GRB 080409

S. T. Holland (CRESST/USRA/GSFC), W. H. Baumgartner (GSFC/UMBC),
D. N. Burrows (PSU), J. R. Cummings (NASA/UMBC), J. A. Kennea (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
K. M. McLean (GSFC/UMD), K. L. Page (U Leicester),
D. M. Palmer (LANL), R. L. C. Starling (U Leicester) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:

At 01:22:57 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080409 (trigger=308812).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 84.333, +5.085 which is 
   RA(J2000) = 05h 37m 20s
   Dec(J2000) = +05d 05' 07"
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 10 sec.  The peak count rate
was ~5000 counts/sec (15-350 keV), at ~0.7 sec after the trigger. 

The XRT began observing the field at 01:24:21.6 UT, 84.0 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 84.33035, 5.08523 which
is equivalent to:
  RA(J2000)  = 05h 37m 19.28s
  Dec(J2000) = +05d 05' 06.8"
with an uncertainty of 2.9 arcseconds (radius, 90% containment). This
location is 9.5 arcseconds from the BAT onboard position, within the
BAT error circle. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (2.34e+21
cm^-2, Kalberla et al. 2005), with an excess column of 4.5
(+4.33/-3.19) x 10^21 cm^-2 (90% confidence). The relation of Grupe et
al. (2007) implies that this burst has a redshift z<4.3, although high
redshift fits to the absorbed XRT spectrum are possible if paired with
an anomalously large column. A summary of the promptly downlinked data
is given at http://www.swift.ac.uk/sper/308812/. 

UVOT took a finding chart exposure of  95 seconds with the White (160-650 nm)
filter starting 87 seconds after the BAT trigger. No 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 19.5 mag. 
No correction has been made for the expected extinction corresponding to E(B-V)
of 0.78 mag. 

Burst Advocate for this burst is S. T. Holland (sholland AT milkyway.gsfc.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.)

P. D'Avanzo, S. Covino, D. Malesani, D. Fugazza, L.A. Antonelli, L. 
Calzoletti, S. Campana, G. Chincarini, M.L. Conciatore, S. Cutini, V. 
D'Elia, F. D'Alessio, F. Fiore, P. Goldoni, D. Guetta, C. Guidorzi, G.L. 
Israel, E. Maiorano, N. Masetti, A. Melandri, E.J.A. Meurs, L. Nicastro, 
E. Palazzi, E. Pian, F. Piranomonte, S. Piranomonte, L. Stella, G. 
Stratta, G. Tagliaferri, G. Tosti, V. Testa, S.D. Vergani, and 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 GRB 080409 (Holland et al., GCN 7573
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 ) 
starting about 81 seconds after the burst. Airmass was large (about 2.9).

Preliminary photometry of our earliest images (R: 30 s, H: 50 s) reveal 
no new sources inside the XRT error circle down to 3sigma limiting 
magnitudes of H ~ 15.0 and R ~ 17.0.

[GCN OPS NOTE(09apr08): Per author's request, the "080309" in the Subject-line
and in the body of the Circular was changed to "080409".]

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

Using 91 s of overlapping XRT Photon Counting mode and UVOT
data for GRB 080409, 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 = 84.32975, +5.08484 which is equivalent
to:

RA (J2000): 05h 37m 19.14s
Dec (J2000): +05d 05' 05.4"

with an uncertainty of 2.0 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.

R.L.C. Starling, P.A. Evans, K.L. Page (U. Leicester) and S.T. Holland 
(CRESST/USRA/GSFC) report, on behalf of the Swift XRT team:

We have analysed the first three orbits of Swift XRT data (5.8 ks of data 
from T0+96s to T0+1.29e4s) for GRB 080409 (Holland et al., GCN Circ. 
7573
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 ). The enhanced position for the X-ray afterglow is given in Evans et 
al. (GCN Circ. 7575
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 ).

The light curve shows an initial increase with slope of alpha1~0.6 up to
T~480s. The light curve then turns over to decay with a slope of
alpha2=-0.8+/-0.1.  

The Photon Counting mode spectrum collected from the first three orbits 
can be fit with an absorbed power law of photon index Gamma=2.2+0.5/-0.7 
and a total absorbing column of NH=(5 +5/-4)e21 cm-2, exceeding the 
Galactic value of 2.4e21 cm-2. The 0.3-10 keV observed (unabsorbed) flux 
is 3.2e-12 (6.7e-12) erg/cm2/s, corresponding to a count rate of 5.8e-2 
count/s and a count rate to flux conversion of 1 count/s = 5.6e-11 erg/cm2/s.

The predicted count rates at T0+24h and T0+48h are 6.8e-3 and 4.0e-3 
count/s respectively, assuming the decay continues with alpha=-0.8.

This is an official product of the Swift XRT team.

Swift/UVOT began settled observations of the field of GRB 080409 starting 
88s after the BAT trigger (Holland et al., GCN Circ 7573
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 ). We do not 
detect an optical/uv afterglow at the enhanced XRT position (Evans et al., 
GCN Circ. 7575
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 ) in the initial finding chart observations or subsequent 
summed images down to the following 3 sigma upper limits:

Filter  T_start T_stop  Exp.    Mag UL (3sig)
 	(s)	(s)	(s)
white   88      187     93      > 20.22
white   682     7079    494     > 21.16
v       188     587     393     > 19.45
v       721     12243   1099    > 20.03
b       667     676     412     > 20.42
u       642     661     432     > 20.13
uvw1    618     637     430     > 19.86
uvm2    593     12940   1070    > 20.23
uvw2    697     11330   1082    > 20.46

The above magnitudes are not corrected for the large Galactic extinction 
in the line of sight to GRB 080409, corresponding to a reddening of 
E(B-V)=0.78 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).

D. Palmer (LANL), S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC) ,
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
S. T. Holland (CRESST/USRA/GSFC), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD),  K. McLean (GSFC/UMD), A. Parsons (GSFC),
T. Sakamoto (GSFC/UMBC), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. 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 080409 (trigger #308812)
(Holland, et al., GCN Circ. 7573
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 ).  The BAT ground-calculated position
is RA, Dec = 84.304, 5.078 deg which is
   RA(J2000)  =  05h 37m 12.9s
   Dec(J2000) = +05d 04' 39.9"
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 46%.

The mask-weighted light curve shows 3 well-separated peaks, at T-13,
T+0, and T+10 sec, that are about 1, 2, and, 2 sec wide respectively.
The first is much smaller than the others, the second at T+0 is the
largest.  T90 (15-350 keV) is 20.2 +- 8.0 sec (estimated error including
systematics).

The time-averaged spectrum from T-13.1 to T+10.4 sec is best fit by a
simple power-law model.  The power law index of the time-averaged
spectrum is 2.10 +- 0.20.  The fluence in the 15-150 keV band is
6.1 +- 0.7 x 10^-07 erg/cm2.  The 1-sec peak photon flux measured from
T+0.00 sec in the 15-150 keV band is 3.7 +- 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/308812/BA/