GRB 080919

S. Immler (CRESST/GSFC/UMD) and S. T. Holland (CRESST/USRA/GSFC), on 
behalf of the Swift Team:

Swift UVOT started observing GRB 080919 (Preger et al. GCN 8270
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 ) 82 
seconds after the BAT trigger. The source detected by REM (Covino et al. 
GCN 8271
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 ) is detected in all optical and in the uvw1 filter and shows no 
signs of fading over a period of ~25 ks after the trigger. It is the 
only optical source detected within the XRT error circle (Preger et al. 
GCN 8276
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 ). The following UVOT magnitudes (and 3-sigma upper limits) are 
measured:

Filter   T_start   T_stop   Exp(s)  Mag (3-sigma upper limit)
-----------------------------------------------------
white      82    18561   2,203   18.4�0.1
v         188    23441   2,766   17.2�0.1
b         670    17648   1,375   18.3�0.1
u         645     7509    510   19.6�0.3
uvw1      620    25158   1,301   20.4�0.5
uvm2      594    24347   1,278    >20.4
uvw2      701    19375   1,809    >20.8

The quoted upper limits have not been corrected for the expected 
Galactic extinction along the line of sight of E(B-V) of 0.49 mag 
(Schlegel et al. 1998). All photometry is on the UVOT flight system 
described in Poole et al. (2008, MNRAS, 383, 627).

B. Preger (ASDC), G. Stratta (ASDC), M. Perri (ASDC) report on behalf
of the Swift XRT team:

The Swift XRT started observing the field of GRB080919 (trigger=325268;
Preger et al., GCN Circ. 8270
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 ) at 00:06:23.8 UT, 70.8 seconds
after the trigger.

The position of the X-ray afterglow is: RA, Dec= 265.223958, -42.368667
which is equivalent to:

RA (J2000): 17 40 53.75
Dec (J2000): -42 22 07.2

with an uncertainty of 2.0 arcsec (90% confidence).

The X-ray light curve from T0+74 s to T0+25 ks shows a fading behavior.
At ~T0 + 200 data show a 200 s long flare peaking
at ~T0 + 240 s with peak count rate of (1.2+/-0.3) cts/s
that is about a factor of 4 above the underlying continuum.
Excluding the flare, the light curve can be well modelled with
a broken power law, with best fit first decay index
alpha_1 = 2.2+/-0.2, a temporal break at ~T0 + 891 s and second
decay index alpha_2= 0.8+/-0.2.

A 4.5 ks exposure X-ray spectrum from T0+100 s to T0+7811 s can be
fit by an absorbed power-law model with a photon index of 2.0 (+0.5 -0.4)
and a column density of 3.9 (+3.2) (-2.3) x 10^21 cm^-2 in addition to
the Galactic column density value in the direction of the burst
(2.6 x 10^21 cm^-2, Kalberla et al. 2005).

Providing the source continues to decay at the same rate, we predict an
observed flux of about 2 x 10^-14 erg cm^-2 s^-1 at T0+1 days.

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

W.H. Baumgartner (GSFC/UMBC),  S. D. Barthelmy (GSFC),
J.R. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
H.A. Krimm (GSFC/USRA), C.B. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD),
D.M. Palmer (LANL), A.M. Parsons (GSFC), B. Preger (ASDC),
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-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 080919 (trigger #325268)
(Preger, et al., GCN Circ. 8270
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 ).  The BAT ground-calculated position is
RA, Dec = 265.221, -42.375 deg which is
 RA(J2000)  =  17h 40m 53.0s
 Dec(J2000) = -42d 22' 29.5"
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 99%.

The mask-weighted light curve shows a broad peak of approximately 750 msec
duration starting at T+0 followed immediately by a weaker ~400 msec
peak seen mostly below 50 keV. T90 (15-350 keV) is 0.6 +- 0.1 sec 
(estimated error including systematics).

The time-averaged spectrum from T+0.1 to T+0.8 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum
is 1.10 +- 0.26.  The fluence in the 15-150 keV band is 7.2 +- 1.1 x 10-8 erg/cm2.
The 1-sec peak photon flux measured from T-0.08 sec in the 15-150 keV band
is 1.2 +- 0.2 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/325268/BA/

S. Covino, L.A. Antonelli, L. Calzoletti,  S. Campana, G. Chincarini,  
M.L. Conciatore, S. Cutini,  V. D'Elia,  F. D'Alessio, P. D'Avanzo,  
F. Fiore, D. Fugazza, P. Goldoni, D. Guetta, C. Guidorzi, G.L.  
Israel, E. Maiorano, N. Masetti, A. Melandri, E. Meurs, L. Nicastro,  
E. Palazzi, E. Pian, S. Piranomonte, L.  Stella,  G.  Stratta, G.  
Tagliaferri, G. Tosti, V.Testa, S.D. Vergani, F. Vitali report on  
behalf of the REM team:


The robotic 60-cm REM telescope located at La Silla (Chile) observed  
automatically the field of the short GRB 080919 (Preger et al. GCN  
8270
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 ) starting from about 74s s after the GRB time. For a technical  
problem the images are of mediocre quality. However, we detect a  
source consistent with the position of the XRT transient and already  
present in the 2MASS catalogue (RA=17:40:53.778, DEC=-42:22:07.36)  
with H = 13.73 +- 0.03. In our frames the source appears at about  
H~14.0, constant within the duration of the REM observations (about  
30min).

At the present stage, beyond the position consistency, we can not  
infer whether this source is related or not to the fading X-ray  
source reported in Preger et al. (GCN 8270
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 ). Further observations are  
then encouraged.

B. Preger (ASDC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), S. D. Hunsberger (PSU),
S. Immler (CRESST/GSFC/UMD), H. A. Krimm (CRESST/GSFC/USRA),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL), M. Perri (ASDC), T. Sakamoto (NASA/UMBC),
M. Stamatikos (NASA/ORAU), G. Stratta (ASDC), M. C. Stroh (PSU) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:

At 00:05:13 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080919 (trigger=325268).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 265.289, -42.396 which is 
   RA(J2000)  =  17h 41m 09s
   Dec(J2000) = -42d 23' 45"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single spike
with a duration of about 1 sec.  The peak count rate
was ~3300 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 00:06:23.8 UT, 70.8 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 265.22379,
-42.36876 which is equivalent to:
   RA(J2000)  = 17h 40m 53.71s
   Dec(J2000) = -42d 22' 07.5"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 199 arcseconds from the BAT onboard position, outside the
BAT error circle. 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 82 seconds after the BAT trigger.  The 2.7'x2.7' sub-image 
covers 25% of the BAT error circle and none of the XRT error circle. 
The 8'x8' region for the list of sources generated on-board covers 90% of the 
BAT error circle and 100% of the XRT error circle. 
No afterglow candidate has been found in the initial data products. Typical
upper limit is ~18th magitude. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.49. We note that this is a crowded field. 

This event lies near to the direction of the Galactic Bulge
(long,lat = 348.03, -6.26) and so we cannot immediately rule out
the possibility that this source is Galactic.  However, the duration
and the spectral hardness of this event are consistent with a
classical Short GRB. 

Burst Advocate for this burst is B. Preger (preger AT asdc.asi.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.)