GRB 060223

J. R. Cummings (NASA/ORAU), S. D. Barthelmy (NASA/GSFC), P. T. Boyd
(NASA/GSFC), D. N. Burrows (PSU), M. Capalbi (ASDC), M. M. Chester
(PSU), J. A. Kennea (PSU), H. A. Krimm (GSFC/USRA), C. B. Markwardt
(GSFC/UMD), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL) and M. 
Perri (ASDC) report on behalf of the Swift Team:

At 06:04:23 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060223 (trigger=192059).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA,Dec 55.216, -17.139 {03h 40m 52s, -17d 08' 19"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 15 sec.  The peak count rate
was ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began taking data at 06:05:49 UT, 86 seconds after the BAT
trigger.  The XRT on-board centroid algorithm did not find a source in the
image and no prompt position is available.  We are waiting for down-linked
data to detect and determine a position for the source. 

In response to the Swift/BAT trigger 192059, UVOT took a finding chart
exposure of nominally 200 seconds with the V filter starting 86.5
seconds after the BAT trigger. There is a candidate afterglow in the
sub-imagae and the list of sources generated on-board at (RA,DEC)
(J2000) of (55.2065, -17.1301) with a 1-sigma error radius of about 1
arcsec. This position is 45.9 arcsec from the center of the BAT error
circle. The estimated V magnitude is 17.6 with a 1-sigma error of
about 0.5 mag.

F. Marshall (GSFC) P. Boyd (GSFC), M. Chester (PSU), J. Cummings (ORAU)
on behalf of the Swift/UVOT team report:

We have further analyzed the four individual finding chart sub-images
sent via TDRSS from the Swift UVOT containing the afterglow of
GRB 060223 (Cummings et al., GCN 4813
Loading...
 
 ).

The source is detected in the first 3 finding charts with an
upper limit in the fourth finding chart as follows:


Filter  T_start(s)      Exp(s)  (mag/UL (detection significance))

V       86              200     18.0 +/- 0.14 (10 sigma)
B       293             200     21.0     0.5  (2.5 sigma)
V       835             200     19.6     0.4  (3.5 sigma)
B       1042            200    >21.3          (2 sigma)

Reported times are in seconds since the BAT trigger.
These magnitudes are uncorrected for the expected
Galactic extinction corresponding to E(B-V) = 0.12.

We note that the higher than expected B-V inferred from the first
three images could be caused by a redshift of z=3.3 or greater.

E. Berger (Carnegie), S. R. Kulkarni, A. Rau (Caltech), and D. B. Fox
(Penn State) report on behalf of a large collaboration:

"Starting on 2006, Feb 23.2875 UT (39 min after the burst) we obtained
spectroscopic observations of the optical afterglow of GRB 060223 (GCNs
4813
Loading...
 
 ,4814
Loading...
 
 ) using LRIS on the Keck-I 10-m telescope.  In a single 720 sec
exposure we detect a broad absorption profile which we identify as
Lyman-alpha at a redshift z=4.41, as well as metal absorption features
from OI, SiII, SiII*, etc at the same redshift."

J. Cummings (GSFC/NRC), S. Barthelmy (GSFC), L. Barbier (GSFC),
E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (GSFC/UMD),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL),
A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS),
J. Tueller (GSFC) on behalf of the Swift-BAT team:

Using the partial data set from T-300 to T+302 sec from telemetry
downlinks, we report further analysis of BAT GRB 060223 (trigger #192059)
(Cummings, et al., GCN 4813
Loading...
 
 ; Marshall et al, GCN 4814
Loading...
 
 ).
The BAT ground-calculated position is RA,Dec = 55.188,-17.130 deg
{3h 40m 45.1s, -17d 7' 46.6"} (J2000) +- 1.2 arcmin, (radius, sys+stat,
90% containment).  The BAT error circle contains the afterglow detected
by UVOT (GCN 4813
Loading...
 
 ).  The partial coding was 69%.

The mask-weighted light curve shows a single episode of emission
from T-4 to T+10 sec.   There is a possible broad, faint precursor
at ~T-25 sec, but no significant emission after T+10 sec.
T90 (15-350 keV) is 11 +- 2 sec (estimated error including systematics).

The time-averaged spectrum from T-2.9 to T+10.0 is best fit by a
simple power-law model. The power-law index of the time-averaged
spectrum is 1.74 +- 0.12.  The fluence in the 15-150 keV band is
6.8 +- 0.5 x 10^-07 erg/cm2.  The 1-sec peak photon flux measured
from T+0.08 sec in the 15-150 keV band is 1.4 +- 0.2 ph/cm2/sec.
All the quoted errors are at the 90% confidence level.  Given the redshift
reported for this burst (Berger et al, GCN 4815
Loading...
 
 ), z = 4.41, we calculate
Eiso = 2.82 10^52 ergs in the 81-812 keV band in the rest frame of the
source.

M. Capalbi, M. Perri, L. Vetere (ASDC), K.L. Page (U. Leicester), J. 
Kennea and D. Burrows (PSU) report on behalf of the Swift XRT team:

We have analysed the Swift XRT data from the first  seven orbits 
observation of GRB 060223 (Cummings et al. GCN 4813
Loading...
 
 ). We find an 
uncatalogued fading source at the following location:

RA(J2000) = 03h  40m  49.74s
Dec(J2000) = -17d  07'  48.0"

We estimate an uncertainty of 3.7 arcseconds  radius (90% containment). 
This position is 44 arcsec from the BAT position and 2.6 arcsec from the 
UVOT position given in GCN 4813
Loading...
 
 .

The large flare in the first orbit makes determination of an afterglow 
slope and extrapolation of the flux unreliable, and we will have to wait 
for further data before an afterglow slope can be established.

A preliminary spectral fit to the Photon Counting mode data with an 
absorbed power law gives  a photon index of 1.9 � 0.3 and NH  consistent 
with the Galactic value  (5.92E+20 cm^-2).

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