GRB 090419

G. Stratta (ASDC), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC),
C. Guidorzi (U Ferrara), S. T. Holland (CRESST/USRA/GSFC),
E. A. Hoversten (PSU), N. P. M. Kuin (MSSL),
V. Mangano (INAF-IASFPA), J. Mao (INAF-OAB),
R. Margutti (Univ Bicocca&OAB), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL), A. M. Parsons (GSFC), M. Perri (ASDC),
P. Romano (INAF-IASFPA) and B. Sbarufatti (INAF-IASFPA) report on
behalf of the Swift Team:

At 13:43:31 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090419 (trigger=349592).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 196.976, -75.609 which is 
   RA(J2000) = 13h 07m 54s
   Dec(J2000) = -75d 36' 30"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a slow single
peak taking 30 seconds to rise to a maximum with a duration of
at least 90 seconds, and an additional peak at T+320.  The peak
count rate was ~800 counts/sec  (15-350 keV), at ~30 sec after 
the trigger. 

The XRT began observing the field at 13:45:31.0 UT, 119.7 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 196.92907,
-75.60534 which is equivalent to:
   RA(J2000)  = 13h 07m 42.98s
   Dec(J2000) = -75d 36' 19.2"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 44 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 (1.2e+21
cm^-2, Kalberla et al. 2005), with an excess column of 1.1
(+0.85/-0.64) x 10^22 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 5.55e-10 erg cm^-2 s^-1 (0.2-10
keV). 


UVOT took a finding chart exposure of 150 seconds with the White filter
starting 126 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 19.6 mag. 
The coverage of the XRT error circle by the 8'x8' region for the list of
sources generated on-board is uncertain because the large number of sources
filled the available telemetry. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.30. 




Burst Advocate for this burst is G. Stratta (giulia.stratta 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.)

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

Using 1541 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 090419, 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 = 196.92894, -75.60586 which is equivalent
to:

RA (J2000): 13h 07m 42.95s
Dec (J2000): -75d 36' 21.1"

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.

H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), A. M. Parsons (GSFC),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU),
G. Stratta (ASDC), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+704 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 090419 (trigger #349592)
(Stratta, et al., GCN Circ. 9161
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 ).  The BAT ground-calculated position is
RA, Dec = 197.006, -75.615 deg, which is 
   RA(J2000)  =  13h 08m 01.5s 
   Dec(J2000) = -75d 36' 55.6" 
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 96%.
 
The mask-weighted light curve shows a long burst with multiple peaks.
The first peak starts at ~T-30 sec.  There are comparably bright peaks
at T+50, 100, and 320 sec.  There is continued emmission out to at least T+1000 sec
and possibly T+1800 sec.  T90 (15-350 keV) is 450 +- 50 sec (estimated error
including systematics).
 
The time-averaged spectrum from T+8.1 to T+522.8 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.38 +- 0.16.  The fluence in the 15-150 keV band is 2.5 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+37.18 sec in the 15-150 keV band
is 0.4 +- 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/349592/BA/

P. Afonso (MPE Garching), S. Klose (Tautenburg) T. Kruehler and J.Greiner 
(both MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 090419 (Swift trigger 349592, G. Stratta et 
al.,GCN #9161) 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 
19 Apr. 2009 at 23:12 UT, 9.5 h after the burst.

Inside the enhanced XRT error circle (J.P. Osborne et al., GCN #9164
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 ) we 
detect a single faint source in the z' and J band at:

RA  (J2000.0) =  13:07:43.13
DEC (J2000.0) = -75:36:22.4

with an uncertainty of 0.5" in each coordinate.

Preliminary photometry yields the following AB magnitudes and upper limits 
in stacked images:

Filter  T_mid[h]  Exp[s]  AB Mag  MagErr
----------------------------------------
g       11.5792   12x369  >24.6
r       11.5792   12x369  >25.1
i       11.5792   12x369  24.9    0.5
z       11.5792   12x369  24.2    0.1
J       11.5859   360x10  23.0    0.2
H       11.5859   360x10  >22.1
K       11.5859   360x10  >21.2


The quoted error is statistical only. There is an additional systematic 
error in the absolute calibration using the GROND zeropoints and 2MASS 
field stars which is expected to be in the 0.2 mag range. Quoted magnitudes 
are not corrected for the significant Galactic foreground extinction 
corresponding to a reddening of E_(B-V)=0.30.

Given the lack of information about variability and the rather high density 
of foreground stars we cannot definitely associate this source with GRB 
090419 at this point. Because of the high Galactic foreground extinction, 
the upper limits in g'r' as well as the i'-z' color are not constraining, and 
the redshift is only constrained to below about 5.

G. Stratta and M. Perri (ASDC) report on behalf of the
Swift-XRT Team:

We have analysed the first 4 orbits of Swift-XRT data obtained from
GRB 090419 (trigger 349592; Stratta, et al., GCN Circ. 9161
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 ),
from T+128 s to T+271 s in Windowed Timing (WT) mode and from
T+303 s to T+4.9 h in Photon Counting (PC) mode.

The best position of the X-ray afterglow is the UVOT enhanced XRT
position given in Osborne et al. (GCN Circ. 9164
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 ).

The 0.3-10 keV X-ray light curve shows an initial flaring activity
superimposed to a constant continuum at a level of ~5 counts/s
up to ~520 s after the trigger that is consistent with being
the X-ray tail of the BAT data (GCN Circ. 9167
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 , Krimm et al.) during
the prompt emission.

Starting from 520 s up to 1200 s the count rate decays as
a power law with alpha1=3.5+/-0.5 and from T+1200
to T+12 ks it features a flattening with index alpha2=1.1+/-0.2.
If decaying at this rate, the afterglow will reach a count-rate of
1.3(0.6)E-3 counts/s at T+24(48)h.

The average WT spectrum (corresponding to the initial flat decay phase)
can be fitted by an absorbed power-law model (reduced chi square 1.0 with
18 degrees of freedom), with photon index 1.3+/-0.3, and equivalent
hydrogen column density NH=(1.1+/-0.6)E22 cm-2 in excess with
respect to the Galactic absorption value of 1.2E21 cm-2 (Kalberla et al.
2005). The average observed(unabsorbed) flux in the 0.3-10 keV band is
4.2(5.4)E-10 ergs cm-2 s-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00349510.

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

M. H. Siegel (PSU), E. A. Hoversten (PSU) and G. Stratta (ASDC) report
on behalf of the Swift/UVOT team.

The Swift/UVOT began observing the field of GRB 090419 126s after the
BAT trigger (Stratta et al., GCN Circ. 9161
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 ).  Data summed over the  
first
orbit reveals a very faint (3.3 sigma) source in the white filter at the
refined position of the X-ray afterglow (Osborne et al., GCN Circ.  
9164
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 ).
This source is not detected in the second orbit data.

The detection and 3-sigma upper limits for the finding chart (fc) and
summed exposures are reported below:

FILTER     T_start(s)  T_stop     Exposure     Mag/3UL
=============================================================
white fc    126          276        147        > 20.69
white       126         1706        410          21.07+-0.31
white      5320         6956        393        > 21.25

v           614         1756        136        > 18.93
v          5732         7367        393        > 19.60

b           540         1682        116        > 19.87
b          5116        13394        572        > 20.69

u           284         1829        362        > 20.25
u          6346        13206       1081        > 20.89

uvw1        664         1805        136        > 19.31
uvw1       6142        12292       1118        > 20.63

uvm2        639         1608         58        > 18.41
uvm2       5936        17728        465        > 19.99

uvw2        590         1731        136        > 19.37
uvw2       5527         7162        393        > 20.13
=============================================================

The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E_{B-V} = 0.296 (Schlegel et al.,
1998, ApJS, 500, 525). The photometry is on the UVOT photometric system
described in Poole et al. (2008, MNRAS, 383, 627).