Astrophysical explosions that contain dense and ram-pressure-dominated ejecta evolve through an interaction phase, during which a forward shock (FS), contact discontinuity (CD), and reverse shock (RS) form and expand with time. We describe new self-similar solutions that apply to this phase and are most accurate in the limit that the ejecta density is large compared to the ambient density. These solutions predict that the FS, CD, and RS expand at different rates in time and not as single temporal power-laws, are valid for explosions driven by steady winds and homologously expanding ejecta, and exist when the ambient density profile is a power-law with power-law index shallower than $sim 3$ (specifically when the FS does not accelerate). We find excellent agreement between the predictions of these solutions and hydrodynamical simulations, both for the temporal behavior of the discontinuities and for the variation of the fluid quantities. The self-similar solutions are applicable to a wide range of astrophysical phenomena and -- although the details are described in future work -- can be generalized to incorporate relativistic speeds with arbitrary Lorentz factors. We suggest that these solutions accurately interpolate between the initial ``coasting'' phase of the explosion and the later, energy-conserving phase (or, if the ejecta is homologous and the density profile is sufficiently steep, the self-similar phase described in Chevalier 1982),
{"title":"From coasting to energy-conserving: new self-similar solutions to the interaction phase of strong explosions","authors":"Eric R. Coughlin","doi":"arxiv-2409.10600","DOIUrl":"https://doi.org/arxiv-2409.10600","url":null,"abstract":"Astrophysical explosions that contain dense and ram-pressure-dominated ejecta\u0000evolve through an interaction phase, during which a forward shock (FS), contact\u0000discontinuity (CD), and reverse shock (RS) form and expand with time. We\u0000describe new self-similar solutions that apply to this phase and are most\u0000accurate in the limit that the ejecta density is large compared to the ambient\u0000density. These solutions predict that the FS, CD, and RS expand at different\u0000rates in time and not as single temporal power-laws, are valid for explosions\u0000driven by steady winds and homologously expanding ejecta, and exist when the\u0000ambient density profile is a power-law with power-law index shallower than\u0000$sim 3$ (specifically when the FS does not accelerate). We find excellent\u0000agreement between the predictions of these solutions and hydrodynamical\u0000simulations, both for the temporal behavior of the discontinuities and for the\u0000variation of the fluid quantities. The self-similar solutions are applicable to\u0000a wide range of astrophysical phenomena and -- although the details are\u0000described in future work -- can be generalized to incorporate relativistic\u0000speeds with arbitrary Lorentz factors. We suggest that these solutions\u0000accurately interpolate between the initial ``coasting'' phase of the explosion\u0000and the later, energy-conserving phase (or, if the ejecta is homologous and the\u0000density profile is sufficiently steep, the self-similar phase described in\u0000Chevalier 1982),","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"29 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142260108","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. A. Hashad, Amr A. El-Zant, Y. Abdou, H. M. Badran
While there has been an increase in interest in the possibility of quasi-periodic oscillations (QPOs) in blazars, the search has hitherto been restricted to sources with well-sampled light curves. Objects with light curves that include gaps have been, to our knowledge, overlooked. Here, we study two such curves, which have the interesting feature of pertaining to relatively high redshift blazars -- FSRQs, PKS 2155-83 and PKS 2255-282 -- observed by Fermi-LAT. Their redshifts border the 'cosmic noon' era of galaxy formation and merging, and their light curves exhibit a distinctive pattern of repetitive high and low (gap dominant) states for $15.6$ years. To accommodate for the gaps in the curves, data is integrated over extended time intervals of 1 month and 2 months. The resulting curves were also examined using methods suitable for sparsely sampled data. This investigation of PKS 2155-83 and PKS 2255-282 suggests QPOs with periods of $4.69pm0.79$ yr ($3sigma$) and $6.82pm2.25$ yr ($2.8sigma$), respectively. The flux PDFs of the blazars, along with the correlation between their flux and spectral index, were also analyzed. Given the epochs the objects are observed, the plausibility of a binary black hole scenario as an origin of the apparent periodicity was examined. We estimated the prospective parameters of such a system using a simple geometric model. The total masses were estimated, and found to be consistent, in principle, with independent (dynamical) measurements of the central black hole masses in the two host galaxies.
{"title":"Quasi-periodic $γ$-ray modulations in the blazars PKS 2155-83 and PKS 2255-282","authors":"M. A. Hashad, Amr A. El-Zant, Y. Abdou, H. M. Badran","doi":"arxiv-2409.10622","DOIUrl":"https://doi.org/arxiv-2409.10622","url":null,"abstract":"While there has been an increase in interest in the possibility of\u0000quasi-periodic oscillations (QPOs) in blazars, the search has hitherto been\u0000restricted to sources with well-sampled light curves. Objects with light curves\u0000that include gaps have been, to our knowledge, overlooked. Here, we study two\u0000such curves, which have the interesting feature of pertaining to relatively\u0000high redshift blazars -- FSRQs, PKS 2155-83 and PKS 2255-282 -- observed by\u0000Fermi-LAT. Their redshifts border the 'cosmic noon' era of galaxy formation and\u0000merging, and their light curves exhibit a distinctive pattern of repetitive\u0000high and low (gap dominant) states for $15.6$ years. To accommodate for the\u0000gaps in the curves, data is integrated over extended time intervals of 1 month\u0000and 2 months. The resulting curves were also examined using methods suitable\u0000for sparsely sampled data. This investigation of PKS 2155-83 and PKS 2255-282\u0000suggests QPOs with periods of $4.69pm0.79$ yr ($3sigma$) and $6.82pm2.25$ yr\u0000($2.8sigma$), respectively. The flux PDFs of the blazars, along with the\u0000correlation between their flux and spectral index, were also analyzed. Given\u0000the epochs the objects are observed, the plausibility of a binary black hole\u0000scenario as an origin of the apparent periodicity was examined. We estimated\u0000the prospective parameters of such a system using a simple geometric model. The\u0000total masses were estimated, and found to be consistent, in principle, with\u0000independent (dynamical) measurements of the central black hole masses in the\u0000two host galaxies.","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"45 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142260106","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Cristóbal M. Espinoza, Lucien Kuiper, Wynn C. G. Ho, Danai Antonopoulou, Zaven Arzoumanian, Alice K. Harding, Paul S. Ray, George Younes
The way pulsars spin down is not understood in detail, but a number of possible physical mechanisms produce a spin-down rate that scales as a power of the rotation rate ($dotnupropto-nu^n$), with the power-law index $n$ called the braking index. PSR B0540-69 is a pulsar that in 2011, after 16 years of spinning down with a constant braking index of 2.1, experienced a giant spin-down change and a reduction of its braking index to nearly zero. Here, we show that following this episode the braking index monotonically increased during a period of at least four years and stabilised at ~1.1. We also present an alternative interpretation of a more modest rotational irregularity that occurred in 2023, which was modelled as an anomalous negative step of the rotation rate. Our analysis shows that the 2023 observations can be equally well described as a transient swing of the spin-down rate (lasting ~65 days), and the Bayesian evidence indicates that this model is strongly preferred.
{"title":"A growing braking index and spin-down swings for the pulsar PSR B0540-69","authors":"Cristóbal M. Espinoza, Lucien Kuiper, Wynn C. G. Ho, Danai Antonopoulou, Zaven Arzoumanian, Alice K. Harding, Paul S. Ray, George Younes","doi":"arxiv-2409.10759","DOIUrl":"https://doi.org/arxiv-2409.10759","url":null,"abstract":"The way pulsars spin down is not understood in detail, but a number of\u0000possible physical mechanisms produce a spin-down rate that scales as a power of\u0000the rotation rate ($dotnupropto-nu^n$), with the power-law index $n$ called\u0000the braking index. PSR B0540-69 is a pulsar that in 2011, after 16 years of\u0000spinning down with a constant braking index of 2.1, experienced a giant\u0000spin-down change and a reduction of its braking index to nearly zero. Here, we\u0000show that following this episode the braking index monotonically increased\u0000during a period of at least four years and stabilised at ~1.1. We also present\u0000an alternative interpretation of a more modest rotational irregularity that\u0000occurred in 2023, which was modelled as an anomalous negative step of the\u0000rotation rate. Our analysis shows that the 2023 observations can be equally\u0000well described as a transient swing of the spin-down rate (lasting ~65 days),\u0000and the Bayesian evidence indicates that this model is strongly preferred.","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"86 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142260103","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lujun Zeng, Mengqing Zhang, Chongyang Ren, Pengfei Zhang, Jingzhi Yan
LS 5039 is one of a handful of $gamma$-ray binary systems in the Milky Way, comprising a pulsar and a massive O-type companion star with an orbital period of 3.9 day. Recently, we conducted a data analysis using approximately 16 year of Fermi-LAT observations, spanning from 2008 August 4 to 2024 July 8. In our timing analysis, we discovered two new periodic signals with frequencies higher and lower than the known orbital period. The higher-frequency signal has a period of 3.63819 day with a 7.1$sigma$ confidence level, while the lower-frequency signal has a period of 4.21654 day with a 6.3$sigma$ confidence level. Additionally, in data from the High Energy Stereoscopic System of Cherenkov Telescopes, two potential signals with periods similar to the two newly discovered ones. Considering that these two signals fall within the same frequency interval as the orbital period, we suggest the possibility of a third body orbiting the barycenter of the LS 5039 binary system, with the new periodic signals arising from specific frequency combinations of the two orbital periods.
LS 5039是银河系中少数几个伽马射线双星系统之一，由一颗脉冲星和一颗大质量O型伴星组成，轨道周期为3.9天。最近，我们利用费米-LAT从2008年8月4日到2024年7月8日大约16年的观测数据进行了数据分析。 在我们的定时分析中，我们发现了两个新的周期信号，其频率比已知的轨道周期要高和低。高频信号的周期为3.63819天，置信度为7.1；低频信号的周期为4.21654天，置信度为6.3。此外，在切伦科夫望远镜高能立体系统的数据中，有两个潜在信号的周期与新发现的两个信号相似。考虑到这两个信号的频率间隔与轨道周期的频率间隔相同，我们认为LS 5039双星系统的双子中心可能有第三个天体在环绕运行，新的周期信号来自两个轨道周期的特定频率组合。
{"title":"Investigating the Potential of LS 5039 as a Triple System Using Fermi-LAT Data","authors":"Lujun Zeng, Mengqing Zhang, Chongyang Ren, Pengfei Zhang, Jingzhi Yan","doi":"arxiv-2409.09908","DOIUrl":"https://doi.org/arxiv-2409.09908","url":null,"abstract":"LS 5039 is one of a handful of $gamma$-ray binary systems in the Milky Way,\u0000comprising a pulsar and a massive O-type companion star with an orbital period\u0000of 3.9 day. Recently, we conducted a data analysis using approximately 16 year\u0000of Fermi-LAT observations, spanning from 2008 August 4 to 2024 July 8. In our\u0000timing analysis, we discovered two new periodic signals with frequencies higher\u0000and lower than the known orbital period. The higher-frequency signal has a\u0000period of 3.63819 day with a 7.1$sigma$ confidence level, while the\u0000lower-frequency signal has a period of 4.21654 day with a 6.3$sigma$\u0000confidence level. Additionally, in data from the High Energy Stereoscopic\u0000System of Cherenkov Telescopes, two potential signals with periods similar to\u0000the two newly discovered ones. Considering that these two signals fall within\u0000the same frequency interval as the orbital period, we suggest the possibility\u0000of a third body orbiting the barycenter of the LS 5039 binary system, with the\u0000new periodic signals arising from specific frequency combinations of the two\u0000orbital periods.","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"19 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142260151","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Papoutsis, I. E. Papadakis, C. Panagiotou, M. Dovčiak, E. Kammoun
Active galactic nuclei (AGNs) are known to be variable across all wavelengths. Significant observational efforts have been invested in the last decade in studying their ultraviolet (UV) and optical variability. Long and densely sampled, multi-wavelength monitoring campaigns of numerous Seyfert galaxies have been conducted with the aim of determining the X-ray/UV/optical continuum time lags. Time-lag studies can be used to constrain theoretical models. The observed time lags can be explained by thermal reprocessing of the X-rays illuminating the accretion disc (known as the X-ray reverberation model). However, the observed light curves contain more information that can be used to further constrain physical models. Our primary objective is to investigate whether, in addition to time lags, the X-ray reverberation model can also explain the UV/optical variability amplitude of nearby Seyferts. To do this, we measured the excess variance of four sources (namely Mrk 509, NGC 4151, NGC 2617, and Mrk 142) as a function of wavelength using data from archival long, multi-wavelength campaigns with Swift, and ground-based telescopes. We also computed the model excess variance in the case of the X-ray reverberation model by determining the disc's transfer function and assuming a bending power law for the X-ray power spectrum. We tested the validity of the model by comparing the measured and model variances for a range of accretion rates and X-ray source heights. We conclude that the X-ray thermal reverberation model can fit both the continuum, UV/optical time lags, as well as the variance in these AGNs, for the same physical parameters. Our results suggest that the accretion disc is constant and that all the observed UV/optical variations, on timescales of days and up to a few weeks, can be fully explained by the variable X-rays as they illuminate the accretion disc.
众所周知，活动星系核（AGN）在所有波长上都是可变的。在过去的十年里，人们投入了大量的观测力量来研究它们的紫外线（UV）和光学变异性。为了确定 X 射线/紫外/光学连续时滞，对许多赛弗星系进行了长时间和密集采样的多波长监测活动。时滞研究可用于约束理论模型。观测到的时滞可以用照射吸积盘的 X 射线的热再处理来解释（称为 X 射线混响模型）。然而，观测到的光变曲线包含更多信息，可以用来进一步约束物理模型。我们的主要目的是研究除了时滞之外，X射线混响模型是否还能解释附近赛弗星的紫外/光学变率振幅。为此，我们利用 Swift 和地基望远镜的长波长、多波长活动的存档数据，测量了四个源（即 Mrk 509、NGC4151、NGC 2617 和 Mrk 142）的超变异与波长的函数关系。我们还通过确定圆盘的传递函数和假定 X 射线功率谱的阶跃幂律，计算了 X 射线反褶模型的模型超方差。我们通过比较一系列增殖速度和 X 射线源高度的测量方差和模型方差，检验了模型的有效性。我们得出的结论是，在相同物理参数下，X射线热反响模型可以同时拟合连续波、紫外/光学时滞以及这些AGN的方差。我们的研究结果表明，吸积盘是恒定的，所有观测到的紫外/光学变化，从几天到几周的时间尺度，都可以用可变的 X 射线照亮吸积盘来解释。
{"title":"X-ray reverberation as an explanation for UV/optical variability in nearby Seyferts","authors":"M. Papoutsis, I. E. Papadakis, C. Panagiotou, M. Dovčiak, E. Kammoun","doi":"arxiv-2409.10417","DOIUrl":"https://doi.org/arxiv-2409.10417","url":null,"abstract":"Active galactic nuclei (AGNs) are known to be variable across all\u0000wavelengths. Significant observational efforts have been invested in the last\u0000decade in studying their ultraviolet (UV) and optical variability. Long and\u0000densely sampled, multi-wavelength monitoring campaigns of numerous Seyfert\u0000galaxies have been conducted with the aim of determining the X-ray/UV/optical\u0000continuum time lags. Time-lag studies can be used to constrain theoretical\u0000models. The observed time lags can be explained by thermal reprocessing of the\u0000X-rays illuminating the accretion disc (known as the X-ray reverberation\u0000model). However, the observed light curves contain more information that can be\u0000used to further constrain physical models. Our primary objective is to\u0000investigate whether, in addition to time lags, the X-ray reverberation model\u0000can also explain the UV/optical variability amplitude of nearby Seyferts. To do\u0000this, we measured the excess variance of four sources (namely Mrk 509, NGC\u00004151, NGC 2617, and Mrk 142) as a function of wavelength using data from\u0000archival long, multi-wavelength campaigns with Swift, and ground-based\u0000telescopes. We also computed the model excess variance in the case of the X-ray\u0000reverberation model by determining the disc's transfer function and assuming a\u0000bending power law for the X-ray power spectrum. We tested the validity of the\u0000model by comparing the measured and model variances for a range of accretion\u0000rates and X-ray source heights. We conclude that the X-ray thermal\u0000reverberation model can fit both the continuum, UV/optical time lags, as well\u0000as the variance in these AGNs, for the same physical parameters. Our results\u0000suggest that the accretion disc is constant and that all the observed\u0000UV/optical variations, on timescales of days and up to a few weeks, can be\u0000fully explained by the variable X-rays as they illuminate the accretion disc.","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"35 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142260148","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The characteristic timescale at which the variability of active galactic nuclei (AGNs) turns from red noise to white noise can probe the accretion physics around supermassive black holes (SMBHs). A number of works have studied the characteristic timescale of quasars and obtained quite different scaling relations between the timescale and quasar physical properties. One possible reason for the discrepancies is that the characteristic timescale can be easily underestimated if the light curves are not long enough. In this work, we construct well-defined AGN samples to observationally test the relationships between the characteristic timescale and AGN properties obtained by previous works. Our samples eliminate the effects of insufficient light-curve lengths. We confirm that the timescale predictions citep{Zhou2024} of the Corona Heated Accretion disk Reprocessing model are consistent with our timescale measurements. The timescale predictions by empirically relations citep[e.g.,][]{Kelly2009} are systematically smaller than our measured ones. Our results provide further evidence that AGN variability is driven by thermal fluctuations in SMBH accretion disks. Future flagship time-domain surveys can critically test our conclusions and reveal the physical nature of AGN variability.
{"title":"How Long Will the Quasar UV/Optical Flickering Be Damped? II. the Observational Test","authors":"Guowei RenXMU, Shuying ZhouXMU, Mouyuan SunXMU, Yongquan XueUSTC","doi":"arxiv-2409.09637","DOIUrl":"https://doi.org/arxiv-2409.09637","url":null,"abstract":"The characteristic timescale at which the variability of active galactic\u0000nuclei (AGNs) turns from red noise to white noise can probe the accretion\u0000physics around supermassive black holes (SMBHs). A number of works have studied\u0000the characteristic timescale of quasars and obtained quite different scaling\u0000relations between the timescale and quasar physical properties. One possible\u0000reason for the discrepancies is that the characteristic timescale can be easily\u0000underestimated if the light curves are not long enough. In this work, we\u0000construct well-defined AGN samples to observationally test the relationships\u0000between the characteristic timescale and AGN properties obtained by previous\u0000works. Our samples eliminate the effects of insufficient light-curve lengths.\u0000We confirm that the timescale predictions citep{Zhou2024} of the Corona Heated\u0000Accretion disk Reprocessing model are consistent with our timescale\u0000measurements. The timescale predictions by empirically relations\u0000citep[e.g.,][]{Kelly2009} are systematically smaller than our measured ones.\u0000Our results provide further evidence that AGN variability is driven by thermal\u0000fluctuations in SMBH accretion disks. Future flagship time-domain surveys can\u0000critically test our conclusions and reveal the physical nature of AGN\u0000variability.","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"31 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142260027","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In galactic centers, stars and binaries can be injected into low-angular-momentum orbits, resulting in close encounters with the central supermassive black hole (SMBH). We use $N$-body simulations to study such encounters systematically under a wide range of conditions. Depending on the system parameters (such as $beta_b$, the ratio of binary tidal radius to pericenter distance $r_p$ to the SMBH, and the compactness of the binary), such close encounters can lead to the break-up of the binary, disruptions of both stars and collision between the stars. Binary break-up produces a hyper-velocity star and a bound star around the SMBH; the peak value of the orbital binding energy depends weakly on $beta_b$. When $r_p$ is comparable to the stellar tidal radius, sequential disruptions of the stars occur within a time interval much shorter than the initial binary orbital period, potentially exhibiting distinct double TDE features. Stellar collisions occur for a range of $beta_b$'s, with a few to 10's percent probabilities (depending on the compactness of the binary). In gentle encounters ($beta_blesssim 1$), stellar collisions occur after the pericenter passage, and the merger remnants are typically ejected from the SMBH at a small velocity. In deep encounters ($beta_bgtrsim 1$), collisions occur near the pericenter, and the merger remnants are typically bound to the SMBH. We suggest that stellar collisions induced by binary-SMBH encounters may produce exotic stars in galactic centers, trigger accretion flares onto the SMBH due to the mass loss, and result in bound merger remnants causing repeated partial TDEs.
{"title":"Binary Stars Approaching Supermassive Black Holes: Tidal Break-up, Double Stellar Disruptions and Stellar Collision","authors":"Fangyuan Yu, Dong Lai","doi":"arxiv-2409.09597","DOIUrl":"https://doi.org/arxiv-2409.09597","url":null,"abstract":"In galactic centers, stars and binaries can be injected into\u0000low-angular-momentum orbits, resulting in close encounters with the central\u0000supermassive black hole (SMBH). We use $N$-body simulations to study such\u0000encounters systematically under a wide range of conditions. Depending on the\u0000system parameters (such as $beta_b$, the ratio of binary tidal radius to\u0000pericenter distance $r_p$ to the SMBH, and the compactness of the binary), such\u0000close encounters can lead to the break-up of the binary, disruptions of both\u0000stars and collision between the stars. Binary break-up produces a\u0000hyper-velocity star and a bound star around the SMBH; the peak value of the\u0000orbital binding energy depends weakly on $beta_b$. When $r_p$ is comparable to\u0000the stellar tidal radius, sequential disruptions of the stars occur within a\u0000time interval much shorter than the initial binary orbital period, potentially\u0000exhibiting distinct double TDE features. Stellar collisions occur for a range\u0000of $beta_b$'s, with a few to 10's percent probabilities (depending on the\u0000compactness of the binary). In gentle encounters ($beta_blesssim 1$), stellar\u0000collisions occur after the pericenter passage, and the merger remnants are\u0000typically ejected from the SMBH at a small velocity. In deep encounters\u0000($beta_bgtrsim 1$), collisions occur near the pericenter, and the merger\u0000remnants are typically bound to the SMBH. We suggest that stellar collisions\u0000induced by binary-SMBH encounters may produce exotic stars in galactic centers,\u0000trigger accretion flares onto the SMBH due to the mass loss, and result in\u0000bound merger remnants causing repeated partial TDEs.","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142260152","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ruancun LiKavli Institute for Astronomy and Astrophysics, Peking University, Claudio Ricci, Luis C. Ho, Benny Trakhtenbrot, Erin Kara, Megan Masterson, Iair Arcavi
Time-domain studies of active galactic nuclei (AGNs) offer a powerful tool for understanding black hole accretion physics. Prior to the optical outburst on 23 December 2017, 1ES 1927+654 was classified as a "true" type~2 AGN, an unobscured source intrinsically devoid of broad-line emission in polarized spectra. Through our three-year monitoring campaign spanning X-ray to ultraviolet/optical wavelengths, we analyze the post-outburst evolution of the spectral energy distribution (SED) of 1ES 1927+654. Examination of the intrinsic SED and subsequent modeling using different models reveal that the post-outburst spectrum is best described by a combination of a disk, blackbody, and corona components. We detect systematic SED variability and identify four distinct stages in the evolution of these components. During the event the accretion rate is typically above the Eddington limit. The correlation between ultraviolet luminosity and optical to X-ray slope ($alpha_mathrm{OX}$) resembles that seen in previous studies of type 1 AGNs, yet exhibits two distinct branches with opposite slopes. The optical bolometric correction factor ($kappa_{5100}$) is $sim 10$ times higher than typical AGNs, again displaying two distinct branches. Correlations among the corona optical depth, disk surface density, and $alpha_mathrm{OX}$ provide compelling evidence of a disk-corona connection. The X-ray corona showcases systematic variation in the compactness-temperature plot. Between 200 and 650 days, the corona is "hotter-when-brighter", whereas after 650 days, it becomes "cooler-when-brighter". This bimodal behavior, in conjunction with the bifurcated branches of $alpha_mathrm{OX}$ and $kappa_{5100}$, offers strong evidence of a transition from a slim disk to thin disk $sim 650$ days after the outburst.
对活动星系核（AGN）的时域研究为了解黑洞吸积物理学提供了有力的工具。在2017年12月23日的光学爆发之前，1ES 1927+654被归类为 "真正的"~2型AGN，是一个在偏振谱图中本质上没有宽线发射的无遮挡源。通过为期三年的X射线紫外/光学波长监测活动，我们分析了1ES 1927+654爆发后光谱能量分布（SED）的演变。对内在 SED 的研究以及随后使用不同模型进行的建模显示，爆发后的光谱最好是由圆盘、黑体和日冕成分组合而成的。我们检测到了系统的 SED 变异，并确定了这些成分演化过程中的四个不同阶段。在事件发生期间，增殖率通常高于爱丁顿极限。紫外光度和光学到X射线斜率（$alpha_mathrm{OX}$）之间的相关性类似于之前对1型AGN的研究，但表现出两个斜率相反的明显分支。光学测光校正因子（$kappa_{5100}$）比典型的AGN高$sim 10$倍，同样显示出两个不同的分支。日冕光学深度、磁盘表面密度和$alpha_mathrm{OX}$之间的相关性为磁盘与日冕之间的联系提供了有力的证据。X射线日冕在紧密度-温度曲线图中显示出系统性的变化。在 200 到 650 天之间，日冕是 "越亮越热"，而在 650 天之后，则是 "越冷越亮"。这种双峰行为与$alpha_mathrm{OX}$和$kappa_{5100}$的分叉分支相结合，有力地证明了在爆发后650天，日冕从一个细长的圆盘过渡到一个薄圆盘。
{"title":"The Interplay between the Disk and Corona of the Changing-look Active Galactic Nucleus 1ES 1927+654","authors":"Ruancun LiKavli Institute for Astronomy and Astrophysics, Peking University, Claudio Ricci, Luis C. Ho, Benny Trakhtenbrot, Erin Kara, Megan Masterson, Iair Arcavi","doi":"arxiv-2409.09264","DOIUrl":"https://doi.org/arxiv-2409.09264","url":null,"abstract":"Time-domain studies of active galactic nuclei (AGNs) offer a powerful tool\u0000for understanding black hole accretion physics. Prior to the optical outburst\u0000on 23 December 2017, 1ES 1927+654 was classified as a \"true\" type~2 AGN, an\u0000unobscured source intrinsically devoid of broad-line emission in polarized\u0000spectra. Through our three-year monitoring campaign spanning X-ray to\u0000ultraviolet/optical wavelengths, we analyze the post-outburst evolution of the\u0000spectral energy distribution (SED) of 1ES 1927+654. Examination of the\u0000intrinsic SED and subsequent modeling using different models reveal that the\u0000post-outburst spectrum is best described by a combination of a disk, blackbody,\u0000and corona components. We detect systematic SED variability and identify four\u0000distinct stages in the evolution of these components. During the event the\u0000accretion rate is typically above the Eddington limit. The correlation between\u0000ultraviolet luminosity and optical to X-ray slope ($alpha_mathrm{OX}$)\u0000resembles that seen in previous studies of type 1 AGNs, yet exhibits two\u0000distinct branches with opposite slopes. The optical bolometric correction\u0000factor ($kappa_{5100}$) is $sim 10$ times higher than typical AGNs, again\u0000displaying two distinct branches. Correlations among the corona optical depth,\u0000disk surface density, and $alpha_mathrm{OX}$ provide compelling evidence of a\u0000disk-corona connection. The X-ray corona showcases systematic variation in the\u0000compactness-temperature plot. Between 200 and 650 days, the corona is\u0000\"hotter-when-brighter\", whereas after 650 days, it becomes\u0000\"cooler-when-brighter\". This bimodal behavior, in conjunction with the\u0000bifurcated branches of $alpha_mathrm{OX}$ and $kappa_{5100}$, offers strong\u0000evidence of a transition from a slim disk to thin disk $sim 650$ days after\u0000the outburst.","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"18 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142269857","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Positronium spectrum and lifetimes are known with a high precision. The situation is different for positronium moving across a magnetic field. The total momentum does not commute with the Hamiltonian and is replaced by conserved pseudomomentum. The internal dynamics is not separated from the motion of the system as a whole. The Coulomb potential well is distorted and a wide outer potential well is created. We analytically determine the energy spectrum for a broad range of the magnetic field and pseudomomentum values. We locate the region of these parameters for which the ground state resides in the outer well. The results may play a role in the supression of pulsars radio emission (polar cap problem).
{"title":"Metamorphosis of Positronium Moving Across a Magnetic Field","authors":"B. O. Kerbikov, A. A. Simovonian","doi":"arxiv-2409.09496","DOIUrl":"https://doi.org/arxiv-2409.09496","url":null,"abstract":"Positronium spectrum and lifetimes are known with a high precision. The\u0000situation is different for positronium moving across a magnetic field. The\u0000total momentum does not commute with the Hamiltonian and is replaced by\u0000conserved pseudomomentum. The internal dynamics is not separated from the\u0000motion of the system as a whole. The Coulomb potential well is distorted and a\u0000wide outer potential well is created. We analytically determine the energy\u0000spectrum for a broad range of the magnetic field and pseudomomentum values. We\u0000locate the region of these parameters for which the ground state resides in the\u0000outer well. The results may play a role in the supression of pulsars radio\u0000emission (polar cap problem).","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"40 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142260111","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ruancun LiKavli Institute for Astronomy and Astrophysics, Peking University, Luis C. Ho, Claudio Ricci, Benny Trakhtenbrot
The properties of slim accretion disks, while crucial for our understanding of black hole growth, have yet to be studied extensively observationally. We analyze the multi-epoch broad-band spectral energy distribution of the changing-look active galactic nucleus 1ES 1927+654 to derive the properties of its complex, time-dependent accretion flow. The accretion rate decays as $dot{M} propto t^{-1.53}$, consistent with the tidal disruption of a $1.1, M_odot$ star. Three components contribute to the spectral energy distribution: a central overheated zone resembling a slim disk, an outer truncated thin disk, and a hot corona. Photon trapping in the slim disk triggered by the high initial $dot{M}$ was characterized by a low radiation efficiency ($3%$), which later more than doubled ($8%$) after $dot{M}$ dropped sufficiently low for the disk to transition to a geometrically thin state. The blackbody temperature profile $T propto R^{-0.60}$ for the inner overheated zone matches the theoretical expectations of a slim disk, while the effective temperature profile of $T propto R^{-0.69}$ for the outer zone is consistent with the predictions of a thin disk. Both profiles flatten toward the inner boundary of the disk as a result of Compton cooling in the corona. Our work presents compelling observational evidence for the existence of slim accretion disks and elucidates the key parameters governing their behavior, paving the way for further exploration in this area.
{"title":"A Two-zone Accretion Disk in the Changing-look Active Galactic Nucleus 1ES 1927+654: Physical Implications for Tidal Disruption Events and Super-Eddington Accretion","authors":"Ruancun LiKavli Institute for Astronomy and Astrophysics, Peking University, Luis C. Ho, Claudio Ricci, Benny Trakhtenbrot","doi":"arxiv-2409.09265","DOIUrl":"https://doi.org/arxiv-2409.09265","url":null,"abstract":"The properties of slim accretion disks, while crucial for our understanding\u0000of black hole growth, have yet to be studied extensively observationally. We\u0000analyze the multi-epoch broad-band spectral energy distribution of the\u0000changing-look active galactic nucleus 1ES 1927+654 to derive the properties of\u0000its complex, time-dependent accretion flow. The accretion rate decays as\u0000$dot{M} propto t^{-1.53}$, consistent with the tidal disruption of a $1.1,\u0000M_odot$ star. Three components contribute to the spectral energy distribution:\u0000a central overheated zone resembling a slim disk, an outer truncated thin disk,\u0000and a hot corona. Photon trapping in the slim disk triggered by the high\u0000initial $dot{M}$ was characterized by a low radiation efficiency ($3%$),\u0000which later more than doubled ($8%$) after $dot{M}$ dropped sufficiently low\u0000for the disk to transition to a geometrically thin state. The blackbody\u0000temperature profile $T propto R^{-0.60}$ for the inner overheated zone matches\u0000the theoretical expectations of a slim disk, while the effective temperature\u0000profile of $T propto R^{-0.69}$ for the outer zone is consistent with the\u0000predictions of a thin disk. Both profiles flatten toward the inner boundary of\u0000the disk as a result of Compton cooling in the corona. Our work presents\u0000compelling observational evidence for the existence of slim accretion disks and\u0000elucidates the key parameters governing their behavior, paving the way for\u0000further exploration in this area.","PeriodicalId":501343,"journal":{"name":"arXiv - PHYS - High Energy Astrophysical Phenomena","volume":"17 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142260154","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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