arXiv subjects

Guohai Chen

Publications and source records attributed to Guohai Chen.

3 recordsLinked to original sources

arXiv2026

Changing-look Active Galactic Nuclei from SDSS, LAMOST and DESI Surveys

Results. We identify 45 CLAGNs, of which 40 are newly reported. The sample is dominated by turn-off events, comprising 43 turn-off and 2 turn-on sources. This may be because Type 2 AGNs either lack a detectable broad-line region or have their broad emission lines obscured by circumnuclear dust, making turn-on events more difficult to identify. Using DESI spectra as a third spectroscopic epoch, we identified 12 RCLAGNs. Of the 14 newly identified CLAGNs with three-epoch spectroscopic coverage, 7 objects, i.e. 50%, are confirmed as RCLAGNs. In the previously reported sample, 5 out of 16 objects with available DESI spectra, corresponding to ~31%, exhibit repeating CL behaviour. The relatively high incidence of repeated CL behaviour suggests that CL transitions are associated with recurrent physical processes, such as accretion-rate fluctuations or accretion-disk instabilities. In the logM_BH--log(L_bol/L_Edd) plane, the RCLAGNs display a clear high--low--high accretion-state evolution, indicating a close connection between repeated CL behaviour and recurrent variations in accretion power. The rest-frame upper limits on the transition timescales are ~10 yr for the first transition and 4 yr for the second transition.

astro-ph.GA↗

arXiv2025

Ultrahigh-Energy Gamma-ray Emission Associated with Black Hole-Jet Systems

Black holes (BH), one of the most intriguing objects in the universe, can manifest themselves through electromagnetic radiation initiated by the accretion flow. Some stellar-mass BHs drive relativistic jets when accreting matter from their companion stars, forming microquasars. Non-thermal emission from the radio to tera-electronvolt (TeV) gamma-ray band has been observed from microquasars, indicating the acceleration of relativistic particles. Here we report detection of four microquasars (SS 433, V4641 Sgr, GRS 1915+105, MAXI J1820+070) of spectrum extending to the ultrahigh-energy (UHE; photon energy $E>100$ TeV) band and one microquasar (Cygnus X-1) of spectrum approaching 100 TeV, using the Large High Altitude Air Shower Observatory (LHAASO). Notably, the total emission associated with SS 433 cannot be interpreted with a single leptonic component. In the UHE band, its emission is in spatial coincidence with a giant atomic cloud, which is consistent with a hadronic origin. An elongated source is discovered from V4641 Sgr with the spectrum continuing up to 800 TeV. The detection of UHE gamma rays demonstrates that accreting BHs and their environments can operate as extremely efficient accelerators of particles out of 1 peta-electronvolt (PeV), suggesting microquasars to be important contributors to Galactic cosmic rays especially around the `knee' region.

astro-ph.HE↗

arXiv2022

An extensive study of blazar broad emission line: Changing-look blazars and Baldwin effect

It is known that the blazar jet emissions are dominated by non-thermal radiation while the accretion disk jets are normally dominated by thermal emission. In this work, our aim is to study the connection between the two types of emission by investigating the correlation between the blazar emission line intensity property, which embodies the nature of accretion disk, and the $γ$-ray flux property, which is the representative of jet emission. We compiled a sample of 656 blazars with available emission line equivalent widths ($EW$), the GeV $γ$-ray flux, and the SED information from the literature. In this work, we found 55 previous BCUs are now identified as FSRQs, and found 52 Changing-look blazars based on their $EW$ and 45 of them are newly confirmed. These Changing-look blazars have a larger accretion ratio (${\dot M}/{\dot M}_{\rm Edd}$) than BL Lac objects. In addition, we suggest that the lower synchrotron peak blazars (LSPs) could be the source of Changing-look blazars because 90.7\% of the Changing-look blazars in this work are confirmed as LSPs. An anti-correlation between $EW$ and continuum intensity, the so-called global Baldwin effect (BEff) has been confirmed. We suggest the steeper global BEff observed for blazar than for radio-quiet active galactic nuclei (RQ-AGNs) is caused by the inverse Compton scattering of broad-emission-line photons. This interpretation is further supported by the positive correlation between the emission line $EW$ and intrinsic inverse Compton luminosity.

astro-ph.HE↗