GRB 150711A

M. G. Bernardini (INAF-OAB), S. D. Barthelmy (GSFC),
D. N. Burrows (PSU), F. E. Marshall (NASA/GSFC),
A. Melandri (INAF-OAB), D. M. Palmer (LANL) and
B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:

At 18:23:03 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150711A (trigger=648601).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 221.631, -35.471 which is 
   RA(J2000)  =  14h 46m 31s
   Dec(J2000) = -35d 28' 15"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single peak
with a duration of about 20 sec.  The peak count rate
was ~2200 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 18:24:50.4 UT, 106.7 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
221.6268, -35.4565 which is equivalent to:
   RA(J2000)  = 14h 46m 30.44s
   Dec(J2000) = -35d 27' 23.4"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 53 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 consistent with the Galactic value of 8.25
x 10^20 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 1.13e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 117 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
0.09. 

Burst Advocate for this burst is M. G. Bernardini (grazia.bernardini AT brera.inaf.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 676 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 150711A, 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 = 221.62678, -35.45603 which is equivalent
to:

RA (J2000): 14h 46m 30.43s
Dec (J2000): -35d 27' 21.7"

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, MNRAS, 397, 1177).

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

Antonio de Ugarte Postigo (DARK/NBI), and Vincent Van Eylen 
(Aarhus University) report on behalf of a larger collaboration:

We observed the field of GRB 150711A (Bernardini et al. GCN 
18011
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 ) with the 2.5m Nordic Optical Telescope (NOT) equipped 
with AlFOSC starting at 21:18 UT (2.80 hrs after the trigger). 
The observation consisted of 3x300s in r-band and 3x300s in 
i-band and was performed at high airmass and with a seeing of 
~ 3". We do not detect any source within the XRT error box 
(Osborne et al. GCN 18012
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 ) down to a limiting magnitude of 
r ~ 21.5.

[GCN OPS NOTE(12jul15): Per author's request, a typo in the spelling
of VVN's name was corrected.]

P. Jenke (UAH) reports on behalf of the Fermi GBM Team:

"At 18:23:00.16 UT on July 11 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 150711A (trigger 458331784/150711766),
which was also detected by 
Swift (M. G. Bernardini (INAF-OAB) et al. 2015, GCN 18011
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 ). 
The GBM on-ground location, using the Fermi GBM trigger
data, is consistent with the Swift/XRT location.  

The angle of the burst direction to the Fermi LAT boresight
 is 28 degrees.

The GBM light curve is a single peak with a 
duration (T90) of about 14s (50-300 keV).
The time-averaged spectrum from T0-13s to T0+19s 
is well fit by a power law with an exponential high-energy cutoff. 
The power law index is -1.16 +/- 0.07
and the cutoff energy, parameterized as Epeak, is 117 +/- 10 keV. 

The event fluence (10-1000 keV) in this time interval is
(2.8 +/- 0.06)E-06 ergs/cm^2. The 1.0-sec peak photon flux measured
starting from T0+4.7s in the 10-1000 keV band
is 4.1 +/- 0.2 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

M.G. Bernardini, A. Melandri, P. D'Avanzo (INAF-OAB) and P.A. Evans
(Leicester) report on behalf of the Swift-XRT team:

We have analysed 6.9 ks of XRT data for GRB 150711A (Bernardini et al.
GCN Circ. 18011
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 ), from 96 s to 28.3 ks after the  BAT trigger. The data
comprise 115 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 Osborne et
al. (GCN Circ. 18012
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 ).

The light curve can be modelled with an initial power-law decay with an
index of alpha=2.90 (+0.17, -0.13), followed by a break at T+446 s to
an alpha of 0.62 (+0.07, -0.06). Flaring activity is observed between
T+150 s and T+225 s.

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.71 (+/-0.14). The
best-fitting absorption column is  4.2 (+/-0.5) x 10^21 cm^-2, in
excess of the Galactic value of 8.2 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.20 (+0.19, -0.18)
and a best-fitting absorption column of 4.2 (+0.9, -0.8) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.5 x 10^-11 (6.3 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.2 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 8.2 x 10^20 cm^-2
Excess significance: 6.8 sigma
Photon index:	     2.20 (+0.19, -0.18)

If the light curve continues to decay with a power-law decay index of
0.62, the count rate at T+24 hours will be 0.022 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.8 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/00648601.

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

[GCN OPS NOTE(12jul15): Per MGB's request, AM, PDA, and PAE
were added to the author list.]

N. P. M. Kuin (UCL-MSSL) and M. G. Bernardini (INAF-OAB) report
on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 150711A
117 s after the BAT trigger (Bernardini et al., GCN Circ. 18011
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 ).
No optical afterglow consistent with the XRT position (Osborne et al.
GCN Circ. 18012
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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           117          267          147         >21.4
u_FC               330          580          246         >20.2
white              117          909          235         >21.9
v                  660          852           39         >19.0
b                  585          778           39         >19.9
u                  330          753          265         >20.2
w1                 709          729           19         >18.8
m2                 684          704           19         >18.9
w2                 636          828           39         >18.8

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.09 in the direction of the burst
(Schlegel et al. 1998).

H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC),  J. R. Cummings (CPI),
N. Gehrels (GSFC), A. Y. Lien (GSFC/UMBC), 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+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 150711A (trigger #648601)
(Bernardini, et al., GCN Circ. 18011
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 ).  The BAT ground-calculated position is
RA, Dec = 221.624, -35.464 deg which is
    RA(J2000)  =  14h 46m 29.7s
    Dec(J2000) = -35d 27' 49.9"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 32%.
  
The mask-weighted light curve shows a cusp-shaped main peak with smaller
preceding and following peaks, each about 20 seconds long.  Emission was
detectable from T-40 to T+70.  T90 (15-350 keV) is 64.2 +- 14.2 sec (estimated
error including systematics).
  
The time-averaged spectrum from T-34.1 to T+70.2 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.79 +- 0.08.  The fluence in the 15-150 keV band is 4.3 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+1.98 sec in the 15-150 keV band
is 3.8 +- 0.4 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/648601/BA/

E. Mazaeva (IKI), V. Nevskiy (ISON) I. Molotov (KIAM), A. Pozanenko 
(IKI) report on behalf of larger GRB follow-up collaboration:

We observed the field of GRB 150711A (Bernardini et al. GCN 18011
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 ) with 
the 40 cm telescope of Burakan-ISON observatory starting on Jul., 11 
(UT) 18:36:16, i.e. ~13 min after burst trigger. We obtained several 
unfiltered images. In a combined image we  do not detect any source 
within the XRT error box (Osborne et al. GCN 18012
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 ) down to a limiting 
magnitude of R = 16.9

Date       UT start  t-T0      Filter   Exp.  OT    UL(3 sigma)
                     (mid, days)         (s)

2015-07-11 18:36:16  0.01250   none     9*60  n/d   16.9

The photometry is based on nearby USNO-B1.0  stars.