138 research outputs found
On the nature of the X-ray absorption in the Seyfert 2 galaxy NGC 4507
No full textWe present results of the ASCA observation of the Seyfert 2 galaxy NGC 4507. The 0.5-10 keV spectrum is rather complex and consists of several components: (i) a hard X-ray power law heavily absorbed by a column density of about 3 x 10(23) cm(-2), (ii) a narrow Fe K alpha line at 6.4 keV, () soft continuum emission well above the extrapolation of the absorbed hard power law and (iv) a narrow emission line at similar to 0.9 keV. The line energy, consistent with highly ionized neon (Ne IX), may indicate that the soft X-ray emission is derived from a combination of resonant scattering and fluorescence in a photoionized gas. Some contribution to the soft X-ray spectrum from thermal emission, as a blend of Fe L lines, by a starburst component in the host galaxy cannot be ruled out with the present data
X-ray emission from faint galaxies and quasars
No full textIn this thesis a study of faint X-ray sources is undertaken to understand the nature and origin of the Cosmic X-ray Background (XRB). A study of the X-ray variability characteristics of the QSO population is also presented. The optical identification of faint ROSAT sources is described. A large fraction of these sources are identified as QSOs. A number of the remaining sources appear to be associated with faint galaxies with a range of morphological types. The discovery of a rare, high redshift obscured QSO is also described and discussed. A method is developed to study the X-ray variability of faint QSOs. Low amplitude variability (~ 25% rms) on timescales of hours to days appears to be characteristic. Contrary to the trends apparent in local AGN, the QSO population show no evidence for a decrease in variability amplitude with luminosity. There is also no trend in variability with redshift, which may favour a short lived model for QSO evolution. A bright, highly variable Seyfert galaxy is analysed in detail. To constrain the galaxy contribution to the XRB a cross-correlation analysis is presented. Cross-correlating faint galaxy catalogues with unidentified X-ray sources suggests that faint b(_i) < 23 galaxies account for ~ 21 ± 6% of all X-ray sources to a flux limit S(0.5 - 2.0 keV) ~ 4 x l0(^-15)ergs(^-1)cm(^-2). Galaxies are then cross-correlated with the remaining unresolved XRB. A highly significant signal is obtained on 3 deep ROSAT fields. Using a formalism to model the galaxy population and its clustering, an estimate of the local X-ray volume emissivity is obtained. The results suggest that b(_j) < 23 galaxies contribute ~ 20% of the unresolved XRB. Comparing the cross-correlation of faint and bright galaxies with theoretical models reveals strong evolution in the X-ray luminosity of galaxies with the form L(_x) oc (1 + z)(^3±1). Extrapolation to high redshift suggests that faint galaxies contribute 50 - 100% of the unresolved XRB. Finally, a study of the X-ray spectra of faint ROSAT sources is presented. The mean source spectra harden significantly at lower flux. Separating the QSOs from the unidentified sources and galaxies, we find no trend in the 0.5 - 2 keV spectra of QSOs. The remaining population produces the spectral hardening. Taking a subset of the most probable X-ray luminous galaxies, these show significantly harder spectra than QSOs with a mean photon index of Γ ~ 1.5 ± 0.1. X-ray luminous galaxies could therefore account for the missing component of the XRB
Suzaku observation of the Phoenix galaxy
No full textContext. In recent years, several Seyfert 2 galaxies have beendiscovered that change state when observed in X-rays a few years apart,switching from Compton-thin to reflection-dominated or viceversa.Aims. We observed a member of this class of "Changing-look" sources,the Phoenix galaxy, with Suzaku, with the aim of better understandingthe nature of the variations.Methods. The Suzaku spectrum was analyzed, and the results comparedwith previous ASCA and XMM-Newton observations.Results. The source was caught in a Compton-thin state, as inXMM-Newton, but differently from ASCA. Comparing the Suzaku andXMM-Newton observations, a variation in the column density of theabsorber on a time scale of years is discovered. A similar change, buton much shorter time scales (i.e. ks) may also explain the count-ratevariations during the Suzaku observations. A soft excess is alsopresent, likely due to continuum and line emission from photoionizedcircumnuclear matter
A search for broad infrared recombination lines in NGC 1068
No full textWe report infrared spectroscopy of the prototypical Seyfert 2 galaxy NGC 1068, aiming at detection of broad components of hydrogen recombination lines that originate in the obscured broad-line region. Using the Short Wavelength Spectrometer on board the Infrared Space Observatory, we have observed for the first time the regions of B beta 2.626 mu m and Pf alpha 7.460 mu m, and present improved data for B alpha 4.052 mu m No significant broad components are detected, implying an equivalent visual extinction to the broad-line region of at least 50 mag and an obscuring column density of at least 10(23) cm(-2). While consistent with a highly obscured broad-line region, as required by the classical unified scenario, these limits are not yet significant enough to discriminate strongly between different torus models or to constrain properties of the gas causing the very large X-ray obscuration. We discuss the systematic limitations of infrared broad-line region searches and suggest that B alpha may often be the most favorable transition for future searches
X-ray observations of the broad line radio galaxy 3C382 - Variability, an iron line and soft X-ray emission
No full textWetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Hitomi (ASTRO-H) X-ray Astronomy Satellite
No full textThe Hitomi (ASTRO-H) mission is the sixth Japanese x-ray astronomy satellite developed by a large international collaboration, including Japan, USA, Canada, and Europe. The mission aimed to provide the highest energy resolution ever achieved at E > 2 keV, using a microcalorimeter instrument, and to cover a wide energy range spanning four decades in energy from soft x-rays to gamma rays. After a successful launch on February 17, 2016, the spacecraft lost its function on March 26, 2016, but the commissioning phase for about a month provided valuable information on the onboard instruments and the spacecraft system, including astrophysical results obtained from first light observations. The paper describes the Hitomi (ASTRO-H) mission, its capabilities, the initial operation, and the instruments/spacecraft performances confirmed during the commissioning operations for about a month
The ASTRO-H mission
No full textThe joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the high-energy universe by performing high-resolution, high-throughput spectroscopy with moderate angular resolution. ASTRO-H covers very wide energy range from 0.3 keV to 600 keV. ASTRO-H allows a combination of wide band X-ray spectroscopy (5-80 keV) provided by multilayer coating, focusing hard X-ray mirrors and hard X-ray imaging detectors, and high energy-resolution soft X-ray spectroscopy (0.3-12 keV) provided by thin-foil X-ray optics and a micro-calorimeter array. The mission will also carry an X-ray CCD camera as a focal plane detector for a soft X-ray telescope (0.4-12 keV) and a non-focusing soft gamma-ray detector (40-600 keV) . The micro-calorimeter system is developed by an international collaboration led by ISAS/JAXA and NASA. The simultaneous broad bandpass, coupled with high spectral resolution of ΔE ~7 eV provided by the micro-calorimeter will enable a wide variety of important science themes to be pursued
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