GRB 150907B

T. G. R. Roegiers (PSU), J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC),
D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU) and
T. N. Ukwatta (LANL) report on behalf of the Swift Team:

At 23:26:27 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150907B (trigger=654803).  Swift could not slew
immediately to the burst due to an observing constraint. 
The BAT on-board calculated location is 
RA, Dec 255.219, -63.819 which is 
   RA(J2000) = 17h 00m 53s
   Dec(J2000) = -63d 49' 07"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Only partial BAT lightcurve data is available,
but the light curve shows a complex structure at least 10 seconds long. 
The peak count rate was ~1500 counts/sec (15-350 keV), at ~0 sec 
after the trigger. 

Due to an observing constraint, Swift will not slew until T0+49.0
minutes. There will be no XRT or UVOT data until this time. 

Burst Advocate for this burst is T. G. R. Roegiers (troegiers AT swift.psu.edu). 
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.
Cusumano (INAF-IASF PA), M. Perri (ASDC) and P.A. Evans (U. Leicester)
report on behalf of the Swift-XRT team:

The XRT began observing the field of GRB 150907B at 00:16:37.8 UT,
3010.0 seconds after the BAT trigger. Using promptly downlinked data we
find an uncatalogued X-ray source located at RA, Dec 255.30809,
-63.78591 which is equivalent to:
   RA(J2000)  = 17h 01m 13.94s
   Dec(J2000) = -63d 47' 09.3"
with an uncertainty of 4.0 arcseconds (radius, 90% containment). This
location is 185 arcseconds from the BAT onboard position, outside 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.  We cannot determine whether the source is
fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 1.52
x 10^21 cm^-2 (Willingale et al. 2013).

P. Wiseman, C. Delvaux and J. Greiner (all MPE Garching) report on behalf
of the GROND team:

We observed the field of GRB 150907B (Swift trigger 654803; Roegiers et
al., GCN #18249
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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).

Observations started at 02:03 UT on 08/09/2015, 2.63 hours after the GRB
trigger. They were performed at an average seeing of 2.5" and an average
airmass of 2.0.

We do not detect a source within the Swift-XRT error circle reported by
Osborne et al. (GCN #18251
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 ) down to limits of:

g' > 24.5 mag,

r' > 23.9 mag,

i' > 23.3 mag,

z' > 23.2 mag,

J > 21.1 mag,

H > 20.6 mag, and

K > 19.2 mag.

We note a source at the eastern edge of the Swift-XRT error circle, at a
position:
RA  =  255.3110
Dec = -63.7860,
or 17h 01m 14.64s -64d 47' 09.6".

This source does not seem to be fading, and with a non GRB-like SED, and
matches to the known source S7FP064671 from The Guide Star Catalogue,
Version 2.3.2 (Lasker B., Lattanzi M.G., McLean B.J., et al. Astron. J.
136, 735 (2008)).

The given limits are derived based on calibrating the images against GROND
zeropoints and 2MASS field stars and are not corrected for the Galactic
foreground extinction corresponding to a reddening of E_(B-V)= 0.1432 in
the direction of the burst (Schlegel et al. 1998).

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

Using 3059 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 150907B, 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 = 255.30407, -63.78510 which is equivalent
to:

RA (J2000): 17h 01m 12.98s
Dec (J2000): -63d 47' 06.4"

with an uncertainty of 1.9 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.Buckley, S. Potter, M.Kotze
South African Astronomical Observatory

V. Lipunov, E.Gorbovskoy,  N.Tyurina, V.Kornilov, P.Balanutsa, 
A.Kuznetsov, D.Kuvshinov, I.Gorbunov
Lomonosov Moscow State University, Sternberg Astronomical Institute

R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres
The Instituto de Astrofisica de Canarias

A. Tlatov, D. Dormidontov, V.Senik
Kislovodsk Solar Station of the Pulkovo Observatory

K.Ivanov, O.Gres, N.M.Budnev, S.Yazev, O.Chuvalaev, V.A.Poleshchuk
Irkutsk State University

V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov, A.Gabovich
Blagoveschensk Educational State University, Blagoveschensk

V.Krushinski, I.Zalozhnih
Ural Federal University, Kourovka

Hugo Levato and Carlos Saffe
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

Carlos Lopez, Claudio Mallamaci and Federico Podest
Observatorio Astronomico Felix Aguilar (OAFA)



MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in SAAO was pointed to the Swift Alert (Roegiers et al., GCN 
18249
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 ) GRB150907B 25 sec after notice time 
and 40 sec after trigger time at 2015-09-07 23:27:10 UT. On our first (10s 
exposure)  set we haven`t found optical transient  within SWIFT error-box 
(ra=17 00 51 dec=-63 49 07 r=0.050000).
The next images limit without OT:

  Id     	Coord             Pro.type Time,UT Exp.time  Lim Filt. Tube

110113	16h 59m 04.1s -63d 41m 01s  Alert  23:27:10  10	    15.5  P  EAST
110114	17h 00m 00.1s -63d 42m 55s  Alert  23:27:10  10     15.7  P  WEST
110115	16h 59m 47.7s -63d 42m 57s  Alert  23:27:34  10     15.4  P  WEST
110116	16h 59m 22.0s -63d 41m 10s  Alert  23:27:34  10     15.2  P  EAST
110117	16h 59m 47.5s -63d 42m 57s  Alert  23:27:56  20	    15.9  P  WEST
110118	16h 59m 21.8s -63d 41m 10s  Alert  23:27:56  20	    15.7  P  EAST
110119	16h 59m 21.6s -63d 41m 09s  Alert  23:28:27  20	    15.9  P  EAST
110120	16h 59m 47.4s -63d 42m 56s  Alert  23:28:27  20	    16.1  P  WEST
110121	16h 59m 21.6s -63d 41m 09s  Alert  23:28:58  30	    13.2  P  EAST
110122	16h 59m 47.4s -63d 42m 56s  Alert  23:28:58  30     13.5  P  WEST
110123	17h 00m 00.1s -63d 42m 55s SumAlert23:27:10  40	    16.3  P  WEST
110124	16h 59m 21.4s -63d 41m 08s  Alert  23:29:39  40	    15.1  P  EAST
110125	16h 59m 47.1s -63d 42m 55s  Alert  23:29:39  40	    15.5  P  WEST
110126	16h 59m 04.1s -63d 41m 01s SumAlert23:27:10  40	    16.1  P  EAST
110127	16h 59m 47.1s -63d 42m 55s  Alert  23:30:30  50	    15.9  P  WEST
110128	16h 59m 21.3s -63d 41m 08s  Alert  23:30:30  50	    15.5  P  EAST
110129	16h 59m 47.4s -63d 42m 56s SumAlert23:28:27  90     15.9  P  WEST
110130	16h 59m 21.2s -63d 41m 08s  Alert  23:31:31  60	    14.8  P  EAST
110131	16h 59m 47.1s -63d 42m 56s  Alert  23:31:31  60	    15.4  P  WEST
110132	16h 59m 21.6s -63d 41m 09s SumAlert23:28:27  110    16.1  P  EAST

There was a short time between rain and clouds. Then the clouds returned.

The message may be cited.

H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. G. R. Roegiers (PSU), 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 downlinks,
we report further analysis of BAT GRB 150907B (trigger #654803)
(Roegiers, et al., GCN Circ. 18249
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 ).  The BAT ground-calculated position is
RA, Dec = 255.265, -63.798 deg, which is 
   RA(J2000)  =  17h 01m 03.5s 
   Dec(J2000) = -63d 47' 51.6" 
with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 50%.
 
The mask-weighted light curve shows a Fred-like starting at ~T-1 sec,
peaking at ~T+1 sec, and ending around T+100 sec.
T90 (15-350 keV) is 62.0 +- 11.1 sec (estimated error including systematics).
 
The time-averaged spectrum from T-1.48 to T+64.53 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.17 +- 1.03, 
and Epeak of 67.4 +- 29.7 keV (chi squared 53.2 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 1.1 +- 0.2 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+0.59 sec in the 15-150 keV band is
1.0 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.47 +- 0.18 (chi squared 59.8 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/654803/BA/

B. Sbarufatti (INAF-OAB/PSU), J.P. Osborne (U. Leicester), K.L. Page
(U. Leicester), C. Pagani (U. Leicester), A. Maselli  (INAF-IASFPA), A.
Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), D.N. Burrows (PSU) and T.
G. R. Roegiers (PSU) report on behalf of the Swift-XRT team:

We have analysed 7.9 ks of XRT data for GRB 150907B (Roegiers et al.
GCN Circ. 18249
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 ), from 3.0 ks to 32.2 ks after the  BAT trigger. The
data are entirely in Photon Counting (PC) mode. The enhanced XRT
position for this burst was given by Beardmore et al. (GCN Circ.
18253
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.61 (+0.37, -0.28).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.02 (+0.28, -0.35). The
best-fitting absorption column is  4.4 (+7.7, -1.8) x 10^21 cm^-2, in
excess of the Galactic value of 1.5 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 4.1 x 10^-11 (6.7 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.4 (+7.7, -1.8) x 10^21 cm^-2
Galactic foreground: 1.5 x 10^21 cm^-2
Excess significance: 2.6 sigma
Photon index:	     2.02 (+0.28, -0.35)

If the light curve continues to decay with a power-law decay index of
1.61, the count rate at T+24 hours will be 3.4 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.4 x
10^-14 (2.3 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00654803.

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