GRB 150626B

L. M. McCauley (PSU), S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC),
H. A. Krimm (CRESST/GSFC/USRA), F. E. Marshall (NASA/GSFC) and
B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:

At 20:22:52 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150626B (trigger=646786).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 187.672, +66.779, which is 
   RA(J2000)  =  12h 30m 41s
   Dec(J2000) = +66d 46' 45"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a FRED-like structure
with a duration of about 30 sec.  The peak count rate
was ~1500 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 20:24:58.9 UT, 126.1 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 187.6342,
66.7722 which is equivalent to:
   RA(J2000)  = 12h 30m 32.22s
   Dec(J2000) = +66d 46' 19.8"
with an uncertainty of 2.4 arcseconds (radius, 90% containment). This
location is 58 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 (1.69 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 1.1
(+0.98/-0.61) x 10^22 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 131 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
0.01. 

Burst Advocate for this burst is L. M. McCauley (marissamc 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.)

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

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

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

A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik
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,  A. Popov
Ural Federal University, Kourovka

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)

MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in Kislovodsk was pointed to the  GRB150626B 216 sec after notice 
time and 260 sec after trigger time at 2015-06-26 20:27:12 UT in two 
polarizations, directly after automatic weather control system give permit 
for observations. On our first (50s exposure)  set we not found  optical 
transient within SWIFT error-box (McCauley et al. GCN 17966
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 ) brighter then 
17.5.
The 5-sigma upper limit has been about 17.5 mag


MASTER-IAC  pointed to the  GRB150626B  46   sec after notice time and 90 
sec after trigger time at 2015-06-26 2015-06-26 20:24:22 UT, but the 
images overexposed due to eveninig sky (Sun alt -4 deg.).

The observations is continued.
The message may be cited.

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

Using 591 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 150626B, 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 = 187.63331, +66.77177 which is equivalent
to:

RA (J2000): 12h 30m 31.99s
Dec (J2000): +66d 46' 18.4"

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.

D. Xu (NAOC/CAS), J. Telting (NOT), J. P. U. Fynbo (DARK/NBI) report on behalf of a larger collaboration:

We observed the field of GRB 150626B (McCauley et al., GCN 17966
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 ) using the 2.56m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. We obtained 2x150s SDSS r-band and 6x180s SDSS z-band frames, with their median time of 1.379 hr and 1.936 hr after the burst, respectively.

No optical source is detected at the (enhanced) XRT position (McCauley et al., GCN 17966
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 ; Goad et al., GCN 17968
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 ) in our stacked r- and z-band images, down to the limiting magnitudes of r~22.3 mag and z~21.6 mag, respectively.

M. De Pasquale (UCL-MSSL) and L. M. McCauley (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 150626B
131 s after the BAT trigger (McCauley et al., GCN Circ. 17966
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 ).
No optical afterglow consistent with the XRT position (Goad et al.
GCN Circ. 17968
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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           131          281          147         >20.7
u_FC               289          539          246         >20.1
white              131         6476          628         >21.6
v                  620         6887          529         >19.5
b                  545         7647          469         >20.8
u                  289         7502          756         >20.7
w1                 669         7298          529         >20.4
m2                 644         7092          510         >20.3
w2                 595         6682          346         >20.4

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.01 in the direction of the burst
(Schlegel et al. 1998).

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

We have analysed 8.9 ks of XRT data for GRB 150626B (McCauley et al.
GCN Circ. 17966
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 ), from 111 s to 23.5 ks after the  BAT trigger. The
data comprise 8 s in Windowed Timing (WT) mode (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. 17968
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 ).
The late-time light curve (from T0+5.3 ks) is consistent with a
constant source of mean count rate 1.9e-01 ct/sec. A power-law fit
gives an index of 0.2 (+0.6, -0.5).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.99 (+/-0.15). The
best-fitting absorption column is  9.6 (+1.4, -1.3) x 10^21 cm^-2, in
excess of the Galactic value of 1.7 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 4.8 x 10^-11 (8.8 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     9.6 (+1.4, -1.3) x 10^21 cm^-2
Galactic foreground: 1.7 x 10^20 cm^-2
Excess significance: 11.7 sigma
Photon index:	     1.99 (+/-0.15)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00646786.

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

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),
L. M. McCauley (PSU), 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 150626B (trigger #646786)
(McCauley et al., GCN Circ. 17966
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 ).  The BAT ground-calculated position is
RA, Dec = 187.627, 66.794 deg which is
  RA(J2000)  =  12h 30m 30.6s
  Dec(J2000) = +66d 47' 39.6"
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 35%.

The mask-weighted light curve shows a single-peaked structure that starts
at ~T-15 s, peaks at ~T+1 s, and ends at ~T+30 s. T90 (15-350 keV)
is 48.0 +- 22.6 sec (estimated error including systematics).

The time-averaged spectrum from T-15.6 to T+32.4 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.36 +- 0.21.  The fluence in the 15-150 keV band is 1.0 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+7.94 sec in the 15-150 keV band
is 0.6 +- 0.2 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/646786/BA/

K. P. Mooley, G. E. Anderson, R. P. Fender, T. D. Staley (University of 
Oxford),
A. J. van der Horst (George Washington University), A. Rowlinson (CASS)

We observed the position of GRB 150626B (McCauley et al., GCN 17966
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 ,
Goad et al., GCN 17968
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 ) at 16 GHz with the Arcminute Microkelvin Imager
(AMI-LA) at 2015 June 26.85, June 27.58, and July 03.56 UT, corresponding
to 0.01 days, 0.73 days and 6.71 days post-burst respectively. The GRB
flux densities at these three epochs were <0.19 mJy (3 sigma upper limit),
0.17+/-0.05 mJy (marginal detection), and 0.29+/-0.06 mJy (confirmed 
detection)
respectively.

Further AMI monitoring is ongoing. We thank the AMI scheduling team for
carrying out these observations.