GRB 160611A

D. Malesani (DARK/NBI), S. D. Barthelmy (GSFC), D. M. Palmer (LANL)
and M. H. Siegel (PSU) report on behalf of the Swift Team:

At 21:40:34 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160611A (trigger=690598).  Swift did not slew due to an observing
constraint.  The BAT on-board calculated location is 
RA, Dec 164.438, -70.395, which is 
   RA(J2000)  =  10h 57m 45s
   Dec(J2000) = -70d 23' 40"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows multiple peaks
with a duration of about 30 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~4 sec after the trigger. 

Due to an observing constraint, Swift will not slew until T0+43.3
minutes. There will be no XRT or UVOT data until this time. 

Burst Advocate for this burst is D. Malesani (malesani AT dark-cosmology.dk). 
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 (U. Leicester), D.N. Burrows (PSU), J.A. Kennea (PSU), G.
Tagliaferri (INAF-OAB), S. Campana (INAF-OAB) and P.A. Evans (U.
Leicester) report on behalf of the Swift-XRT team:

The XRT began observing the field of GRB 160611A at 22:25:16.5 UT,
2682.1 seconds after the BAT trigger. Using promptly downlinked data we
find an uncatalogued X-ray source located at RA, Dec 164.42342,
-70.39301 which is equivalent to:
   RA(J2000)  = 10h 57m 41.62s
   Dec(J2000) = -70d 23' 34.8"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 19 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 (1.70 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 7.6
(+2.39/-2.15) x 10^21 cm^-2 (90% confidence).

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

Using 4788 s of XRT Photon Counting mode data and 10 UVOT
images for GRB 160611A, 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 = 164.42229, -70.39243 which is equivalent
to:

RA (J2000): 10h 57m 41.35s
Dec (J2000): -70d 23' 32.7"

with an uncertainty of 1.5 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, MNRAS, 397, 1177).

This circular was automatically generated, and is an official product of the
Swift-XRT team.

V. Lipunov (MASTER, LMSU)


The OT wich published in GCN 19525
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  is the result
  of the false identification.
I am sorry for my mistake.

The message may be cited.

T.G.R. Roegiers (PSU), L.M. McCauley (PSU), J.P. Osborne (U.
Leicester), K.L. Page (U. Leicester), B. Mingo (U. Leicester), P.
D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), J.A.
Kennea (PSU) and D. Malesani report on behalf of the Swift-XRT team:

We have analysed 7.9 ks of XRT data for GRB 160611A (Malesani et al.
GCN Circ. 19522
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 ), from 2.7 ks to 44.8 ks after the  BAT trigger. The
data comprise 50 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Osborne et al. (GCN Circ. 19524
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 ).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=1.54 (+0.48, -0.21). At T+5128 s  the
decay flattens to an alpha of -0.7 (+1.3, -0.8) before breaking again
at T+7161 s to a final decay with index alpha=1.28 (+0.10, -0.09).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.01 (+0.12, -0.11). The
best-fitting absorption column is  5.0 (+0.7, -0.6) x 10^21 cm^-2, in
excess of the Galactic value of 1.7 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 4.0 x 10^-11 (6.6 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     5.0 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 1.7 x 10^21 cm^-2
Excess significance: 8.5 sigma
Photon index:	     2.01 (+0.12, -0.11)

If the light curve continues to decay with a power-law decay index of
1.28, the count rate at T+24 hours will be 0.021 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.4 x
10^-13 (1.4 x 10^-12) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00690598.

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

T. Sakamoto (AGU), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC),
D. Malesani (DARK/NBI), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):
  
Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 160611A (trigger #690598)
(Malesani, et al., GCN Circ. 19522
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 ).  The BAT ground-calculated position is
RA, Dec = 164.417, -70.396 deg which is
    RA(J2000)  =  10h 57m 40.0s
    Dec(J2000) = -70d 23' 45.8"
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 45%.
  
The mask-weighted light curve shows a single episode with several overlapping
pulses.  The emission starts at T-15 sec, peaks at T+3 sec and ends at T+20 sec.
T90 (15-350 keV) is 34.1 +- 5.6 sec (estimated error including systematics).
A pre-planned spacecraft slew moved the source out of the field of view at
about T+165 sec.
  
The time-averaged spectrum from T-31.38 to T+10.37 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.67 +- 0.12.  The fluence in the 15-150 keV band is 1.7 +- 0.1 x 10^-6  erg/cm2.
The 1-sec peak photon flux measured from T+2.84 sec in the 15-150 keV band
is 2.0 +- 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/690598/BA/

M. De Pasquale (UCL-MSSL) and D. Malesani (DARK/NBI)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 160611A
2687 s after the BAT trigger (Malesani et al., GCN Circ. 19522
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 ).

Very close to the XRT error circle (Osborne et al. GCN Circ. 19523
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 ), two
sources are detected in the UVOT images. These sources are also detected
in the Digitized Sky Survey (DSS) and are listed in the USNO catalog.
Their light would blend with any new source at the XRT position, making
the analysis more delicate.

None of the two sources shows any significant flux decrease in the white
filter between the first two white exposures (mid-time: 3071 s after
the trigger) and the last three white exposures (mid-time: 10030 s after
the trigger). Similarly, we find no significant decrease of the flux
of the two sources in the u filter between the first u filter exposure
(mid-time: 2946 s) and the last one (mid-time: 8560 s).
We conclude that no optical afterglow consistent with the XRT position
is detected in the UVOT exposures.

Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are:

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

white             2687         3456          344         >19.6
white             9578        10478          880         >19.8
v                 3668         3867          197         >18.1
b                 3051         9573         1082         >18.9
u                 2846         8660          393         >19.6
w1                4078         5167          191         >19.7
m2                3873         4072          197         >19.4
w2                3463        10905          611         >20.6

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.22 in the direction of the burst
(Schlegel et al. 1998).