GRB 081230

V. La Parola (INAF-IASFPA), S. D. Barthelmy (GSFC), P. J. Brown (PSU),
J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU),
J. A. Kennea (PSU), W.B Landsman (GSFC), V. Mangano (INAF-IASFPA),
J. P. Osborne (U Leicester), K. L. Page (U Leicester),
B. Sbarufatti (INAF-IASFPA) and T. N. Ukwatta (GSFC/GWU) report on
behalf of the Swift Team:

At 20:36:12 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081230 (trigger=338633).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 37.315, -25.142 which is 
   RA(J2000) = 02h 29m 16s
   Dec(J2000) = -25d 08' 29"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single peak
with a duration of about 50 sec.  The peak count rate
was ~600 counts/sec (15-350 keV), at ~50 sec after the trigger. 

The XRT began observing the field at 20:38:16.7 UT, 124.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 37.33148,
-25.14645 which is equivalent to:
   RA(J2000)  = 02h 29m 19.56s
   Dec(J2000) = -25d 08' 47.2"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 56 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 in excess of the Galactic value (1.68e+20
cm^-2, Kalberla et al. 2005), with an excess column of 3.2
(+2.81/-2.34) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
132 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 100% of the
XRT error circle. The typical 3-sigma upper limit has been about 19.2 mag. The
8'x8' region for the list of sources generated on-board covers 100% of the XRT
error circle. The list of sources is typically complete to about 18.0 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.01. 

Burst Advocate for this burst is V. La Parola (laparola AT ifc.inaf.it). 
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.)

F. Yuan (U Mich), E.S. Rykoff (UCSB), report on behalf of the ROTSE  
collaboration:

ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia,  
responded to GRB 081230 (Swift trigger 338633). The first image was at  
20:47:53.4 UT, 700.8 s after the burst (8.4 s after the GCN notice  
time). The unfiltered images are calibrated relative to USNO A2.0. We  
detect a 19.1 magnitude, steady source in the XRT error box with  
coordinates:

      02:29:19.35      -25:08:49.22    (J2000), with positional  
uncertainty of 1" or better

start UT    	mag     mlim(of image)
----------------------------------
20:49:23.0     19.1     19.2


This source is not visible in DSS (second epoch), 2MASS or the  
MPChecker database.

A jpeg image is available at http://www.rotse.net/images/gsb338633_3c021-030_key.jpg

Continuing observations are in progress.

S. T. Holland (CRESST/GSFC/USRA), P. J. Brown (PSU), and V. La Parola
(INAF-IASFPA) report on the behalf of the Swift UVOT team:

        The Swift/UVOT detects a faint source in the XRT error circle
for GRB 081230 (La Parola, et al. 2008, GCN Circ. 8753
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 ).  The source
has a preliminary position of

     RA (J2000)   02:29:19.48  =   37.33117 (deg)
     Dec (J2000) -25:08:48.5   =  -25.14682 (deg)

and a preliminary u-band magnitude of u = 20.6 +/- 0.3 mag in a 250 s
exposure starting 131 s after the BAT trigger.  The quoted magnitude
has not been corrected for the expected Galactic extinction along the
line of sight corresponding to a reddening of E_{B-V} = 0.01 mag
(Schlegel, et al., 1998, ApJS, 500, 525).  The photometry is on the
UVOT flight system described in Poole et al. (2008, MNRAS, 383, 627).

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

Using 1640 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 081230, 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 = 37.3314, -25.1477 which is equivalent
to:

RA (J2000): 02h 29m 19.53s
Dec (J2000): -25d 08' 51.8"

with an uncertainty of 1.8 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
http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an
extension of this method.

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

S. R. Oates (MSSL-UCL) and V. La Parola (INAF-IASFPA) report on behalf  
of the Swift/UVOT team:

The Swift/UVOT began observerving the field of GRB 081230 132 s
after the BAT trigger ( La Parola et al., GCN Circ. 8753
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 ). We detect the
optical afterglow in the white, v, b and u filters at the position:

RA(J2000.0)  = 02:29:19.467
DEC(J2000.0) = -25:08:51.0

with an estimated uncertainty of 0.9 arcsec (radius, 90% confidence).
This position is consistent with the UVOT-enhanced XRT position  
(Osborne et al., GCN 8756
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 )
and the optical afterglow position reported by ROTSE-III (Yuan et al.,  
GCN 8754
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 ).

The magnitudes and 3 sigma upper limits are reported below:

Filter    T_start (s) T_stop  Exposure    Mag/3sig UL
------------------------------------------------------------
white       4060  4210   147   20.45 +/- 0.35
v	         587    607     19     18.30 +/- 0.48
b	         388    408     19     18.92 +/- 0.36
u	         132    382     246   20.28 +/- 0.38
u	         511    531 	19     19.04 +/- 0.52
uvw1	 487    5854   435   > 21.23
uvm2       462    5649   255   > 20.95
uvw2       414	    6575   353   > 21.44
------------------------------------------------------------

The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E_{B-V} = 0.01 mag (Schlegel et al.,
1998, ApJS, 500, 525). The photometry is on the UVOT flight system
described in Poole et al. (2008, MNRAS, 383,627).

V. La Parola, B. Sbarufatti, V. Mangano (INAF-IASF Pa)
report on behalf of the Swift XRT team:


We have analysed the first 35 ks of XRT observations for GRB 081230
(La Parola et al. GCN Circ 8753
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 ), with an exposure time of 104 s in WT mode and
11.4 ks in PC mode. The astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources to
the USNO-B1 catalogue) is RA, Dec = 37.3314 -25.1477, corresponding to:

RA (J2000): 02h 29m 19.53s
Dec (J2000): -25d 08' 51.8


with an uncertainty of 1.8 arcsec (radius, 90% confidence, Osborne et al.
GCN Circ 8756
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 ).

The lightcurve can be fitted with a broken power-law with the following
parameters:
alpha1=-6.910+/-0.007
T_break=298+/-9
alpha2=-0.62+/-0.5
There is evidence for a late flare a peaking at 5000s.

The spectrum of the data collected in WT mode can be fitted with a powerlaw
with photon index Gamma = 1.96 +/- 0.11, absorbed by the Galactic column in
this direction of 1.7x10^20 cm^-2, plus an intrinsic column of
(6.4+/-2.2)x10^20 cm^-2. The observed (unabsorbed) flux over this time
is 1.03x10^-9 (1.3x10^-9) erg cm^-2 s^-1,
corresponding to a counts to observed flux conversion of 4.1x10^-11 erg
cm^-2 count^-1.
The spectrum of the data collected in PC mode can be fitted with a powerlaw
with photon index Gamma = 2.14 (+0.10,-0.20), with an intrinsic column of
(5.3 [+2.2,-3.7])x10^20 cm^-2. The observed (unabsorbed) flux over this time
is 2.1x10^-12 (2.7x10^-9) erg cm^-2 s^-1,

With the present decay law, the count rate at 24 hours is predicted to be
1.1x10^-2 c/s (corresponding to an observed flux of 3.7x10^-13 erg cm^-2 s^-1)

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




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D. M. Palmer (LANL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), V. La Parola (INAF-IASFPA), C. B. Markwardt 
(GSFC/UMD),
K. McLean (GSFC/UMD), A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC),
G. Sato (ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC),
T. N. Ukwatta (GWU) (i.e. the Swift-BAT team):

Using the data set from T-300 to T+1197 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 081230 (trigger #338633)
(La Parola, et al., GCN Circ. 8753
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 ).  The BAT ground-calculated position is
RA, Dec = 37.330, -25.145 deg which is 
   RA(J2000)  =  02h 29m 19.2s 
   Dec(J2000) = -25d 08' 42.6" 
with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
 
The mask-weighted light curve consists of a series of overlapping peaks ranging
from T+5 sec to T+70 sec, with the strongest emission at ~T+50 seconds.
T90 (15-350 keV) is 60.7 +- 13.8 sec (estimated error including systematics).
 
The time-averaged spectrum from T-14.4 to T+62.4 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.97 +- 0.16.  The fluence in the 15-150 keV band is 8.2 +- 0.8 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+46.63 sec in the 15-150 keV band
is 0.7 +- 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/338633/BA/

GRB 081230: GROND confirmation of the afterglow 


P. Afonso (MPE), C. Clemens (MPE), S. Klose (Tautenburg), J. Greiner
(MPE) and G. Szokoly (Eotvos Univ. Budapest) report on behalf of the
GROND team: 

GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m ESO/MPI
telescope at La Silla Observatory (Chile) imaged the field of GRB 081230
(Swift trigger 338633, La Parola et al., GCN #8753
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 ) simultaneously in
g'r'i'z'JHK bands 

We detected and confirm the afterglow candidate in all bands, at the 
position: 

RA(J2000): 02:29:19.51
DEC(J2000): -25:08:49.95 

with uncertainties of 0.5" in each coordinate. 

This position is compatible with UVOT (Oates et alia, GCN #8757
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 ) and
ROTSE-III (Yuan et alia, GCN #8754
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 ) reported positions. 

Observations started on Dec. 31 at 00h48 UT, 15123 seconds, or ~ 4.2 hours
after the burst. 

We used 4 images of 375 s exposure in g'r'i'z' and 120 images of 10s
exposure in JHK, for each epoch. 

The images mid time for the 1st epoch is 5.99h (or 21564 seconds) after the 
burst. Observations were done at an average air mass = 1.128 and seeing ~ 
1.5''. 

We took a 2nd epoch on January 1st, 2009, starting at 03h21 UT. 

The images mid time for the 2nd epoch is 30.99h (or 111564 seconds) after 
the burst. Observations were done at an average air mass = 1.334 and seeing 
~ 1.3''. 

The preliminary data for the 2nd epoch clearly confirms the fading of the 
afterglow: 

We present preliminary photometric results for g'r'i'z'. The AB magnitudes, 
using GROND zero points are as follows: 

     1st epoch       2nd epoch 

g' = 21.32 +- 0.02   23.67 +- 0.08
r' = 20.96 +- 0.01   23.07 +- 0.06
i' = 20.74 +- 0.02   22.79 +- 0.09
z' = 20.66 +- 0.03   22.84 +- 0.17 

No correction for galactic extinction was done. 

The quoted error is statistical only. There is an additional
systematic error in the absolute calibration using the GROND zeropoints
which is expected to be in the 0.2 mag range. 

Further data analysis is ongoing for JHK - the aftegrlow being clearly 
visible on the first epoch, but not on the 2nd.