GRB 060919

C. Guidorzi (Univ Bicocca&INAF-OAB), S. D. Barthelmy (GSFC),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), C. Gronwall (PSU),
J. A. Kennea (PSU), H. A. Krimm (GSFC/USRA), V. Mangano (INAF-IASFPA),
A. Moretti (INAF-OAB), K. L. Page (U Leicester), D. M. Palmer (LANL),
P. Romano (INAF-OAB) and S. D. Vergani (DIAS-DCU) report on behalf of
the Swift Team:

At 07:48:38 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060919 (trigger=230115).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA,Dec 276.911, -51.028 {18h 27m 39s, -51d 01' 38"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked 
structure with an initial main peak of duration ~ 2 sec and lower level 
emission out to T+20 sec.  This is followed by a second peak at T+ ~300 sec
of duration ~30 sec seen only in the 15-50 keV band.  The peak 
count rate was ~2500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began taking data at 07:50:05 UT, 87 seconds after the BAT
trigger. The XRT on-board centroid algorithm did not find a source in the
image. 
Ground analysis reveals a possible faint source at the following coordinates:   
RA(J2000): 18h 27m 42.35s
Dec(J2000): -51 00 51.2   
with an error of 5.1 arcseconds (90% confidence). Further analysis of 
ground data is necessary to determine the properties of the possible
source. The current flux is 8.3x10^-9 erg cm-2 s-1. 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 91 seconds after the BAT trigger. No
afterglow candidate has been found in the initial data products. The
overlap of the 8'x8' region for the list of sources generated
on-board and the BAT error circle is 100%. No correction has
been made for the expected extinction corresponding to E(B-V) of
0.07.

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

We imaged the field of GRB 060919 detected by SWIFT
(trigger 230115) with the new TAROT robotic telescope (D=25cm)
located at the La Silla observatory, Chile.

First image was acquired 28.3s after the GRB trigger
(5.2s after the notice). The field elevation decreased
from only 2 degrees above horizon and weather conditions
were good. Images were taken during the prompt emission.

Date of trigger : t0 = 2006-09-19T07:48:38.880

First image is 60.0s exposure trailed. No OT is visible:
t0+28.3s to t0+88.3s : R > 15.4

Second image is 30.0s exposure. No OT is visible:
t0+94.2s to t0+124.2s : R > 15.8

We co-added a series of the 3
firsts not trailed exposures. No OT is visible:
t0+94.2s to t0+196.4s : R > 15.9

Fourth non trailed image is a 90.0s exposure
and covers the second gamma peak described by
Guidorzi et al. GCNC 5575. No OT is visible:
t0+292.3s to t0+382.3s : R > 15.8

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

N.B. Galactic coordinates are lon=343.8526 lat=-17.2471
and the galactic extinction in R band is 0.5 magnitudes
estimated from D. Schlegel et al. 1998ApJ...500..525S.

This message may be cited.

C. Guidorzi, P. Romano, A. Moretti, S. Vergani on behalf of the
Swift XRT team report:


we have analysed the first orbit of XRT data from GRB 060919
(Guidorzi et al., GCN Circ 5575
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 ). A 1.3 ks Photon Counting mode image
provides a refined XRT position:

RA(J2000)  =  18h 27m 42.21s,
Dec(J2000) = -51d 00m 50.4s

with an uncertainty of 4.1 arcsec (90% containment). This position is 1.6
arcsec away from the previous XRT position and 56 arcsec from the onboard
BAT position (Guidorzi et al., GCN Circ 5575
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 ).

The X-ray light curve can be fit with a single power law with index
0.85 +- 0.2 (90%) from 100 to 1400 seconds after the BAT trigger.

A power-law fit to the 0.3-10 keV spectrum yields a photon index
of 1.7+-0.5 and a column density of (9+-4)x1e21 cm-2 (90%),
significantly in excess of the Galactic hydrogen column density
in the direction of the burst (6.4e20cm-2).

The average unabsorbed flux of the first orbit is (1.1+-0.3)e-11 erg 
cm-2 s-1.
If the burst decays at the current rate we estimate a
0.3-10 keV unabsorbed flux of ~1.2e-13 ergs cm-2 s-1 at T+24hr.

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

G. Sato (GSFC/ISAS), L. Barbier (GSFC), S. D. Barthelmy (GSFC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
C. Guidorzi (Univ Bicocca&INAF-OAB), D. Hullinger (BYU-Idaho),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL),
A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC)
on behalf of the Swift-BAT team:
 
Using the data set from T-239 to T+950 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 060919 (trigger #230115)
(Guidorzi, et al., GCN Circ. 5575
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 ).  The BAT ground-calculated position
is RA,Dec = 276.900, -50.994 deg {18h 27m 36.0s, -50d 59' 39.8"} (J2000)
+- 1.6 arcmin, (radius, sys+stat, 90% containment).  The partial coding was 29%.
 
There is an initial FRED peak starting at T-1 sec, peaking at T+0,
and lasting out to T+5 sec.  There is smaller, 4-sec wide FRED-like peak
starting at T+6 sec.  There is an even smaller, 4-sec wide peak centered
at T+24 sec.  We note that our initial circular using the raw TDRSS rate
lightcurves described a second episode of emission at T+300 sec.
Now using the masked-tagged light curves, this second episode was due
to a noisy detector in the instrument.  T90 (15-350 keV) is 9.1 +- 0.2 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-1.0 to T+9.0 is best fit by 
a simple power-law model.  The power law index of the time-averaged
spectrum is 1.85 +- 0.19.  The fluence in the 15-150 keV band
is 5.5 +- 0.6 x 10^-7 erg/cm2.  The 1-sec peak photon flux measured
from T-0.49 sec in the 15-150 keV band is 2.2 +- 0.3 ph/cm2/sec.
All the quoted errors are at the 90% confidence level.

A. Melandri, A. Gomboc, R.J. Smith, N. Tanvir on behalf of 
the Robonet collaboration report:

We imaged the field of GRB 060919 (Guidorzi et al., GCN 5575
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 )
with the Faulkes South Telescope starting at 10:36:10.50 UT
(about 2.8 hours aftert the burst event).

We acquired a first sequence of images in the R-band (6 
exposures each lasting 150 seconds) and a second sequence in 
R and SDSS-I filters (12 exposures lasting 150 seconds in 
each filter).

We did not detect any obvious optical counterpart inside the 
XRT refined error circle (Guidorzi et al., GCN 5577
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 ) down to 
a limiting magnitude of R > 19.5 (about 2.92 hours after the
event).

Further analysis and observation are still ongoing.

A. Breeveld (MSSL/UCL) and C. Guidorzi (Univ Bicoca&INAF-OAB) report on 
behalf of the Swift/UVOT team:

The Swift/UVOT began taking data on 2006-09-19 73s after the burst 
(Guidorzi et al. GCN 5575
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 ). At the position of the XRT error circle 
(Guidorzi et al. GCN 5577
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 ) there are no new sources. In the summed UVOT 
images we obtain the following 3 sigma upper limits:

Filter          T_range(s)      Exp(s)          3sig_UL(mag)
V               73-11544        2310            20.24
B               674-24585       1330            21.02
U               650-24547       2202            20.88
UVW1    626-23633       1869            20.99
UVM2    602-12448       1134            21.10
UVW2    703-7232        424             20.65
White   91-18800        982.1           21.00
(160-650 nm)
These magnitudes are not corrected for the expected extinction of E(B-V)=0.072