellent support from the ESO staff, who carried out 
this difficult observation, in particular Swetlana Hubrig.

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

Using 1122 s of overlapping XRT Photon Counting mode and UVOT
data for GRB 080411, 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 = 37.97852, -71.30188 which is equivalent
to:

RA (J2000): 02h 31m 54.84s
Dec (J2000): -71d 18' 06.8"

with an uncertainty of 1.5 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.

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

The long GRB 080411 (Swift-BAT trigger #309010: Marshall et al., GCN
7584
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 ) triggered Konus-Wind at T0=76532.496 s UT (21:15:32.496).

The burst light curve shows several pulses with a total duration of ~70s.

As observed by Konus-Wind the burst
had a fluence of 6.29(-0.29, +0.31)x10^-5 erg/cm2,
and a 64-ms peak flux measured from T0+17.936 s
of (1.28 +/- 0.16)x10^-5 erg/cm2/s
(both in the 20 keV - 2 MeV energy range).

The time-integrated spectrum of the burst
(from T0 to T0+74.24 s) can be fitted (in the 20 keV-2 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -1.51(-0.05, +0.04),
and Ep = 259(-27, +35) keV (chi2 = 64.5/59 dof).

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

Assuming z = 1.03 (Thoene et al., GCN 7587
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 ) and a standard
cosmology model with H_0 = 70 km/s/Mpc, Omega_M = 0.27, Omega_\Lambda =
0.73, the isotropic energy release is E_iso ~1.81x10^53 erg,
the maximum luminosity is (L_iso)_max ~7.48x10^52 erg/s, and
Ep_rest ~524 keV.

The Konus-Wind light curve of this GRB is available
at http://www.ioffe.rssi.ru/LEA/GRBs/GRB080411_T76532/

O. Godet, A. P. Beardmore, K. Page (U. Leicester) reports on behalf the Swift-XRT team: 

The XRT began observing the field of GRB 080411 (trigger=309010, Marshall et
al., GCN Circ. 7584
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 ) at 21:16:42 UT, 71 seconds after the BAT trigger.  We
analysed the first orbit of WT data (0.9 s) at T0+209s and the first 4 orbits
of PC data (~3.6 ks) from T0+4.2ks to T0+17.4ks.

The X-ray light-curve shows a broken power-law behaviour. Since there are 
no data between the WT and PC observations, it is difficult to constrain 
the initial decay and break time. The late decay from the PC data gives a 
decay slope of 0.98+/-0.05. Using ground data, we confirmed that the initial 
intense flux reported by Marshall et al. (GCN Circ. 7584
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 ) from the 0.1s image 
taken at T0+71s is real and is likely to correspond to the end of the activity 
observed in the BAT. That implies an initial rapid decay in the XRT light-curve.

The WT spectrum contains only 20 counts. So, the fitting parameters are not
well constrained when the spectrum is fitted by an absorbed power-law (N_H <
4.6e21 cm^-2 in excess with respect to the Galactic absorption along the burst
line of sight (5.7e20 cm^-2, Kalberla et al. 2005) and a photon index of 2.85
+1.54/-1.05).  The PC spectrum from T0+4.2ks to T0_17.4ks is fitted well by 
an absorbed power-law with a photon index of 2.14 +/- 0.09 and an absorption 
column of (1.5 +/- 0.3)e21 cm^-2, in excess with respect to the Galactic one.

The observed (unabsorbed) flux in the 0.3-10 keV band is 7.1e-10 (1.7e-9) erg
cm^-2 s^-1 for the WT spectrum and 7.2e-11 (1.1e-10) erg cm^-2 s^-1 for the PC
spectrum.

The predicted XRT count rate at T0+1d (T0+3d) is 0.26 (0.07) count s^-1, which
corresponds to an observed 0.3-10 keV flux of 2.7e-11 (7.1e-12) erg cm^-2 s^-1.

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

G. Sato (GSFC/ISAS), 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), F. E. Marshall (GSFC),
K. McLean (GSFC/UMD), D. Palmer (LANL), T. Sakamoto (GSFC/UMBC),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-187 to T+723 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 080411 (trigger #309010)
(Marshall, et al., GCN Circ. 7584
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 ).  The BAT ground-calculated position is
RA, Dec = 37.961, -71.297 deg, which is 
   RA(J2000)  =  02h 31m 50.6s 
   Dec(J2000) = -71d 17' 49.6" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 86%.
 
The mask-weighted light curve shows two clusters of overlapping peaks.
The first starts at T+0.0 sec and rises to a peak in 1 sec.  The second peak
is at T+7 sec; the third at T+10 sec, and the 4th at T+19 sec at 25 cnt/cm2/sec
(15-150 keV).  The lightcurve returns to background before the beginning
of the second cluster of peaks.  The 5th peak starts at ~T+39 sec,
rises linearly, peaking at ~T+41 src at 43 cnts/cm2/sec.  There are two more
much smaller peaks at T+55 and T+64 sec.  The lightcurve returns to background
by ~T+95 sec.  There is a gap in the downlinked data from T+300 to T+420 sec.
It appears that the burst has returned to background well before this gap,
but should later downlinks show on-going activity, we will issue an updated
circular.  T90 (15-350 keV) is 56 +- 1 sec (estimated error including
systematics).
 
The time-averaged spectrum from T-0.0 to T+84.3 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.75 +- 0.03.  The fluence in the 15-150 keV band is 2.64 +- 0.01 x 10^-5 erg/cm2.
The 1-sec peak photon flux measured from T+40.45 sec in the 15-150 keV band
is 43.2 +- 0.9 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/309010/BA/

S. R. Oates and F. Marshall report on behalf of the Swift/UVOT team.

The Swift/UVOT observed the field of GRB 080411 starting at 4202s
after the BAT trigger (Marshall et al., GCN 7584
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 ).  We detect the
afterglow in white, v, b, u and uvw2 filters at the position:

RA(J2000.0)  =  02:31:55.19
DEC(J2000.0) = -71:18:07.30

with an etimated uncertainty of 0.5 arcsec (radius, 90% confidence).
This position is consistent with the optical afterglow position
reported by GROND (Kruehler et al., GCN 7586
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 ). The UVOT did not
perform observations in uvw1 and uvm2 filters. The following
magnitudes were obtained:

Filter    T_Mid(s)   Expo(s)            Magnitude
-----------------------------------------------------
White      4251        98              17.01 +/- 0.03
White      22869       295             18.09 +/- 0.03
v          16808       177             18.05 +/- 0.12
b          4615        197             17.43 +/- 0.05
b          21653       295             18.39 +/- 0.09
u          4410        197             16.46 +/- 0.04
uvw2       16260       886             18.41 +/- 0.07
-----------------------------------------------------

The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E_{B-V} = 0.04 mag (Schlegel et al.,
1998, ApJS, 500, 525). The photometry is on the UVOT flight system
described in Poole et al.  (2008, MNRAS, 383, 627).

F.E. Marshall (NASA/GSFC), O. Godet (U. Leicester) and S.R. Oates (MSSL-UCL)
report on behalf of the Swift team:

The XRT and UVOT instruments on Swift continue to detect GRB 080411 
19 days after the BAT trigger (Marshall et al., GCN Circ. 7584
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 ). 
The X-ray light curve shows a broken power-law behaviour with 
breaks at about T+8 ks and T+240 ks and additional short-term features
at late times. Since the latter break,
the decay index has been 1.54 +/- 0.12, and the 0.6-10 keV flux
at T+1600 ks was 1.3 x 10^-13 ergs/s/cm^2.
The optical light curve also shows a similar broken power-law behaviour.
At T+1600 ks the magnitude (uncorrected for Galactic extinction)
in the broad-band white filter was 22.7 +/- 0.2 using the UVOT 
photometric system (Poole et al. MNRAS 383, 627 (2008)). Recently the 
decay index has been 1.30 +/- 0.03.

Additional Swift observations of GRB 080411 are planned.
Since the optical afterglow is approaching the sensitivity
limit for UVOT, ground-based observations are encouraged.

Please contact the Swift Burst Advocate for this burst
at marshall AT milkyway.gsfc.nasa.gov if you desire
additional information regarding the Swift followup
of this burst.

Aquib Moin (Curtin Institute of Radio Astronomy / Australia Telescope
National Facility), Steven Tingay (Curtin Institute of Radio Astronomy),
Chris Phillips (Australia Telescope National Facility), Gregory Taylor
(University of New Mexico), Mark Wieringa (Australia Telescope National
Facility) and Ralph Martin (Perth Observatory) report:

We observed the BAT refined position of the GRB 080411 (GCN 7591
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 ) at 4.8
and 8.456 GHz with the Australia Telescope Compact Array (ATCA) on June
01, 2008 between 03:43:05 UT and 09:43:35 UT.

We did not detect a radio source at the BAT position of the GRB 080411
(GCN 7591
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 ). The radio flux density at the GRB position is -0.101 +/-
0.324 mJy at 4.8 GHz and 0.188 +/- 0.374 mJy at 8.456 GHz (1-sigma).

The Australia Telescope Compact Array (/ Parkes telescope / Mopra
telescope / Long Baseline Array) is part of the Australia Telescope
which is funded by the Commonwealth of Australia for operation as a
National Facility managed by CSIRO.

See field image at:

http://astronomy.ivec.org/dokuwiki/doku.php/grb/grb_080411_field_image