NASA SWIFT Update 8 May 2007

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TITLE:   GCN CIRCULAR
NUMBER:  6383
SUBJECT: GRB 070508: Swift detection of an intense burst with an optical counterpart
DATE:    07/05/08 04:47:27 GMT
FROM:    Scott Barthelmy at NASA/GSFC  

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. 

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TITLE:   GCN CIRCULAR
NUMBER:  6384
SUBJECT: GRB 070508: TAROT La Silla observatory optical observations
DATE:    07/05/08 05:11:57 GMT
FROM:    Alain Klotz at CESR-CNRS  

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.

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TITLE:   GCN CIRCULAR
NUMBER:  6385
SUBJECT: GRB 070508: REM observations
DATE:    07/05/08 05:18:53 GMT
FROM:    Stefano Covino at Brera Astronomical Observatory  

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) 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.


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TITLE:   GCN CIRCULAR
NUMBER:  6386
SUBJECT: GRB 070508: Optical afterglow detection
DATE:    07/05/08 05:22:41 GMT
FROM:    Edo Berger at Carnegie Obs  

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

"We observed the position of GRB 070508 (GCN 6383) 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."

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TITLE:   GCN CIRCULAR
NUMBER:  6387
SUBJECT: GRB 070508: Optical observation limiting magnitude
DATE:    07/05/08 09:56:54 GMT
FROM:    Alan Gilmore at U of Canterbury,Mt John Obs  

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) 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.

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TITLE:   GCN CIRCULAR
NUMBER:  6388
SUBJECT: GRB 070508: Swift-XRT refined analysis
DATE:    07/05/08 12:41:59 GMT
FROM:    Claudio Pagani at PSU/Swift-XRT  

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) 
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 and 1.9" from the optical 
position given in GCN 6386 (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.

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TITLE:   GCN CIRCULAR
NUMBER:  6389
SUBJECT: GRB 070508: Multicolor optical observations and possible redshift
DATE:    07/05/08 13:33:42 GMT
FROM:    Christina Thoene at Niels Bohr Institute,DARK Cosmo Ctr  

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

We observed the OT of GRB 070508 (GCN 6383, 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.


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TITLE:   GCN CIRCULAR
NUMBER:  6390
SUBJECT: GRB 070508, Swift-BAT refined analysis
DATE:    07/05/08 13:35:12 GMT
FROM:    Scott Barthelmy at NASA/GSFC  

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).  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.