GRB 110223B

Swift UVOT observations of GRB110223b

M. De Pasquale (MSSL-UCL) and M. Stamatikos (GSFC) report, on behalf of 
the Swift team:

Swift/UVOT began settled exposures of GRB110223b (Stamatikos et al. GCN 
circ. 11754
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 ) 77 s after the trigger with a white finding chart. There is 
an uncatalogued source 1.5 arcseconds from the enhanced XRT afterglow 
position (Beardmore et al., GCN  circ. 11758
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 ). This position is also 
consistent with the optical transient found by GROND (Sudilovsky et al., 
GCN circ. 11756
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 )

This source, which we identify as the optical afterglow of the burst, is 
detected in white, v, b, u. Magnitudes and 3 sigma upper limits, derived 
using the UVOT photometric system  (Poole et al. 2008, MNRAS, 383, 627),
are shown in the table below. We caution that the photometry is complicated
by a crowded field.

Filter        T_start(s)    T_end(s)        exp           Magnitude

white (FC)       77            227          147.4       18.98 � 0.10
white           620            814           39.0       19.70 � 0.30
white           870           1546          206.0       19.61 � 0.13

v               620           1596          117.3       17.88 � 0.15

b               546           1522           97.4       19.57 � 0.30

u (FC)          290            540          245.8       19.20 � 0.19
u               694           1496           77.8       >19.30

uw1             670           1471           97.4       >19.16

um2             645           1445           97.4       >18.78

uw2             596          1572           116.7       >19.16

These magnitudes are not corrected for the strong Galactic extinction 
along the line of sight, corresponding to E(B-V) = 0.23 (Schlegel et al. 
1998)

A. Rowlinson (U. Leicester) and M. Stamatikos (OSU/NASA/GSFC) report on
behalf of the Swift-XRT team:

We have analysed 5.3 ks of XRT data for GRB 110223B (Stamatikos  et al.
GCN Circ. 11754
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 ), from 56 s to 24.6 ks after the  BAT trigger. The data
comprise 85 s in Windowed Timing (WT) mode (the first 9 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Beardmore
et al. (GCN. Circ 11758).

The light curve can be modelled with an initial power-law decay with an
index of alpha=2.8 (+0.9, -0.7), followed by a break at T+99.5 s to an
alpha of 0.92 (+/-0.04).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.85 (+/-0.16). The
best-fitting absorption column is  1.7 (+0.5, -0.4) x 10^21 cm^-2,
consistent with the Galactic value of 1.3 x 10^21 cm^-2 (Kalberla et
al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum  is 4.5 x 10^-11 (5.9 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.7 (+0.5, -0.4) x 10^21 cm^-2
Galactic foreground: 1.3 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.85 (+/-0.16)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00446677.

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

A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 2282 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 110223B, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 150.23341, -68.30155 which is equivalent
to:

RA (J2000): 10h 00m 56.02s
Dec (J2000): -68d 18' 05.6"

with an uncertainty of 1.5 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).

This circular was automatically generated, and is an official product of the
Swift-XRT team.

S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), M. Stamatikos (OSU),
J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
 
Using the data set from T-120 to T+293 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 110223B (trigger #446677)
(Stamatikos, et al., GCN Circ. 11754
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 ).  The BAT ground-calculated position is
RA, Dec = 150.340, -68.329 deg, which is 
   RA(J2000)  =  10h 01m 21.6s 
   Dec(J2000) = -68d 19' 44.3" 
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
 
The mask-weighted light curve shows the burst start with a small peak
at ~T-45 sec, a slightly larger peak at ~T+2 sec out to ~T+20 sec, with on-going
low-level emission out to ~T+150 sec.  T90 (15-350 keV) is 54.0 +- 8.5 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-45 to T+20 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.65 +- 0.21.  The fluence in the 15-150 keV band is 6.1 +- 0.8 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.99 sec in the 15-150 keV band
is 0.6 +- 0.1 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/446677/BA/

V. Sudilovsky, J. Elliott, F. Olivares E., and J. Greiner (MPE
Garching) report on behalf of the GROND team:

We observed the field of GRB 110223B (Swift trigger 446677; Stamatikos
et al., GCN #11754
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 ) simultaneously in g'r'i'z'JHK with GROND (Greiner
et al. 2008, PASP 120, 405) mounted at the 2.2 m MPI/ESO telescope at
La Silla Observatory (Chile).

Observations started at 00:05 UT on February 24th, 2.7 hours after the
GRB trigger, and are continuing. They were performed at an average
seeing of 1.4" and at an average airmass of 1.6.

We found a single point source within the 2.1" Swift/XRT error circle
reported by Stamatikos et al. (GCN #11754
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 ) at

�RA (J2000.0) = 10h 00m 55.98s
�DEC (J2000.0) = -68d 18' 06.0"

with an uncertainty of 0.3" in each coordinate.

Based on 7.7 min exposure started at 00:30 UT, we estimate a
preliminary r'-band magnitude of 22.1 +/- 0.1 calibrated against GROND
zero points (AB system). No statements about the variability can be
made at this stage. This measurement is not corrected for the
considerable Galactic foreground extinction corresponding to a
reddening of E(B-V)=0.226 mag in the direction of the burst (Schlegel
et al. 1998).

M. Stamatikos (OSU/NASA/GSFC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
S. Campana (INAF-OAB), P. A. Evans (U Leicester), J. M. Gelbord (PSU),
C. Guidorzi (U Ferrara), S. T. Holland (CRESST/USRA/GSFC),
E. A. Hoversten (PSU), J. A. Kennea (PSU),
H. A. Krimm (CRESST/GSFC/USRA), N. P. M. Kuin (UCL-MSSL),
F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),
C. Pagani (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), J. L. Racusin (NASA/GSFC),
E. Sonbas (GSFC/USRA/Adiyaman Univ.), R. L. C. Starling (U Leicester),
C. A. Swenson (PSU) and E. Troja (NASA/GSFC/ORAU) report on behalf of
the Swift Team:

At 21:25:48 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 110223B (trigger=446677).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 150.276, -68.329 which is 
   RA(J2000) = 10h 01m 06s
   Dec(J2000) = -68d 19' 44"
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 5 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 21:27:00.0 UT, 72.0 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 150.2339,
-68.3019 which is equivalent to:
   RA(J2000)  = 10h 00m 56.15s
   Dec(J2000) = -68d 18' 06.7"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 112 arcseconds from the BAT onboard position, within the
BAT error circle. This position may be improved as more data are
received; the latest position is available at
http://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 1.29
x 10^21 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 77 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers none of
the XRT error circle. The coverage of the XRT error circle by the 8'x8' region
for the list of sources generated on-board is uncertain because the large
number of sources filled the available telemetry. No correction has been made
for the expected extinction corresponding to E(B-V) of 0.23. 

Burst Advocate for this burst is M. Stamatikos (Michael.Stamatikos-1 AT nasa.gov). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)