Galaxies

13 pages, 361 KiB

Open AccessArticle

Superluminal Motion and Jet Parameters in the Gamma-ray-Emitting Narrow-Line Seyfert 1 Galaxy TXS 1206+549

by Bettina Kozák, Sándor Frey and Krisztina Éva Gabányi

Galaxies 2024, 12(1), 8; https://doi.org/10.3390/galaxies12010008 - 17 Feb 2024

Cited by 1 | Viewed by 2116

Narrow-line Seyfert 1 (NLS1) galaxies are a peculiar subclass of active galactic nuclei (AGN). Among them, TXS 1206+549 belongs to a small group of radio-loud and

γ

-ray-emitting NLS1 galaxies. We focus on the radio properties of this galaxy by analysing archival, high-resolution, [...] Read more.

Narrow-line Seyfert 1 (NLS1) galaxies are a peculiar subclass of active galactic nuclei (AGN). Among them, TXS 1206+549 belongs to a small group of radio-loud and

γ

-ray-emitting NLS1 galaxies. We focus on the radio properties of this galaxy by analysing archival, high-resolution, very long baseline interferometry (VLBI) imaging observations taken at 8 GHz frequency in six epochs between 1994 and 2018. Using the milliarcsecond-scale radio structure, we can resolve a core and a jet component whose angular separation increases by

(0.055 \pm 0.006)

mas yr⁻¹. This corresponds to an apparent superluminal jet component motion of

(3.5 \pm 0.4) c

. From the core brightness temperature and the jet component proper motion, we determine the characteristic Doppler-boosting factor, the bulk Lorentz factor, and the jet viewing angle. We find no compelling evidence for a very closely aligned blazar-type jet. The parameters for TXS 1206+549 resemble those of radio-loud quasar jets with a moderate Lorentz factor (

Γ \approx 4

) and

ϑ \approx 24^{\circ}

inclination to the line of sight. Full article

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43 pages, 2383 KiB

Open AccessReview

Spin Evolution of Neutron Stars

by Pavel Abolmasov, Anton Biryukov and Sergei B. Popov

Galaxies 2024, 12(1), 7; https://doi.org/10.3390/galaxies12010007 - 10 Feb 2024

Cited by 8 | Viewed by 2028

Abstract

In this paper we review the basics of magneto-rotational properties of neutron stars focusing on spin-up/spin-down behavior at different evolutionary stages. The main goal is to provide equations for the spin frequency changes in various regimes (radio pulsar, propeller, accretor, etc.). Since presently [...] Read more.

In this paper we review the basics of magneto-rotational properties of neutron stars focusing on spin-up/spin-down behavior at different evolutionary stages. The main goal is to provide equations for the spin frequency changes in various regimes (radio pulsar, propeller, accretor, etc.). Since presently the spin behavior of neutron stars at all stages remains a subject of many uncertainties, we review different suggestions made over the years in the literature. Full article

(This article belongs to the Special Issue The 10th Anniversary of Galaxies: The Astrophysics of Neutron Stars)

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27 pages, 2182 KiB

Open AccessReview

X-ray Polarization from Magnetar Sources

by Roberto Taverna and Roberto Turolla

Galaxies 2024, 12(1), 6; https://doi.org/10.3390/galaxies12010006 - 10 Feb 2024

Cited by 5 | Viewed by 1860

Abstract

The launch of the IXPE telescope in late 2021 finally made polarization measurements in the 2–

8 keV

band a reality, more than 40 years after the pioneering observations of the OSO-8 satellite. In the first two years of operations, IXPE targeted more [...] Read more.

The launch of the IXPE telescope in late 2021 finally made polarization measurements in the 2–

8 keV

band a reality, more than 40 years after the pioneering observations of the OSO-8 satellite. In the first two years of operations, IXPE targeted more than 60 sources, including four magnetars, neutron stars with magnetic fields in the petaGauss range. In this paper we summarize the IXPE main findings and discuss their implications for the physics of ultra-magnetized neutron stars. Polarimetric observations confirmed theoretical predictions, according to which X-ray radiation from magnetar sources is highly polarized, up to ≈

80 %

, the highest value detected so far. This provides an independent confirmation that magnetars are indeed endowed with a super-strong magnetic field and that the twisted magnetosphere scenario is the most likely explanation for their soft X-ray emission. Polarization measurements allowed us to probe the physical conditions of the star’s outermost layers, showing that the cooler surface regions are in a condensed state, with no atmosphere on top. Although no smoking-gun of vacuum QED effects was found, the phase-dependent behavior of the polarization angle strongly hints that vacuum birefringence is indeed at work in magnetar magnetospheres. Full article

(This article belongs to the Special Issue The 10th Anniversary of Galaxies: The Astrophysics of Neutron Stars)

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16 pages, 1217 KiB

Open AccessArticle

Parameter Inference of a State-of-the-Art Physical Afterglow Model for GRB 190114C

by Enrico Rinaldi, Nissim Fraija and Maria Giovanna Dainotti

Galaxies 2024, 12(1), 5; https://doi.org/10.3390/galaxies12010005 - 7 Feb 2024

Cited by 1 | Viewed by 1499

Abstract

A state-of-the-art semi-analytic gamma-ray burst (GRB) afterglow model with synchrotron self-Compton (SSC) emission has been applied for the first time for parameter inference using real GRB data. We analyzed the famous GRB 190114C as a case study. GRB 190114C, characterized by its long [...] Read more.

A state-of-the-art semi-analytic gamma-ray burst (GRB) afterglow model with synchrotron self-Compton (SSC) emission has been applied for the first time for parameter inference using real GRB data. We analyzed the famous GRB 190114C as a case study. GRB 190114C, characterized by its long duration and high luminosity, was observed by many ground-based and orbiting telescopes spanning a wide range of electromagnetic wavelengths, from radio to GeV gamma rays. We used two advanced algorithms for inference: a nested sampling algorithm called UltraNest and an MCMC algorithm emcee. Evoking the standard afterglow model, the inference result and the best-fit values lead to an initial bulk Lorentz factor (a rough estimate of

Γ = 526

), which aligns with the values often seen in GRBs identified by the Fermi-LAT instrument. Similarly to the best-fit values of other studies in the literature, the derived values of microphysical parameters, the circumburst density, and the kinetic efficiency are consistent with those found after modeling the multi-wavelength observations in GRB 190114C. We show that the SSC from the forward-shock region can only describe the highest-energy photons above a few GeVs. Full article

(This article belongs to the Special Issue Gamma-Ray Bursts in Multiwavelength: Theory, Observational Correlations and GRB Cosmology)

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34 pages, 3834 KiB

Open AccessArticle

The Scavenger Hunt for Quasar Samples to Be Used as Cosmological Tools

by Maria Giovanna Dainotti, Giada Bargiacchi, Aleksander Łukasz Lenart and Salvatore Capozziello

Galaxies 2024, 12(1), 4; https://doi.org/10.3390/galaxies12010004 - 23 Jan 2024

Cited by 4 | Viewed by 1600

Abstract

Although the

Λ

Cold Dark Matter model is the most accredited cosmological model, information at high redshifts (z) between type Ia supernovae (

z = 2.26

) and the Cosmic Microwave Background (

z = 1100

) is crucial to validate [...] Read more.

Although the

Λ

Cold Dark Matter model is the most accredited cosmological model, information at high redshifts (z) between type Ia supernovae (

z = 2.26

) and the Cosmic Microwave Background (

z = 1100

) is crucial to validate this model further. To this end, we have discovered a sample of 1132 quasars up to

z = 7.54

exhibiting a reduced intrinsic dispersion of the relation between ultraviolet and X-ray fluxes,

δ_{F} = 0.22

vs.

δ_{F} = 0.29

(

24 %

less), than the original sample. This gold sample, once we correct the luminosities for selection biases and redshift evolution, enables us to determine the matter density parameter

Ω_{M}

with a precision of 0.09. Unprecedentedly, this quasar sample is the only one that, as a standalone cosmological probe, yields such tight constraints on

Ω_{M}

while being drawn from the same parent population of the initial sample. Full article

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5 pages, 3685 KiB

Open AccessEditorial

The Revised Third Cambridge Catalogue at 60: To Jet or Not to Jet …

by Peter Barthel and Paolo Padovani

Galaxies 2024, 12(1), 3; https://doi.org/10.3390/galaxies12010003 - 11 Jan 2024

Viewed by 1633

Abstract

The Revised Third Cambridge Catalogue of Radio Sources (in the northern sky), or 3CR, published sixty years ago by Bennett (1962) [...] Full article

(This article belongs to the Special Issue The Symbiosis between Radio Source and Galaxy Evolution)

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13 pages, 480 KiB

Open AccessArticle

A Lepton–Hadron Model for the Multi-Wavelength Emission from Extreme High-Frequency Peaked BL Lacertae 1ES 1218+304

by Wenjing Dong, Qian Dong and Yonggang Zheng

Galaxies 2024, 12(1), 2; https://doi.org/10.3390/galaxies12010002 - 29 Dec 2023

Cited by 1 | Viewed by 1691

Abstract

We develop a lepton–hadron model for the possible origin of hard very high energy (VHE) spectra from a distant blazar. The model includes synchrotron self-Compton (SSC) and hadronic components. The lepton components include synchrotron radiation and inverse Compton scattering of relativistic electrons. For [...] Read more.

We develop a lepton–hadron model for the possible origin of hard very high energy (VHE) spectra from a distant blazar. The model includes synchrotron self-Compton (SSC) and hadronic components. The lepton components include synchrotron radiation and inverse Compton scattering of relativistic electrons. For the hadronic components, we consider proton synchrotron radiation and investigate the interaction of protons with the synchrotron emission soft photons or cosmic microwave background (CMB) photons. Upon adopting the parametrization of the observed spectrum of 1ES 1218+304, we obtain the following results: (1) the model is able to match the spectral energy distribution of 1ES 1218+304; (2) we find that in

E_{p} \approx 10^{10} \sim 10^{17} eV

, the

π^{0} \to γ

-ray process contributes the majority of the secondary photons; and (3) the interaction of protons with the low-energy photons may occur in or outside the jet. Full article

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29 pages, 27073 KiB

Open AccessArticle

Formation of Transitional cE/UCD Galaxies through Massive/Dwarf Disc Galaxy Mergers

by Alexander V. Khoperskov, Sergey S. Khrapov and Danila S. Sirotin

Galaxies 2024, 12(1), 1; https://doi.org/10.3390/galaxies12010001 - 25 Dec 2023

Cited by 1 | Viewed by 1635

Abstract

The dynamics of the merger of a dwarf disc galaxy with a massive spiral galaxy of the Milky Way type were studied in detail. The remnant of such interaction after numerous crossings of the satellite through the disc of the main galaxy was [...] Read more.

The dynamics of the merger of a dwarf disc galaxy with a massive spiral galaxy of the Milky Way type were studied in detail. The remnant of such interaction after numerous crossings of the satellite through the disc of the main galaxy was a compact stellar core, the characteristics of which were close to small compact elliptical galaxies (cEs) or large ultra-compact dwarfs (UCDs). Such transitional cE/UCD objects with an effective radius of 100–200 pc arise as a result of stripping the outer layers of the stellar core during the destruction of a dwarf disc galaxy. Numerical models of the satellite before interaction included baryonic matter (stars and gas) and dark mass. We used N-body to describe the dynamics of stars and dark matter, and we used smoothed-particle hydrodynamics to model the gas components of both galaxies. The direct method of calculating the gravitational force between all particles provided a qualitative resolution of spatial structures up to 10 pc. The dwarf galaxy fell onto the gas and stellar discs of the main galaxy almost along a radial trajectory with a large eccentricity. This ensured that the dwarf crossed the disc of the main galaxy at each pericentric approach over a time interval of more than 9 billion years. We varied the gas mass and the initial orbital characteristics of the satellite over a wide range, studying the features of mass loss in the core. The presence of the initial gas component in a dwarf galaxy significantly affects the nature of the formation and evolution of the compact stellar core. The gas-rich satellite gives birth to a more compact elliptical galaxy compared to the merging gas-free dwarf galaxy. The initial gas content in the satellite also affects the internal rotation in the stripped nucleus. The simulated cE/UCD galaxies contained very little gas and dark matter at the end of their evolution. Full article

(This article belongs to the Special Issue Galactic Structure and Dynamics)

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Galaxies, Volume 12, Issue 1 (February 2024) – 8 articles

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