GRB 090607

F. E. Marshall (NASA/GSFC), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), M. M. Chester (PSU),
C. Guidorzi (U Ferrara), H. A. Krimm (CRESST/GSFC/USRA),
K. L. Page (U Leicester), D. M. Palmer (LANL),
T. N. Ukwatta (GSFC/GWU) and H. Ziaeepour (UCL-MSSL) report on behalf
of the Swift Team:

At 05:30:17 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090607 (trigger=354299).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 191.209, +44.130 which is 
   RA(J2000)  = 12h 44m 50s
   Dec(J2000) = +44d 07' 47"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows several spikes
with a duration of about 5 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 05:31:27 UT, 70 seconds
after the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 191.16903, 44.10541 which
is equivalent to:
   RA(J2000)  = 12h 44m 40.57s
   Dec(J2000) = +44d 06' 19.5"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 136 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 (1.84e+20
cm^-2, Kalberla et al. 2005), with an excess column of 4.1
(+2.44/-2.19) x 10^21 cm^-2 (90% confidence). 

Because of the presence of a magnitude 6.3 star in the UVOT
Field of View, 2.3 arcmin from the XRT location, 
UVOT will not be able to observe this burst. 

There was some extra delay in processing this burst.  It was originally
a subthreshold trigger (Image_signif=6.49 sigma).  The automated processing
for the XRT position had a problem.  This circular is based on manual processing. 

Burst Advocate for this burst is F. E. Marshall (marshall 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.)

C. Guidorzi (U. Ferrara), A. Melandri (Liverpool JMU), P. O'Brien,
N. Tanvir (U. Leicester) on behalf of a large collaboration report:

On 2009 June 07 at 06:01:12 UT we observed the Swift-BAT GRB 090607
(Marshall et al., GCN Circ. 9491
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 ) with the 2-m Faulkes Telescope North.

Observations started 31 minutes after the BAT trigger time and were
performed using the B, V, R and i' filters. We could not find any
uncatalogued object inside the XRT error circle down to the following
limiting magnitudes:

Time Interval   Total Exp  Filter     Limit
(min from GRB)  (s)                  (mag)
-------------------------------------------
31 - 82          720        R        > 21.8
35 - 75          520        i'       > 21.6
-------------------------------------------

Magnitudes in the R and i' filters have been calibrated against
nearby field stars using USNOB1-R2 and SDSS-i catalogue values,
respectively.

Markku Nissinen (Taurus Hill Observatory) and Veli-Pekka Hentunen (Taurus
Hill Observatory) report:

We used Global-rent-a-scope GRAS001 Tak Mewlon 0.30m telescope with FLI 
IMG1024 Dream Machine at RAS Observatory Mayhill H06 (New Mexico, USA) 
for follow-up observations of GRB090607 (F. E. Marshall et al., GCN 9491
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 ).
The observations were started on June 7, at 06:11 UTC (1.0 hours after the
burst) and stopped on June 7, at 07:12 UTC. Three unfiltered 120s and two
unfiltered 600s images were taken. We did not find any new object in the
XRT error circle. Upper limit for the observations is >18.5 mag (3UL).
Quoted upper limit has been derived using POSSII J and USNO-B1.0 field 
stars as reference.

Filter          Tmid(s)       Exp(s)     Mag (CR) USNO-B1.0

unfiltered         07:01:32      2x600      >18.5

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), F. E. Marshall (NASA/GSFC) D. M. Palmer (LANL),
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-60 to T+243 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090607 (trigger #354299)
(Marshall, et al., GCN Circ. 9491
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 ).  The BAT ground-calculated position is
RA, Dec = 191.194, 44.108 deg, which is 
   RA(J2000)  =  12h 44m 46.7s 
   Dec(J2000) = +44d 06' 28.4" 
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 96%.
 
The mask-weighted light curve shows two narrow peaks.  The first starts
at T-0.1 sec, peaks at T+0.1 sec, and ends at T+0.7sec.  The second peak
starts at ~T+1.7 sec, peaks at T+2.2 sec, and ends at T+2.5 sec.  There is
no hint of emission out to at least T+243 sec.  T90 (15-350 keV) is
2.3 +- 0.1 sec (estimated error including systematics).
 
The time-averaged spectrum from T+0.1 to T+2.5 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.25 +- 0.30.  The fluence in the 15-150 keV band is 1.1 +- 0.2 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.01 sec in the 15-150 keV band
is 0.7 +- 0.1 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 

Based on the shortness of the duration and the spectral hardness, we believe
this to be a short hard burst.
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/354299/BA/

P.A. Curran (UCL-MSSL) and F. Marshall (NASA/GSFC)
report on behalf of the Swift/UVOT team:


The Swift/UVOT began settled observations of the field of GRB 090607
75 s after the BAT trigger (Marshall et al., GCN Circ. 9491
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 ). No optical 
afterglow consistent with the XRT position (Marshall et al., GCN Circ. 
9491
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 ) is detected in the initial UVOT exposures. Preliminary 3-sigma 
upper limits using the UVOT photometric system (Poole et al. 2008, 
MNRAS, 383, 627) for the first finding chart (FC) exposure and 
subsequent exposures are:


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

uvw1           12715       13943       1209         >20.8
u              75          1233        1140         >21.2
v              11448       12707       1239         >20.4


The values quoted above are not corrected for the Galactic extinction 
due to the reddening of E(B-V) = 0.02 in the direction of the burst
(Schlegel et al. 1998).

K.L. Page, A.P. Beardmore, P.A. Evans (U. Leicester) & F.E. Marshall 
(NASA/GSFC) report on behalf of the Swift-XRT team:

We have analysed the four orbits of XRT data obtained for GRB 090607 
(Marshall et al., GCN Circ. 9491
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 ), comprising 108 s of Windowed Timing 
(WT) mode and 9.5 ks of Photon Counting (PC) mode. The refined XRT 
position is RA, Dec = 191.16914, 44.10503, which is equivalent to

RA (J2000) =  12 44 40.59 
Dec(J2000) = +44 06 18.10

with an uncertainty of 3.7 arcsec (radius, 90% containment).

The X-ray light-curve initially brightens slightly, with a power-law of 
alpha = -0.8 +/- 0.5 until 150 +10/-8 s, at which point the afterglow 
starts to decay with alpha = 5.6 +0.5/-0.3. Between ~200 and 400 s after 
the trigger there is a deviation from the decay in the form of a flare. 
The afterglow is no longer detected after the end of the first orbit of 
data (~2365 s after the trigger).

The WT data show a softening trend with time. A spectrum formed from the 
PC mode data from the first orbit can be fitted with a power-law of photon 
index Gamma = 1.88 +/- 0.21, absorbed by the Galactic column of 1.8x10^20 
cm^-2. The observed (unabsorbed) 0.3-10 keV flux over this time is 
5.5x10^-12 (5.8x10^-12) erg cm^-2 s^-1, which corresponds to a counts to 
observed (unabsorbed) flux conversion factor of 3.9x10^-11 (4.1x10^-11) 
erg cm^-2 count^-1.

Because of the lack of detection after the first orbit of data, we cannot 
sensibly predict the future count rate.

The results of the XRT-team automatic analysis are available at 
http://www.swift.ac.uk/xrt_products/00354299.

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