arXiv subjects

Hong-Bo Zhang

Publications and source records attributed to Hong-Bo Zhang.

7 recordsLinked to original sources

arXiv2026

Probing Coronal Activity Using Radio Signals Based on the 2021 superior conjunction of Mars: the Downlink Data from Tianwen-1

During the first superior conjunction of the Tianwen-1 Mars probe in October 2021, its downlink signal received by the Wuqing 70-m radio telescope passed within 4.53 solar radii of the Sun. The signal was significantly perturbed by the solar wind, providing a mechanism to probe coronal activity. We analyze the Doppler frequency scintillation spectrum of the solar wind within 10 solar radii to derive a characteristic frequency scintillation parameter. Statistical analysis indicates this parameter increases as the signal path approaches the Sun, with notable anomalies observed on October 5, 13, and 15. Comparisons with SOHO and SDO data reveal strong spatio-temporal correlations between these scintillation anomalies and coronal activity. We demonstrate that this parameter effectively identifies solar phenomena, including coronal streamers, high-speed solar wind, and coronal mass ejections (CMEs). Quantitative analysis confirms a distinct temporal correlation and delay between frequency scintillation and solar wind speed changes, validating the feasibility of spatially localizing solar activity.

astro-ph.SR↗

arXiv2012

IPS Observation System for Miyun 50m Radio Telescope and Its Acceptance Observation

Ground-based observation of Interplanetary Scintillation(IPS) is an important approach of monitoring solar wind. A ground-based IPS observation system is newly implemented on 50m radio telescope, Miyun station, National Astronomical Observatories, Chinese Academy of Sciences(NAOC). This observation system is constructed for purpose of observing the solar wind speed and scintillation index by using the normalized cross-spectrum of simultaneous dual-frequency IPS measurement. The system consists of a universal dual-frequency front-end and a dual-channel multi-function back-end specially designed for IPS. After careful calibration and testing, IPS observations on source 3C273B and 3C279 are successfully carried out. The preliminary observation results show that this newly developed observation system is capable of doing IPS observation.The system sensitivity for IPS observation can reach over 0.3Jy in terms of IPS polarization correlator with 4MHz bandwidth and 2s integration time.

astro-ph.IM↗

arXiv2011

Scalar graviton in the healthy extension of Hořava-Lifshitz theory

In this note we study the linear dynamics of scalar graviton in a de Sitter background in the infrared limit of the healthy extension of Hořava-Lifshitz gravity with the dynamical critical exponent $z=3$. Both our analytical and numerical results show that the non-zero Fourier modes of scalar graviton oscillate with an exponentially damping amplitude on the sub-horizon scale, while on the super-horizon scale, the phases are frozen and they approach to some asymptotic values. In addition, as the case of the non-zero modes on super-horizon scale, the zero mode also initially decays exponentially and then approaches to an asymptotic constant value.

hep-th↗

arXiv2010

Notes on Ghost Dark Energy

We study a phenomenological dark energy model which is rooted in the Veneziano ghost of QCD. In this dark energy model, the energy density of dark energy is proportional to Hubble parameter and the proportional coefficient is of the order $Λ^3_{QCD}$, where $Λ_{QCD}$ is the mass scale of QCD. The universe has a de Sitter phase at late time and begins to accelerate at redshift around $z_{acc}\sim0.6$. We also fit this model and give the constraints on model parameters, with current observational data including SnIa, BAO, CMB, BBN and Hubble parameter data. We find that the squared sound speed of the dark energy is negative, which may cause an instability. We also study the cosmological evolution of the dark energy with interaction with cold dark matter.

astro-ph.CO↗

arXiv2010

Acoustic signatures in the Cosmic Microwave Background bispectrum from primordial magnetic fields

Using the full radiation transfer function, we numerically calculate the CMB angular bispectrum seeded by the compensated magnetic scalar density mode. We find that, for the string inspired primordial magnetic fields characterized by index $n_B=-2.9$ and mean-field amplitude $B_{\lam}=9{\rm nG}$, the angular bispectrum is dominated by two primordial magnetic shapes. The first magnetic shape looks similar to the one from local-type primordial curvature perturbations, so both the amplitude and profile of the Komatsu-Spergel estimator (reduced bispectrum) seeded by this shape are almost the same as those of the primary CMB anisotropies. However, for different parameter sets ($l_1,l_2$), this "local-type" reduced bispectrum oscillates around different asymptotic values in the high-$l_3$ regime because of the effect of the Lorentz force, which is exerted by the primordial magnetic fields on the charged baryons. This feature is different from the standard case where all modes approach to zero asymptotically in the high-$l$ limit. On the other hand, the second magnetic shape appears only in the primordial magnetic field model. The amplitude of the Komatsu-Spergel estimator sourced by the second shape diverges in the low-$l$ regime because of the negative slope of shape. In the high-$l$ regime, this amplitude is approximately equal to that of the first estimator, but with a reversal phase.

astro-ph.CO↗

arXiv2010

Probing the dynamical behavior of dark energy

We investigate dynamical behavior of the equation of state of dark energy $w_{de}$ by employing the linear-spline method in the region of low redshifts from observational data (SnIa, BAO, CMB and 12 $H(z)$ data). The redshift is binned and $w_{de}$ is approximated by a linear expansion of redshift in each bin. We leave the divided points of redshift bins as free parameters of the model, the best-fitted values of divided points will represent the turning positions of $w_{de}$ where $w_{de}$ changes its evolving direction significantly (if there exist such turnings in our considered region). These turning points are natural divided points of redshift bins, and $w_{de}$ between two nearby divided points can be well approximated by a linear expansion of redshift. We find two turning points of $w_{de}$ in $z\in(0,1.8)$ and one turning point in $z\in (0,0.9)$, and $w_{de}(z)$ could be oscillating around $w=-1$. Moreover, we find that there is a $2σ$ deviation of $w_{de}$ from -1 around $z=0.9$ in both correlated and uncorrelated estimates.

astro-ph.CO↗

arXiv2009

Dynamical Scalar Degree of Freedom in Horava-Lifshitz Gravity

We investigate the linear cosmological perturbations of Hořava-Lifshitz gravity in a FRW universe without any matter. Our results show that a new gauge invariant dynamical scalar mode emerges, due to the gauge transformation under the "foliation-preserving" diffeomorphism and "projectability condition", and it can produce a scale invariant power spectrum. In the infrared regime with $λ=1$, the dynamical scalar degree of freedom turns to be a non-dynamical one at the linear order level.

hep-th↗