TITLE:   GCN CIRCULAR
NUMBER:  17370
SUBJECT: GRB 150201A: Fermi GBM observation
DATE:    15/02/02 02:08:31 GMT
FROM:    Veronique Pelassa at UAH  <vero.pelassa@gmail.com>

H.-F. Yu (MPE) and V. Pelassa (UAH) report on behalf of the Fermi GBM Team:

"At 13:46:55.15 UT on 01 Feb 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 150201A (trigger 444491218 / 150201574),
which was also detected by the Swift (Cannizzo et al. 2015, GCN 17368).
The GBM on-ground location is consistent with the Swift position.
The trigger resulted in an Autonomous Repoint Request (ARR) that was
accepted and the spacecraft slewed to the GBM in-flight location.
The angle from the Fermi LAT boresight is about 60 degrees.

The GBM light curve shows a double-peaked pulse with a duration (T90)
of about 16 s (50-300 keV). The time-averaged spectrum from T0-2.816 s
to T0+36.097 s is well fit by a Band function with Epeak = 131 +/- 2 keV,
alpha = -1.02 +/- 0.01, and beta = -2.70 +/- 0.06. The event fluence
(10-1000 keV) in this time interval is (6.63 +/- 0.05)E-05 erg/cm^2.
The 1.024-sec peak photon flux measured starting from T0+4.608 s in
the 10-1000 keV band is 88.7 +/- 0.7 ph/s/cm^2.

GBM triggered on GRB 150201590 23 minutes after GRB 150201A,
at 14:09:56 UT (MET 444492598). The GBM localization of this 2nd trigger
is RA, Dec = 2.1, -40.7 with an uncertainty of 2.7 deg (radius, 1-sigma
containment,statistical only; there is additionally a systematic error
which is currently estimated to be 2 to 3 degrees).  This is consistent
with the position of GRB 150201A.

As seen by GBM, this second event shows a multi-peaked pulse with a
duration (T90) of about 26 s (50-300 keV). The time-averaged spectrum
from T0-0.512 s to T0+22.016 s is well fit by a power law function with
an exponential high-energy cutoff. The power law index is -0.61 +/- 0.15
and the cutoff energy, parameterized as Epeak, is 105 +/- 8 keV. The
event fluence (10-1000 keV) in this time interval is
(2.13 +/- 0.11)E-06 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0+7.104 s in the 10-1000 keV band is 2.1 +/- 0.2 ph/s/cm^2.

At the time of this 2nd trigger the position of 150201A was occulted by
the Earth to the Swift spacecraft. The GBM data suggest the two events may
have a common origin. Because of the uncertainty in the GBM localization,
we cannot exclude the possibility that this is a chance coincidence and
that GRB 150201590 is unrelated to GRB 150201A.

Owing to the possible relationship between the two triggers, which would make
this an unusually long GRB, Fermi is observing the position of GRB 150201A
as a target of opportunity for a period of 24 hours, subject to Earth limb
constraints.

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