arXiv subjects

Efrain Gatuzz

Publications and source records attributed to Efrain Gatuzz.

24 records · Page 2Linked to original sources

arXiv2021

Probing the physical properties of the intergalactic medium using blazars

We use Swift blazar spectra to estimate the key intergalactic medium (IGM) properties of hydrogen column density(Nhxigm), metallicity and temperature over a redshift range of 0.03 leq z leq 4.7, using a collisional ionisation equilibrium(CIE) model for the ionised plasma. We adopted a conservative approach to the blazar continuum model given its intrinsic variability and use a range of power law models. We subjected our results to a number of tests and found that the Nhxigm parameter was robust with respect to individual exposure data and co-added spectra for each source, and between Swift and XMM-Newton source data. We also found no relation between Nhxigm and variations in source flux or intrinsic power laws. Though some objects may have a bulk Comptonisation component which could mimic absorption, it did not alter our overall results. The Nhxigm from the combined blazar sample scales as(1+z)^1.8+\-0.2. The mean hydrogen density at z = 0 is n0 = (3.2+\-0.5) x 10^-7 cm^-3. The mean IGM temperature over the full redshift range is log(T\K) = 6.1+\-0.1 and the mean metallicity is [X\H] = -1.62+\-0.04 (Z sim0.02) When combining with the results with a gamma-ray burst (GRB) sample, we find the results are consistent over an extended redshift range of 0.03 leq z leq 6.3. Using our model for blazars and GRBs, we conclude that the IGM contributes substantially to the total absorption seen in both blazar and GRB spectra.

astro-ph.HE↗

arXiv2021

Nitrogen X-ray absorption in the local ISM

Nitrogen is one of the most abundant metals in the interstellar medium (ISM), and thus it constitutes an excellent test to study a variety of astrophysical environments, ranging from nova to active galactic nuclei. We present a detailed analysis of the gaseous component of the N K~edge using high-resolution {\it XMM-Newton} spectra of 12 Galactic and 40 extragalactic sources. For each source, we have estimated column densities for {\rm N}~{\sc i}, {\rm N}~{\sc ii}, {\rm N}~{\sc iii}, {\rm N}~{\sc v}, {\rm N}~{\sc vi} and {\rm N}~{\sc vii} ionic species, which trace the cold, warm and hot phases of the local Galactic interstellar medium. We have found that the cold-warm component column densities decrease with the Galactic latitude while the hot component does not. Moreover, the cold column density distribution is in good agreement with UV measurements. This is the first detailed analysis of the nitrogen K-edge absorption due to ISM using high-resolution X-ray spectra.

astro-ph.HE↗

arXiv2019

Conflicting disk inclination estimates for the black hole X-ray binary XTE J1550-564

XTE J1550-564 is a black hole X-ray binary for which the dynamical characteristics are well established, and the broadband spectral evolution of the source has been well studied. Its orbital inclination is known to be high, at $\sim75^{\circ}$, with the jet estimated to align well with the orbital axis. We explore simultaneous observations made with ASCA and RXTE, covering the $1$--$200$~keV band, during the early stages of the first outburst of XTE J1550-564 in its hard-intermediate state, on 1998-09-23/24. We show that the most up-to-date reflection models, applied to these data, yield an inclination estimate much lower than found in previous studies, at $\sim40^{\circ}$, grossly disagreeing with the dynamically estimated orbital inclination. We discuss the possible explanations for this disagreement and its implications for reflection models, including possible physical scenarios in which either the inner disk is misaligned both with binary orbit and the outer jet, or either the inner accretion flow, corona, and/or jet have vertical structure which leads to lower inferred disk inclination through various physical means.

astro-ph.HE↗

arXiv2019

Astro 2020: Astromineralogy of interstellar dust with X-ray spectroscopy

X-ray absorption fine structure (XAFS) in the 0.2-2 keV band is a crucial component in multi-wavelength studies of dust mineralogy, size, and shape -- parameters that are necessary for interpreting astronomical observations and building physical models across all fields, from cosmology to exoplanets. Despite its importance, many fundamental questions about dust remain open. What is the origin of the dust that suffuses the interstellar medium (ISM)? Where is the missing interstellar oxygen? How does iron, predominantly produced by Type Ia supernovae, become incorporated into dust? What is the main form of carbon in the ISM, and how does it differ from carbon in stellar winds? The next generation of X-ray observatories, employing microcalorimeter technology and $R \equiv λ/Δλ\geq 3000$ gratings, will provide pivotal insights for these questions by measuring XAFS in absorption and scattering. However, lab measurements of mineralogical candidates for astrophysical dust, with R > 1000, are needed to fully take advantage of the coming observations.

astro-ph.EP↗

arXiv2018

The Soft-Excess in Mrk 509: Warm Corona or Relativistic Reflection?

We present the analysis of the first NuSTAR observations ($\sim 220$ ks), simultaneous with the last SUZAKU observations ($\sim 50$ ks), of the active galactic nucleus of the bright Seyfert 1 galaxy Mrk 509. The time-averaged spectrum in the $1-79$ keV X-ray band is dominated by a power-law continuum ($Γ\sim 1.8-1.9$), a strong soft excess around 1 keV, and signatures of X-ray reflection in the form of Fe K emission ($\sim 6.4$ keV), an Fe K absorption edge ($\sim 7.1$ keV), and a Compton hump due to electron scattering ($\sim 20-30$ keV). We show that these data can be described by two very different prescriptions for the soft excess: a warm ($kT\sim 0.5-1$ keV) and optically thick ($τ\sim10-20$) Comptonizing corona, or a relativistically blurred ionized reflection spectrum from the inner regions of the accretion disk. While these two scenarios cannot be distinguished based on their fit statistics, we argue that the parameters required by the warm corona model are physically incompatible with the conditions of standard coronae. Detailed photoionization calculations show that even in the most favorable conditions, the warm corona should produce strong absorption in the observed spectrum. On the other hand, while the relativistic reflection model provides a satisfactory description of the data, it also requires extreme parameters, such as maximum black hole spin, a very low and compact hot corona, and a very high density for the inner accretion disk. Deeper observations of this source are thus necessary to confirm the presence of relativistic reflection, and to further understand the nature of its soft excess.

astro-ph.HE↗

arXiv2017

Probing the structure of the gas in the Milky Way through X-ray high resolution spectroscopy

We have developed a new X-ray absorption model, called {\tt IONeq}, which computes the optical depth $τ(E)$ simultaneously for ions of all abundant elements, assuming ionization equilibrium and taking into account turbulent broadening. We use this model to analyze the interstellar medium (ISM) absorption features in the Milky Way for a sample of 18 galactic (LMXBs) and 42 extragalactic sources (mainly Blazars). The absorbing ISM was modeled as a combination of three components/phases - neutral ($T\lesssim1\times10^{4}$ K), warm ($T\sim5\times 10^{4}$ K) and hot ($T\sim2\times10^{6}$ K). We found that the spatial distribution of both, neutral and warm components, are difficult to describe using smooth profiles due to nonuniform distribution of the column densities over the sky. For the hot phase we used a combination of a flattened disk and a halo, finding comparable column densities for both spatial components, in the order of $\sim 6-7\times10^{18}\;{\rm cm^{-2}}$, although this conclusion depends on the adopted parametrization. If the halo component has sub-solar abundance $Z$, then the column density has be scaled up by a factor $\frac{Z_\odot}{Z}$. The vertically integrated column densities of the disk components suggests the following mass fractions for these three ISM phases in the Galactic disk: neutral $\sim~89\%$, warm $\sim 8\%$ and hot $\sim 3\%$ components, respectively. The constraints on the radial distribution of the halo component of the hot component are weak.

astro-ph.HE↗