GRB 160607A

T. N. Ukwatta (LANL), A. P. Beardmore (U Leicester),
P.A. Evans (U Leicester), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU),
H. A. Krimm (CRESST/GSFC/USRA), K. L. Page (U Leicester) and
D. M. Palmer (LANL) report on behalf of the Swift Team:

At 11:14:00 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160607A (trigger=689597).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 13.663, -4.948 which is 
   RA(J2000) = 00h 54m 39s
   Dec(J2000) = -04d 56' 52"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 70 sec.  The peak count rate
was ~33000 counts/sec (15-350 keV), at ~12 sec after the trigger. 

The XRT began observing the field at 11:15:16.3 UT, 75.5 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 13.6655, -4.9481 which is equivalent to:
   RA(J2000)  = +00h 54m 39.72s
   Dec(J2000) = -04d 56' 53.2"
with an uncertainty of 5.2 arcseconds (radius, 90% containment). This
location is 9.0 arcseconds from the BAT onboard position, within the
BAT error circle. No event data are yet available to determine the
column density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 1.72e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 83 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 8'x8' region for the list of sources generated on-board covers 100% of the
XRT error circle. 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
0.05. 

Burst Advocate for this burst is T. N. Ukwatta (tilan.ukwatta AT gmail.com). 
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.)

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

Using 616 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 160607A, 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 = 13.66744, -4.94858 which is equivalent
to:

RA (J2000): 00h 54m 40.19s
Dec (J2000): -04d 56' 54.9"

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.

D.N. Burrows (PSU), T.G.R. Roegiers (PSU), L.M. McCauley (PSU), S.L.
Gibson (U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia
(ASDC) and T.N. Ukwatta report on behalf of the Swift-XRT team:

We have analysed 7.1 ks of XRT data for GRB 160607A (Ukwatta et al. GCN
Circ. 19502
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 ), from 65 s to 24.3 ks after the  BAT trigger. The data
comprise 935 s in Windowed Timing (WT) mode (the first 9 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Goad et al.
(GCN Circ. 19503
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 ).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=1.38 (+0.38, -0.21). At T+125 s  the decay
flattens to an alpha of 0.66 (+/-0.04) before breaking again at T+2142
s to a final decay with index alpha=1.25 (+0.08, -0.07).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.85 (+0.06, -0.05). The
best-fitting absorption column is  1.87 (+0.23, -0.22) x 10^21 cm^-2,
in excess of the Galactic value of 5.1 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.98 (+/-0.09) and a
best-fitting absorption column of 2.3 (+/-0.3) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.6 x 10^-11 (5.1 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.3 (+/-0.3) x 10^21 cm^-2
Galactic foreground: 5.1 x 10^20 cm^-2
Excess significance: 9.0 sigma
Photon index:	     1.98 (+/-0.09)

If the light curve continues to decay with a power-law decay index of
1.25, the count rate at T+24 hours will be 0.048 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x
10^-12 (2.4 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/00689597.

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

A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC),  J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), 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-60 to T+243 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 160607A (trigger #689597)
(Ukwatta, et al., GCN Circ. 19502
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 ).  The BAT ground-calculated position is
RA, Dec = 13.661, -4.952 deg which is
    RA(J2000)  =  00h 54m 38.8s
    Dec(J2000) = -04d 57' 08.0"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 84%.

The mask-weighted light curve shows a complex structure of multiple peaks.  The 
first complex begins at T-3 sec, peaks at T+12 and decays to baseline by T+24 
sec.  This is followed by another weaker peak from T+30 to T+36 sec and then 
very weak emission out to T+80 sec. T90 (15-350 keV) is 33.4 +- 0.45 sec 
(estimated error including systematics).

The time-averaged spectrum from T-13.89 to T+44.08 sec is best fit by a power 
law with an exponential cutoff.  This fit gives a photon index 1.15 +- 0.10,
and Epeak of 245.1 +- 92.7 keV (chi squared 28.56 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 2.1 +- 0.0 x 10^-5 erg/cm2
and the 1-sec peak flux measured from T+11.65 sec in the 15-150 keV band is
21.8 +- 0.5 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.37 +- 0.02 (chi squared 44.40 for 57 d.o.f.).  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/689597/BA/

D. Malesani (DARK/NBI), D. Xu (NAOC/CAS), H. Jonsson (Lund Univ.), and 
P. Jakobsson (Univ. Iceland) report on behalf of a larger collaboration:

We observed the field of GRB 160607A (Ukwatta et al., GCN 19502
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 ) with 
the Nordic Optical Telescope (NOT), located in La Palma (Canary 
Islands). Observations were carried out at large airmass (~3) in the 
SDSS i filter, for a total of 20 min on source, at a mean epoch 2016 
June 8.19 UT (0.725 days after the BAT trigger).

Within the refined XRT position (Goad et al., GCN 19503
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 ), we detect a 
single, faint source at coordinates (J2000):

RA = 00:54:40.14
Dec = -04:56:53.3

Carrying out photometry against the SDSS catalog, we derive a magnitude 
i = 23.45 +- 0.20 AB. As this value is fainter than the SDSS limit, and 
as we lack variability information, we cannot presently conclude whether 
this source is the afterglow of GRB 160607A. Further observations are 
planned, but will be probably delayed until the field has a better 
visibility from La Palma.

A. Tsvetkova, S. Golenetskii, R.Aptekar, D. Frederiks, P. Oleynik,
M. Ulanov, D. Svinkin, A. Lysenko, A. Kozlova and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration 160607A (Swift-BAT trigger #689597:
Ukwatta et al., GCN 19502
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 ; Lien et al., GCN 19506
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 )
triggered Konus-Wind at T0=40436.923 s UT (11:13:56.923).

The burst light curve shows a complex structure of multiple peaks
with a total duration of ~38 s.
The emission is seen up to ~15 MeV.

As observed by Konus-Wind, the burst
had a fluence of 4.12(-0.51,+0.64)x10^-5 erg/cm2,
and a 64-ms peak energy flux, measured from T0+11.952 s,
of 8.13(-1.59,+1.64)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst
(measured from T0 to T0+38.912 s)
is best fit in the 70 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.68(-0.43,+1.47),
the high energy photon index beta = -2.51(-0.35,+0.26),
the peak energy Ep = 176(-42,+25) keV,
chi2 = 84/76 dof.

The spectrum near the peak count rate
(measured from T0+8.448 to T0+14.336 s)
is best fit in the 70 keV - 15 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.68(-0.31,+0.39),
the high energy photon index beta = -2.76(-0.37,+0.23),
the peak energy Ep = 188(-17,+17) keV,
chi2 = 56/74 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB160607_T40436/

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.

T.-W. Chen, F. Knust, J. Greiner (all MPE Garching), and D. A. Kann (TLS) report on behalf of the GROND team:

We observed the field of GRB 160607A (Swift trigger 689597; Ukwatta et al., GCN #19502
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 ) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile).

At the enhanced XRT position (Goad et al., GCN #19503
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 ), an afterglow candidate was discovered by NOT (Malesani et al., GCN #19507
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 ) at i' = 23.45 +/- 0.20 (AB mag), 0.725 days after the BAT trigger.

GROND observations started at 08:48 UT on 2016 June 8, 0.899 days after the GRB trigger, and are continuing. They were performed at an average seeing of 1.5" and at an average airmass of 1.48.

We found a single point source at the edge of the 1.5" Swift-XRT error circle at

RA (J2000.0) = 00 h 54 m 40.164 s

DEC (J2000.0) = -04d 56' 53.23"

with an uncertainty of 0.13" in each coordinate.

The position is consistent with the NOT position, we find that the source has faded significantly.

Based on the 100.83 min of total exposures in g'r'i'z' and 38.00 min in JHK, we estimate preliminary magnitudes for detections and the detection limits (all in AB system) of:

g' > 25.4 mag,
r' = 24.49 +/- 0.19 mag,
i' = 24.51 +/- 0.46 mag,
z' > 24.0 mag,
J = 22.34 +/- 0.34 mag,
H = 21.29 +/- 0.21 mag, and
K > 21.3 mag.

Given magnitudes are calibrated against SDSS field stars as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.05 mag in the direction of the burst (Schlafly & Finkbeiner 2011).

S. J. LaPorte (PSU) and T. N. Ukwatta (LANL)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 160607A
84 s after the BAT trigger (Ukwatta et al., GCN Circ. 19502
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 ).
No optical afterglow consistent with the enhanced XRT position
(Goad et al., GCN Circ. 19503
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 ) nor at the position of the NOT source
(Malesani et al., GCN 19507
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 ), is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

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

white_FC            84          233          147         >20.4
u_FC               296          546          246         >19.9
white               84         1658          299         >20.6
v                  626         1707          117         >18.7
b                  552         1633          115         >19.5
u                  296         1088          393         >19.9
w1                 849         1237           39         >19.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.05 in the direction of the burst
(Schlegel et al. 1998).

M. Moriyama, A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Yamada (AGU),
K. Yamaoka (Nagoya U), S. Nakahira (JAXA), I. Takahashi (IPMU), Y. Asaoka,
S. Ozawa, S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), W. Ishizaki (ICRR),
M. L. Cherry (LSU), S. Ricciarini (U of Florence) P. S. Marrocchesi (U of Siena)
and the CALET collaboration:

The long-duration GRB 160607A (Swift, Ukwatta et al. GCN Circ. 19502
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 ; Konus-Wind
trigger time on 11:13:56.92 UT; INTEGRAL-ACS trigger #7487) triggered the CALET
Gamma-Ray Burst Monitor (CGBM) at 11:13:57.49 on 7 June 2016.   The burst signal
was seen by all CGBM instruments.

The light curve of the SGM shows a complex structure with multiple spikes.
The emission starts at T0 and ends at T0+30 sec.  The multiple spikes peak
at T0+2 sec, T0+4 sec, T0+7 sec, T0+11 sec,  T0+14 sec, T0+15 sec and T0+21 sec.
The T90 duration measured by the SGM data is 18.9 +- 2.9 sec (40-1000 keV).
The light curve is available at

http://cgbm.calet.jp/cgbm_trigger/flight/1149333220/

The CGBM data used in this analysis are provided by the Waseda CALET Operation Center
located at the Waseda University.