分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yibo Wang
Ning Jiang
Tinggui Wang
Jiazheng zhu
LiMing Dou
Zheyu Lin
LuMing Sun
Hui Liu
Zhenfeng Sheng
摘要： We hereby report the discovery of ATLAS17jrp as an extraordinary TDE in star-forming galaxy SDSSJ162034.99+240726.5 in our recent sample of mid-infrared outbursts in nearby galaxies. Its optical/UV light curves rise to a peak luminosity $\sim1.06\times10^{44}\rm\,erg\,s^{-1}$ in about a month and then decay as $\rm t^{-5/3}$ with a roughly constant temperature around 19000~K, and the optical spectra show a blue continuum and very broad Balmer lines with FWHM$\sim$15000 km/s which gradually narrowed to 1400 km/s within 4 years, all agreeing well with other optical TDEs. A delayed and rapidly rising X-ray flare with a peak luminosity $\rm \sim 1.27\times10^{43}\,erg\,s^{-1}$ was detected at $\rm \sim$ 170 days after the optical peak. The high MIR luminosity of ATLAS17jrp ($\sim2\times10^{43} \rm\,erg\,s^{-1}$) has revealed a distinctive dusty environment with covering factor as high as $\sim0.2$, that is comparable with that of torus in active galactic nuclei but at least one order of magnitude higher than normal optical TDEs. Therefore, ATLAS17jrp turns out to be one of the rare unambiguous TDE found in star-forming galaxies and its high dust covering factor implies that the dust extinction could play an important role in the absence of optical TDEs in star-forming galaxies.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ruqiu Lin
Zhen-Ya Zheng
Weida Hu
Chunyan Jiang
Xiang Pang
Chenwei Yang
Fang-Ting Yuan
Rahna P. T.
Jian-Guo Wang
Yibo Wang
Ning Jiang
Shuairu Zhu
摘要： Emission-line galaxies (ELGs) are crucial in understanding the formation and evolution of galaxies, while little is known about their variability. Here we report the study on the optical variability of a sample of ELGs selected in the COSMOS field, which has narrow-band observations in two epochs separated by $\gtrsim$ 12 years. This sample was observed with Suprime-Cam (SC) and Hyper Suprime-Cam (HSC) on the $Subaru$ telescope in NB816 and $i'/i$ bands, respectively. After carefully removing the wing effect of a narrow-band filter, we check the optical variability in a sample of 181 spectroscopically confirmed ELGs. We find that 0 (0/68) Ha emitters, 11.9% (5/42) [OIII] emitters, and 0 (0/71) [OII] emitters show significant variability ($|\Delta m_{NB}| \geq 3\,\sigma_{\Delta m_{NB,AGN}} = 0.20\, mag$) in the two-epoch narrow-band observations. We investigate the presence of active galactic nucleus (AGN) in this variable ELG (var-ELG) sample with three methods, including X-ray luminosity, mid-infrared activity, and radio-excess. We find zero bright AGN in this var-ELG sample, but cannot rule out the contribution from faint AGN. We find that SNe could also dominate the variability of the var-ELG sample. The merger morphology shown in the HST/F814W images of all the var-ELG sample is in agreement with the enhancement of star formation, i.e., the SNe activity.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The high-cadence survey of Zwicky Transient Facility (ZTF) has completely dominated the discovery of tidal disruption events (TDEs) in the past few years and resulted in the largest sample of TDEs with optical/UV light curves well-sampled around their peaks, providing us an excellent opportunity to construct a peak luminosity function (LF) of tidal disruption flares (TDFs). The new construction is necessary particularly considering that the most updated LF reported in literature has been inferred from only 13 sources from 5 different surveys. Here we present the optical and blackbody LFs calculated by 33 TDFs discovered in the ZTF-I survey. The optical LF can be described by both a power-law profile $dN/dL_g\propto L_g^{-2.3\pm0.2}$, and a Schechter-like function. The blackbody LF can be described by a power-law profile $dN/dL_{\rm bb}\propto L_{\rm bb}^{-2.2\pm0.2}$, shallower than the LF made of previous van Velzen (2018) sample. A possible low-luminosity turnover in the optical LF supports an Eddington-limited emission scenario. The drop of volumetric rate at high luminosity suggests a rate suppression due to direct captures of the black hole. The total volumetric rate is one order of magnitude lower than the previous estimation, which is probably not simply caused by the high fraction post-peak sources (7/13) in the previous sample. Instead, the normalization step during the previous LF construction to reconcile various surveys might adversely amplify the influence of serendipitous discoveries. Therefore, TDFs selected from ongoing and upcoming uniform surveys like ZTF, Vera Rubin Observatory (VRO) and Wide-Field Survey Telescope (WFST) should yield more accurate LFs.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Optical time-domain survey has been the dominant means of hunting for rare tidal disruption events (TDEs) in the past decade and remarkably advanced the TDE study. Particularly, the Zwicky Transient Facility (ZTF) has opened the era of population studies and the upcoming Large Synoptic Survey Telescope (LSST) at the Vera Rubin Observatory (VRO) is believed to further revolutionize the field soon. Here we present the prospects of finding TDEs with another powerful survey to be performed by 2.5-metre Wide-Field Survey Telescope (WFST). The WFST, located in western China, will be the most advanced facility dedicated to optical time-domain surveys in the northern hemisphere once commissioning. We choose to assess its TDE detectability on the basis of mock observations, which is hitherto closest to reality by taking into consideration of site conditions, telescope parameters, survey strategy and transient searching pipeline. Our mock observations on 440 deg$^2$ field (CosmoDC2 catalogue) show that $29\pm6$ TDEs can be robustly found per year if observed at $u, g, r, i$ bands with 30-second exposure every 10 days, in which a discovery is defined as $\geq$10 epochal detections in at least two filters. If the WFST survey is fully optimized for discovering TDE, we would expect to identify $392\pm74$ of TDEs every year, with the redshift up to $z\sim0.8$, which poses a huge challenge to follow-up resources.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： GSN 069 is an ultra-soft X-ray active galactic nucleus that previously exhibited a huge X-ray outburst and a subsequent long-term decay. It has recently presented X-ray quasi-periodic eruptions (QPEs). We report the detection of strong nitrogen lines but weak or undetectable carbon lines in its far ultraviolet spectrum. With a detailed photoionization model, we use the C IV/N IV] ratio and other ratios between nitrogen lines to constrain the [C/N] abundance of GSN 069 to be from -3.33 to -1.91. We argue that a partially disrupted red giant star can naturally explain the abnormal C/N abundance in the UV spectrum, while the surviving core orbiting the black hole might produce the QPEs.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Xiang Pan
Hongyan Zhou
Chenwei Yang
Luming Sun
Paul S. Smith
Tuo Ji
Ning Jiang
Peng Jiang
Wenjuan Liu
Honglin Lu
Xiheng Shi
Xuejie Dai
Shaohua Zhang
摘要： We present new spectrophotometric and spectropolarimetric observations of Mrk 1239, one of the 8 prototypes that defines type-1 narrow-line Seyfert galaxies (NLS1s). Unlike the other typical NLS1s though, a high degree of polarization ($P\sim$5.6%) and red optical-IR ($g-W_4$ = 12.35) colors suggest that Mrk 1239 is more similar to type-2 active galactic nuclei like NGC 1068. Detailed analysis of spectral energy distribution in the UV-optical-IR yields two components from the nucleus: a direct and transmitted component that is heavily obscured ($E_{B-V} \approx 1.6$), and another indirect and scattered one with mild extinction ($E_{B-V} \sim$ 0.5). Such a two-light-paths scenario is also found in previous reports based on the X-ray data. Comparison of emission lines and the detection of He\,{\footnotesize I}*$\lambda$10830 BAL at [-3000,-1000] km s$^{-1}$ indicates that the obscuring clouds are at physical scale between the sublimation radius and that of the narrow emission line regions. The potential existence of powerful outflows is found as both the obscurer and scatterer are outflowing. Similar to many other type-2s, jet-like structure in the radio band is found in Mrk 1239, perpendicular to the polarization angle, suggesting polar scattering. We argue that Mrk 1239 is very probably a type-2 counterpart of NLS1s. The identification of 1 out of 8 prototype NLS1s as a type-2 counterpart implies that there can be a substantial amount of analogs of Mrk 1239 misidentified as type-1s in the optical band. Properties of these misidentified objects are going to be explored in our future works.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ruqiu Lin
Zhen-Ya Zheng
Weida Hu
Chunyan Jiang
Xiang Pang
Chenwei Yang
Fang-Ting Yuan
Rahna P. T.
Jian-Guo Wang
Yibo Wang
Ning Jiang
Shuairu Zhu
摘要： Emission-line galaxies (ELGs) are crucial in understanding the formation and evolution of galaxies, while little is known about their variability. Here we report the study on the optical variability of a sample of ELGs selected in the COSMOS field, which has narrow-band observations in two epochs separated by $\gtrsim$ 12 years. This sample was observed with Suprime-Cam (SC) and Hyper Suprime-Cam (HSC) on the $Subaru$ telescope in NB816 and $i'/i$ bands, respectively. After carefully removing the wing effect of a narrow-band filter, we check the optical variability in a sample of 181 spectroscopically confirmed ELGs. We find that 0 (0/68) Ha emitters, 11.9% (5/42) [OIII] emitters, and 0 (0/71) [OII] emitters show significant variability ($|\Delta m_{NB}| \geq 3\,\sigma_{\Delta m_{NB,AGN}} = 0.20\, mag$) in the two-epoch narrow-band observations. We investigate the presence of active galactic nucleus (AGN) in this variable ELG (var-ELG) sample with three methods, including X-ray luminosity, mid-infrared activity, and radio-excess. We find zero bright AGN in this var-ELG sample, but cannot rule out the contribution from faint AGN. We find that SNe could also dominate the variability of the var-ELG sample. The merger morphology shown in the HST/F814W images of all the var-ELG sample is in agreement with the enhancement of star formation, i.e., the SNe activity.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Liming Dou
Ning Jiang
Tinggui Wang
Xinwen Shu
Huan Yang
Zhen Pan
Jiazheng Zhu
Tao An
Zhen-Ya Zheng
Yanli Ai
摘要： Recently we discovered an unprecedented supermassive black hole binary (SMBHB) candidate in the nearby Seyfert galaxy SDSS J1430+2303, which is predicted to merge within three years. X-ray spectroscopy may bring unique kinematic evidence for the last inspiraling stage, when the binary is too close to allow each of them to hold an individual broad line region. We try to confirm the unique SMBHB merger event and understand the associated high-energy processes from a comprehensive X-ray view. We observed SDSS J1430+2303 with XMM-Newton, NuSTAR, Chandra, and Swift spanning the first ~200 days since its discovery. X-ray variability, up to a factor of 7, has been detected on a timescale of a few days. The broadband spectrum from 0.2-70 keV can be well fitted with a model consisting of a power law and a relativistic reflection covered by a warm absorber. The properties of the warm absorber changed dramatically, for example, with a decrease in the line-of-sight velocity from ~0.2c to ~0.02c, between the two XMM-Newton observations separated by only 19 days, which can be naturally understood in the context of the SMBHB; although, the clumpy wind scenario cannot be completely excluded. Broad Fe Kalpha emission has been robustly detected, though its velocity shift or profile change is not yet measurable. Further longer X-ray observations are highly encouraged to detect the expected orbital motion of the binary.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present the discovery of a sample of 18 low-redshift (z5) in the epoch I (2017-2019) observations of Very Large Array Sky Survey (VLASS). All the 18 galaxies have been detected in the epoch II VLASS observations in 2020-2021, for which the radio flux is found to evolve slowly (by a factor of ~40%) over a period of about three years. 15 galaxies have been observed in the Rapid ASKAP Continuum Survey, and a flat or inverted spectral slope between 888 MHz and 3 GHz is found. Based on the Sloan Digital Sky Survey spectra taken before the radio brightening, 14 out of 18 can be classified to be LINERs or normal galaxies with weak or no nuclear activity. Most galaxies are red and massive, with more than half having central black hole masses above 10^8Msun. We find that only one galaxy in our sample displays optical flare lasting for at least two months, and a long decay in the infrared light curve that can be explained as the dust-heated echo emission of central optical flare, such as a stellar tidal disruption event. We discuss several possibilities for the transient radio emission and conclude that it is likely associated with a new-born radio jet triggered by short sporadic fueling of supermassive black hole. Such a scenario can be tested with further multi-frequency radio observations of these sources through measuring their radio flux variability and spectral evolution.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The high-cadence survey of Zwicky Transient Facility (ZTF) has completely dominated the discovery of tidal disruption events (TDEs) in the past few years and resulted in the largest sample of TDEs with optical/UV light curves well-sampled around their peaks, providing us an excellent opportunity to construct a peak luminosity function (LF) of tidal disruption flares (TDFs). The new construction is necessary particularly considering that the most updated LF reported in literature has been inferred from only 13 sources from 5 different surveys. Here we present the optical and blackbody LFs calculated by 33 TDFs discovered in the ZTF-I survey. The optical LF can be described by both a power-law profile $dN/dL_g\propto L_g^{-2.3\pm0.2}$, and a Schechter-like function. The blackbody LF can be described by a power-law profile $dN/dL_{\rm bb}\propto L_{\rm bb}^{-2.2\pm0.2}$, shallower than the LF made of previous van Velzen (2018) sample. A possible low-luminosity turnover in the optical LF supports an Eddington-limited emission scenario. The drop of volumetric rate at high luminosity suggests a rate suppression due to direct captures of the black hole. The total volumetric rate is one order of magnitude lower than the previous estimation, which is probably not simply caused by the high fraction post-peak sources (7/13) in the previous sample. Instead, the normalization step during the previous LF construction to reconcile various surveys might adversely amplify the influence of serendipitous discoveries. Therefore, TDFs selected from ongoing and upcoming uniform surveys like ZTF, Vera Rubin Observatory (VRO) and Wide-Field Survey Telescope (WFST) should yield more accurate LFs.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Lei Yang
Xinwen Shu
Fabao Zhang
Yogesh Chandola
Daizhong Liu
Yi Liu
Minfeng Gu
Margherita Giustini
Ning Jiang
Ya-Ping Li
Di Li
David Elbaz
Stephanie Juneau
Maurilio Pannella
Luming Sun
Ningyu Tang
Tinggui Wang
Hongyan Zhou
摘要： RX J1301.9+2747 is a unique active galaxy with supersoft X-ray spectrum that lacks significant emission at energies above 2 keV. In addition, it is one of few galaxies displaying quasi-periodic X-ray eruptions that recur on a timescale of 13-20 ks. We present multi-epoch radio observations of RX J1301.9+2747 using GMRT, VLA and VLBA. The VLBA imaging at 1.6 GHz reveals a compact radio emission unresolved at a scale of 5x10^7 K. The radio emission is variable by more than a factor of 2.5 over a few days, based on the data taken from VLA monitoring campaigns. The short-term radio variability suggests that the radio emitting region has a size as small as 8x10^{-4} pc, resulting in an even higher brightness temperature of T_b ~10^{12} K. A similar limit on the source size can be obtained if the observed flux variability is not intrinsic and caused by the interstellar scintillation effect. The overall radio spectrum is steep with a time-averaged spectral index alpha=-0.78+/-0.03 between 0.89 GHz and 14 GHz. These observational properties rule out a thermal or star-formation origin of the radio emission, and appear to be consistent with the scenario of episodic jet ejections driven by magnetohydrodynamic process. Simultaneous radio and X-ray monitoring observations down to a cadence of hours are required to test whether the compact and variable radio emission is correlated with the quasi-periodic X-ray eruptions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Renjie Li
Huiyuan Wang
H. J. Mo
Shuiyao Huang
Neal Katz
Xiong Luo
Weiguang Cui
Hao Li
Xiaohu Yang
Ning Jiang
Yuning Zhang
摘要： Using reconstructed initial conditions in the SDSS survey volume, we carry out constrained hydrodynamic simulations in three regions representing different types of the cosmic web: the Coma cluster of galaxies; the SDSS great wall; and a large low-density region at $z\sim 0.05$. These simulations, which include star formation and stellar feedback but no AGN formation and feedback, are used to investigate the properties and evolution of intergalactic and intra-cluster media. About half of the warm-hot intergalactic gas is associated with filaments in the local cosmic web. Gas in the outskirts of massive filaments and halos can be heated significantly by accretion shocks generated by mergers of filaments and halos, respectively, and there is a tight correlation between gas temperature and the strength of the local tidal field. The simulations also predict some discontinuities associated with shock fronts and contact edges, which can be tested using observations of the thermal SZ effect and X-rays. A large fraction of the sky is covered by Ly$\alpha$ and OVI absorption systems, and most of the OVI systems and low-column density HI systems are associated with filaments in the cosmic web. The constrained simulations, which follow the formation and heating history of the observed cosmic web, provide an important avenue to interpret observational data. With full information about the origin and location of the cosmic gas to be observed, such simulations can also be used to develop observational strategies.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yibo Wang
Ning Jiang
Tinggui Wang
Lin Yan
Zhenfeng Sheng
Liming Dou
Jiani Ding
Zheng Cai
Luming Sun
Chenwei Yang
Xinwen Shu
摘要： Infrared echo has proven to be an effective means to discover transient accretion events of supermassive black holes (SMBHs), such as tidal disruption events (TDEs) and changing-look active galactic nuclei (AGNs), in dusty circumnuclear environments. To explore the dusty populations of SMBH transient events, we have constructed a large sample of Mid-infrared Outbursts in Nearby Galaxies (MIRONG) and performed multiwavelength observations. Here we present the results of multiepoch spectroscopic follow-up observations of a subsample of 54 objects spanning a time scale of 4 yr. Emission-line variability was detected in 22 of them with either emergence or enhancement of broad Balmer emission lines in comparison with pre-outburst spectra. Coronal lines, HeII{\lambda}4686 and Bowen line NIII{\lambda}4640 appeared in the spectra of nine,seven and two sources, respectively. These results suggest that MIRONG is a mixed bag of different transient sources. We have tentatively classified them into different subclass according to their spectral evolution and light curves. Two sources have been in a steady high broad H{\alpha} flux up to the latest observation and might be turn-on AGNs. Broad lines faded out in the remaining sources, indicating a transient ionizing source ignited by TDE or sporadic gas accretion. Thirty-one sources do not show noticeable spectral change with respect to their pre-outburst spectra. They have a statistically redder MIR color and lower MIR luminosity of the outbursts,which are consistent with heavily obscured events.
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