Poster abstract details
A re-analysis of the NuSTAR broad-band spectrum of Ser~X-1
Abstract
Ser X-1 is a persistent accreting LMXB of the atoll class. This type of
binaries is characterized by two states of emission: 'soft state' and
'hard state'. During the soft state, continuum emission is normally
described by a blackbody or a multi-color blackbody, (possibly originated
by the accretion disk) and a saturated Comptonization, whereas, during the
hard state, it consists of an unsaturated Comptonization plus a weaker
blackbody component. In addition to these continuum components, in the
energy range 6.4-6.97 keV, the K$\alfa$ transition of iron at different
ionization stages is often observed. These lines are thought to originate
by the reflection of the primary Comptonization spectrum over the accretion
disk. As such they are a powerful tool since they allow us to investigate
the structure of the accretion flow close to the central source. Miller
et al. (2013, ApJ, 779, L2) have recently analyzed the same Ser~X-1
\emph{NuSTAR} data. Initially they fitted the spectrum using a simple
continuum model formed by a bbody, plus a diskbbody, plus a powerlaw and,
for the iron line, they added a \texttt{kerrdisk} component. They have
found an iron line at 6.97$\pm$0.01 keV. Afterwards they have carried
out a fit with a new model obtained replacing the \texttt{kerrdisk}
component with a reflection component, \texttt{reflionx}, convolved with
\texttt{kerrconv}. In particular they explored the sensitivity of the fit
upon different values of the spin parameter (a=0, a=0.12, a=0.14), iron
abundance (Afe=1, Afe=2, Afe=3) and R$_{in}$ (1.0 R$_{ISCO}$ or free to
vary). They have found out that the best fit is insensible to 'a',
prefers an abundance of Afe=3 and a value of R$_{in}$ equal to 1.0 R$_{ISCO}$.
In this work we re-analyze all the available public \emph{NuSTAR}
and \emph{XMM-Newton} observations of Ser X-1, using a slightly different
continuum and fitting the iron line and other reflection features with
self-consistent reflection models as \texttt{reflionx} and \texttt{rfxconv}.
Our results are in line with those already found by Miller et al. (2013)
but less extreme. For example our results for the inner disk radius and
inclination are $R_{in} = 13.4\pm$2.4\;R_g$ and $Incl = 27.1\pm$2.4\;\;deg$,
respectively
binaries is characterized by two states of emission: 'soft state' and
'hard state'. During the soft state, continuum emission is normally
described by a blackbody or a multi-color blackbody, (possibly originated
by the accretion disk) and a saturated Comptonization, whereas, during the
hard state, it consists of an unsaturated Comptonization plus a weaker
blackbody component. In addition to these continuum components, in the
energy range 6.4-6.97 keV, the K$\alfa$ transition of iron at different
ionization stages is often observed. These lines are thought to originate
by the reflection of the primary Comptonization spectrum over the accretion
disk. As such they are a powerful tool since they allow us to investigate
the structure of the accretion flow close to the central source. Miller
et al. (2013, ApJ, 779, L2) have recently analyzed the same Ser~X-1
\emph{NuSTAR} data. Initially they fitted the spectrum using a simple
continuum model formed by a bbody, plus a diskbbody, plus a powerlaw and,
for the iron line, they added a \texttt{kerrdisk} component. They have
found an iron line at 6.97$\pm$0.01 keV. Afterwards they have carried
out a fit with a new model obtained replacing the \texttt{kerrdisk}
component with a reflection component, \texttt{reflionx}, convolved with
\texttt{kerrconv}. In particular they explored the sensitivity of the fit
upon different values of the spin parameter (a=0, a=0.12, a=0.14), iron
abundance (Afe=1, Afe=2, Afe=3) and R$_{in}$ (1.0 R$_{ISCO}$ or free to
vary). They have found out that the best fit is insensible to 'a',
prefers an abundance of Afe=3 and a value of R$_{in}$ equal to 1.0 R$_{ISCO}$.
In this work we re-analyze all the available public \emph{NuSTAR}
and \emph{XMM-Newton} observations of Ser X-1, using a slightly different
continuum and fitting the iron line and other reflection features with
self-consistent reflection models as \texttt{reflionx} and \texttt{rfxconv}.
Our results are in line with those already found by Miller et al. (2013)
but less extreme. For example our results for the inner disk radius and
inclination are $R_{in} = 13.4\pm$2.4\;R_g$ and $Incl = 27.1\pm$2.4\;\;deg$,
respectively