NASA SWIFT Update 6 May 2007

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TITLE:   GCN CIRCULAR
NUMBER:  6375
SUBJECT: GRB 070506: Swift detection of a burst with optical afterglow
DATE:    07/05/06 06:05:32 GMT
FROM:    David Palmer at LANL  

C. Pagani (PSU), M. M. Chester (PSU),
C. Guidorzi (Univ Bicocca&INAF-OAB), S. Immler (GSFC/USRA),
C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), J. L. Racusin (PSU),
T. Sakamoto (NASA/ORAU), M. Stamatikos (NASA/ORAU) and L. Vetere (PSU)
report on behalf of the Swift Team:

At 05:35:58 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070506 (trigger=278693).  Swift slewed to the burst
immediately after the end of the 64 second image trigger. 
The BAT on-board calculated location is RA, Dec 347.217, +10.728 which is 
   RA(J2000) = 23h 08m 52s
   Dec(J2000) = +10d 43' 42"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 6 sec.  The peak count rate
was ~1700 counts/sec (15-350 keV), at ~6 sec after the trigger. 

The XRT began observing the field at 05:38:05 UT, 127 seconds after
the BAT trigger. Using ground-processed quick-look data, XRT found an
uncatalogued X-ray source located at RA, Dec 347.2192, +10.7224 which
is
   RA(J2000) = 23h 08m 52.6s
   Dec(J2000) = 10d 43' 20.7" 
with an uncertainty of 9.0 arcseconds (radius, 90% containment). This
location is 22 arcseconds from the BAT on-board position, within the
BAT error circle. The initial flux in the 2.5s image was 2.5e-10
erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 459 seconds after the BAT trigger. There
is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image
at     
   RA(J2000) =	23h 08m 52.39s (= 347.2183d)   
   DEC(J2000) = +10d 43' 20.3" (= 10.7223d) 
with a 1-sigma error radius of about 0.5 arc sec. This position is 
3.0 arcseconds 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 galactic reddening of E(B-V) = 0.040. 

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TITLE:   GCN CIRCULAR
NUMBER:  6376
SUBJECT: GRB 070506, Swift-BAT Refined Analysis
DATE:    07/05/06 16:38:17 GMT
FROM:    Michael Stamatikos at GSFC  

L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E.
Fenimore (LANL), N. Gehrels (GSFC), 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-239 to T+963 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 070506 (trigger #278693)
(Pagani, et al., GCN Circ. 6375).  The BAT ground-calculated position is RA,
Dec = 347.203, 10.711 deg which is 
   RA(J2000) = 23h 8m 48.8s 
   Dec(J2000) = 10d 42' 40.3" 
with an uncertainty of 2 arcmin, (radius, sys+stat, 90% containment). The
partial coding was 96%.
 
The mask-weighted light curve begins to rises at ~T+2 sec, peaks at ~T+6.5
sec, and returns to the background level by ~T+10 sec, with trivial emission
above 100 keV. T90 (15-350 keV) is 4.3 +- 0.3 sec (estimated error including
systematics).
 
The time-averaged spectrum from T+4.1 to T+9.0 is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is 1.72
+- 0.17. The fluence in the 15-150 keV band is 2.1 +- 0.2 x 10^-7 erg/cm^2.
The 1-sec peak photon flux measured from T+6.16 sec in the 15-150 keV band
is 1.0 +- 0.1 ph/cm^2/sec.  All the quoted errors are at the 90% confidence
level.


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TITLE:   GCN CIRCULAR
NUMBER:  6377
SUBJECT: GRB070506: Swift XRT refined analysis
DATE:    07/05/06 17:16:51 GMT
FROM:    Claudio Pagani at PSU/Swift-XRT  

C. Pagani, L. Vetere, J. L. Racusin and J. A. Kennea (PSU) report on  
behalf of the Swift Team:

We have analysed the first two orbits of Swift XRT data from GRB  
070506 (trigger number 278693, GCN Circ 6375.), for a total photon  
counting mode exposure of 2.8ks.
The XRT started collecting data in Image mode at 05:38:05 UT, 127  
seconds after the BAT trigger, but observations in Photon Counting  
mode were delayed due to the SAA, starting 432 seconds after the  
trigger. The refined XRT position from 2.8ks of PC data is
RA,DEC(J200) = 347.2179, +10.7217
which is
RA(J2000) = 23d 08m 52.30s
DEC(J200) = +10d 43' 18.2"

with an uncertainty of 5.4 arcsec (radius, 90% containment).
This is  5.1 arcsec from the initial X-ray position and 2.4 arcsec  
from the UVOT optical counterpart (GCN 6375).

The XRT light curve created from the first two orbits of PC data  
reveals a decaying source with hints of flaring activity. A power law  
fit yields a decay slope of 0.55+/-0.06.

The X-ray spectrum of the PC data, modeled with an absorbed power law  
gives a photon index of 2.5+/-0.5 and a total column density of NH= 
(1.8+/-1.1)e21 cm**-2, in excess of the Galactic value of 0.4e21 cm**-2.
The absorbed (unabsorbed) 0.3-10.0keV flux for this spectrum was  
3.0E-12 (5.5E-12) ergs cm^-2 s^-1.

Assuming the source continues to decay at the same rate, we predict  
an XRT count rate of 2.2e-2 count/s at T+24 hours, which corresponds  
to an observed (unabsorbed) flux of 0.8E-12 (1.5E-12) ergs cm^-2 s^-1.

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

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TITLE:   GCN CIRCULAR
NUMBER:  6378
SUBJECT: GRB070506: Swift/UVOT Observations
DATE:    07/05/07 02:58:56 GMT
FROM:    Wayne Landsman at GSFC/SSAI  

W. Landsman (SSAI/GSFC) and C. Pagani (PSU) report on behalf of the 
Swift/UVOT team:

The Swift/UVOT began taking data in the field of GRB070506 459s after 
the BAT trigger (Pagani et al., GCN 6375). A fading afterglow is weakly 
detected in the White, B and V UVOT  filters, but not in the U or UV 
filters.      We use the combined white image to obtain an improved 
position of

RA(J2000) = 23h 08m 52.39s  Dec(J2000) = +10d 43' 20.8"

with a 1-sigma uncertainty radius of about 0.5".    This is 0.5" from 
the UVOT position reported by Pagani et al. (GCN 6375) and 2.9" from the 
refined XRT position reported by Pagani et al. (GCN 6377).

Photometry results are given for the 7 UVOT filters below.

           Tstart   Tstop    Exp          Mag

White        459      558      98         19.7+/-0.18
             868      967      98         19.9+/-0.22
            7371     7570     196         20.4+/-0.28

V            974     1373     393         19.1+/-0.2
            7781     7980     197        >19.3 (3 sigma)
 
B            638     2245     136         19.8+/-0.34
            7167     7366     197        >20.4 (3 sigma)

U            638     5853     261        >20.1 (3 sigma)
UVW1         614     5741     352        >20.4 (3-sigma)
UWM2        7984     8142     155        >19.6 (3-sigma)
UVW2         840     7775     294        >20.4 (3-sigma)

No correction has been made for the expected Galactic reddening of 
E(B-V)=0.04

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TITLE:   GCN CIRCULAR
NUMBER:  6379
SUBJECT: GRB 070506: VLT redshift
DATE:    07/05/07 11:03:32 GMT
FROM:    Christina Thoene at Niels Bohr Institute,DARK Cosmo Ctr  

Christina C. Thoene (DARK), Andreas O. Jaunsen (Univ. Oslo), Johan P. U.
Fynbo (DARK), Pall Jakobsson (Univ. of Hertfordshire) and Paul M.
Vreeswijk (ESO) report:


We obtained 2x15min spectra of the OT of GRB 070506 (Pagani et al., GCN
6375 and 6378) on May 6.41 with FORS1/VLT during twilight. The grism used
(300V) covers the wavelength range from 3000 to 9000 A.

The identification of a strong Lyman-alpha absorption together with SiII,
FeII, CIV, AlII, AlIII and ZnII absorption lines leads to a redshift of z=2.31
for GRB 070506.


We thank the staff at Paranal for excellent support.