GRB 160905A

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, hard-spectrum GRB 160905A (Swift-BAT trigger #711084:
D'Avanzo et al., GCN 19887
Loading...
 
 ; Barthelmy et al., GCN 19896
Loading...
 
 ;
Fermi GBM observation: Bissaldi, GCN 19889
Loading...
 
 ;
Fermi-LAT detection: McEnery et al., GCN 19890
Loading...
 
 )
triggered Konus-Wind at T0=40735.196 s UT (11:18:55.196).

The burst light curve shows a double-peaked structure with a total 
duration of ~44 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst
had a fluence of 1.50(-0.11,+0.11)x10^-4 erg/cm2,
and a 64-ms peak energy flux, measured from T0+10.224 s,
of 1.17(-0.23,+0.23)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst
(measured from T0 to T0+42.240 s)
is best fit in the 20 keV - 18 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.70(-0.05,+0.06),
the high energy photon index beta = -2.39(-0.26,+0.16),
the peak energy Ep = 594(-50,+56) keV,
chi2 = 124/97 dof.

The spectrum near the peak count rate
(measured from T0+7.424 to T0+12.288 s)
is best fit in the 20 keV - 18 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.65(-0.08,+0.09),
the high energy photon index beta = -2.53(-0.44,+0.25),
the peak energy Ep = 664(-81,+88) keV,
chi2 = 96/83 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB160905_T40735/

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

S.W.K. Emery (UCL-MSSL) and P. D'Avanzo (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 160905A
67 s after the BAT trigger (D'Avanzo et al., GCN Circ. 19887
Loading...
 
 ), which was
also detected by Fermi-GBM (GCN 19889
Loading...
 
 ) and Fermi-LAT (GCN 19890
Loading...
 
 ).
A fading source consistent with the XRT position
(Osborne et al. GCN Circ. 19891
Loading...
 
 ) 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          67           216          147         15.8 � 0.03
white                 67         2234          469         17.1 � 0.05
u_FC              280           530          246         18.3 � 0.15
u                      280         2185          401         18.8 � 0.16
v                      610         2285          195         17.4 � 0.12
b                      536         2210          175         18.7 � 0.16
w1                   660         2160          175         >19.1
m2                   635         2296          162         >19.1
w2                   586         2260          195         >19.4

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.45 in the direction of the burst
(Schlegel et al. 1998).

S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), P. D'Avanzo (INAF-OAB),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), 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-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 160905A (trigger #711084)
(D'Avanzo, et al., GCN Circ. 19887
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 162.249, -50.803 deg which is
    RA(J2000)  =  10h 48m 59.7s
    Dec(J2000) = -50d 48' 09.2"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 98%.

The mask-weighted light curve shows a bright main episode with several
overlapping peaks starting at ~T-10 sec, peaking at ~T+10 sec and ending
at ~T+25 sec.  The additional peak is seen starting at ~T+30 sec, peaking
at ~T+35 sec and ending at ~T+40 sec.  The further weak extended emission
is visible up to ~T+180 sec.  T90 (15-350 keV) is 64 +- 16 sec (estimated
error including systematics).
  
The time-averaged spectrum from T-15.2 to T+96.8 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.04 +- 0.03.  The fluence in the 15-150 keV band is 1.50 +- 0.02 x 10^-5 erg/cm2.
The 1-sec peak photon flux measured from T+8.30 sec in the 15-150 keV band
is 6.3 +- 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/711084/BA/

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

We have analysed 7.2 ks of XRT data for GRB 160905A (D'Avanzo et al.
GCN Circ. 19887
Loading...
 
 ), from 50 s to 29.8 ks after the  BAT trigger. The data
comprise 2.2 ks in Windowed Timing (WT) mode (the first 6 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. 19891
Loading...
 
 ).

The late-time light curve (from T0+5.6 ks) can be modelled with a
series of power-law decays. The initial decay index is alpha=0.5 (+0.6,
-0.4). At T+7998 s  the decay steepens to an alpha of 7.92 (+0.08,
-5.15). The light curve breaks again at T+9660 s to a decay with
alpha=-1.5 (+0.0, -0.4),  before a final break at T+15.0 ks s after
which the decay index is 1.0 (+/-0.3).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.729 (+/-0.024). The
best-fitting absorption column is  4.89 (+0.18, -0.17) x 10^21 cm^-2,
in excess of the Galactic value of 3.8 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.84 (+0.12, -0.11)
and a best-fitting absorption column of 5.9 (+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 4.7 x 10^-11 (7.1 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     5.9 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 3.8 x 10^21 cm^-2
Excess significance: 4.4 sigma
Photon index:	     1.84 (+0.12, -0.11)

If the light curve continues to decay with a power-law decay index of
1.0, the count rate at T+24 hours will be 0.10 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.7 x
10^-12 (7.1 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/00711084.

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

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

Using 854 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 160905A, 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 = 162.24585, -50.80095 which is equivalent
to:

RA (J2000): 10h 48m 59.00s
Dec (J2000): -50d 48' 03.4"

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, MNRAS, 397, 1177).

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

J. E. McEnery (NASA/GSFC), F. Longo (University & INFN Trieste),
E. Bissaldi (Politecnico & INFN Bari) and D. Kocevski (NASA/GSFC)
report on behalf of the Fermi-LAT team:

At 11:18:55.91 on September, 05, 2016 Fermi-LAT detected
high-energy emission from GRB 160905*A*, which was also
detected by Swift (GCN 19887
Loading...
 
 ) and Fermi-GBM
(trigger 494767139/160905471; GCN 19889
Loading...
 
 ).

The data from the Fermi-LAT show a significant increase in
the event rate that is spatially and temporally correlated
with the trigger with high significance.

The best LAT on-ground location is found to be
RA, Dec = 162.02, -50.88 (J2000)
with an error radius of 0.08 deg (90 % containment, statistical error 
only).

This was 18 deg from the LAT boresight at the time of the trigger.

The highest-energy photon is a *8 GeV* event which was
observed *350* seconds after the GBM trigger.

The Fermi-LAT point of contact for this burst is *
Dan Kocevski (daniel.kocevski@nasa.gov <mailto:daniel.kocevski@nasa.gov>)*.

The Fermi-LAT is a pair conversion telescope designed to cover the energy
band from 20 MeV to greater than 300 GeV. It is the product of an 
international
collaboration between NASA and DOE in the U.S. and many scientific
institutions across France, Italy, Japan and Sweden.

E. Bissaldi (Politcenico & INFN Bari)
reports on behalf of the Fermi GBM Team:

"At 11:18:55.91 UT on 5 September 2016, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 160905A (trigger 494767139 / 160905471),
which was also detected by the Swift/BAT (D'Avanzo et al. 2016, GCN 19887
Loading...
 
 ).
The GBM on-ground location is consistent with the Swift position.

The trigger resulted in an Autonomous Repoint Request (ARR)
by the GBM Flight Software owing to the high peak flux of the GRB.
This ARR was accepted and the spacecraft slewed to the GBM in-flight
location. The initial angle from the Fermi LAT boresight to
the GBM ground location is 18 degrees.

The GBM light curve consists of two peaks
with a duration (T90) of about 34 s (50-300 keV).
The time-averaged spectrum from T0 to T0+40 s is
adequately fit by a Band function with Epeak = 830 � 30 keV,
alpha = -0.77 � 0.01, and beta = -2.43 � 0.09.

The event fluence (10-1000 keV) in this time interval is
(9.0 � 0.1)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+20 s in the 10-1000 keV band
is 16.2 � 0.3 ph/s/cm^2.

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

P. D'Avanzo (INAF-OAB), A. P. Beardmore (U Leicester),
A. A. Breeveld (UCL-MSSL), D. N. Burrows (PSU),
P.A. Evans (U Leicester), J. A. Kennea (PSU),
N. P. M. Kuin (UCL-MSSL), F. E. Marshall (NASA/GSFC),
P. T. O'Brien (U Leicester), D. M. Palmer (LANL) and
B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:

At 11:18:58 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160905A (trigger=711084).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 162.237, -50.800 which is 
   RA(J2000) = 10h 48m 57s
   Dec(J2000) = -50d 47' 59"
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 50 sec.  The peak count rate
was ~13000 counts/sec (15-350 keV), at ~18 sec after the trigger. 

The XRT began observing the field at 11:19:56.0 UT, 57.7 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 162.2448, -50.8014 which is equivalent to:
   RA(J2000)  = +10h 48m 58.75s
   Dec(J2000) = -50d 48' 05.0"
with an uncertainty of 4.8 arcseconds (radius, 90% containment). This
location is 18 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 6.05e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 66 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	10:48:59.18 = 162.24658
  DEC(J2000) = -50:48:04.3  = -50.80120
with a 90%-confidence error radius of about 0.61 arc sec. This position is 4.1
arc sec. from the center of the XRT error circle. The estimated magnitude is
15.88 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.46. 

Burst Advocate for this burst is P. D'Avanzo (paolo.davanzo 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.)