GRB 060708

A. Moretti (INAF-OAB), L. M. Barbier (NASA/GSFC),
S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU),
C. B. Markwardt (GSFC/UMD), K. M. McLean (LANL/UTD),
D. M. Palmer (LANL), A. M. Parsons (GSFC), P. Romano (INAF-OAB) and
D. E. Vanden Berk (PSU) report on behalf of the Swift Team:

At 12:15:59 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060708 (trigger=217805).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA,Dec 7.798, -33.730 {00h 31m 12s, -33d 43' 46"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single, roughly
triangular peak structure with a duration of ~12 sec.  The peak count rate
was ~5000 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 12:17:01 UT, 62 seconds after the
BAT trigger. XRT found a bright and fading X-ray source
located at RA(J2000) =  00 31 13.50, Dec(J2000) = -33 45 33.8, with an
estimated uncertainty of 4.1 arcseconds (90% confidence radius). 
This location is 103 arcseconds from the BAT on-board position, within
the BAT error circle and it is 4.6" from the UVOT candidate (see below). 
The initial flux in the 2.5s image was 3.4e-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 72 seconds after the BAT trigger.  There
is a candidate afterglow in the list of sources generated on-board at
(RA,DEC) (J2000) of (7.8077,-33.7590) or (00h31m13.85s,-33o45'32.4") 
with a 1-sigma error radius of about 0.5 arcsec.  This position is
4.5 arcsec from the center of the XRT error circle.  The estimated
magnitude is 17.4 with a 1-sigma error of about 0.5 mag. 
No correction has been made for the expected extinction corresponding to
E(B-V) of 0.01.

E. Fenimore (LANL), L. Barbier (GSFC), S. D. Barthelmy (GSFC),
J. Cummings (GSFC/ORAU), N. Gehrels (GSFC), D. Hullinger (BYU-Idaho),
H. Krimm (GSFC/USRA), M. Koss (GSFC/UMD), 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-119 to T+183 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 060708 (trigger #217805)
(Moretti, et al., GCN 5292
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 ).  The BAT ground-calculated position is
RA,Dec = 7.830,-33.752 deg {0h 31m 19.2s, -33d 45' 7.7"} (J2000) +- 1.0 arcmin,
(radius, sys+stat, 90% containment).  The partial coding was 100%.
 
The mask-tagged lightcurve shows a single, roughly triangular peak
starting at T-2 sec, peaking at T+1 sec, and ending at ~T+9 sec.
T90 (15-350 keV) is 9.8 +- 1 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.3 to T+14.2 is best fit by 
a simple power-law model.  The power law index of the time-averaged spectrum
is 1.68 +- 0.12.  The fluence in the 15-150 keV band is 5.0 +- 0.4 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+1.11 sec in the 15-150 keV
band is 2.0 +- 0.1 ph/cm2/sec.  All the quoted errors are at the 90%
confidence level.

S.D. Vergani (DIAS & DCU), C. Guidorzi (Univ. Bicocca & INAF-OABr), P. 
Romano (INAF-OABr), and A. Moretti (INAF-OABr), report on behalf of the 
Swift-XRT team:

We have analyzed the first two orbits of data of GRB 060708 (Moretti et 
al., GCN 5292
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 ). The XRT data set consists of 169 s exposure in windowed 
timing (WT) mode followed by 2.67 ks exposure in photon counting (PC) mode.

The refined position of the source is

  RA  (J2000) =  00h 31m 13.53s
  Dec (J2000) = -33d 45' 33.3"

with an uncertainty of 3.8 arcsec (90% containment).

This position is 4.0 arcsec from the XRT on board position, 2.9 arcsec 
and 4.1 arcsec from the XRT and UVOT positions respectively, reported by 
Moretti at al. (GCN 5292
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 ).

The 0.3-10 keV X-ray light curve shows a double broken power-law decay, 
starting with a steep segment (alpha ~ 4) that become shallower (alpha ~ 
0.8) after ~200 s from BAT trigger time.

The WT spectrum is fitted by an absorbed power law with photon index 3.3 
+/- 0.1 and N_H of about 1.5E21 cm^-2, in excess with respect to the 
Galactic value (1.8E20 cm^-2).

The PC spectrum is fitted by an absorbed power law with photon index 2.3 
+/- 0.1 and N_H of about 8.8E20 cm^-2.

Assuming alpha ~ 0.8, the extrapolated unabsorbed flux (0.3-10 KeV) at 
24 hours is 9.7E-13 erg cm^-2 s^-1.

This Circular is an official product of the Swift XRT Team.

S. Parris, A. Smith, M. Nysewander, D. Reichart, K. Ivarsen, A. Foster, A.
LaCluyze, J.A. Crain report:

SkyNet observed the localization of GRB 060708 (Moretti et al. GCN 5292
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 )
with four of the 16" PROMPT telescopes at CTIO beginning 15.4 hours after
the burst in UBgriz.

We were unable to see the afterglow down to 3-sigma limiting magnitudes of
z' > 19.0 at a mean time of 15.7 hours after the burst, i' > 19.2 at 18.6
hours, and r' > 19.3 at 15.7 hours.

PROMPT is currently being built and commissioned.

H. Swan (U Mich), E. Rykoff (U Mich), S. Yost (U Mich), T. McKay (U  
Mich), C. Akerlof (U Mich), I. Smith (Rice), report on behalf of the  
MARGE collaboration:


The AEOS Burst Camera (ABC) on the AEOS 3.63m telescope, located at  
the Maui Space Surveillance System on Haleakala, observed the optical  
counterpart to GRB 060708 (Swift trigger 217805, Moretti, et al, GCN  
5292
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 ). Over 160 10-s images were taken between 2006-07-08 12:33:14.19  
UT  (1035 s after the burst), and 14:16:21.78 UT (7222s after the  
burst), with low resolution (R~10) grating spectroscopy.  The OT is  
clearly detected in individual images, and fades during the  
observation.  The position of the OT is:

      00:31:13.85   -33:45:33.0    (J2000)

consistent with the UVOT position (Schady and Moretti, GCN 5296
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 ).  At  
12:33:14.19 UT, the OT is approximately 17.7 mag (R equivalent,  
relative to a nearby 14th magnitude USNO B1.0 star).  The low  
resolution grating on the ABC is designed to study the color  
evolution of the early afterglow.

Pall Jakobsson (U. Hertfordshire), Paul Vreeswijk (ESO),
Sara Ellison (U. Victoria), Javier Gorosabel (IAA-CSIC Granada),
Nial Tanvir (U. Hertfordshire), Johan P.U. Fynbo, Brian L. Jensen,
Jens Hjorth (DARK, NBI), D. Alexander Kann (TLS Tautenburg),
Klaas Wiersema and Ralph A.M.J. Wijers (University of Amsterdam)
report on behalf of a larger collaboration:

Using FORS2 on the Very Large Telescope, we have obtained 3*30 min
spectra (300V) of the GRB 060708 field (Moretti et al., GCN 5292
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 ).
The UVOT optical afterglow candidate (Moretti et al., GCN 5292
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 ;
Schady & Moretti, GCN 5296
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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 ~ 22.9 on July 10.290
(1.778 days post-burst).

The combined spectrum does not display any obvious features. However,
a firm upper limit of z < 2.3 can be placed on the redshift of
GRB 060708 from the lack of Ly-alpha forest lines in the spectrum
of the afterglow. This is consistent with the UVOT observations
(Schady & Moretti, GCN 5296
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 ).

The slit was aligned to cover the galaxy, 8 arcsec south of the
afterglow (just outside the XRT error circle). This galaxy has a
magnitude of R ~ 19.5 and displays numerous absorption features,
such as Ca II (K & H), G-band, H-beta, Mg I, Na I (D) and H-alpha,
corresponding to a redshift of z = 0.249.

An image of the field is shown at:

http://star-www.herts.ac.uk/~palli/grb060708/grb060708.jpg