GRB 150206A

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

The long-duration GRB 150206A
(Swift BAT trigger 630019: Hagen et al., GCN 17413
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 ;
Barthelmy  et al., GCN 17426
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 ;
MAXI/GSC detection: Negoro et al., GCN 17414
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 )
triggered Konus-Wind at T0=52280.265 s UT (14:31:20.265).

The burst light curve shows a broad, multi-peaked pulse
with a total duration of ~60 s.
The emission is seen up to ~10 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB150206_T52280/

As observed by Konus-Wind, the burst
had a fluence of 5.52(-0.64,+0.69)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+4.320 s,
of 7.92(-1.78,+1.83)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+32.256 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.73(-0.14,+0.18),
the high energy photon index beta = -2.20(-0.22,+0.15),
the peak energy Ep = 228(-35,+37) keV
(chi2 = 74/97 dof)

The spectrum near the maximum count rate
(measured from T0 to T0+7.680 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.48(-0.17,+0.21),
the high energy photon index beta = -2.20(-0.22,+0.15),
the peak energy Ep = 242(-35,+38) keV
(chi2 = 84/90 dof)

Assuming the redshift z=2.087 (Kruehler et al., GCN 17420
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 )
and a standard cosmology model with H_0 = 70 km/s/Mpc,
Omega_M = 0.27, and Omega_Lambda = 0.73,
we estimate the following rest-frame parameters:
the isotropic energy release E_iso is 6.0(-0.7,+0.8)x10^53 erg,
the peak luminosity L_iso is 2.7(-0.6,+0.6)x10^53 erg/s,
and the rest-frame peak energy of the time-integrated spectrum,
Ep,i, is 703(-109,+114) keV.

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

S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), L. M. Z. Hagen (PSU), H. A. Krimm (GSFC/USRA),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), M. Stamatikos (OSU), J. Tueller (GSFC),
T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):
 
Using the data set from T-60 to T+243 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 150206A (trigger #630019)
(Hagen, et al., GCN Circ. 17413
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 ).  The BAT ground-calculated position is
RA, Dec = 10.076, -63.181 deg, which is 
   RA(J2000)  =  00h 40m 18.1s 
   Dec(J2000) = -63d 10' 50.8" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 48%.
 
The mask-weighted light curve shows a slowly rising level starting at ~T-15 sec,
with two strong clusters of peaks at ~T+85 and ~T+98 sec, and returning
to baseline at ~T+230 sec.  T90 (15-350 keV) is 83.2 +- 7.8 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-22.3 to T+164.1 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.33 +- 0.04.  The fluence in the 15-150 keV band is 1.39 +- 0.03 x 10^-5 erg/cm2.
The 1-sec peak photon flux measured from T+98.82 sec in the 15-150 keV band
is 10.1 +- 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/630019/BA/

S. R. Oates (IAA-CSIC/UCL-MSSL) and L. M. Z. Hagen (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 150206A
483 s after the BAT trigger (Hagen et al., GCN Circ. 17413
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 ).
A source consistent with the XRT position
(Goad et al. GCN Circ. 17418
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 )
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
 RA  (J2000) =  00:40:17.63 =  10.07346 (deg.)
 Dec (J2000) = -63:10:55.7  = -63.18214 (deg.)
with an estimated uncertainty of 0.52 arc sec. (radius, 90% confidence).

Preliminary detections and 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: 

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white              483          577           93         18.76 +/- 0.17
v                 2091         6690          201        >18.8
b                 2190         2912          255         19.56 +/- 0.22
u                 2165         2707           78        >19.0
w1                2140         2683           78        >18.9
w2                2414         6560          216        >19.7

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.02 in the direction of the burst
(Schlegel et al. 1998).

B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), J.A. Kennea (PSU), V.
Mangano (PSU), C. Pagani (U. Leicester), A.P. Beardmore (U. Leicester),
P.A. Evans (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC) and
L.M.Z. Hagen report on behalf of the Swift-XRT team:

We have analysed 8.9 ks of XRT data for GRB 150206A (Hagen et al. GCN
Circ. 17413
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 ), from 464 s to 47.9 ks after the  BAT trigger. The data
comprise 1.1 ks 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 Goad et al.
(GCN Circ. 17418
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 ).

The late-time light curve (from T0+6.4 ks) can be modelled with a
power-law decay with a decay index of alpha=2.7 (+1.0, -1.2).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.69 (+0.08, -0.07). The
best-fitting absorption column is  2.4 (+0.4, -0.3) x 10^21 cm^-2, in
excess of the Galactic value of 2.3 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.85 (+0.08, -0.07)
and a best-fitting absorption column of 9.6 (+2.1, -2.0) x 10^20 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.6 x 10^-11 (4.2 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     9.6 (+2.1, -2.0) x 10^20 cm^-2
Galactic foreground: 2.3 x 10^20 cm^-2
Excess significance: 6.0 sigma
Photon index:	     1.85 (+0.08, -0.07)

If the light curve continues to decay with a power-law decay index of
2.7, the count rate at T+24 hours will be 2.2 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.0 x
10^-14 (9.4 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/00630019.

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

T. Kruehler (ESO Chile), D. Xu, J. P. U. Fynbo, D. Malesani
(DARK/NBI),  Z. Cano (U. Iceland), A. de Ugarte Postigo (IAA-CSIC,
DARK/NBI)
report on behalf of a larger collaboration:

We observed the afterglow of GRB 150206A (Hagen et al. GCN 17413
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 ) with
the VLT/X-shooter spectrograph, equipped with the UVB/VIS/NIR arms and
covering the wavelength range 3000-25000 AA. In a 4x600 s spectrum we
detect absorption features of ZnII, FeII, and MgII at a common
redshift of z=2.087. The spectral trace is down to ~3760 AA, being
consistent with a Lya feature at the same redshift. We thus think this
is the redshift of the GRB.

We acknowledge excellent support from the observing staff at Paranal,
in particular Dimitri Gadotti.

T. Schweyer (MPE Garching), S. Schmidl (TLS Tautenburg), and J. Greiner
(MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 150206A (Swift trigger 630019; Hagen et al.,
GCN 17413
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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 00:32 UT on February 07, 2015, 10 hrs after the
GRB trigger. They were performed at an average seeing of 1.4" and at an
average airmass of 1.7.

We detect the optical aftergow canditate reported by Hagen et al. (GCN
17413
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 ).

Based on total exposures of 8.8 minutes in g'r'i'z' and 8.0 minutes in
JHK, at a midtime of 10.3 hrs after the burst, we measure the following
preliminary magnitudes and upper limits (all AB magnitude system):

g' = 22.6 +/- 0.2 mag,
r' = 21.9 +/- 0.1 mag,
i' = 21.2 +/- 0.1 mag,
z' = 20.8 +/- 0.1 mag,
J = 20.0 +/- 0.2 mag,
H > 20.2 mag, and
K > 19.4 mag.

The magnitudes are calibrated against GROND zeropoints and 2MASS field
stars and are not corrected for the Galactic foreground extinction
corresponding to a reddening of E_(B-V)= 0.02 in the direction of the
burst (Schlegel et al. 1998).

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

Using 3576 s of XRT Photon Counting mode data and 11 UVOT
images for GRB 150206A, 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 = 10.07362, -63.18223 which is equivalent
to:

RA (J2000): 00h 40m 17.67s
Dec (J2000): -63d 10' 56.0"

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.

H. Negoro (Nihon U.), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, 
Y. E. Nakagawa (JAXA), T. Mihara, M. Sugizaki, M. Serino, M. Morii, 
J. Sugimoto, T. Takagi, A. Yoshikawa, M. Matsuoka (RIKEN),
N. Kawai, T. Yoshii, Y. Tachibana (Tokyo Tech), 
A. Yoshida, T. Sakamoto, Y. Kawakubo, H. Ohtsuki (AGU),
H. Tsunemi, D. Uchida (Osaka U.), M. Nakajima, K. Fukushima, T. Onodera, 
K. Suzuki, M. Fujita, F. Honda, T. Namba (Nihon U.),
Y. Ueda, M. Shidatsu, T. Kawamuro, T. Hori (Kyoto U.),
Y. Tsuboi, A. Kawagoe (Chuo U.), M. Yamauchi, Y. Morooka, D. Itoh (Miyazaki U.),
K. Yamaoka (Nagoya U.) report on behalf of the MAXI team:

We report the MAXI/GSC detection of GRB 150206A (Hagen et al. GCN 17413
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 ) 
in the scan transit at 14:50 on 2015 February 06 UT, about 20 min after
the BAT trigger.

Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (10.174 deg, -63.382 deg) = (00 40 41, -63 22 55) (J2000) 
with a statistical 90% C.L. elliptical error region 
with long and short radii of 0.34 deg and 0.28 deg respectively. 
The roll angle of long axis from the north direction is 82.0 deg 
counterclockwise. There is an additional systematic uncertainty of 0.1 deg 
(90% containment radius). 
The position is consistent with that of GRB 150206A.

The X-ray flux averaged over the scan was 116 +- 25 mCrab (4-10keV, 1 sigma 
error). 
There was no significant excess flux in the previous transit at UT 13:21
with an upper limit of 20 mCrab.

L. M. Z. Hagen (PSU), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), C. Gronwall (PSU), M.E. Gropp (PSU),
J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU) and
M. H. Siegel (PSU) report on behalf of the Swift Team:

At 14:30:02 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150206A (trigger=630019).  Swift did not immediately slew
due to observing constraint.  The BAT on-board calculated location is 
RA, Dec 10.088, -63.182, which is 
   RA(J2000)  =  00h 40m 21s
   Dec(J2000) = -63d 10' 53"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a weak beginning
with a strong increase starting at ~T+70 sec.  The duration is 
about 150 sec.  The peak count rate was ~8000 counts/sec (15-350 keV),
at ~97 sec after the trigger. 

The XRT began observing the field at 14:37:57.3 UT, 474.5 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 10.0774, -63.1852 which is equivalent to:
   RA(J2000)  = +00h 40m 18.58s
   Dec(J2000) = -63d 11' 06.7"
with an uncertainty of 5.1 arcseconds (radius, 90% containment). This
location is 20 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 2.35e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of  94 seconds with the White filter
starting 483 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	00:40:17.66 =  10.07358
  DEC(J2000) = -63:10:55.6  = -63.18211
with a 90%-confidence error radius of about 0.78 arc sec. This position is 12.7
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.62 with a 1-sigma error of about  0.16. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.02. 

Burst Advocate for this burst is L. M. Z. Hagen (lea.zernow.hagen AT gmail.com). 
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.)