GRB 070508

D. Grupe (PSU), S. D. Barthelmy (GSFC), M. M. Chester (PSU),
G. Cusumano (INAF-IASFPA), C. B. Markwardt (GSFC/UMD),
F. E. Marshall (NASA/GSFC), C. Pagani (PSU), D. M. Palmer (LANL),
J. L. Racusin (PSU), M. Stamatikos (NASA/ORAU) and L. Vetere (PSU)
report on behalf of the Swift Team:

At 04:18:17 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070508 (trigger=278854).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 312.783, -78.368 which is 
   RA(J2000)  =  20h 51m 08s
   Dec(J2000) = -78d 22' 04"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a complex multi-peaked
structure with a duration of at least 40 sec.  The peak count rate
was ~45000 counts/sec (15-350 keV), at ~15 sec after the trigger. 

The XRT began observing the field at 04:19:33 UT, 76 seconds after the
BAT trigger. XRT found a bright, uncatalogued X-ray source
located at RA, Dec 312.7959, -78.3850 which is
RA(J2000)  =  20h 51m 11.0s
Dec(J2000) = -78d 23' 06.0"
with an uncertainty of 5.0 arcseconds (radius, 90% containment). 
This location is 62 arcseconds from the BAT on-board position,
within the BAT error circle. The initial flux in the 2.5s image
was 1.6e-09 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 85 seconds after the BAT trigger. There is a candidate
afterglow in the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	20:51:11.81 = 312.7992
  DEC(J2000) = -78:23:04.9  = -78.3847
with a 1-sigma error radius of about 0.5 arc sec. This position is 2.6 arc sec. 
from the center of the XRT error circle. The estimated magnitude is 19.4 with a
1-sigma error of about 0.5 mag. No correction has been made for the expected
reddening of E(B-V) of 0.14.

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

We imaged the field of GRB 070508 detected by SWIFT
(trigger 278854) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 829s after the GRB trigger
(6s after the notice). The elevation of the field increased from
from 28 degrees above horizon and weather conditions
were good.

The date of trigger : t0 = 2007-05-08T04:18:17.6

The first image is 90.0s exposure in tracking mode
with no filter.
We do not detect the UVOT candidate couterpart mentioned
by Grupe et al. (GCNC 6383) with a limiting magnitude of:
t0+829s to t0+919s : R > 17.8

We co-added a series of exposures with no filter:
t0+829s to t0+1704s : R > 19.7

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

N.B. Galactic coordinates are lon=314.8792 lat=-32.4208
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.

S. Piranomonte, S. Covino, L.A. Antonelli, A. Burzi, L. Calzoletti,  
S. Campana, G.  Chincarini, M.L. Conciatore, S. Cutini, P. D'Avanzo,  
V. D'Elia, F. Dalessio, F.  Fiore, D. Fugazza, P. Goldoni, D. Guetta,  
C. Guidorzi, G.L. Israel,  D. Malesani, N. Masetti, A. Melandri, E.  
Meurs, L. Nicastro, E. Palazzi, E. Pian, D. Rizzuto,  L.  Stella, G.  
Stratta, G. Tagliaferri, G. Tosti, V. Testa, S.D. Vergani,  F. Vitali  
report on behalf of the REM team:

We observed the field of the GRB 070508 (Grupe et al. GCN 6383
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 ) with  
the robotic 60-cm REM telescope located at La Silla (Chile). A
set of observations was performed automatically in the optical and  
near infrared filters (V, R, I and J, H, K, z).

Preliminary analysis of the first frames at 4:34:11 UT (~16 min after  
the burst, ~2 min after the BAT trigger) shows a marginal detection  
of the UVOT afterglow at H~15.2.

Further observations are in progress.

This message may be cited.

E. Berger (Carnegie) and A. Burgasser (MIT) report:

"We observed the position of GRB 070508 (GCN 6383
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 ) with MAGIC on the 
Magellan/Clay 6.5 m telescope starting 28 min after the burst.  In a 180 
sec I-band image we detect a bright object not visible in DSS within the 
XRT error circle at:
 	RA  = 20:51:12.07
 	DEC = -78:23:07.0
with an uncertainty of about 0.5".  This is about 2.5" away from the UVOT 
position."

A. C. Gilmore and P. M. Kilmartin (Mt John Observatory of the University of 
Canterbury) report:

We stacked 20 x 120 second clear exposures of the GRB 070508 taken with a SBIG 
ST9e CCD on a 0.6 m f/6.4 reflector at Mt John Observatory. The exposure set was 
centred on May 8 07:49 UT (3.5 hours after the burst).  Our images do not show 
any object at the coordinates given by Berger (GCN 6386
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 ) to a limiting R 
magnitude of approximately 20.5 based on USNO B1.0 stars.

These observations were made as part of the AAVSO GRB Network, and supported by 
a grant from the Curry Foundation.

D. Grupe, J. Racusin, & C. Pagani (PSU) report on behalf of the Swift/XRT team

We have analyzed the first three orbits of GRB 070508 (Grupe et al., GCN 6383
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 ) 
with total observing times of 1.3 ks in Windowed Timing mode and 1.3 ks in 
Photon Counting mode in the Swift XRT.
The Photon Counting mode image of the third orbit provides a refined XRT 
position at RA, DEC= 312.7993, -78.3848, which is

RA(J2000) = 20h 51m 11.84s
Dec(J2000) = -78d 23' 05.4"

with an error of 5.6" (90% confidence). This position is 2.6" away from the 
preliminary XRT position reported in GCN 6383
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  and 1
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 .9" from the optical 
position given in GCN 6386
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  (Berger & Burgasser).

The XRT observations in Windowed Timing more started at the end of a flare and 
both Windowed timing and Photon Counting mode display the rapid decay of the 
afterglow with a decay slope of 1.15+/-0.11 measured from the PC data. The 
prediction 24h after the burst is a 0.3-10.0 keV flux of 3.2e-12 ergs/s/cm2 
or about 0.04 XRT counts/s.

The Windowed Timing mode data can be fitted by a single power law with a 
photon index Gamma=2.05+-0.04 and an absorption column density of 
NH=(3.8+/-0.2)e21cm-2. The Galactic absorption density in the direction of 
the burst is 8.60e20cm-2 (Dickey & Lockman, 1990). The PC data are consistent 
with this result. According to the relation given in Grupe et al. (2007, AJ, 
133, 2216) the excess absorption suggests that the burst has a redshift of 
less than 2.6.

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

Christina C. Thoene, Johan P. U. Fynbo (DARK) and Andrew Williams (Perth
Observatory) report:

We observed the OT of GRB 070508 (GCN 6383
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 , Grupe et al.) with DFOSC at
the Danish 1.54m on La Silla in V, R and I band, starting at May 8, 08:15
UT (3.8h after the burst) until sunrise.
The burst is clearly detected in 300s exposures in R and I band, but
undetected in 600s V band images. At a mean time of 4.1h after the burst,
we measure the following magnitudes (based on preliminary photometric
zeropoints):

I = 20.5 +- 0.2
R = 21.5 +- 0.2
V > 22.9

which indicates a red color. The nondetection in V together with the red
color might suggest a redshift of z > 3.5.
The afterglow is clearly fading between 3.8h and 5.8h after the burst,
showing a rather steep temporal slope in the I band of alpha = 3.1 +-0.6.

[GCN OPS NOTE(08may07): Per author's request, the word 'limit'
was added to the Subject line.]

S. D. Barthelmy (GSFC), L. Barbier (GSFC), J. Cummings (GSFC/UMBC),
E. Fenimore (LANL), N. Gehrels (GSFC), D. Grupe (PSU),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), 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-240 to T+962 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 070508 (trigger #278854)
(Grupe, et al., GCN Circ. 6383
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 ).  The BAT ground-calculated position is
RA, Dec = 312.832, -78.382 deg, which is 
   RA(J2000)  =  20h 51m 19.8s 
   Dec(J2000) = -78d 22' 54.8" 
with an uncertainty of 0.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 62%.
 
The mask-weighted lightcurve consists of ~20 main peaks (between T+0 and T+20 sec).
The emission starts at ~T-20 sec and clearly extends out to T+30 sec
and at a lesser level extends out past T+800 sec.  T90 (15-350 keV) is
21 +- 1 sec (estimated error including systematics).
 
The time-averaged spectrum from T-13.8 to T+33.1 is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.14 +- 0.12, 
and Epeak of 258 +- 134 keV (chi squared 27.7 for 56 d.o.f.).  
For this model the total fluence in the 15-150 keV band is
2.0 +- 0.0 x 10^-5 erg/cm2 and the 1-sec peak flux measured from T+10.84 sec
in the 15-150 keV band is 24.7 +- 0.6 ph/cm2/sec.  
A fit to a simple power law gives a photon index of 1.36 +- 0.03
(chi squared 38.4 for 57 d.o.f.).  All the quoted errors are at the 90%
confidence level.

We note that the TDRSS messages for this burst were delayed in transmission
to the ground because the burst occurred at the beginning of an 11-minute
Malindi downlink session.

B. E. Cobb (Yale), part of the larger SMARTS consortium, reports:

Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
obtained optical imaging of the error region of GRB 070508
(GCN 6383
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 , Grupe et al.) with a mid-exposure time of
2007-05-08 06:25 UT (~2.1 hrs post-burst).  The total summed exposure
time amounted to 36 minutes in I.

A source is detected at the UVOT afterglow coordinates (GRB 6383, Grupe et 
al.) with a magnitude of I=20.7+/-0.3, calibrated using USNO-B1.0 values.

F.E. Marshall (NASA/GSFC) and D. Grupe (PSU) report on behalf of the 
Swift/UVOT team:

UVOT began observing GRB 070508 68s after the BAT trigger 
(Grupe et al., GCN Circ. 6383
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 ). A fading afterglow is  
detected in the White and V filters, while no afterglow is seen
in the B, U, or UV  filters. We use the first white exposure 
to obtain an improved position of

RA(J2000) = 20h 51m 11.68s  Dec(J2000) = -78d 23' 05.0"

with a 90% confidence statistical uncertainty in each axis of 0.5".
There is also a 1-sigma systematic uncertainty in the UVOT
aspect solution of about 0.3". This revised position is 0.6" from 
the initial UVOT position reported by Grupe et al. and 2.3" from the 
position for the I-band object reported by Berger and Burgasser 
(GCN Circ. 6386
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 ).

Thoene et al. (GCN Circ. 6389
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 ) have suggested a redshift of
greater than 3.5 based on their detections in the I and R bands
and lack of detection in V band. The UVOT detection in the V filter 
indicates a redshift of less than 5.

Photometry results with statistical errors are given below
for the 7 UVOT filters. The start and stop times (in seconds)
are referenced to the trigger time, and the total exposure
time (Exp.) is given in seconds.

           T_start  T_stop    Exp.          Mag

White         86      185      98         19.8+/-0.12 (1-sigma)
V            192      571     393         19.7+/-0.22 (1-sigma)
B            669     1946      86        >19.6 (90% confidence)
U            644     1933     117        >18.4 (90% confidence)
UVW1         620     7389     283        >18.2 (90% confidence)
UWM2        1705     7215     236        >17.8 (90% confidence)
UVW2         698     6806     294        >18.6 (90% confidence)

No correction has been made for the expected Galactic reddening of 
E(B-V)=0.14

T. Uehara, M. Ohno, T. Takahashi, Y. Fukazawa, C. Kira (Hiroshima U.),
T. Enoto, R. Miyawaki, K. Nakawaza, K. Makishima (Univ. of Tokyo),
K. Yamaoka, Y. E. Nakagawa, S. Sugita (Aoyama Gakuin U.),
Y. Urata, K. Onda, M. Suzuki, K. Morigami, N. Kodaka, M. Tashiro (Saitama U.),
M. Suzuki, T. Tamagawa, Y. Terada (RIKEN), S. Hong (Nihon U.),
M. Kokubun, T. Takahashi (ISAS/JAXA), 
E. Sonoda, M.Yamauchi (Univ. of Miyazaki), and Suzaku WAM team report

The bright, long burst, GRB 070508 (Swift/BAT trigger #278854 ; D. Grupe et al., GCN Circ. 6383
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  ),
was detected at 04:18:21 UT (=T0) by the Suzaku Wide-band All-sky 
Monitor (WAM) which covers an energy range of 50 keV - 5 MeV.
The observed light curve shows multiple peaked structures 
with a duration (T90) of nearly 12 seconds.
The fluence in 100-1000 keV was (3.0+/-0.1) * 10^-5 erg/cm^2.
The 1-s peak flux was 11.6+/-0.5 photons/cm^2/s
in the same energy range.


Preliminary result shows that the time-averaged spectrum from T0-4 to T0+26 s
can be described by a power law with an exponential cutoff model, 
in the 100 keV - 1000 keV range as follows:

dN/dE =  E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
alpha = 0.96 +/- 0.21 and
Epeak = 233 +/- 12 keV (chi^2/d.o.f. = 29/20).
   

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

The WAM light curve of this event is available at
http://www.astro.isas.ac.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html

Pall Jakobsson (U. Hertfordshire), Johan P. U. Fynbo (DARK, NBI), 
Michael I. Andersen (Potsdam), Andreas O. Jaunsen (U. Oslo),
Christina C. Thoene, Darach Watson, Jens Hjorth, Bo Milvang-Jensen
(DARK, NBI), Nial R. Tanvir (U. Leicester) and P. Moller (ESO) 
report on behalf of a larger collaboration:

Using FORS1 on the Very Large Telescope, we have obtained 3*30 min 
spectra (grism 300V) of GRB 070508 (Grupe et al., GCN 6383
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 ). The 
UVOT optical afterglow candidate (Marshall & Grupe, GCN 6392
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 ) has 
clearly faded in our acquisition image. Using photometric zeropoints 
from the ESO webpages we estimate the afterglow magnitude to be
R ~ 22.0 on May 8.337 (3.79 hours post-burst).

The combined spectrum does not display any obvious absorption 
features. However, a firm upper limit of z < 2.3 can be placed on 
the redshift of GRB 070508 from the lack of Ly-alpha forest lines in 
the spectrum of the afterglow. This is consistent with the UVOT 
observations (Marshall & Grupe, GCN 6392
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 ).

We do detect a tentative emission line at 6781 A. If it corresponds 
to H-alpha at z = 0.033, we would expect to detect H-beta and the 
[O III] doublet in our spectrum. However, no features are visible 
at their predicted locations. The most probable association is with 
[O II] 3728, corresponding to a redshift of z = 0.82. We caution
that the magnitude reported above is then most likely affected by
host galaxy emission.

We thank the Paranal staff for excellent support.

E. Bellm, C. Wigger, M. Bandstra, S. Boggs, W. Hajdas,
D. M. Smith, and K. Hurley on behalf of the RHESSI team report:

As observed by RHESSI, GRB070508 (Grupe et al., GCN 6383
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 )
had a duration of ~18 s starting at about T0=04:18:20 UT.
RHESSI detected significant emission up to ~300 keV.
The preliminary fit to the time-integrated RHESSI spectrum
from T0 - T0+16 s between 30 keV and 10 MeV is a cutoff power law with

alpha = -0.76 +0.52/-0.41
Epeak = 254 +71/-45 keV
(90% confidence levels).

The 30 keV-10 MeV fluence is 1.95 +0.28/-0.23 E-5 erg/cm^2.

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

The long bright GRB 070508 (Swift-BAT trigger #278854:
Grupe et al., GCN 6383
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 ; Barthelmy et al., GCN 6390
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 ), triggered 
Konus-Wind at T0=15502.779 s UT (04:18:22.779).
This burst also triggered Konus-A at T0=15503.790 s UT
(04:18:23.790)

The burst started at T-T0 ~-13 s and had a duration of ~40 s.
As observed by Konus-Wind the burst
had a fluence of 3.97(-0.23, +0.07)x10^-5 erg/cm2,
and a 64-ms peak flux measured from T0+8.832 s
8.30(-1.11, +1.03)x10^-6 erg/cm2/s
(both in the 20 keV - 1 MeV energy range).
The burst shows strong spectral evolution.

The time-integrated spectrum of the burst
(from T0 to T0+27.904 s) can be fitted (in the 25 keV - 1 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ E^(-alpha)*exp(-E*(2-alpha)/Ep)
with alpha = 0.81 +/- 0.07
and Ep = 188 +/- 8 keV (chi2 = 65/52 dof).

Assuming z = 0.82 (Jakobsson et al., GCN 6398
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 )
and a standard cosmology model with H_0 = 70 km/s/Mpc,
Omega_M = 0.3, Omega_\Lambda = 0.7,
the isotropic bolometric energy release is E_iso ~7.0x10^52 erg, and
the maximum bolometric luminosity is (L_iso)_max ~1.1x10^53 erg/s.

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/GRB070508_T15502/

A. Pelangeon & J-L. Atteia (LATT-OMP) report:

The intense burst GRB 070508 detected by SWIFT-BAT
(Grupe et al., GCNC 6383) was also observed by other spacecrafts.
Thanks to the published spectral parameters obtained from the different
spectral analyses performed, we have computed 4 pseudo-redshift(**)
for this burst.

Here are the results (the errors on the pseudo-z are at the 90% c.l.):

- From the spectral parameters obtained with the Konus-WIND data
(Golenetskii et al., GCNC 6403)
we obtain: pz = 1.15 +/- 0.15

- From the spectral parameters obtained with the Swift-BAT data
(Barthelmy et al., GCNC 6390; Grupe et al., GCNR 54.1)
we obtain: pz = 1.06 +/- 0.30

- From the spectral parameters obtained with the Suzaku-WAM data
(Uehara et al., GCNC 6396)
we obtain: pz = 1.25 +/- 0.30

- From the spectral parameters obtained with the RHESSI data
(Bellm et al., GCNC 6399)
we obtain: pz = 2.53 +/- 1.40

These values are compatible with the spectroscopic redshift
z=0.82 derived by Jakobsson et al. (GCNC 6398).



(**) cf. http://www.ast.obs-mip.fr/grb/pz