TITLE:   GCN CIRCULAR
NUMBER:  17318
SUBJECT: GRB 150101B/Swift J123205.1-105602: XMM-Newton observation
DATE:    15/01/20 11:20:51 GMT
FROM:    Sergio Campana at INAF-OAB  <sergio.campana@brera.inaf.it>

S. Campana (INAF-Osservatorio astronomico di Brera) reports

XMM-Newton observed GRB 150101B/Swift J123205.1-10560
(Cummings 2015, GCN 17267) on Jan 07, 2015 10:13:31 UT
(5.79 d after the burst discovery). The last ~16 ks of the observation were
affected by a mildly-enhanced background and were filtered out.
The resulting EPIC/pn exposure times is 33.2 ks.

A source is well detected at a position consistent with the Swift's
(Cummings et al. 2015, GCN 17268), Chandra's (Troja et al. 2015, GCN
17289), and radio (Fong 2015, GCN 17288) ones.
No X-ray source is detected at the position of a second radio source (Fong
2015), whereas the two closeby sources detected by Chandra are too close
to be separated by XMM-Newton.
The source is relatively bright with a pn count rate of (2.8+/-0.1)x10^{-1}
cts/s.
We extracted 8620 source photons from the pn and fitted the X-ray spectrum
with a power law model including a non-negligible absorption component
at the galaxy redshift (z=0.134, Levan et al 2015, GCN 17281) in addition
to the Galactic one (3.5x10^{20} cm^{-2}).
The best fit power law (chi2=1.03 with 244 degrees of freedom) implies
a photon index of Gamma=2.29+/-0.06 (90% c.l. for one parameter of
interest) and an additional column density marginally not consistent
with zero NH_z=(1.3+/-0.9)x10^{20} cm^{-2} (90% c.l.).
Any unresolved iron emission line (6.4-6.9 keV interval) should have an
equivalent width <230 eV.
The 0.5-8 keV unabsorbed flux is (4.3+/-0.1)x10^{-13} erg/cm^2/s, fully
consistent with the with the Chandra observation (Troja et al 2015).

This testifies that we are observing emission from a low luminosity Active
Galactic Nucleus (2x10^{43} erg/s) and not from the GRB afterglow.