Jun Yang

Chalmers University of Technology

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Z. Paragi

Joint Institute for VLBI ERIC

Tao An

Shanghai Astronomical Observatory

Leonid Gurvits

Joint Institute for VLBI ERIC

M. Giroletti

Istituto di Radioastronomia di Bologna

Xiaoyu Hong

Chinese Academy of Sciences

S. Frey

Konkoly Observatory

B. Marcote

Joint Institute for VLBI ERIC

Xiang Liu

Chinese Academy of Sciences

Xiaolong Yang

Shanghai Astronomical Observatory

P. Mohan

Shanghai Astronomical Observatory

Cooperative Institutions

Chinese Academy of Sciences

301

University of Chinese Academy of Sciences

159

Max Planck Society

139

Shanghai Astronomical Observatory

105

Netherlands Institute for Radio Astronomy

104

Max Planck Institute for Radio Astronomy

102

National Astronomical Observatories

100

National Institute for Astrophysics

Centre National de la Recherche Scientifique

Astronomy and Space

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Puzzling two-stage size evolution of an ultraluminous gamma-ray burst jet

Research Square (Research Square) (2024)

Tao An Jin-Jun Geng Yingkang Zhang Hao-Xuan Gao Fan Xu

Abstract Gamma-ray bursts (GRBs) are the most luminous stellar explosions in the Universe, in which relativistic jets are involved. GRB 221009A stands out as the brightest GRB ever observed, providing a unique opportunity to probe the properties of an ultrarelativistic jet. Here, we report our very long baseline interferometry (VLBI) observation on the extremely bright GRB 221009A from 5 to 26 days after the burst. An intriguing two-stage evolution of the source size of this GRB is revealed by combining this data with later VLBI data. The observed size initially increases slowly as ~ t obs 0.15 during the first month, but expands with a much faster rate as ~ t obs 2.21 at later times. This unprecedented two-stage size evolution cannot be explained by the existing theoretical models invoking a non-spreading top-hat jet or a conventional structured jet and thus challenges our current understanding of this GRB jet. The transition may suggest the beginning of rapid sideways expansion of a narrow jet as the relativistic jet decelerates enough or the emergence of a new emission component. Our findings unveil the complex jet dynamics of GRB 221009A, highlighting the necessity of direct measurements of the size and geometry of the emission region in studying low-redshift GRBs in the multi-wavelength era.

10.21203/rs.3.rs-4123241/v1

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Determining the Rational Completion Cable Forces Based on Influence Matrix Method United Minimum Bending Energy Method

Traffic and Transportation Studies (2010)

Jun Yang

There are many methods to determine a rational completion state. However, it is difficult to determine the optimal cable tension using just one method, besides, different methods must be adopted for different types of bridges. As a result, it is feasible to combine minimum bending energy with the influence matrix method. The basic approach is: the initial cable tension can be determined through the minimum bending energy method, then the cable tension is adjusted through influence matrix, whose constraint conditions are stresses of key sections and support reaction from the top of pier, at last, the optimal cable tension of the finished state is determined. This method is not only simple but also very clear, and it achieves a good effect in determining the rational completion state of this type of bridges.

Tension (geology)

Matrix (chemical analysis)

Energy method

10.1061/41123(383)136

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Citations (4)

The X-shaped Radio Galaxy J0725+5835 is Associated with an AGN Pair

The Astrophysical Journal (2022)

Xiaolong Yang Jialu Ji Ravi Joshi Jun Yang Tao An

Abstract X-shaped radio galaxies (XRGs) are those that exhibit two pairs of unaligned radio lobes (main radio lobes and wings). One of the promising models for the peculiar morphology is jet reorientation. To clarify this, we conducted a 5 GHz observation with the European VLBI Network (EVN) of XRG J0725+5835, which resembles the archetypal binary active galactic nuclei (AGNs) 0402+379 in radio morphology, but it is larger in angular size. In our observation, two milliarcsecond-scale radio components with nonthermal radio emission are detected. Each of them coincides with an optical counterpart with similar photometric redshift and (optical and infrared) magnitude, corresponding to dual active nuclei. Furthermore, with the improved Very Large Array (VLA) images, we find a bridge between the two radio cores and a jet bending in the region surrounding the companion galaxy. This further supports the interplay between the main and companion galaxies. In addition, we also report the discovery of an arcsecond-scale jet in the companion. Given the projected separation of ∼100 kpc between the main and companion galaxies, XRG J0725+5835 is likely associated with a dual jetted-AGN system. In both EVN and VLA observations, we find signatures that the jet is changing its direction, which is likely responsible for the X-shaped morphology. For the origin of jet reorientation, several scenarios are discussed.

Very-long-baseline interferometry

X-shaped radio galaxy

10.3847/1538-4357/ac71aa

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A centi-pc-scale compact radio core in the nearby galaxy M60

arXiv (Cornell University) (2023)

Xiaofeng Li Jun Yang Xiaopeng Cheng Mai Liao Xiaoyu Hong

M60, an elliptical galaxy located 16.5~Mpc away, has an active nucleus with a very low luminosity and an extremely low accretion rate. Its central supermassive black hole has a mass of $M_{\rm BH}\sim4.5\times10^{9}\, M_{\odot}$ and a Schwarzschild radii corresponding to $R_{\rm S}\sim5.4\,\mu\mathrm{as}$. To investigate the nature of its innermost radio nucleus, data from the Very Long Baseline Array (VLBA) at 4.4 and 7.6~GHz were reduced. The VLBA images reveal a compact component with total flux densities of $\sim$20~mJy at both frequencies, a size of $\leq$0.27~mas (99.7$\%$ confidence level), about 0.022~pc ($50\,R_{\rm S}$) at 7.6~GHz, and a brightness temperature of $\geq6\times10^{9}$~K. This suggests that the observed centi-parsec-scale compact core could be attributed to a nonthermal jet base or an advection-dominated accretion flow (ADAF) with nonthermal electrons. The extremely compact structure also supports the presence of an SMBH in the center. Our results indicate that M60 is a promising target for broad-band VLBI observations at millimeter wavelengths to probe ADAF scenarios and tightly constrain the potential photon ring (about 28\,$\mu$as) around its SMBH.

Very-long-baseline interferometry

10.48550/arxiv.2311.06126

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Intermediate-mass black holes: finding of episodic, large-scale, and powerful jet activity in a dwarf galaxy

Monthly Notices of the Royal Astronomical Society (2023)

Jun Yang Z. Paragi S. Frey Leonid Gurvits Mai Liao

ABSTRACT Dwarf galaxies are characterized by a very low luminosity and low mass. Because of significant accretion and ejection activity of massive black holes, some dwarf galaxies also host low-luminosity active galactic nuclei (AGNs). In a few dwarf AGNs, very long baseline interferometry (VLBI) observations have found faint non-thermal radio emission. SDSS J090613.77+561015.2 is a dwarf AGN owning an intermediate-mass black hole (IMBH) with a mass of $M_\mathrm{BH} = 3.6^{+5.9}_{-2.3}\times 10^5 \mathrm{ M}_{\odot }$ and showing a rarely seen two-component radio structure in its radio nucleus. To further probe their nature, i.e. the IMBH jet activity, we performed additional deep observations with the European VLBI Network (EVN) at 1.66 and 4.99 GHz. We find the more diffuse emission regions and structure details. These new EVN imaging results allow us to reveal a two-sided jet morphology with a size up to about 150 mas (projected length ∼140 pc) and a radio luminosity of about 3 × 1038 erg s−1. The peak feature has an optically thin radio spectrum and thus more likely represents a relatively young ejecta instead of a jet base. The EVN study on SDSS J090613.77+561015.2 demonstrates the existence of episodic, relatively large-scale, and powerful IMBH jet activity in dwarf AGNs. Moreover, we collected a small sample of VLBI-detected dwarf AGNs and investigated their connections with normal AGNs. We notice that these radio sources in the dwarf AGNs tend to have steep spectra and small linear sizes, and possibly represent ejecta from scaled-down episodic jet activity.

Very-long-baseline interferometry

10.1093/mnras/stad493

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Citations (15)

Very long baseline interferometry detection of the Galactic black hole binary candidate MAXI J1836−194

Monthly Notices of the Royal Astronomical Society Letters (2012)

Jun Yang Yonghua Xu Zhixuan Li Z. Paragi R. M. Campbell

Abstract The X-ray transient MAXI J1836—194 is a newly identified Galactic black hole binary candidate. As most X-ray transients, it was discovered at the beginning of an X-ray outburst. After the initial canonical X-ray hard state, the outburst evolved into a hard intermediate state and then went back to the hard state. The existing RATAN-600 radio monitoring observations revealed that it was variable on a time-scale of days and had a flat or inverted spectrum, consistent with optically thick synchrotron emission, possibly from a self-absorbed jet in the vicinity of the central compact object. We observed the transient in the hard state near the end of the X-ray outburst with the European very long baseline interferometry (VLBI) Network (EVN) at 5 GHz and the Chinese VLBI Network (CVN) at 2.3 and 8.3 GHz. The 8.3-GHz observations were carried out at a recording rate of 2048 Mbps using the newly developed Chinese VLBI data acquisition system, twice higher than the recording rate used in the other observations. We successfully detected the low-declination source with a high confidence level in both observations. The source was unresolved (≤0.5 mas), which is in agreement with an au-scale compact jet.

Very-long-baseline interferometry

Black hole (networking)

10.1111/j.1745-3933.2012.01327.x

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Citations (8)

A Composite Model for GHz Peaked Spectra of Radio Sources

Chinese Journal of Astronomy and Astrophysics (2005)

Jun Yang Xiang Liu Zhi-Qiang Shen

GHz-Peaked Spectrum (GPS) radio sources are powerful and compact sources with convex spectra. With increasing observational findings, it has been realized that either Synchrotron Self-Absorption (SSA) alone or Free-Free Absorption (FFA) alone is not enough to account for all the spectral features. We present a model consisting of an SSA region partially covered by FFA plasma, and derive a composite spectral formula. By applying the model to a sample of 19 GPS sources having strong absorption, it is found that the external FFA process makes the SSA peak frequency linearly shift to a higher (observed) peak frequency. The shift indicates that the FFA does play a role at the frequency close to the observed peak frequency.

10.1088/1009-9271/5/6/001

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Citations (2)

A repeating fast radio burst source in a globular cluster

Nature (2022)

Franz Kirsten B. Marcote Kenzie Nimmo J. W. T. Hessels Mohit Bhardwaj

Magnetar

10.1038/s41586-021-04354-w

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Citations (186)

LIGO/Virgo G275404: European VLBI Network (EVN) follow-up of the near-IR transient in the AGL J1914+1043 field

GRB Coordinates Network (2017)