40 research outputs found
The jet-disk symbiosis without maximal jets: 1-D hydrodynamical jets revisited
In this work we discuss the recent criticism by Zdziarski of the maximal jet
model derived in Falcke & Biermann (1995). We agree with Zdziarski that in
general a jet's internal energy is not bounded by its rest-mass energy density.
We describe the effects of the mistake on conclusions that have been made using
the maximal jet model and show when a maximal jet is an appropriate assumption.
The maximal jet model was used to derive a 1-D hydrodynamical model of jets in
agnjet, a model that does multiwavelength fitting of quiescent/hard state X-ray
binaries and low-luminosity active galactic nuclei. We correct algebraic
mistakes made in the derivation of the 1-D Euler equation and relax the maximal
jet assumption. We show that the corrections cause minor differences as long as
the jet has a small opening angle and a small terminal Lorentz factor. We find
that the major conclusion from the maximal jet model, the jet-disk symbiosis,
can be generally applied to astrophysical jets. We also show that isothermal
jets are required to match the flat radio spectra seen in low-luminosity X-ray
binaries and active galactic nuclei, in agreement with other works.Comment: 7 pages, accepted by A&
Multi-wavelength astronomical searches for primordial black holes
If primordial black holes of O(1–100) M_⊙ constitute a significant portion of the dark matter in the Universe, they should be very abundant in our Galaxy. We present here a detailed analysis of the radio and X-ray emission that these objects are expected to produce due to the accretion of gas from the interstellar medium. With respect to previous studies, we relax the assumption of a monochromatic mass function, and introduce an improved treatment of the physics of gas accretion onto isolated, moving compact objects, based on a set of state-of-the-art numerical simulations. By comparing our predictions with known radio and X-ray sources in the Galactic center region, we show that the maximum relic density of primordial black holes in the mass range of interest is ~ 10^(−3) smaller than that of dark matter. The new upper bound is two orders of magnitude stronger with respect to previous results, based on a conservative phenomenological treatment of the accretion physics. We also provide a comprehensive critical discussion on the reliability of this bound, and on possible future developments in the field. We argue in particular that future multi-wavelength searches will soon start to probe the galactic population of astrophysical black holes
Multi-wavelength astronomical searches for primordial black holes
If primordial black holes of constitute a
significant portion of the dark matter in the Universe, they should be very
abundant in our Galaxy. We present here a detailed analysis of the radio and
X-ray emission that these objects are expected to produce due to the accretion
of gas from the interstellar medium. With respect to previous studies, we relax
the assumption of a monochromatic mass function, and introduce an improved
treatment of the physics of gas accretion onto isolated, moving compact
objects, based on a set of state-of-the-art numerical simulations. By comparing
our predictions with known radio and X-ray sources in the Galactic center
region, we show that the maximum relic density of primordial black holes in the
mass range of interest is smaller than that of dark matter. The
new upper bound is two orders of magnitude stronger with respect to previous
results, based on a conservative phenomenological treatment of the accretion
physics. We also provide a comprehensive critical discussion on the reliability
of this bound, and on possible future developments in the field. We argue in
particular that future multi-wavelength searches will soon start to probe the
galactic population of astrophysical black holes.Comment: 21 pages, 6 figures. Prepared for submission to JCA
The Nature of Soft Excess in ESO 362-G18 Revealed by XMM-Newton and NuSTAR Spectroscopy
© 2021. The American Astronomical Society. All rights reserved. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.3847/1538-4357/abf430We present a detailed spectral analysis of the joint XMM-Newton and NuSTAR observations of the active galactic nuclei (AGN) in the Seyfert 1.5 Galaxy ESO 362-G18. The broadband (0.3\mbox{--}79 keV) spectrum shows the presence of a power-law continuum with a soft excess below keV, iron K emission ( keV), and a Compton hump (peaking at keV). We find that the soft excess can be modeled by two different possible scenarios: a warm ( keV) and optically thick () Comptonizing corona; or with relativistically-blurred reflection off a high-density () inner disk. These two models cannot be easily distinguished solely from their fit statistics. However, the low temperature ( keV) and the thick optical depth () of the hot corona required by the warm corona scenario are uncommon for AGNs. We also fit a 'hybrid' model, which includes both disk reflection and a warm corona. Unsurprisingly, as this is the most complex of the models considered, this provides the best fit, and more reasonable coronal parameters. In this case, the majority of the soft excess flux arises in the warm corona component. However, based on recent simulations of warm coronae, it is not clear whether such a structure can really exist at the low accretion rates relevant for ESO 362-G18 (). This may therefore argue in favor of a scenario in which the soft excess is instead dominated by the relativistic reflection. Based on this model, we find that the data would require a compact hot corona () around a highly spinning () black hole.Peer reviewe
Multi-wavelength astronomical searches for primordial black holes
If primordial black holes of O(1–100) M_⊙ constitute a significant portion of the dark matter in the Universe, they should be very abundant in our Galaxy. We present here a detailed analysis of the radio and X-ray emission that these objects are expected to produce due to the accretion of gas from the interstellar medium. With respect to previous studies, we relax the assumption of a monochromatic mass function, and introduce an improved treatment of the physics of gas accretion onto isolated, moving compact objects, based on a set of state-of-the-art numerical simulations. By comparing our predictions with known radio and X-ray sources in the Galactic center region, we show that the maximum relic density of primordial black holes in the mass range of interest is ~ 10^(−3) smaller than that of dark matter. The new upper bound is two orders of magnitude stronger with respect to previous results, based on a conservative phenomenological treatment of the accretion physics. We also provide a comprehensive critical discussion on the reliability of this bound, and on possible future developments in the field. We argue in particular that future multi-wavelength searches will soon start to probe the galactic population of astrophysical black holes
Evidence for Returning Disk Radiation in the Black Hole X-Ray Binary XTE J1550–564
We explore the accretion properties of the black hole X-ray binary XTE J1550−564 during its outbursts in 1998/99 and 2000. We model the disk, corona, and reflection components of X-ray spectra taken with the Rossi X-ray Timing Explorer, using the relxill suite of reflection models. The key result of our modeling is that the reflection spectrum in the very soft state is best explained by disk self-irradiation, i.e., photons from the inner disk are bent by the strong gravity of the black hole and reflected off the disk surface. This is the first known detection of thermal disk radiation reflecting off the inner disk. There is also an apparent absorption line at ~6.9 keV, which may be evidence of an ionized disk wind. The coronal electron temperature (kT_e) is, as expected, lower in the brighter outburst of 1998/99, explained qualitatively by more efficient coronal cooling due to irradiating disk photons. The disk inner radius is consistent with being within a few times the innermost stable circular orbit throughout the bright-hard-to-soft states (10 s of r_g in gravitational units). The disk inclination is low during the hard state, disagreeing with the binary inclination value, and very close to 90° in the soft state, recovering to a lower value when adopting a blackbody spectrum as the irradiating continuum
The Soft-Excess in Mrk 509: Warm Corona or Relativistic Reflection?
We present the analysis of the first NuSTAR observations ( ks),
simultaneous with the last SUZAKU observations ( ks), of the active
galactic nucleus of the bright Seyfert 1 galaxy Mrk 509. The time-averaged
spectrum in the keV X-ray band is dominated by a power-law continuum
(), a strong soft excess around 1 keV, and signatures of
X-ray reflection in the form of Fe K emission ( keV), an Fe K
absorption edge ( keV), and a Compton hump due to electron scattering
( keV). We show that these data can be described by two very
different prescriptions for the soft excess: a warm ( keV) and
optically thick () 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.Comment: Accepted for publication in ApJ, 18 pages, 7 figure