GRB 090429A

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

The onboard XRT position for GRB 090429A (Markwardt et al. GCN. Circ 
9280) delivered as an XRT position notice and given in GCN 9280
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  was 
incorrect. Inspection of the images reveals a cosmic ray 52 arcsec from 
the GRB which affected the onboard centroid.

The correct position of the XRT afterglow is: RA, Dec= 90.5568, -52.3886
which is equivalent to:

RA(J2000)  = 06 02 13.63
Dec(J2000) = -52 23 18.9

with an uncertainty of 4.8 arcsec (radius, 90% confidence).

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

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),
C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), 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-61 to T+302 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090429A (trigger #350853)
(Markwardt, et al., GCN Circ. 9280
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 ).  The BAT ground-calculated position is
RA, Dec = 90.573, -52.389 deg, which is 
   RA(J2000)  =  06h 02m 17.5s 
   Dec(J2000) = -52d 23' 19.0" 
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
 
The mask-weighted light curve shows a relatively smooth structure
with a couple overlapping peaks starting at ~T-12 sec and peaking at T_zero.
The main peak ends around T+40 sec with a long weak tail extending out
to ~T+200 sec.  T90 (15-350 keV) is 188 +- 37 sec (estimated error
including systematics).
 
The time-averaged spectrum from T-10.8 to T+203.0 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.55 +- 0.22.  The fluence in the 15-150 keV band is 1.0 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-0.35 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/350853/BA/

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

Using 945 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 090429A, 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 = 90.55469, -52.38758 which is equivalent
to:

RA (J2000): 06h 02m 13.13s
Dec (J2000): -52d 23' 15.3"

with an uncertainty of 3.2 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, arXiv:0812.3662).

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

F. Olivares, T. Kruehler, J. Greiner (all MPE) report on behalf of the 
GROND team:

We observed the field of GRB 090429A (Swift trigger 350853, Markwardt et 
al.,GCN #9280) simultaneously in g'r'i'z'JHK with GROND mounted at the 2.2m 
ESO/MPI telescope at La Silla Observatory (Chile).

Observations started on 30 Apr. 2009 at 01:05 UT, 20.2 h after the burst, 
and consisted of a set of images with a total integration time of 28 min in 
JHK and 32 min in g'r'i'z'.

In stacked images we do not detect any object inside the enhanced XRT 
errorcircle (Evans et al., GCN #9297
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 ) down to the following AB magnitudes:

g' > 23.4
r' > 23.3
i' > 22.6
z' > 22.2
J > 21.8
H > 20.7
K > 20.0

These upper limits have been obtained using 2MASS field stars and the GROND 
zeropoints as reference.

P.A. Evans (U. Leicester) and C. B. Markwardt (CRESST/GSFC/UMD) report
on behalf of the Swift-XRT team:

We have analysed 6 ks of XRT data for GRB 090429A (Markwardt et al. GCN
Circ. 9280
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 ). The first observation comprises a continuous observation
from T0+64 s to T0+255 s  with the data  entirely in Windowed Timing
(WT) mode. The second observation covers the range T0+35 to T0+64 ks,
and contains 5.8 ks of Photon Counting (PC) mode data. The enhanced XRT
position for this burst was given by Evans et al. (GCN. Circ 9297).

The first observation shows a number of flares superimposed on a short,
initial rise which breaks at T0+100s to a power-law decay with index 2.7
(+0.3, -0.2). The later PC mode data lie orders of magnitude above the
extrapolation of this decay; the addition of a break around T0+1 ks to a
decay with power-law index 0.56 (+0.12, -0.06) produces a good fit to
the data. Due to the large observing gap the behaviour of the light
curve in the interval T0+255 s to T0+35 ks is unknown; if it is more
complex than the simple behaviour we have modelled the final decay index
could differ significantly from the 0.56 (+0.12, -0.06) value we obtained.

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.0 (+1.0, -0.7). The
best-fitting absorption column is 1.20 (+2.36, -0.77) x 10^21 cm^-2,
consistent with the Galactic value of 4.2 x 10^20 cm^-2 (Kalberla et al.
2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum is 3.8 x 10^-11 (5.0 x 10^-11) erg
cm^-2 count^-1.

If the light curve continues to decay with a power-law decay index of
0.56, the count rate at T+48 hours will be 5.9 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.2 x
10^-13 (2.9 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00350853.

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

M. M. Chester (PSU), S. T. Holland (CRESST/GSFC/USRA) and
C. B. Markwardt (CRESST/GSFC/UMD) report on the behalf of the Swift
UVOT team:

       The Swift/UVOT observed the field of GRB 090429A starting 49 s
after the BAT trigger (Markwardt, et al., 2009, GCN Circ. 9280
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 ).
Settled exposures started at T+67 s.  We do not find any new source,
relative to the DSS, USNO-B1.0, or 2MASS at the position of the XRT
afterglow (Evans, et al. 2009, GCN Circ. 9297
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 ).  Preliminary 3-sigma
upper limits for detecting a source in the white finding chart and the
co-added images, using a 2.5 arcsecond radius circular aperture, are

Filter      T_start   T_stop    Exp(s)     Mag
----------------------------------------------
white (fc)       67      217       147   >21.7

v            35,736   58,902       114   >19.8
b            40,727   63,010      1697   >22.1
u            52,833   53,121       284   >21.0
uvw1         50,447   86,297      3336   >22.2
uvm2         44,777   47,341       659   >20.9
uvw2         34,829   57,197      1746   >21.9
white        63,015   63,137       120   >21.5
----------------------------------------------

The quoted upper limits have not been corrected for the expected
Galactic extinction along the line of sight corresponding to a
reddening of E_{B-V} = 0.06 mag (Schlegel, et al., 1998, ApJS, 500,
525).  All photometry is on the UVOT photometry system described in
Poole et al. (2008, MNRAS, 383, 627).

Richard L. Pearson and J. Ward Moody report for Brigham Young
Univerisity�s ROVOR team:

We observed the field around GRB 090429A (Swift trigger 350853,
Markwardt et al., GCN 9280
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 ) with the ROVOR (Robotic Observatory for
Variable Object Research) 16� telescope from Delta, Utah. Beginning 30
April 2009 at 03:46:50 UT (22.3 hours after outburst), observations
were obtained for a complete integration time of 50 minutes in white
light. No detection was made after stacking the images. Using the
magnitude limits established by Olivares et al., GCN Circ. 9303
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  on the
2.2m ESO/MPI telescope at La Silla Observatory, we estimate a
magnitude limit of 22 � 1 mag on these observations.