GRB 151001B

H. A. Krimm (CRESST/GSFC/USRA), S. D. Barthelmy (GSFC),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),
C. Pagani (U Leicester), B. Sbarufatti (INAF-OAB/PSU) and
M. H. Siegel (PSU) report on behalf of the Swift Team:

At 18:29:36 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 151001B (trigger=657321).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 336.845, +64.661, which is 
   RA(J2000)  =  22h 27m 23s
   Dec(J2000) = +64d 39' 39"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is typical for image triggers, there is nothing
significant in the real-time TDRSS light curve. 

The XRT began observing the field at 18:31:55.6 UT, 138.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
336.8384, 64.6937 which is equivalent to:
   RA(J2000)  = 22h 27m 21.22s
   Dec(J2000) = +64d 41' 37.4"
with an uncertainty of 2.4 arcseconds (radius, 90% containment). This
location is 118 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 (6.51 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 6.8
(+6.23/-4.70) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 1.89e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 148 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
1.71. 

Burst Advocate for this burst is H. A. Krimm (hans.krimm AT nasa.gov). 
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.)

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

Using 1574 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 151001B, 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 = 336.83909, +64.69375 which is equivalent
to:

RA (J2000): 22h 27m 21.38s
Dec (J2000): +64d 41' 37.5"

with an uncertainty of 1.6 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.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov
Blagoveschensk Educational State University, Blagoveschensk

E. Gorbovskoy, V. Lipunov, M.Pruzhinskaya, V.Kornilov, D.Kuvshinov, 
N.Tyurina, N.Shatskiy, P.Balanutsa, D.Zimnukhov, A.Kuznetsov, V.V.Chazov, 
D.Denisenko,  A.Sankovich
Lomonosov Moscow State University,
Sternberg Astronomical Institute, Moscow State University

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

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

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

D.Buckley, S. Potter, A.Kniazev, M.Kotze
South African Astronomical Observatory

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

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

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


MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in Blagoveschensk was pointed to the  GRB151001B   20 sec after 
notice time and 96 sec after trigger time at 2015-10-01 18:31:13 UT. On 
our first (20s exposure)  set we haven`t found optical transient  within 
SWIFT error-box (Krimm et. al GCN 18374
Loading...
 
 ).
The 5-sigma upper limit has been about 18.0 mag
The message may be cited.

T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
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),
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+963 sec from the recent telemetry downlinks,
we report further analysis of BAT GRB 151001B (trigger #657321)
(Krimm, et al., GCN Circ. 18374
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 336.974, 64.637 deg, which is 
   RA(J2000)  =  22h 27m 53.7s 
   Dec(J2000) = +64d 38' 13.5" 
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 28%.
 
The mask-weighted light curves shows several overlapping peaks starting
at ~T-40 sec, peaking at ~T+50 sec, and ending at ~T+150 sec.
T90 (15-350 keV) is 109 +- 17 sec (estimated error including systematics).
 
The time-averaged spectrum from T-23.3 to T+97 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.12 +- 0.27.  The fluence in the 15-150 keV band is 1.4 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+47.47 sec in the 15-150 keV band
is 0.5 +- 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/657321/BA/

T.G.R. Roegiers (PSU), L.M. McCauley (PSU), J.A. Kennea (PSU), C.
Pagani (U. Leicester), A.P. Beardmore (U. Leicester), P.A. Evans (U.
Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'ai
(INAF-IASFPA) and H.A. Krimm report on behalf of the Swift-XRT team:

We have analysed 6.4 ks of XRT data for GRB 151001B (Krimm et al. GCN
Circ. 18374
Loading...
 
 ), from 129 s to 59.3 ks after the  BAT trigger. The data
comprise 132 s in Windowed Timing (WT) mode (the first 8 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 Evans et
al. (GCN Circ. 18377
Loading...
 
 ).

The light curve can be modelled with an initial power-law decay with an
index of alpha=2.38 (+/-0.08), followed by a break at T+963 s to an
alpha of 1.12 (+0.12, -0.13).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.78 (+0.17, -0.16). The
best-fitting absorption column is  1.09 (+0.19, -0.18) x 10^22 cm^-2,
in excess of the Galactic value of 6.5 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.20 (+0.31, -0.30)
and a best-fitting absorption column of 1.9 (+0.5, -0.4) x 10^22 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 5.4 x 10^-11 (1.4 x 10^-10) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.9 (+0.5, -0.4) x 10^22 cm^-2
Galactic foreground: 6.5 x 10^21 cm^-2
Excess significance: 5.2 sigma
Photon index:	     2.20 (+0.31, -0.30)

If the light curve continues to decay with a power-law decay index of
1.12, the count rate at T+24 hours will be 2.0 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x
10^-13 (2.8 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00657321.

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

A. A. Breeveld (UCL-MSSL) and H. A. Krimm (CRESST/GSFC/USRA)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 151001B 
148 s after the BAT trigger (Krimm et al., GCN Circ. 18374
Loading...
 
 ).
No optical afterglow consistent with the XRT position (Evans et al. GCN 
Circ. 18377
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           148          298          147         >20.6
white              148         6765          805         >21.8
u_FC               307          557          246         >19.9
v                  636         7175          529         >20.2
b                  563         6561          333         >20.9
u                  307        11107          685         >20.7
w1                 686         7585          510         >20.2
m2                 661         7380          529         >20.2
w2                 613         6970          529         >20.6

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 1.71 in the direction of the 
burst (Schlegel et al. 1998).

S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik,
M. Ulanov, D. Svinkin, A. Tsvetkova, A.Lysenko, A. Kozlova,
and T. Cline on behalf of the Konus-Wind team, report:

At ~16 minutes before the Swift-BAT trigger on GRB 151001B
(Krimm, et al., GCN Circ. 18374
Loading...
 
 ; T0(BAT)=18:29:36 UT)
Konus-Wind detected, in the waiting mode, a burst of high X-ray/soft
gamma-ray emission which had a duration of ~191 s.

Taking into account the proximity of this burst to the Swift-BAT trigger
and consistency of the KW ecliptic latitude response with the position
of GRB 151001B we suggest this burst is the main part of GRB 151001B.

The K-W light curve of this burst is available at
http://www.ioffe.ru/LEA/GRBs/GRB151001B/
The count rate increase in the soft KW energy band, which follows the
burst from T0(BAT)-838 s to T0(BAT)+2488 s, can not be unambiguously
attributed to GRB 151001B.

As observed by Konus-Wind, the burst had a fluence of
8.5(-2.3,+0.6)x10^-6 erg/cm2 and a 2.944-s peak flux,
measured from ~T0(BAT)-1007.1 s, of 1.8(-0.6,+0.4)x10^-7 erg/cm2/s
(both in the 20 - 1000 keV energy range).

Modeling the K-W 3-channel time-integrated spectrum
(from T0(BAT)-1018.9 s to T0(BAT)-827.5 s)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = -0.9(-0.3,+0.5) and Ep = 179 (-52,+75) keV.

All the quoted errors are at 1 sigma confidence level.
All the quoted values are preliminary.