GRB 090728

V. Mangano (INAF-IASFPA), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
P.A. Curran (MSSL-UCL), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), S. T. Holland (CRESST/USRA/GSFC),
E. A. Hoversten (PSU), J. A. Kennea (PSU), N. P. M. Kuin (MSSL),
F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),
P. Romano (INAF-IASFPA), T. Sakamoto (NASA/UMBC),
B. Sbarufatti (INAF-IASFPA), M. H. Siegel (PSU),
M. Stamatikos (NASA/ORAU) and M. A. Stark (PSU) report on behalf of
the Swift Team:

At 14:45:45 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090728 (trigger=358574).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 29.660, +41.647 which is 
   RA(J2000) = 01h 58m 38s
   Dec(J2000) = +41d 38' 49"
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 20 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 14:47:36.5 UT, 110.6 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 29.65234, 41.63270 which
is equivalent to:
   RA(J2000)  = 01h 58m 36.56s
   Dec(J2000) = +41d 37' 57.7"
with an uncertainty of 4.2 arcseconds (radius, 90% containment). This
location is 55 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
7.35e+20 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 3.90e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
116 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 3-sigma upper limit is 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
0.07. The XRT position is near a bright (< 6.5 mag) star. 

Burst Advocate for this burst is V. Mangano (vanessa 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.)

Sub:GRB 090728, RIMOTS optical upper limits  

K.Noda, H.Hayasi, E.Sonoda, N.Ohmori, K.Kono  
A.Daikyuji, Y.Nisioka, M.Yamauchi
(University of Miyazaki)

 We have observed the field covering the error circle of
GRB 090728 (Swift trigger 358574, GCN 9725
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 , V. Mangano et al.) 
with the unfiltered CCD camera on the 30-cm telescope 
at University of Miyazaki.
The observation was started 14:46:53 UT, about 23 sec
after the Swift trigger time. 
We have compared our data of 30 sec exposures
with the USNO-A2.0 catalog,
There is no new source at the reported position. 
(Swift trigger 358574, GCN 9725
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 , V. Mangano et al.) 

the upper limits are as follows:
--------------------------------------------------------------
Start(UT)   End(UT)    Num. of frames    Limit (mag.)
--------------------------------------------------------------
14:59:59	15:00:29          1            13.8
14:46:53	15:00:29         11            15.4
---------------------------------------------------------------

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

Using 2365 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 090728, 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 = 29.65290, +41.63313 which is equivalent
to:

RA (J2000): 01h 58m 36.70s
Dec (J2000): +41d 37' 59.3"

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) and Evans
et al. (2009, arXiv:0812.3662).

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

GRB 090728: Swift/UVOT Upper Limits

P.A. Curran (MSSL-UCL), V. Mangano (INAF-IASFPA), report on behalf of
the Swift/UVOT team:


The Swift/UVOT began settled observations of the field of GRB 090728
117s after the BAT trigger (Mangano et al., GCN 9725
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 ). No optical
afterglow consistent with the refined XRT position (Osborne et al., GCN
9729
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 )  or the optical counterpart (Melandri et al. , GCN 9726
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 ) is
detected in the UVOT exposures.  This is consistent with the R-band
non-detection of Melandri et al.


Preliminary 3-sigma upper limits using the UVOT photometric system
(Poole et al. 2008, MNRAS, 383, 627) for the initial finding chart (FC)
and subsequent exposures are:

Filter   T_start(s)    T_stop(s)    Exp(s)    Mag

v       422             6883           479        > 20.70
b       372             6643           491        > 21.45
u       117             366            150        > 20.00 (FC)
u       117             6437           842        > 21.34
uw1     472             6233           452        > 21.05
um2     447             6026           452        > 20.75
uw2     398             6849           490        > 20.89

The values quoted above are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.07 in the direction of the burst
(Schlegel et al. 1998).

V. Mangano, B. Sbarufatti (INAF IASF Pa)
report on beahalf the Swift XRT Team:


We have analysed 9.8 ks of XRT data for GRB 090728 (Mangano et al. GCN
Circ. 9725
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 ), from 116.9 s to 53.1 ks after the BAT trigger. The data
comprise 55.3 s in Windowed Timing (WT) mode from T+116.9 s to T+172.2
s, with  the remainder in Photon Counting (PC) mode. The enhanced XRT
position for this burst was given by Osborne et al. (GCN. Circ 9729).

The 0.3-10 keV XRT light curve is well modeled by a doubly broken
power law with initial decay slope -5.5 � 0.5, first break at
T+204 � 10 s, plateau phase slope -0.11 � 0.14, second break
at T+1.8 � 1.2 ks and final slope -1.7 � 0.1.
Decaying at the present rate the source will reach a level of
2e-4 counts/s on July 30 at 14:45 UT (48 h after the trigger).

We extracted the average WT spectrum of the early decay phase (55.3 s
exposure), and the average PC spectra of the plateau phase (866 s
exposure, from T+174 s to T+1071 s) and the final decay phase (7.4 ks
exposure, from T+4383 s to T+18.4 ks). The three spectra are well fitted
by an absorbed power law model with NH consistent with the Galactic
value of 7.35e20 cm-2 (Kalberla et al. 2005) and photon indices of
2.4 � 0.4, 1.8 � 0.2, and 2.0 � 0.3, respectively.
The average 0.3-10 keV observed [unabsorbed] fluxes are
1.6e-10 [2.9e-10] erg cm-2 s-1, 2.7e-11 [3.0e-11] erg cm-2 s-1,
and 1.5e-12 [2.3e-12] erg cm-2 s-1, respectively.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00358574.

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

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. Mangano (INAF-IASFPA), C. B. Markwardt (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-240 to T+962 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 090728 (trigger #358574)
(Mangano, et al., GCN Circ. 9725
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 ).  The BAT ground-calculated position is
RA, Dec = 29.644, 41.632 deg which is 
   RA(J2000)  =  01h 58m 34.5s 
   Dec(J2000) = +41d 37' 53.7" 
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 37%.
 
The mask-weighted light curve shows a single pulse starting at ~T-10 sec,
peaking at ~T+2 sec, and ending at ~T+70 sec.  T90 (15-350 keV) is
59 +- 18 sec (estimated error including systematics).
 
The time-averaged spectrum from T-5.0 to T+63.2 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.05 +- 0.26.  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+1.25 sec in the 15-150 keV band
is 1.0 +- 0.3 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/358574/BA/