scholarly journals The confrontation of the shock-powered synchrotron maser model with the Galactic FRB 200428

2020 ◽  
Vol 500 (2) ◽  
pp. 2704-2710 ◽  
Author(s):  
Yun-Wei Yu ◽  
Yuan-Chuan Zou ◽  
Zi-Gao Dai ◽  
Wen-Fei Yu
Keyword(s):  
Line Of Sight ◽  
Model Parameters ◽  
Observational Constraints ◽  
Synchrotron Emission ◽  
Physical Processes ◽  
X Ray ◽  
Emission Efficiency ◽  
Free Parameters ◽  
Fast Radio Burst ◽  
Parameter Constraints

ABSTRACT The association of FRB 200428 with an X-ray burst (XRB) from the Galactic magnetar SGR 1935+2154 offers important implications for the physical processes responsible for the fast radio burst (FRB) phenomena. By assuming that the XRB emission is produced in the magnetosphere, we investigate the possibility that the FRB emission is produced by shock-powered synchrotron maser (SM), which is phenomenologically described with a number of free parameters. The observational constraints on the model parameters indicate that the model can in principle be consistent with the FRB 200428 observations, if the ejecta lunched by magnetar activities can have appropriate ingredients and structures and the shock processes occur on the line of sight. To be specific, a complete burst ejecta should consist of an ultra-relativistic and extremely highly collimated e± component and a sub-relativistic and wide-spreading baryonic component. The internal shocks producing the FRB emission arise from a collision between the e± ejecta and the remnant of a previous baryonic ejecta at the same direction. The parameter constraints depend on the uncertain spectrum and efficiency of the SM emission. While the spectrum is tentatively described by a spectral index of −2, we estimate the emission efficiency to be around 10−4 by requiring that the synchrotron emission of the shocked material cannot be much brighter than the magnetosphere XRB emission.

scholarly journals refnx: neutron and X-ray reflectometry analysis in Python

2019 ◽  
Vol 52 (1) ◽  
pp. 193-200 ◽  
Author(s):  
Andrew R. J. Nelson ◽  
Stuart W. Prescott
Keyword(s):  
Bayesian Approach ◽  
Volume Fraction ◽  
Scattering Length ◽  
Distribution Functions ◽  
Monte Carlo Algorithm ◽  
Reproducible Research ◽  
Model Parameters ◽  
X Ray ◽  
Multiple Data Sets ◽  
Parameter Constraints

refnx is a model-based neutron and X-ray reflectometry data analysis package written in Python. It is cross platform and has been tested on Linux, macOS and Windows. Its graphical user interface is browser based, through a Jupyter notebook. Model construction is modular, being composed from a series of components that each describe a subset of the interface, parameterized in terms of physically relevant parameters (volume fraction of a polymer, lipid area per molecule etc.). The model and data are used to create an objective, which is used to calculate the residuals, log-likelihood and log-prior probabilities of the system. Objectives are combined to perform co-refinement of multiple data sets and mixed-area models. Prior knowledge of parameter values is encoded as probability distribution functions or bounds on all parameters in the system. Additional prior probability terms can be defined for sets of components, over and above those available from the parameters alone. Algebraic parameter constraints are available. The software offers a choice of fitting approaches, including least-squares (global and gradient-based optimizers) and a Bayesian approach using a Markov-chain Monte Carlo algorithm to investigate the posterior distribution of the model parameters. The Bayesian approach is useful for examining parameter covariances, model selection and variability in the resulting scattering length density profiles. The package is designed to facilitate reproducible research; its use in Jupyter notebooks, and subsequent distribution of those notebooks as supporting information, permits straightforward reproduction of analyses.

scholarly journals Using quasar X-ray and UV flux measurements to constrain cosmological model parameters

2020 ◽  
Vol 497 (1) ◽  
pp. 263-278 ◽  
Author(s):  
Narayan Khadka ◽  
Bharat Ratra
Keyword(s):  
Cosmological Parameters ◽  
Hubble Constant ◽  
Acoustic Oscillation ◽  
Joint Analysis ◽  
Model Parameters ◽  
Density Parameter ◽  
Current Standard ◽  
X Ray ◽  
Flux Measurements ◽  
Parameter Constraints

ABSTRACT Risaliti and Lusso have compiled X-ray and UV flux measurements of 1598 quasars (QSOs) in the redshift range 0.036 ≤ z ≤ 5.1003, part of which, z ∼ 2.4 − 5.1, is largely cosmologically unprobed. In this paper we use these QSO measurements, alone and in conjunction with baryon acoustic oscillation (BAO) and Hubble parameter [H(z)] measurements, to constrain cosmological parameters in six different cosmological models, each with two different Hubble constant priors. In most of these models, given the larger uncertainties, the QSO cosmological parameter constraints are mostly consistent with those from the BAO + H(z) data. A somewhat significant exception is the non-relativistic matter density parameter Ωm0 where QSO data favour Ωm0 ∼ 0.5 − 0.6 in most models. As a result, in joint analyses of QSO data with H(z) + BAO data the 1D Ωm0 distributions shift slightly towards larger values. A joint analysis of the QSO + BAO + H(z) data is consistent with the current standard model, spatially-flat ΛCDM, but mildly favours closed spatial hypersurfaces and dynamical dark energy. Since the higher Ωm0 values favoured by QSO data appear to be associated with the z ∼ 2 − 5 part of these data, and conflict somewhat with strong indications for Ωm0 ∼ 0.3 from most z < 2.5 data as well as from the cosmic microwave background anisotropy data at z ∼ 1100, in most models, the larger QSO data Ωm0 is possibly more indicative of an issue with the z ∼ 2 − 5 QSO data than of an inadequacy of the standard flat ΛCDM model.

scholarly journals Simulations of stellar winds from X-ray bursts

2020 ◽  
Vol 638 ◽  
pp. A107
Author(s):  
Y. Herrera ◽  
G. Sala ◽  
J. José
Keyword(s):  
Neutron Star ◽  
Stellar Wind ◽  
Nuclear Reactions ◽  
Gravitational Energy ◽  
Model Parameters ◽  
Wind Model ◽  
X Ray ◽  
Physical Conditions ◽  
Free Parameters

Context. Photospheric radius expansion during X-ray bursts can be used to measure neutron star radii and help constrain the equation of state of neutron star matter. Understanding the stellar wind dynamics is important for interpreting observations, and therefore stellar wind models, though studied in past decades, have regained interest and need to be revisited with updated data and methods. Aims. Here, we study the radiative wind model in the context of X-ray bursts with modern techniques and physics input. We focus on characterization of the solutions and the study of observable magnitudes as a function of free model parameters. Methods. We implemented a spherically symmetric nonrelativistic wind model in a stationary regime, with updated opacity tables and modern numerical techniques. Total mass and energy outflows (Ṁ, Ė) were treated as free parameters. Results. A high-resolution parameter-space exploration was performed to allow better characterization of observable magnitudes. High correlation was found between different photospheric magnitudes and free parameters. For instance, the photospheric ratio of gravitational energy outflow to radiative luminosity is directly proportional to the photospheric wind velocity. Conclusions. The correlations found here could help determine the physical conditions of the inner layers, where nuclear reactions take place, by means of observable photospheric values. Further studies are needed to determine the range of physical conditions in which the correlations are valid.

scholarly journals Constraining the fast radio burst properties using the joint distributions of dispersion measure and fluence of the events detected at Parkes, ASKAP, CHIME, and UTMOST

2021 ◽  
Vol 502 (1) ◽  
pp. 904-914
Author(s):  
Siddhartha Bhattacharyya ◽  
Somnath Bharadwaj
Keyword(s):  
Density Variation ◽  
Dispersion Measure ◽  
Model Parameters ◽  
Source Population ◽  
Joint Distributions ◽  
The Common ◽  
The Mean ◽  
Fast Radio Burst ◽  
Parameter Constraints ◽  
Pulse Broadening

ABSTRACT The Parkes, ASKAP, CHIME, and UTMOST telescopes, which have all detected fast radio bursts (FRBs), each works at a different frequency and has a different detection criteria. Using simulations, we have combined the constraints from all four telescopes to identify an allowed range of model parameters $(\alpha , \overline{E}_{33})$ for the FRB source population. Here, α is the spectral index and $\overline{E}_{33}$ is the mean FRB energy in units of $10^{33} \, {\rm J}$ across a 2128–2848 MHz band in the FRB rest frame. We have considered several different FRB energy distributions, and also different scenarios for the scattering pulse broadening, the event rate density variation with z and the host dispersion measure (DM). We find that in all cases, the common allowed region includes the range −3.9 ≤ α ≤ −1.3 and $0.42\le \overline{E}_{33}\le 1$. In all case, large values α > 4 and $\overline{E}_{33} \gt 60$ are ruled out. Considering the allowed $(\alpha , \overline{E}_{33})$ parameter range, we predict that CHIME is unlikely to detect an FRB with extragalactic dispersion measure (DMEx) exceeding $3700\, {\rm pc\, cm}^{-3}$. A substantially larger DMEx in the large FRB sample anticipated from CHIME would falsify the assumptions of the present analysis. Our analysis is expected to yield tighter parameter constraints with the advent of more FRB data.

scholarly journals Bayesian parameter constraints for neutron star masses and radii using X-ray timing observations of accretion-powered millisecond pulsars

2018 ◽  
Vol 618 ◽  
pp. A161 ◽  
Author(s):  
T. Salmi ◽  
J. Nättilä ◽  
J. Poutanen
Keyword(s):  
Probability Distributions ◽  
A Priori ◽  
Synthetic Data ◽  
Black Body ◽  
Model Parameters ◽  
Affine Invariant ◽  
Pulse Profile ◽  
Millisecond Pulsars ◽  
X Ray ◽  
Parameter Constraints

We present a Bayesian method to constrain the masses and radii of neutron stars (NSs) using the information encoded in the X-ray pulse profiles of accreting millisecond pulsars. We model the shape of the pulses using “oblate Schwarzschild” approximation, which takes into account the deformed shape of the star together with the special and general relativistic corrections to the photon trajectories and angles. The spectrum of the radiation is obtained from an empirical model of Comptonization in a hot slab in which a fraction of seed black-body photons is scattered into a power-law component. By using an affine-invariant Markov chain Monte Carlo ensemble sampling method, we obtain posterior probability distributions for the different model parameters, especially for the mass and the radius. To test the robustness of our method, we first analysed self-generated synthetic data with known model parameters. Similar analysis was then applied for the observations of SAX J1808.4−3658 by the Rossi X-ray Timing Explorer (RXTE). The results show that our method can reproduce the model parameters of the synthetic data, and that accurate constraints for the radius can be obtained using the RXTE pulse profile observations if the mass is a priori known. For a mass in the range 1.5–1.8 M⊙, the radius of the NS in SAX J1808.4−3658 is constrained between 9 and 13 km. If the mass is accurately known, the radius can be determined with an accuracy of 5% (68% credibility). For example, for the mass of 1.7 M⊙ the equatorial radius is Req = 11.9+0.5−0.4 km. Finally, we show that further improvements can be obtained when the X-ray polarization data from the Imaging X-ray Polarimeter Explorer will become available.

scholarly journals Precessing Jet Model for the Supernova Remnant G109.1–1.0

1983 ◽  
Vol 101 ◽  
pp. 429-436
Author(s):  
P. C. Gregory ◽  
G. G. Fahlman
Keyword(s):  
Radio Emission ◽  
Large Scale ◽  
Supernova Remnant ◽  
Line Of Sight ◽  
Synchrotron Emission ◽  
Radio Structure ◽  
X Ray ◽  
Ss 433 ◽  
Half Angle

We propose that the central X-ray pulsar in G109.1–1.0, designated 1E 2259+586, ejects two oppositely directed precessing jets or beams, which give rise to the observed radio structure. The radio emission is interpreted as synchrotron emission from electrons accelerated at the interface of the jets with the walls of the SNR. Thus the observed intersecting arcs of radio emission represent the trace of the precessing jets on the supernova remnant walls. The precession axis is inclined at 37 degrees to the line of sight and the precession cone half angle is 55 degrees. The observed large scale X-ray jet in G109.1–1.0 is found to coincide in position with the precession axis as was found for the X-ray jets from SS 433.

scholarly journals Mass outflow of the X-ray emission line gas in NGC 4151

2020 ◽  
Vol 15 (S359) ◽  
pp. 131-135
Author(s):  
S. B. Kraemer ◽  
T. J. Turner ◽  
D. M. Crenshaw ◽  
H. R. Schmitt ◽  
M. Revalski ◽  
...  
Keyword(s):  
Emission Line ◽  
Total Mass ◽  
High Energy ◽  
Model Parameters ◽  
Zeroth Order ◽  
Space Telescope ◽  
X Ray ◽  
Ngc 4151 ◽  
Outflow Rate ◽  
Mass Outflow

AbstractWe have analyzed Chandra/High Energy Transmission Grating spectra of the X-ray emission line gas in the Seyfert galaxy NGC 4151. The zeroth-order spectral images show extended H- and He-like O and Ne, up to a distance r ˜ 200 pc from the nucleus. Using the 1st-order spectra, we measure an average line velocity ˜230 km s–1, suggesting significant outflow of X-ray gas. We generated Cloudy photoionization models to fit the 1st-order spectra; the fit required three distinct emission-line components. To estimate the total mass of ionized gas (M) and the mass outflow rates, we applied the model parameters to fit the zeroth-order emission-line profiles of Ne IX and Ne X. We determined an M ≍ 5.4 × 105Mʘ. Assuming the same kinematic profile as that for the [O III] gas, derived from our analysis of Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra, the peak X-ray mass outflow rate is approximately 1.8 Mʘ yr–1, at r ˜ 150 pc. The total mass and mass outflow rates are similar to those determined using [O III], implying that the X-ray gas is a major outflow component. However, unlike the optical outflows, the X-ray emitting mass outflow rate does not drop off at r > 100pc, which suggests that it may have a greater impact on the host galaxy.

scholarly journals Multiwavelength Modeling the SED of Strongly Interacting Binaries

2011 ◽  
Vol 7 (S282) ◽  
pp. 65-66
Author(s):  
Augustin Skopal
Keyword(s):  
Physical Parameters ◽  
X Rays ◽  
Physical Processes ◽  
Short Contribution ◽  
Composite Spectrum ◽  
X Ray ◽  
Strongly Interacting ◽  
Low Mass ◽  
X Ray Binaries

AbstractThe spectrum of strongly interacting binaries, as for example, high and low mass X-ray binaries, symbiotic (X-ray) binaries and/or classical and recurrent novae, consists of more components of radiation contributing from hard X-rays to radio wavelengths. To understand the basic physical processes responsible for the observed spectrum we have to disentangle the composite spectrum into its individual components, i.e. to determine their physical parameters. In this short contribution I demonstrate the method of modeling the multiwavelength SED on the example of the extragalactic super-soft X-ray source RX J0059.1-7505 (LIN 358).

scholarly journals Radio and X-ray connection in radio mini-halos: Implications for hadronic models

2020 ◽  
Vol 640 ◽  
pp. A37 ◽  
Author(s):  
A. Ignesti ◽  
G. Brunetti ◽  
M. Gitti ◽  
S. Giacintucci
Keyword(s):  
Magnetic Field ◽  
Large Fraction ◽  
Cosmic Ray ◽  
Physical Parameters ◽  
Model Parameters ◽  
Relativistic Electrons ◽  
X Rays ◽  
X Ray ◽  
Hadronic Model ◽  
Radio Halos

Context. A large fraction of cool-core clusters are known to host diffuse, steep-spectrum radio sources, called radio mini-halos, in their cores. Mini-halos reveal the presence of relativistic particles on scales of hundreds of kiloparsecs, beyond the scales directly influenced by the central active galactic nucleus (AGN), but the nature of the mechanism that produces such a population of radio-emitting, relativistic electrons is still debated. It is also unclear to what extent the AGN plays a role in the formation of mini-halos by providing the seeds of the relativistic population. Aims. In this work we explore the connection between thermal and non-thermal components of the intra-cluster medium in a sample of radio mini-halos and we study the implications within the framework of a hadronic model for the origin of the emitting electrons. Methods. For the first time, we studied the thermal and non-thermal connection by carrying out a point-to-point comparison of the radio and the X-ray surface brightness in a sample of radio mini-halos. We extended the method generally applied to giant radio halos by considering the effects of a grid randomly generated through a Monte Carlo chain. Then we used the radio and X-ray correlation to constrain the physical parameters of a hadronic model and we compared the model predictions with current observations. Results. Contrary to what is generally reported in the literature for giant radio halos, we find that the mini-halos in our sample have super-linear scaling between radio and X-rays, which suggests a peaked distribution of relativistic electrons and magnetic field. We explore the consequences of our findings on models of mini-halos. We use the four mini-halos in the sample that have a roundish brightness distribution to constrain model parameters in the case of a hadronic origin of the mini-halos. Specifically, we focus on a model where cosmic rays are injected by the central AGN and they generate secondaries in the intra-cluster medium, and we assume that the role of turbulent re-acceleration is negligible. This simple model allows us to constrain the AGN cosmic ray luminosity in the range ∼1044−46 erg s−1 and the central magnetic field in the range 10–40 μG. The resulting γ-ray fluxes calculated assuming these model parameters do not violate the upper limits on γ-ray diffuse emission set by the Fermi-LAT telescope. Further studies are now required to explore the consistency of these large magnetic fields with Faraday rotation studies and to study the interplay between the secondary electrons and the intra-cluster medium turbulence.

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