Search

Fast transitions between different types of power density spectra (PDS) happening over time-scales of several tens of seconds are rare phenomena in black hole X-ray binaries. In this paper, we report a broad-band spectral-timing analysis of the fast transitions observed in the 2021 outburst of GX 339−4 using NICER and Insight-HXMT observations. We observe transitions between band-limited noise-dominated PDS and type-B quasi-periodic oscillations (QPOs), and their rapid appearance or disappearance. We also make a detailed comparison between the fast transitions in GX 339−4 with those seen in MAXI J1820+070 and MAXI J1348−630. By comparing the spectra of the periods with and without type-B QPOs, we find that the spectral ratios above 10 keV are nearly constant or slightly decreasing, and the values are different between sources. Below 10 keV, the flux change of the Comptonization component is inversely proportional to the flux change of the thermal component, suggesting that the appearance of type-B QPOs is associated with a redistribution of the accretion power between the disc and the Comptonizing emission region. The spectral ratios between the periods with type-B QPO and those with broad-band noise are significantly different from that with type-B QPO and without type-B QPO, where the ratios (type-B QPO/broad-band noise) show a maximum at around 4 keV and then decrease gradually towards high energies. Finally, we discuss the possible change of the geometry of the inner accretion flow and/or jet during the transitions.

Here we present a detailed study of the broadband noise in the power density spectra of the black hole X-ray binary MAXI J1820+070 during the hard state of its 2018 outburst, using Hard X-ray Modulation Telescope observations. The broadband noise shows two main humps, which might separately correspond to variability from a variable disk and two Comptonization regions. We fitted the two humps with multiple Lorentzian functions and studied the energy-dependent properties of each component up to 90–150 keV and their evolution with spectral changes. The lowest-frequency component is considered as the subharmonic of the quasiperiodic oscillation component and shows a different energy dependence compared with other broadband noise components. We found that although the fractional rms of all the broadband noise components mainly decreases with the energy, their rms spectra are different in shape. Above ∼20–30 keV, the characteristic frequencies of these components increase sharply with the energy, meaning that the high-energy component is more variable on short timescales. Our results suggest that the hot inner flow in MAXI J1820+070 is likely to be inhomogeneous. We propose a geometry with a truncated accretion disk and two Comptonization regions.

We report the results of a multiyear spectroscopic and photometric monitoring campaign of two luminous quasars, PG 0923+201 and PG 1001+291, both located at the high-luminosity end of the broad-line region (BLR) size-luminosity relation with optical luminosities above 1045 erg s-1. PG 0923+201 is monitored for the first time, while PG 1001+291 was previously monitored but our campaign has a much longer temporal baseline. We detect time lags of variations of the broad Hβ, Hγ, and Fe ii lines with respect to those of the 5100 Å continuum. The velocity-resolved delay map of Hβ in PG 0923+201 indicates a complicated structure with a mix of Keplerian disk-like motion and outflow, and the map of Hβ in PG 1001+291 shows a signature of Keplerian disk-like motion. Assuming a virial factor of f BLR = 1 and FWHM line widths, we measure the black hole mass to be for PG 0923+201 and for PG 1001+291. Their respective accretion rates are estimated to be and, indicating that PG 0923+201 is a sub-Eddington accretor and PG 1001+291 is a super-Eddington accretor. While the Hβ time lag of PG 0923+201 agrees with the size-luminosity relation, the time lag of PG 1001+291 shows a significant deviation, confirming that in high-luminosity active galactic nuclei (AGNs), the BLR size depends on both luminosity and Eddington ratio. Black hole mass estimates from single-AGN spectra will be overestimated at high luminosities and redshifts if this effect is not taken into account. © 2021. The American Astronomical Society. All rights reserved., This work is supported by the National Key R&D Program of China (2016YFA0400701, 2016YFA0400702), by the National Science Foundation of China (NSFC-11721303, 11773029, 11833008, 11873048, 11922304, 11973029, 11991051, 11991052, 11991053, 11991054, 12003036, 12022301), by the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences (CAS; YZDJ-SSW-SLH007), by the CAS Key Research Program (KJZDEW-M06), by the CAS International Partnership Program (113111KYSB20200014), and by the Strategic Priority Research Program of the CAS (XDB23000000, XDB23010400). We acknowledge the support of the staff of the Lijiang 2.4 m telescope. Funding for the telescope has been provided by the CAS and the People's Government of Yunnan Province. We also acknowledge the support of the staff of the CAHA 2.2 m telescope. Y.-R.L. acknowledges financial support from the Youth Innovation Promotion Association CAS. K.H. acknowledges support from STFC grant ST/R000824/1. Based on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, Lawrence Livermore National Laboratory, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, and Institut national de physique nucleaire et de physique des particules. Operations are conducted by COO, IPAC, and University of Washington. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration., With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.

Here we report the spectral-timing results of the black hole X-ray binary 4U 1630–47 during its 2021 outburst using observations from the Hard X-ray Modulation Telescope (Insight-HXMT). Type C quasi-periodic oscillations (QPOs) in ∼1.6–4.2 Hz and quasi-regular modulation (QRM) near 60 mHz are detected during the outburst. The mHz QRM has a fractional rms of ∼10%–16% in the 8–35 keV energy band with a Q factor (frequency/width) of ∼2–4. Benefiting from the broad energy band of Insight-HXMT, we study the energy dependence of the ∼60 mHz QRM in 1–100 keV for the first time. We find that the fractional rms of the mHz QRM increases with photon energy, while the time lags of the mHz QRM are soft and decrease with photon energy. Fast recurrence of the mHz QRM, in a timescale of less than 1 hr, has been observed during the outburst. During this period, the corresponding energy spectra moderately change when the source transitions from the QRM state to the non-QRM state. The QRM phenomenon also shows a dependence with the accretion rate. We suggest that the QRM could be caused by an unknown accretion instability aroused from the corona.

In this paper, we report the new results of spectroscopic observations of $\gamma$-ray blazar S5 0716+714 from 2019 September to 2020 March with the 2.4 m optical telescope at Lijiang Observatory of Yunnan Observatories. The median cadence of observations is $\sim$ 1 day. During the second observation period (Epoch2), the observational data reveal an extremely bright state and a bluer-when-brighter (BWB) chromatism. The BWB trend of Epoch2 differs significantly from that of the first observation period (Epoch1). A significantly brightness-dependent BWB chromatism emerges in the total data of Epoch1 and Epoch2. The BWB trend becomes weaker towards the brighter states, and likely becomes saturated at the highest state. Based on a log-parabolic function, a power-law of synchrotron peak flux and frequency $\nu_{\rm{p}}$, and a power-law of the curvature of synchrotron spectrum and its $\nu_{\rm{p}}$, simulation well reproduces the brightness-dependent BWB trend of S5 0716+714. The BWB trend is seemingly controlled by the shift of $\nu_{\rm{p}}$ with respect to the observational window, and effectively may be dominated by the variations of electron average energy and magnetic field in emitting region., Comment: 16 pages, 5 figures, Accepted for publication in ApJ

The changes of broad emission lines should be a crucial issue to understanding the physical properties of changing-look active galactic nucleus (CL-AGN). Here, we present the results of an intensive and homogeneous 6-month long reverberation mapping (RM) monitoring campaign during a low-activity state of the CL-AGN Seyfert galaxy NGC 3516. Photometric and spectroscopic monitoring was carried out during 2018--2019 with the Lijiang 2.4 m telescope. The sampling is 2 days in most nights, and the average sampling is $\sim$3 days. The rest frame time lags of H$\alpha$ and H$\beta$ are $\tau_{\rm{H}\alpha}=7.56^{+4.42}_{-2.10}$ days and $\tau_{\rm{H}\beta}=7.50^{+2.05}_{-0.77}$ days, respectively. From a RMS H$\beta$ line dispersion of $\sigma_{\rm{line}} = 1713.3 \pm 46.7$ $\rm{km}$ $\rm{s^{-1}}$ and a virial factor of $f_{\sigma}$ = 5.5, the central black hole mass of NGC 3516 is estimated to be $M_{\rm{BH}}= 2.4^{+0.7}_{-0.3} \times 10^{7} M_{\odot}$, which is in agreement with previous estimates. The velocity-resolved delays show that the time lags increase towards negative velocity for both H$\alpha$ and H$\beta$. The velocity-resolved RM of H$\alpha$ is done for the first time. These RM results are consistent with other observations before the spectral type change, indicating a basically constant BLR structure during the changing-look process. The CL model of changes of accretion rate seems to be favored by long-term H$\beta$ variability and RM observations of NGC 3516., Comment: 25 pages, 6 figures, Accepted for publication in ApJ

NGC 2617 has attracted a lot of attention after the detection of the changes in spectral type, and its geometry and kinematics of broad-line region (BLR) are still ambiguous. In this paper, we present the high cadence ($\sim$ 2 days) reverberation mapping campaign of NGC 2617 from 2019 October to 2020 May undertaken at Lijiang 2.4 m telescope. For the first time, the velocity-resolved reverberation signature of the object was successfully detected. Both H$\alpha$ and H$\beta$ show an asymmetrical profile with a peak in the velocity-resolved time lags. For each of both lines, the lag of the line core is longer than those of the relevant wings, and the peak of the velocity-resolved lags is slightly blueshifted. These characteristics are not consistent with the theoretical prediction of the inflow, outflow or Keplerian disk model. Our observations give the time lags ofH$\alpha$, H$\beta$, H$\gamma$, and He I, with a ratio of $\tau_{\rm{H}\alpha}$:$\tau_{\rm{H}\beta}$:$\tau_{\rm{H}\gamma}$:$\tau_{\rm{He~I}}$ = 1.27:1.00:0.89:0.20, which indicates a stratified structure in the BLR of the object. It is the first time that the lags of H$\alpha$ and He I are obtained. Assuming a virial factor of $f$ = 5.5 for dispersion width of line, the masses of black hole derived from H$\alpha$ and H$\beta$ are $\rm{23.8^{+5.4}_{-2.7}}$ and $\rm{21.1^{+3.8}_{-4.4}} \times 10^{6}M_{\odot}$, respectively. Our observed results indicate the complexity of the BLR of NGC 2617., Comment: 19 pages, 5 figures, Accepted for publication in ApJ

Authors: Hu, Chen; Li, Sha-Sha; Guo, Wei-Jian; Yang, Sen; Yang, Zi-Xu; Bao, Dong-Wei; Jiang, Bo-Wei; Du, Pu; Li, Yan-Rong; Xiao, Ming; Songsheng, Yu-Yang; Yu, Zhe; Bai, Jin-Ming; Ho, Luis C.; Bian, Wei-Hao; Brotherton, Michael S.; Yuan, Ye-Fei; Aceituno, Jesús; Winkler, Hartmut; Wang, Jian-Min; SEAMBH Collaboration, We report on the results of a new spectroscopic monitoring campaign of the quasar PG 0026+129 at the Calar Alto Observatory 2.2 m telescope from 2017 July to 2020 February. Significant variations in the fluxes of the continuum and broad emission lines, including Hβ and He ii, were observed in the first and third years, and clear time lags between them are measured. The broad Hβ line profile consists of two Gaussian components: an intermediate-width H with an FWHM of 1964 ± 18 and another very broad H with an FWHM of 7570 ± 83 . H has long time lags of ∼40-60 days in the rest frame, while H shows nearly zero time delay with respect to the optical continuum at 5100 Å. The velocity-resolved delays show consistent results: lags of ∼30-50 days at the core of the broad Hβ line and roughly zero lags at the wings. H has a redshift of ∼400 , which seems to be stable for nearly 30 yr by comparing with archived spectra, and may originate from an infall. The rms spectrum of H shows a double-peaked profile with brighter blue peak and extended red wing in the first year, which matches the signature of a thin disk. Both the double-peaked profile and the near-zero lag suggest that H comes from a region associated with the part of the accretion disk that emits the optical continuum. Adopting the FWHM (in the rms spectrum) and the time lag measured for the total Hβ line, and a virial factor of 1.5, we obtain a virial mass of for the central black hole in this quasar. © 2020. The American Astronomical Society. All rights reserved.., We acknowledge the support of the staff of the CAHA 2.2 m telescope. This work is based on observations collected at the Centro Astronomico Hispanoen Andalucia (CAHA) at Calar Alto, operated jointly by the Andalusian Universities and the Instituto de Astrofisica de Andalucia (CSIC). This research is supported by the National Key R&D Program of China (2016YFA0400701, 2016YFA0400702), by the National Science Foundation of China (11721303, 11773029, 11833008, 11873048, 11922304, 11973029, 11991051, 11991052, 11991054, 12003036, 12022301), by the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences (CAS; QYZDJ-SSW-SLH007), by the CAS Key Research Program (KJZDEW-M06), and by the Strategic Priority Research Program of the CAS (XDB23000000, XDB23010400). J.A. acknowledges financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofisica de Andalucia (SEV-2017-0709).