GRB 090407

H. Ziaeepour (UCL-MSSL), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), O. Godet (U Leicester),
C. Guidorzi (U Ferrara), S. T. Holland (CRESST/USRA/GSFC),
J. A. Kennea (PSU), N. P. M. Kuin (MSSL), J. Mao (INAF-OAB),
P. T. O'Brien (U Leicester), S. R. Oates (UCL-MSSL),
J. P. Osborne (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), P. Romano (INAF-IASFPA),
B. A. Rowlinson (U Leicester), B. Sbarufatti (INAF-IASFPA),
P. Schady (MSSL-UCL) and G. Stratta (ASDC) report on behalf of the
Swift Team:

At 10:28:25 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090407 (trigger=348650).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 68.959, -12.665 which is 
   RA(J2000) = 04h 35m 50s
   Dec(J2000) = -12d 39' 53"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multiple-peaked
structure with a duration of at least 150 sec, including a small
peak at T+135 sec, during the XRT/UVOT observations.  The peak count rate
was ~2390 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 10:29:58.7 UT, 93.0 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 68.98074, -12.67921 which
is equivalent to:
   RA(J2000)  = 04h 35m 55.38s
   Dec(J2000) = -12d 40' 45.2"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 91 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 (3.68e+20
cm^-2, Kalberla et al. 2005), with an excess column of 2.5
(+1.79/-1.62) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White 
filter  starting 97 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 25% of the BAT error circle and 0% of the
XRT error circle. The typical 3-sigma upper limit has been about 19.6
mag. The 8'x8'  region for the list of sources generated on-board
covers 100% of the  BAT and XRT error circles. The list of sources is
typically complete to about  18 mag. No correction has been made for
the expected extinction  corresponding to E(B-V) of 0.07. 

Burst Advocate for this burst is H. Ziaeepour (hz AT mssl.ucl.ac.uk). 
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.)

B. E. Schaefer (Louisiana State), F. Yuan (U Mich), report on behalf of 
the ROTSE collaboration:

ROTSE-IIIa, located at Siding Spring Observatory, Australia, responded to
GRB 090407 (Swift trigger 348650; H. Ziaeepour et al., GCN 9101
Loading...
 
 ),
producing images beginning 8.8 s after the GCN notice time. An automated
response took the first image at 10:29:05.8 UT, 40.2 s after the burst,
and during the gamma-ray emission, under fair conditions. We took 10
5-sec, 10 20-sec and 33 60-sec exposures. These unfiltered images are
calibrated relative to USNO A2.0 (R). Imaging is on going but the 
source is getting low.

Comparison to the DSS (second epoch) reveals no new sources within the 
3-sigma Swift/BAT error circle or the XRT error circle, for both single 
images and coadding into sets of 10; the field is not crowded. Individual 
images have limiting magnitudes ranging from 13.9-15.5; we set the 
following specific limits.

start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
10:29:05.8   10:29:10.8         5     14.1           40.2       N
10:29:05.8   10:31:19.0       133     16.1           40.2       Y

T. N. Ukwatta (GWU) 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),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), H. Ziaeepour (UCL-MSSL)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+627 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 090407 (trigger #348650)
(Ziaeepour, et al., GCN Circ. 9101
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 68.979, -12.684 deg, which is 
   RA(J2000)  =  04h 35m 54.9s 
   Dec(J2000) = -12d 41' 02.4" 
with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 84%.
 
The mask-weighted light curve shows two clusters of peaks.  The first cluster
starts at ~T-15 sec, peaks at ~T+2 sec, and returns to baseline at ~T+10 sec.
The second clutser starts at ~T+130 sec, peaks at ~T+140 sec, and returns
to baseline at ~T+340 sec.  T90 (15-350 keV) is 310 +- 70 sec
(estimated error including systematics).
 
The time-averaged spectrum from -17.7 to 368.6 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.73 +- 0.29.  The fluence in the 15-150 keV band is 1.1 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+0.45 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/348650/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 8297 s of XRT Photon Counting mode data and 13 UVOT
images for GRB 090407, 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 = 68.97908, -12.67929 which is equivalent
to:

RA (J2000): 04h 35m 54.98s
Dec (J2000): -12d 40' 45.5"

with an uncertainty of 1.4 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.

S. R.  Oates (MSSL-UCL) and H. Ziaeepour (MSSL-UCL) report on behalf  
of the Swift/UVOT team:

The Swift/UVOT began observing the field of GRB 090407 98 s
after the BAT trigger (Ziaeepour et al., GCN Circ. 9101
Loading...
 
 ). No
optical afterglow is detected in the initial UVOT exposures at
the refined position of the X-ray afterglow (Evans et al., GCN Circ.  
9105
Loading...
 
 ).

The 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    98          248          147         <20.50
u fc	          310       559          246         <19.89
white        590       2050        303         <21.04
v               640        5550        352         <19.25
u    	         713        2001        136         <19.61
b    	         565        2026        156         <19.99
uvw1       689	        1977        136         <19.35
uvm2       664        5607        207         <19.49
uvw2       615	        2071        170         <19.74
	

The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E_{B-V} =  0.40 mag (Schlegel et al.,
1998, ApJS, 500, 525).  The photometry is on the UVOT photometric system
described in Poole et al. (2008, MNRAS, 383,627).

A.P. Beardmore (U. Leicester) and H. Ziaeepour (UCL-MSSL) report on 
behalf of the Swift-XRT team:

We have analysed the first five orbits of Swift-XRT data obtained from
GRB 090407 (trigger #348650; Ziaeepour, et al., GCN Circ. 9101
Loading...
 
 ),
comprising 273 s taken in Windowed Timing (WT) mode, starting at
T+96.7 s, followed by 10.2 ks in Photon Counting (PC) mode from 
T+398 s to T+24.2 ks. The UVOT-enhanced position was given by Evans 
et al. (GCN Circ. 9105
Loading...
 
 ).

The 0.3-10 keV X-ray light curve shows a number of flares in the first
400 s, the largest occurring from T+120 s to T+180 s, reaching a peak
rate of 90 count s^-1 at T+140 s. This flare is also seen by the
Swift-BAT (Ukwatta et al., GCN Circ. 9104
Loading...
 
 ).  Further flaring is seen
from ~T+200s to ~T+350 s, ending with a steep decay of slope
~4.0. After T+950 s the X-ray light curve breaks to a much shallower
decay slope of 0.28 +/- 0.06.

The data show spectral evolution during the flaring intervals, after
which the PC mode spectrum can be modelled by an absorbed powerlaw
with a photon index of 2.43 +/- 0.13 and a total absorbing column
density of (2.51 +/- 0.35) x 10^21 cm^-2, which is in excess of the
Galactic value of 3.7 x 10^20 cm^-2 (Kalberla et al. 2005) in the
direction of the burst. The observed 0.3-10 keV flux at this time
(~T+6.2 ks) is (6.29 +0.41 -0.56) x 10^-12 erg cm^-2 s^-1, which
corresponds to an unabsorbed flux of 1.3 x 10^-11 erg cm^-2 s^-1. The
count to observed flux conversion factor for this spectrum is 
3.5 x 10^-11 erg cm-^2 count^-1.

If the light curve continues to decay with the same slope of 0.28 we
predict an X-ray count rate of 0.047 count s^-1 at T+24 hours after
the trigger, which corresponds to an observed 0.3-10 keV flux of 
1.6 x 10^-12 erg cm^-2 s^-1.  However, we  note that it is unlikely 
the light curve decay will remain this shallow at T+24 hours.

The results of the XRT-team automatic analysis are available at 
http://www.swift.ac.uk/xrt_curves/00348650.

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

Daniele Malesani and Johan Peter Uldall Fynbo report on behalf of a 
larger collaboration:

We observed the field of GRB 090407 (Ziaeepour et al., GCN 9101
Loading...
 
 ) with 
the ESO VLT equipped with FORS2. Observations were carried out with mean 
time Apr 8.0 UT (13.7 hr after the GRB), partially during evening twilight.

Inside the X-ray error circle (Evans et al., GCN 9105
Loading...
 
 ), no source is 
detected down to limiting magnitudes R > 23.8 and z(AB) > 23.8, based on 
archival zeropoints (accurate up to ~0.2 mag).

We encourage deeper observations, possibly in the near infrared.

We acknowledge significant support from the ESO staff at Paranal, in 
particular Gianni Marconi and Elena Mason.

P. Afonso, F. Olivares, J. Greiner and T. Kruehler (MPE Garching) report
on behalf of the GROND team: 

GROND (Greiner et al. 2008, PASP 120, 405), mounted at the 2.2m ESO/MPI
telescope at La Silla Observatory (Chile), observed the field of GRB 090407
(H. Ziaeepour et al. 2009, GCN #9101
Loading...
 
 ) simultaneously in the g'r'i'z'JHK
bands. 

Observations started on April 7, at 23:34 UTC (13.1 h after the burst)
and lasted for 87 minutes. 

In stacked images of 24 min total integration time in griz and 20 min in 
JHK, we do not detect any new object inside the enhanced XRT error circle
(Evans et al., GCN #9105
Loading...
 
 ), down to the following limiting magnitudes
(all in the AB system): 

g' > 23.7
r' > 24.1
i' > 23.5
z' > 23.3
J  > 21.6
H  > 21.0
K  > 20.4 

The upper limits have been obtained using GROND zero points and 2MASS
field stars as reference. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.07 mag.