New XMM-Newton observation of the Phoenix cluster: properties of the
  cool core
  (Abridged) We present a spectral analysis of a deep (220 ks) XMM-Newton
observation of the Phoenix cluster (SPT-CL J2344-4243), which we also combine
with Chandra archival ACIS-I data. We extract CCD and RGS X-ray spectra from
the core region to search for the signature of cold gas, and constrain the mass
deposition rate in the cooling flow which is thought to be responsible of the
massive star formation episode observed in the BCG. We find an average mass
deposition rate of $\dot M = 620 (-190 +200)_{stat} (-50 +150)_{syst}
M_\odot$/yr in the temperature range 0.3-3.0 keV from MOS data. A
temperature-resolved analysis shows that a significant amount of gas is
deposited only above 1.8 keV, while upper limits of the order of hundreds of
$M_\odot$/yr can be put in the 0.3-1.8 keV temperature range. From pn data we
obtain $\dot M = 210 (-80 +85)_{stat} ( -35 +60)_{syst} M_\odot$/yr, and the
upper limits from the temperature-resolved analysis are typically a factor of 3
lower than MOS data. In the RGS spectrum, no line emission from ionization
states below Fe XXIII is seen above $12 \AA$, and the amount of gas cooling
below $\sim 3$ keV has a best-fit value $\dot M = 122_{-122}^{+343}$
$M_{\odot}$/yr. In addition, our analysis of the FIR SED of the BCG based on
Herschel data provides $SFR = (530 \pm 50) M_\odot$/yr, significantly lower
than previous estimates by a factor 1.5. Current data are able to firmly
identify substantial amount of cooling gas only above 1.8 keV in the core of
the Phoenix cluster. While MOS data analysis is consistent with values as high
as $\dot M \sim 1000$ within $1 \sigma$, pn data provide $\dot M < 500 M_\odot$
yr$^{-1}$ at $3\sigma$ c.l. at temperature below 1.8 keV. At present, this
discrepancy cannot be explained on the basis of known calibration uncertainties
or other sources of statistical noise.
