GRB 150202B

M. Axelsson (KTH Royal Institute of Technology, Stockholm) and G. Vianello (Stanford)
report on behalf of the Fermi-LAT team:

At 23:59:08.27 UT on February 2, 2015, Fermi-LAT detected
emission from GRB 150202B, which was also detected by Fermi-GBM
(trigger 444614351/150202999).

The GBM location was initially inside the LAT field of view at an angle of
~17 degrees to the LAT boresight and triggered an autonomous repoint
of the spacecraft. Using standard analysis procedures, we detect the GRB
with a significance barely above our 5-sigma threshold, when looking at
events >500 MeV in the interval 0s to 1300s relative to the trigger time. The
corresponding best location is

RA = 86.6 deg (J2000)
Dec = 59.1 deg (J2000)

with an estimated uncertainty of 0.4 degrees (90% containment). This is
0.5 deg from the GBM position.

Given the low significance, and the fact that there are only 4 photons compatible
with the position of the GBM trigger, we cannot firmly establish this excess as
the high-energy counterpart of GRB 150202B.

Using the LAT Low Energy (LLE) data selection, over 70 counts above
background were detected within a 20s interval coinciding with the time of
the GBM emission. This data selection has insufficient spatial resolution to
provide a reliable LAT localization. Since an excess of events was not firmly
seen using the standard analysis selection, this detection is likely due to low
energy gamma-rays (below 100 MeV).

The Fermi LAT point of contact for this burst is
Magnus Axelsson (magnus.axelsson@astro.su.se<mailto:magnus.axelsson@astro.su.se>).

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.

[GCN OPS NOTE(03feb15):  Per author's request, the "0127A" was changed to "202B"
in the phrase "counterpart of GRB 150202B".]

V. Pelassa (UAH) reports on behalf of the Fermi GBM Team:

"At 23:59:08.27 UT on 02 Feb 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 150202B (trigger 444614351 / 150202999).

The on-ground calculated location, using the GBM trigger data, is
RA = 86.8, Dec = 58.6 (J2000 degrees, equivalent to +05h 47m, +58d 32'),
with an uncertainty of 1.0 degrees (radius, 1-sigma containment,
statistical only; there is additionally a systematic error which is
currently estimated to be 2 to 3 degrees). The angle from the Fermi LAT
boresight is 17 degrees.  This trigger resulted in an Autonomous Repoint
Request (ARR) that was not accepted by the spacecraft.  Following
this observation the Fermi Large Area Telescope also detected
this burst in the ground-based analysis (Axelsson et al. 2015, GCN 17385
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 ).

This GRB was also detected by Integral/SPI-ACS.

The GBM light curve consists of a bright peak lasting about 25 s, 
followed at T0+ 100 s by a fainter second episode of emission, 
with a total duration (T90) of about 167 s (50-300 keV). 
The 1.024-sec peak photon flux measured starting from T0+7.808 s 
in the 10-1000 keV band is 23.8 +/- 0.4 ph/s/cm^2.

The time-averaged spectrum of the first episode, from T0-5.120 s to
T0+24.576 s, is best fit by a Band function with Epeak = 253 +/- 12 keV,
alpha = -0.82 +/- 0.02, and beta = -2.36 +/- 0.13. The event fluence 
(10-1000 keV) in this time interval is (3.15 +/- 0.05)E-05 erg/cm^2.

The time-averaged spectrum of the second episode, from T0+103.426 s to
T0+205.827 s, is well fit a power law function with an exponential
high-energy cutoff. The power law index is -1.23 +/- 0.13 and
the cutoff energy, parameterized as Epeak, is 154 +/- 36 keV. 
The event fluence (10-1000 keV) in this time interval 
is (1.37 +/- 0.15)E-06 erg/cm^2.

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

[GCN OPS NOTE(03feb15): The third sentence in the second paragraph
was changed to say the ARR was rejected by the spacecraft.]

P. A. Evans (U. Leicester) reports on behalf of the Swift team:

Swift has initiated a series of observations, tiled on the sky, of the
Fermi/LAT GRB 150202B. Automated analysis of the XRT data will
be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00039

Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. The probability of finding
serendipitous sources, unrelated to the Fermi/LAT event is high: any X-ray source
considered to be a probable afterglow candidate will be reported via a GCN Circular
after manual consideration.

Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).

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

K. Hurley and J. Goldsten, on behalf of the MESSENGER NS GRB team,

S. Golenetskii, R. Aptekar, V. Pal'shin, D. Frederiks,
D. Svinkin, and T. Cline on behalf of the Konus-Wind team,

V. Connaughton, M. S. Briggs, C. Meegan, V. Pelassa,
and A. Goldstein, on behalf of the Fermi GBM team,

A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo, and C.
Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team, and

S. Barthelmy, J. Cummings, N. Gehrels, H. Krimm, and D. Palmer,
on behalf of the Swift-BAT team, report:

The long-duration GRB 150202B (Axelsson and Vianello., GCN Circ. 17385
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 ) 
has been detected by Fermi (Pelassa., GCN Circ. 17388
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 ), Konus-Wind, 
MESSENGER (GRNS), INTEGRAL (SPI-ACS), and Swift (BAT), so far, at about 
86348 s UT (23:59:08). The burst was outside the coded field of view of 
the BAT.

We have triangulated it to a Konus-MESSENGER annulus centered at 
RA(2000)=126.992 deg (08h 27m 58s)  Dec(2000)=+15.280 deg (+15d 16' 
50"), whose radius is 52.564 +/- 0.201 deg (3 sigma).

The annulus intersects the LAT (statistical-only) error circle (GCN 
17385
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 ) thereby confirming the association of the high-energy emission 
with GRB 150202B. The area of the combined IPN/LAT error region is 570 
sq. arcmin.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB150202_T86354/IPN/

The Konus-Wind time history and spectrum will be given in a forthcoming 
GCN Circular.

B. Sbarufatti (INAF-OAB/PSU), F. E. Marshall (NASA/GSFC), A. Maselli 
(INAF-IASFPA), A. Melandri (INAF-OAB),	V. Mangano (PSU), M.C. Stroh
(PSU), D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), C. Pagani (U. Leicester) and P.A. Evans (U. Leicester)
report on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the
Fermi/LAT-detected burst GRB 150202B (Axelsson et al. GCN Circ. 17385
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 )
in a series of observations tiled on the sky. The total exposure time
is 4.2 ks, distributed over 2 tiles; the maximum exposure at a single
sky location was 4.7 ks. The data were collected between T0+95.4 ks and
T0+107.3 ks, and are entirely in Photon Counting (PC) mode. 

Four uncatalogued X-ray sources have been detected, however none of
them is above the RASS limit or shows definitive signs of fading.
Therefore, at the present time we cannot identify which, if any, is the
afterglow. Details of these sources are given below:

Source 1:
  RA (J2000.0):  86.9565  =  05:47:49.57
  Dec (J2000.0): +58.8301  =  +58:49:48.2
  Error: 4.1 arcsec (radius, 90% conf.)
  Count-rate: 0.0183 +/- 0.0030 ct s^-1
  Flux: (6.1 +/- 1.0)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 2:
  RA (J2000.0):  86.5922  =  05:46:22.14
  Dec (J2000.0): +58.9223  =  +58:55:20.5
  Error: 5.7 arcsec (radius, 90% conf.)
  Count-rate: (5.9 +/- 1.9) -3 ct s^-1
  Flux: (3.2 +/- 1.0)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 3:
  RA (J2000.0):  86.7927  =  05:47:10.25
  Dec (J2000.0): +58.7852  =  +58:47:06.8
  Error: 6.4 arcsec (radius, 90% conf.)
  Count-rate: (4.0 +/- 1.7) -3 ct s^-1
  Flux: (1.60 +/- 0.67)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 4:
  RA (J2000.0):  86.8219  =  05:47:17.25
  Dec (J2000.0): +58.9746  =  +58:58:28.7
  Error: 5.5 arcsec (radius, 90% conf.)
  Count-rate: (3.03 +/- 0.99) -3 ct s^-1
  Flux: (6.5 +/- 2.1)e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Sources 3 and 4 are positionally coincident with stars from the USNO B1
catalogue.

The results of the XRT-team automatic analysis of the tiled XRT
observations, including a position-specific upper limit calculator, are
available at http://www.swift.ac.uk/xrt_products/TILED_GRB00039.

The UVOT observation covers sources 1 and 3 in the UVW1 filter. There
is nothing at the position of source 1; source 3 is bright as expected
from the catalogued source.

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

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 150202B
(Fermi LAT detection: Axelsson and Vianello, GCN 17385
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 ;
Fermi GBM detection: Pelassa, GCN 17388
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 ;
IPN triangulation: Hurley et al., GCN 17398
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 )
triggered Konus-Wind at T0=86354.293 s UT (23:59:14.293).

The KW light curve shows a bright main pulse lasting about 15 s,
which is followed by a fainter second episode which
started at ~T0+100 s and lasted up to ~T0+210 s.
The emission in the main pulse is seen up to 10 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB150202_T86354/

As observed by Konus-Wind, the burst
had a fluence of 4.56(-0.51,+0.67)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+3.600 s,
of 1.07(-0.20,+0.20)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the main pulse
(measured from T0 to T0+12.544 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 = -0.75(-0.11,+0.14),
the high energy photon index beta = -2.39(-0.22,+0.15),
the peak energy 234(-26,+27) keV
(chi2 = 88/89 dof)

The spectrum near the maximum count rate
(measured from T0 to T0+5.888 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 = -0.69(-0.17,+0.21),
the high energy photon index beta = -2.18(-0.19,+0.12),
the peak energy 240(-38,+49) keV
(chi2 = 79/79 dof)

The time-averaged spectrum of the second episode
(measured from T0+94.464 to T0+209.152 s)
is best fit in the 20 keV - 5 MeV range
by a power law with spectral index = -1.95(-0.19,+0.21)
(chi2 = 77/78 dof).

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

B. Sbarufatti (INAF-OAB/PSU), P.A. Evans (U. Leicester) and M. H. Siegel (PSU) report on behalf of the Swift team.

Swift took a second epoch of data for the LAT/IPN GRB 150202B (Axelsson et al. GCN Circ. 17385
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 , Hurley et al. GCN Circ. 17398
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 ) between T+515.2 ks and T+516.4 ks, with a 1.2 ks exposure time. 
Of the two unknown sources reported by Sbarufatti et al. (GCN 17405
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 ), Source #2 is still detected at a level of 8.4E-3 counts/s (3.7E-13 erg cm^-2 s^-2), comparable with the previous observation, while Source #1 has faded below detection, to a 3-sigma upper limit of 4.8E-3 counts/s (1.6E-13 erg cm^-2 s^-1).
We therefore confirm that Source #1 is the X-ray afterglow of GRB 150202B.

The results of the XRT-team automatic analysis of the likely afterglow
are at http://www.swift.ac.uk/xrt_products/TILED_GRB00039/index_1.php.
The results of the full analysis of the XRT observations are available
at http://www.swift.ac.uk/xrt_products/TILED_GRB00039/.

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