We study the influence of parameter
α
on the optical features of Schwarzschild-MOG black holes with different thin accretions in scalar-tensor-vector gravity. As
α
increases from 0, the radii of the ...event horizon, photon sphere, and observed shadow increase in comparison with the Schwarzschild black hole. We constrain the parameter
α
with the experimental data reported by the Event Horizon Telescope Collaboration for M87
∗
and Sagittarius A
∗
. In the situation of spherical accretions, we unveil that the parameter
α
has a positive effect on the shadow size but a negative effect on the observed specific intensities. Considering that the Schwarzschild-MOG black hole is surrounded by an optical and geometrically thin accretion disk, we find that the total observed specific intensities are mainly contributed by the direct emissions, while the photon rings and lensed rings provide small contributions. It is also found that with the increase of
α
, the black hole shadow expands, the photon rings and lensed rings become larger and thicker. Besides, we emphasize that the boundary of the observed shadow cast by the aim black hole in the disk accretion scenario is determined by the direct emissions rather than the photon ring emissions. Consequently, we unveil that there is a linear relationship involving the critical impact parameter and the starting point of the direct emissions. This finding helps to use the experimental results of the Event Horizon Telescope to infer the critical impact parameter and to test General Relativity.
Using atomistic simulations, we characterize the adsorption process of organic molecules on carbon nanoparticles, both of which have been reported to be abundant in the interstellar medium (ISM). The ...aromatic organics are found to adsorb more readily than the aliphatic ones. This selectivity would favor the formation of polycyclic aromatic hydrocarbons (PAHs) or fullerene-like structures in the ISM due to a structural similarity. In our simulations, we also observed that the molecules form a monolayer over the nanoparticle surface before stacking up in aggregates. This suggests a possible layer-by-layer formation process of onion-like nanostructures in the ISM. These findings reveal the possible role of carbon nanoparticles as selective catalysts that could provide reaction substrates for the formation of interstellar PAHs, high fullerenes, and soots from gas-phase molecules.
The present paper contains the investigations with respect to the optical appearance, redshift distribution, and observed energy flux of the thin accretion disk described by the Novikov-Thorne model ...in modified gravity (MOG) proposed by Moffat. The results show that the gravity coupling parameter
α
plays an indispensable role in the size of direct and secondary images of the accretion disk, while the image profile is mainly affected by the observational angles. In addition, an increase of the parameter
α
leads to that of the redshift factor, but a decrease in the radiation energy flux of the accretion disk. These results are due to the enhancement of the parameter
α
that strengthens the black hole’s gravitational effects. By comparing the accretion disk images of the Schwarzschild-MOG black hole, the Schwarzschild black hole, and the Reissner–Nordström black hole, we point out that the Schwarzschild-MOG black hole exhibits the largest inner shadow and the lowest luminosity. This finding provides a potential way to distinguish Schwarzschild-MOG black holes from their counterparts in General Relativity.
Without imposing any theoretical models and assumptions, we present a multivariable regression analysis to several observable quantities for a sample of 15 gamma-ray bursts (GRBs). The observables ...used in the analysis include the isotropic gamma-ray energy (E sub(g,iso)), the peak energy of the vF sub(v) spectrum in the rest frame (E'p), and the rest-frame break time of the optical afterglow light curves (t'b). A strong dependence of E sub(g,iso) on E'p and t'b is derived, which reads E sub(g,iso)/10 super(52) ergs = (0.85 c 0.21)(E'p /100 keV) super(1.94c0.17)(t'b/1 day) super(-1.24c0.23) in a flat universe with sub(M) = 0.28 and H sub(0) = 71.3 km s super(-1) Mpc super(-1). We also extend the analysis to the isotropic afterglow energies in the X-ray and optical bands, respectively, and find that they are essentially not correlated with E'p and t'b. Regarding the E sub(g,iso) (E' sub(p), t' sub(b)) relationship as a luminosity indicator, we explore the possible constraints on the cosmological parameters using the GRB sample. Since there is no low-redshift GRB sample to calibrate this relationship, we weight the probability of using the relationship in each cosmology to serve as a standard candle by x super(2) statistics and then use this cosmology-weighted standard candle to evaluate cosmological parameters. Our results indicate that 0.05 < sub(M) < 0.50 at the 1 s level, with the most probable value of sub(M)being 0.28. The best value of sub( )is 0.64, but it is less constrained. Only a loose limit of sub( )< 1.2 is obtained at the 1 s level. In the case of a flat universe, the 1 s constraints are 0.13 < sub(M) < 0.49 and 0.50 < sub( )< 0.85, respectively. The deceleration factor (q) and its cosmological evolution (dq/dz) are also investigated with an evolutionary form of q = q sub(0) + z dq/dz. The best-fit values are (q sub(0),dq/dz) = (-1.00, 1.12), with -2.23 < sub(q0) < 0.26 and -0.07 < dq/dz < 3.48 at the 1 s level. The inferred transition redshift between the deceleration and acceleration phases is 0.78 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(3) sub(2) super(2) sub(3) (1 s). Through Monte Carlo simulations, we find that the GRB sample satisfying our relationship observationally tends to be a soft and bright one and that the constraints on the cosmological parameters can be much improved either by enlarging the sample size or by increasing the observational precision. Although the sample may not expand significantly in the Swift era, a significant increase of the sample is expected in the long-term future. Our simulations indicate that with a sample of 50 GRBs satisfying our multivariable standard candle, one can achieve a constraint to the cosmological parameters comparable to that derived from 157 Type la supernovae. Furthermore, the detections of a few high-redshift GRBs satisfying the correlation could greatly tighten the constraints. Identifying high-z GRBs and measuring their E'p and t'b are therefore essential for the GRB cosmology in the Swift era.
Abstract
In order to study the initial conditions of massive star formation, we have previously built a sample of 463 high-mass starless clumps (HMSCs) across the inner Galactic plane covered by ...multiple continuum surveys. Here, we use
13
CO(2–1) line data from the SEDIGISM survey, which covers 78° in longitude (−60° <
l
< 18°, ∣
b
∣ < 0.°5) with 30″ resolution, to investigate the global dynamical state of these parsec-scale HMSCs (207 sources with good-quality data, mass 10
2
–10
5
M
⊙
, size 0.1–3.6 pc). We find that most HMSCs are highly turbulent with a median Mach number
∼
8.2
, and 44%–55% of them are gravitationally bound (with virial parameter
α
vir
≲ 2) if no magnetic fields are present. A median magnetic field strength of 0.33–0.37 mG would be needed to support these bound clumps against collapse, in agreement with previous observations of magnetic fields in regions of massive star formation. Luminosity-to-mass ratio, an important tracer of evolutionary stage, is strongly correlated with dust temperature. Magnetic field strength is also correlated with density. The Larson line width–size scaling does not hold in HMSCs. This study advances our understanding of the global properties of HMSCs, and our high-resolution observations with the Atacama Large Millimeter/submillimeter Array are in progress to study the resolved properties.
Abstract We observed the nearby radio pulsar B0950+08, which has a 100% duty cycle, using the Five-hundred-meter Aperture Spherical Radio Telescope. We obtained the polarization profile for its ...entire rotation, which enabled us to investigate its magnetospheric radiation geometry and the sparking pattern of the polar cap. After we excluded part of the profile in which the linear polarization factor is low (≲30%) and potentially contaminated by jumps in position angle, the rest of the swing in polarization position angle fits a classical rotating vector model (RVM) well. The best-fit RVM indicates that the inclination angle, α , and the impact angle, β , of this pulsar, are 100.°5 and −33.°2, respectively, suggesting that the radio emission comes from two poles. We find that, in such RVM geometry, either the annular vacuum gap model or the core vacuum gap model would require that the radio emissions come from a high-altitude magnetosphere with heights from ∼0.25 R LC to ∼0.56 R LC , with R LC being the light cylinder radius. Both the main and interpulses’ sparking points are located away from the magnetic pole, which could relate to the physical conditions on the pulsar surface.
Abstract Recently, a lack of supernova-associated with long-duration gamma-ray burst (GRB 230307A) at such a low redshift z = 0.065, but associated with a possible kilonova emission, has attracted ...great attention. Its heavy element nucleosynthesis and the characteristic of soft X-ray emission suggest that the central engine of GRB 230307A is a magnetar that is originated from a binary compact star merger. The calculated lower value of ε ∼ 0.05 suggests that GRB 230307A seems to have an ambiguous progenitor. The lower value of f eff = 1.23 implies that GRB 230307A is not likely to be from the effect of “tip of iceberg.” We adopt the magnetar central engine model to fit the observed soft X-ray emission with varying efficiency and find that the parameter constraints of the magnetar falls into a reasonable range, i.e., B < 9.4 × 10 15 G and P < 2.5 ms for Γ sat = 10 3 , and B < 3.6 × 10 15 G and P < 1.05 ms for Γ sat = 10 4 . Whether the progenitor of GBR 230307A is from the mergers of neutron star–white dwarf (NS–WD) or neutron star–neutron star (NS–NS) remains unknown. The difference of GW radiation between NS–NS merger and NS–WD merger may be a probe to distinguish the progenitor of GRB 230307A-like events in the future.
Swift BAT has detected similar to 200 long-duration GRBs, with redshift measurements for similar to 50 of them. We derive the luminosity function ( Phi super(HL)) and the local event rate ( rho ...super(H) sub(0) super(L)) of the conventional high-luminosity (HL) GRBs by using the z-known Swift GRBs. Our results are generally consistent with that derived from the CGRO BATSE data. However, the fact that Swift detected a low-luminosity (LL) GRB, GRB 060218, at z = 0.033 within similar to 2 years of operation, together with the previous detection of the nearby GRB 980425, suggests a much higher local rate for these LL-GRBs. We explore the possibility that LL-GRBs are a distinct GRB population from the HL-GRBs. We find that rho super(L) sub(0) super(L) is similar to 325 super(+) sub(-) super(3) sub(1) super(5) sub(7) super(2) sub(7) Gpc super(-3) yr super(-1), which is much higher than rho super(H) sub(0) super(L) (1.12 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(4) sub(2) super(3) sub(0) Gpc super(-3) yr super(-1)). This rate is similar to 0.7% of the local Type Ib/c SNe. Our results, together with the finding that less than 10% of Type Ib/c SNe are associated with off-beam GRBs, suggest that LL-GRBs have a beaming factor typically less than 14, or a jet angle typically wider than 31 degree . The high local GRB rate, small beaming factor, and low-luminosity make the LL-GRBs distinct from the HL-GRBs. Although the current data could not fully rule out the possibility that both HL- and LL-GRBs are the same population, our results suggest that LL-GRBs are likely a unique GRB population and that the observed low-redshift GRB sample is dominated by the LL-GRBs.
The observed radio-optical-X-ray spectral energy distributions (SEDs) of 22 hot spots and 45 knots in the jets of 35 active galactic nuclei are complied from the literature and modeled with ...single-zone lepton models. It is found that the observed luminosities at 5 GHz (L{sub 5{sub GHz}}) and at 1 keV (L{sub 1{sub keV}}) are tightly correlated, and the two kinds of sources can be roughly separated with a division of L{sub 1{sub keV}} = L{sub 5{sub GHz}}. Our SED fits show that the mechanisms of the X-rays are diverse. While the X-ray emission of a small fraction of the sources is a simple extrapolation of the synchrotron radiation for the radio-to-optical emission, an inverse Compton (IC) scattering component is necessary to model the X-rays for most of the sources. Considering the sources at rest (the Doppler factor delta = 1), the synchrotron-self-Compton (SSC) scattering would dominate the IC process. This model can interpret the X-rays of some hot spots with a magnetic field strength (B {sup delta}{sup =1}{sub ssc}) being consistent with the equipartition magnetic field (B {sup delta}{sup =1}{sub eq}) in 1 order of magnitude, but an unreasonably low B {sup delta}{sup =1}{sub ssc} is required to model the X-rays for all knots. Measuring the deviation between B {sup delta}{sup =1}{sub ssc} and B {sup delta}{sup =1}{sub eq} with ratio R{sub B} {identical_to} B {sup delta}{sup =1}{sub eq}/B {sup delta}{sup =1}{sub ssc}, we find that R{sub B} is greater than 1 and it is tightly anti-correlated with ratio R{sub L} {identical_to} L{sub 1{sub keV}}/L{sub 5{sub GHz}} for both the knots and the hot spots. We propose that the deviation may be due to the neglect of the relativistic bulk motion for these sources. Considering this effect, the IC/cosmic microwave background (CMB) component would dominate the IC process. We show that the IC/CMB model well explains the X-ray emission for most sources under the equipartition condition. Although the derived beaming factor (delta) and co-moving equipartition magnetic field (B'{sub eq}) of some hot spots are comparable to the knots, the delta values of the hot spots tend to be smaller and their B'{sub eq} values tend to be larger than that of the knots, favoring the idea that the hot spots are jet termination and knots are a part of a well-collimated jet. Both B{sub eq}{sup '} and delta are tentatively correlated with R{sub L} . Corrected by the beaming effect, the L'{sub 5{sub GHz}}-L'{sub 1{sub keV}} relations for the two kinds of sources are even tighter than the observed ones. These facts suggest that, under the equipartition condition, the observational differences of the X-rays from the knots and hot spots may be mainly due to the differences on the Doppler boosting effect and the co-moving magnetic field of the two kinds of sources. Our IC scattering models predict a prominent GeV-TeV component in the SEDs for some sources, which are detectable with H.E.S.S. and Fermi/LAT.
Many force–gradient explicit symplectic integration algorithms have been designed for the Hamiltonian H=T(p)+V(q) with kinetic energy T(p)=p2/2 in the existing references. When a force–gradient ...operator is appropriately adjusted as a new operator, it is still suitable for a class of Hamiltonian problems H=K(p,q)+V(q) with integrable part K(p,q)=∑i=1n∑j=1naijpipj+∑i=1nbipi, where aij=aij(q) and bi=bi(q) are functions of coordinates q. The newly adjusted operator is not a force–gradient operator but is similar to the momentum-version operator associated to the potential V. The newly extended (or adjusted) algorithms are no longer solvers of the original Hamiltonian, but are solvers of slightly modified Hamiltonians. They are explicit symplectic integrators with symmetry or time reversibility. Numerical tests show that the standard symplectic integrators without the new operator are generally poorer than the corresponding extended methods with the new operator in computational accuracies and efficiencies. The optimized methods have better accuracies than the corresponding non-optimized counterparts. Among the tested symplectic methods, the two extended optimized seven-stage fourth-order methods of Omelyan, Mryglod and Folk exhibit the best numerical performance. As a result, one of the two optimized algorithms is used to study the orbital dynamical features of a modified Hénon–Heiles system and a spring pendulum. These extended integrators allow for integrations in Hamiltonian problems, such as the spiral structure in self-consistent models of rotating galaxies and the spiral arms in galaxies.
PDF
