Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCyclotron resonant scattering feature simulations. I. Thermally averaged cyclotron scattering cross sections, mean free photon-path tables, and electron momentum sampling
51
0
0.0
(
0
)
Authors
F.-W. Schwarm
Ask ChatGPT about the research
No Arabic abstract
Electron cyclotron resonant scattering features (CRSFs) are observed as absorption-like lines in the spectra of X-ray pulsars. A significant fraction of the computing time for Monte Carlo simulations of these quantum mechanical features is spent on the calculation of the mean free path for each individual photon before scattering, since it involves a complex numerical integration over the scattering cross section and the (thermal) velocity distribution of the scattering electrons. We aim to numerically calculate interpolation tables which can be used in CRSF simulations to sample the mean free path of the scattering photon and the momentum of the scattering electron. The tables also contain all the information required for sampling the scattering electrons final spin. The tables were calculated using an adaptive Simpson integration scheme. The energy and angle grids were refined until a prescribed accuracy is reached. The tables are used by our simulation code to produce artificial CRSF spectra. The electron momenta sampled during these simulations were analyzed and justified using theoretically determined boundaries. We present a complete set of tables suited for mean free path calculations of Monte Carlo simulations of the cyclotron scattering process for conditions expected in typical X-ray pulsar accretion columns (0.01<B/B_{crit}<=0.12, where B_{crit}=4.413x10^{13} G and 3keV<=kT<15keV). The sampling of the tables is chosen such that the results have an estimated relative error of at most 1/15 for all points in the grid. The tables are available online at http://www.sternwarte.uni-erlangen.de/research/cyclo.
rate research
Read More
Cyclotron resonant scattering features (CRSFs) are formed by scattering of X-ray photons off quantized plasma electrons in the strong magnetic field (of the order 10^12 G) close to the surface of an accreting X-ray pulsar. The line profiles of CRSFs cannot be described by an analytic expression. Numerical methods such as Monte Carlo (MC) simulations of the scattering processes are required in order to predict precise line shapes for a given physical setup, which can be compared to observations to gain information about the underlying physics in these systems. A versatile simulation code is needed for the generation of synthetic cyclotron lines. Sophisticated geometries should be investigatable by making their simulation possible for the first time. The simulation utilizes the mean free path tables described in the first paper of this series for the fast interpolation of propagation lengths. The code is parallelized to make the very time consuming simulations possible on convenient time scales. Furthermore, it can generate responses to mono-energetic photon injections, producing Greens functions, which can be used later to generate spectra for arbitrary continua. We develop a new simulation code to generate synthetic cyclotron lines for complex scenarios, allowing for unprecedented physical interpretation of the observed data. An associated XSPEC model implementation is used to fit synthetic line profiles to NuSTAR data of Cep X-4. The code has been developed with the main goal of overcoming previous geometrical constraints in MC simulations of CRSFs. By applying this code also to more simple, classic geometries used in previous works, we furthermore address issues of code verification and cross-comparison of various models. The XSPEC model and the Greens function tables are available online at http://www.sternwarte.uni-erlangen.de/research/cyclo .
(Abridged) We present a systematic fit of a model of resonant cyclotron scattering (RCS) to the X-ray data of ten magnetars, including canonical and transient anomalous X-ray pulsars (AXPs), and soft gamma repeaters (SGRs). In this scenario, non-thermal magnetar spectra in the soft X-rays (i.e. below ~10 keV) result from resonant cyclotron scattering of the thermal surface emission by hot magnetospheric plasma. We find that this model can successfully account for the soft X-ray emission of magnetars, while using the same number of free parameters than the commonly used empirical blackbody plus power-law model. However, while the RCS model can alone reproduce the soft X-ray spectra of AXPs, the much harder spectra of SGRs below ~10 keV, requires the addition of a power-law component (the latter being the same component responsible for their hard X-ray emission). Although this model in its present form does not explain the hard X-ray emission of a few of these sources, we took this further component into account in our modeling not to overlook their contribution in the ~4-10 keV band. We find that the entire class of sources is characterized by magnetospheric plasma with a density which, at resonant radius, is about 3 orders of magnitudes higher than n_{GJ}, the Goldreich-Julian electron density. The inferred values of the intervening hydrogen column densities, are also in better agreement with more recent estimates inferred from the fit of single X-ray edges. For the entire sample of observations, we find indications for a correlation between the scattering depth and the electron thermal velocity, and the field strength. Moreover, in most transient anomalous X-ray pulsars the outburst state is characterized by a relatively high surface temperature which cools down during the decay.
Based on phase-resolved broadband spectroscopy using $XMM$-$Newton$ and $NuSTAR$, we report on a potential cyclotron resonant scattering feature at $E sim 13$ keV in the pulsed spectrum of the recently discoverd ULX pulsar NGC 300 ULX1. If this interpretation is correct, the implied magnetic field of the central neutron star is $B sim 10^{12}$ G (assuming scattering off electrons), similar to that estimated from the observed spin-up of the star, and also similar to known Galactic X-ray pulsars. We discuss the implications of this result for the connection between NGC 300 ULX1 and the other known ULX pulsars, particularly in light of the recent discovery of a likely proton Cyclotron line in another ULX, M51 ULX-8.
We present timing and broad-band spectral studies of the high mass X-ray binary pulsar 4U 1909+07 using data from Suzaku observation during 2010 November 2-3. The pulse period of the pulsar is estimated to be 604.11+/-0.14 s. Pulsations are seen in the X-ray light curve up to ~70 keV. The pulse profile is found to be strongly energy-dependent: a complex, multi-peaked structure at low energy that becomes a simple single peak at higher energy. We found that the 1-70 keV pulse averaged continuum can be fitted by the sum of a black body and a partial covering Negative and Positive power-law with EXponential cutoff (NPEX) model. A weak iron fluorescence emission line at 6.4 keV was detected in the spectrum. An absorption like feature at ~44 keV was clearly seen in the residue of the spectral fitting, independent of the continuum model adopted. To check the possible presence of a CRSF in the spectrum, we normalized the pulsar spectrum with the spectrum of the Crab Nebula. The resulting Crab ratio also showed a clear dip centered at ~44 keV. We performed statistical tests on the residue of the spectral fitting and also on the Crab spectral ratio to determine the significance of the absorption like feature and identified it as a CRSF of the pulsar. We estimated the corresponding surface magnetic field of the pulsar to be 3.8 x 10^12 Gauss.
We present analysis of 4U 1626-67, a 7.7 s pulsar in a low-mass X-ray binary system, observed with the hard X-ray detector of the Japanese X-ray satellite Suzaku in March 2006 for a net exposure of sim88 ks. The source was detected at an average 10-60 keV flux of sim4 x10^-10 erg cm^-2 s^-1. The phase-averaged spectrum is reproduced well by combining a negative and positive power-law times exponential cutoff (NPEX) model modified at sim 37 keV by a cyclotron resonance scattering feature (CRSF). The phase-resolved analysis shows that the spectra at the bright phases are well fit by the NPEX with CRSF model. On the other hand, the spectrum in the dim phase lacks the NPEX high-energy cutoff component, and the CRSF can be reproduced by either an emission or an absorption profile. When fitting the dim phase spectrum with the NPEX plus Gaussian model, we find that the feature is better described in terms of an emission rather than an absorption profile. The statistical significance of this result, evaluated by means of an F-test, is between 2.91 x 10^-3 and 1.53 x 10^-5, taking into account the systematic errors in the background evaluation of HXD-PIN. We find that, the emission profile is more feasible than the absorption one for comparing the physical parameters in other phases. Therefore, we have possibly detected an emission line at the cyclotron resonance energy in the dim phase.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
