By: Wen-Long Xu, Yu-Zhe Li, Yi-Gu Chen, Hui Li, Wei-Hua Lei
Stellar-mass binary black holes (BBH) may form, evolve, and merge within the dense environments of active galactic nuclei (AGN) disks, thereby contributing to the BBH population detected by gravitational wave (GW) observatories. Mergers occurring in AGN disks may be gravitationally lensed by the supermassive black hole at the AGN centre. The probability of such lensing events has been approximately estimated by using the Einstein criterion ... more
Stellar-mass binary black holes (BBH) may form, evolve, and merge within the dense environments of active galactic nuclei (AGN) disks, thereby contributing to the BBH population detected by gravitational wave (GW) observatories. Mergers occurring in AGN disks may be gravitationally lensed by the supermassive black hole at the AGN centre. The probability of such lensing events has been approximately estimated by using the Einstein criterion in previous work. However, a more reasonable approach to calculating the lensing probability should be based on whether the detector can distinguish the lensed GW waveform from the unlensed one. In this work, we calculate the lensing probability of LIGO sources embedded in AGN disk by relating threshold mismatch to the signal-to-noise ratio of the observed events. For the sensitivity of LIGO-Virgo-KAGRA O3 observation runs, our results indicate that the lensing probability is several times higher than previous estimates. If AGNs are indeed the primary formation channel for BBHs, we could quantify the probability of detecting the lensed GW events in such a scenario. The non-detections, on the other hand, will place stricter constraints on the fraction of AGN disk BBHs and even the birthplaces of BBH mergers. less
By: Amitesh Singh, Nathan K. Johnson-McDaniel, Anuradha Gupta, Khun Sang Phukon
To describe a general bound binary black hole system, we need to consider orbital eccentricity and the misalignment of black holes' spin vectors with respect to the orbital angular momentum. While binary black holes produced through many formation channels have negligible eccentricity close to merger, they often have a non-negligible eccentricity at formation, and dynamical interactions could produce binaries with non-negligible eccentricit... more
To describe a general bound binary black hole system, we need to consider orbital eccentricity and the misalignment of black holes' spin vectors with respect to the orbital angular momentum. While binary black holes produced through many formation channels have negligible eccentricity close to merger, they often have a non-negligible eccentricity at formation, and dynamical interactions could produce binaries with non-negligible eccentricity in the bands of current and proposed gravitational-wave (GW) detectors. Another quantity that carries information about the formation channel is the angle between each black hole's spin vector and the binary's orbital angular momentum (referred to as the spin tilt) at formation. The spin tilts inferred in GW astronomy are usually those when the binary is in the band of a GW detector, but these can differ significantly from those at formation. Therefore, it is necessary to evolve the binary back in time to compute the tilts at formation. For many formation scenarios, the tilts in the formal limit of infinite orbital angular momentum, also known as tilts at infinity, are a good approximation to those at formation. We thus generalize the publicly available \texttt{tilts\_at\_infinity} code to compute the tilts at infinity for eccentric, spin-precessing binaries. This code employs hybrid post-Newtonian evolution, starting with orbit-averaged evolution for higher frequencies and then transitioning to precession-averaged evolution to compute the tilts at infinity. We find that the transition frequency used in the quasicircular case still gives acceptably small errors in the eccentric case, and show that eccentricity and hybrid evolution both have a significant effect on the tilts at infinity for many binaries. Finally, we give examples of cases where the tilts at infinity are and are not a good approximation to the tilts at formation in the eccentric case. less
By: Shilpa Sarkar, I. M. Kulikov
Flows around compact objects are necessarily transonic. Due to their dissipative nature, finding of sonic points is not trivial. Becker and Le in 2003 (BL03) proposed a novel methodology to obtain global transonic solutions, using iterative relaxation technique and exploiting the inner boundary conditions of the central object. In the current work, we propose a generic methodology -- IRM-SP and IRM-SHOCK to obtain any class of global accret... more
Flows around compact objects are necessarily transonic. Due to their dissipative nature, finding of sonic points is not trivial. Becker and Le in 2003 (BL03) proposed a novel methodology to obtain global transonic solutions, using iterative relaxation technique and exploiting the inner boundary conditions of the central object. In the current work, we propose a generic methodology -- IRM-SP and IRM-SHOCK to obtain any class of global accretion and wind solutions, given a set of constants of motion. We have considered viscosity in the system, which transports angular momentum outwards. In addition, it heats the system. Radiative processes like bremsstrahlung which cools the system is also incorporated. An interplay between heating and cooling process, along with gravity and centrifugal forces gives rise to multiple sonic points and hence shocks. The proposed methodology successfully generates any class of accretion as well as wind solutions, allowing us to unify them. Additionally, we report here rigorously the mathematical as well as the computational algorithm needed, to find sonic point(s) and thus obtain global transonic flows around compact objects. less
By: K. Perger, S. Frey, K. É. Gabányi, E. Kun
The radio quasar NVSS~J171822+423948 (J1718+4239) was proposed as the counterpart of the IceCube neutrino event IC-201221A. To reveal the nature of the source, we conducted new very long baseline interferometry (VLBI) observations of this blazar candidate with the Very Long Baseline Array (VLBA). The observations were carried out in dual-band mode between $4$ and $7$~GHz. Archival radio data from the literature were also collected for compa... more
The radio quasar NVSS~J171822+423948 (J1718+4239) was proposed as the counterpart of the IceCube neutrino event IC-201221A. To reveal the nature of the source, we conducted new very long baseline interferometry (VLBI) observations of this blazar candidate with the Very Long Baseline Array (VLBA). The observations were carried out in dual-band mode between $4$ and $7$~GHz. Archival radio data from the literature were also collected for comparison. Our analysis revealed highly variable, Doppler-boosted radio emission of the source, with compact structure at both kpc and pc scales, a slightly inverted spectrum, and a maximum jet inclination angle of $\theta\le5\degr$. These results confirm J1718+4239 as a blazar-type object. less
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By: Giulia Gianfagna, Luigi Piro, Gabriele Bruni, Aishwarya Linesh Thakur, Hendrik Van Eerten, Alberto Castro-Tirado, Yong Chen, Ye-hao Cheng, Han He, Shumei Jia, Zhixing Ling, Elisabetta Maiorano, Rosita Paladino, Roberta Tripodi, Andrea Rossi, Shuaikang Yang, Jianghui Yuan, Weimin Yuan, Chen Zhang
X-Ray Flashes (XRFs) are fast X-ray transients discovered by the BeppoSAX satellite, showing an isotropic sky distribution and a prompt emission duration between 10-1000 seconds. The observed prompt X-ray spectrum is similar to Gamma Ray Bursts (GRBs), but with a softer peak energy of the spectrum. Several pieces of evidence indicate that XRFs are connected to GRBs and likely represent their softer analogues, but their origin is still uncle... more
X-Ray Flashes (XRFs) are fast X-ray transients discovered by the BeppoSAX satellite, showing an isotropic sky distribution and a prompt emission duration between 10-1000 seconds. The observed prompt X-ray spectrum is similar to Gamma Ray Bursts (GRBs), but with a softer peak energy of the spectrum. Several pieces of evidence indicate that XRFs are connected to GRBs and likely represent their softer analogues, but their origin is still unclear. Several models have been proposed to explain the observed properties of XRF, mostly in the context of collapsar scenario, similar to GRBs but with different geometrical or physical conditions of the progenitor. These include off-axis GRBs and baryon-loaded explosions, that either produce a low Lorentz factor jet or a spherical mildly (or non-) relativistic ejecta, known as cocoons. In this paper, we present multi-wavelength observations of the afterglow of EP241021a, a soft X-ray transient detected by EP, consistent with being an XRF. We present the results of our multiwavelength campaign from radio (uGMRT, ATCA, e-MERLIN, ALMA), optical (LBT, GTC, CAHA) and X-rays (EP-FXT). EP241021a afterglow is characterized by multiple components. They represent the imprints of the interaction of a jet with the complex environment of the pre-existing progenitor, that is likely shaping its structure from a highly relativistic narrow cone to much broader and mildly relativistic cocoon components. less
By: Jacco Vink Anton Pannekoek Institute/GRAPPA, University of Amsterdam, Netherlands SRON Netherlands Institute for Space Research, Leiden, Netherlands, Manan Agarwal Anton Pannekoek Institute/GRAPPA, University of Amsterdam, Netherlands, Aya Bamba Department of Physics, Graduate School of Science, The University of Tokyo, Japan Research Center for the Early Universe, School of Science, The University of Tokyo, Japan Trans-Scale Quantum Science Institute, The University of Tokyo, Japan, Liyi Gu SRON Netherlands Institute for Space Research, Leiden, Netherlands, Paul Plucinsky Harvard-Smithsonian Center for Astrophysics, Cambridge MA, USA, Ehud Behar Department of Physics, Technion, Technion City, Haifa, Israel, Lia Corrales Department of Astronomy, University of Michigan, USA, Adam Foster Harvard-Smithsonian Center for Astrophysics, Cambridge MA, USA, Shin-ichiro Fujimoto National Institute of Technology Kumamoto College, Kumamoto, Japan, Masahiro Ichihashi Department of Physics, Graduate School of Science, The University of Tokyo, Japan, Kazuhiro Ichikawa Faculty of Engineering, University of Miyazaki, Miyazaki, Japan, Satoru Katsuda Graduate School of Science and Engineering, Saitama University, Saitama, Japan, Hironori Matsumoto Department of Earth and Space Science, Osaka University, Osaka, Japan, Kai Matsunaga Department of Physics, Kyoto University, Kyoto, Japan, Tsunefumi Mizuno Department of Physics, Hiroshima University, Hiroshima, Japan, Koji Mori Faculty of Engineering, University of Miyazaki, Miyazaki, Japan, Hiroshi Murakami Department of Data Science, Tohoku Gakuin University, Miyagi, Japan, Hiroshi Nakajima College of Science and Engineering, Kanto Gakuin University, Kanagawa, Japan, Toshiki Sato School of Science and Technology, Meiji University, Kanagawa, Japan, Makoto Sawada Department of Physics, Rikkyo University, Tokyo, Japan, Haruto Sonoda ISAS/JAXA, Sagamihara, Kanagawa, Japan, Shunsuke Suzuki ISAS/JAXA, Sagamihara, Kanagawa, Japan, Dai Tateishi Department of Physics, Graduate School of Science, The University of Tokyo, Japan Present address: Collaborative Laboratories for Advanced Decommissioning Science, Japan Atomic Energy Agency, Fukushima, Japan, Yukikatsu Terada Graduate School of Science and Engineering, Saitama University, Saitama, Japan ISAS/JAXA, Sagamihara, Kanagawa, Japan, Hiroyuki Uchida Department of Physics, Kyoto University, Kyoto, Japan
Young supernova remnants (SNRs) provide crucial insights into explosive nucleosynthesis products and their velocity distribution soon after the explosion. However, these velocities are influenced by the dynamics of the circumstellar medium (CSM), which originates from the progenitor's late-phase mass loss. Cas A, the youngest known Galactic core-collapse SNR, was studied to analyze the spatial distribution of Si and S radial velocities usin... more
Young supernova remnants (SNRs) provide crucial insights into explosive nucleosynthesis products and their velocity distribution soon after the explosion. However, these velocities are influenced by the dynamics of the circumstellar medium (CSM), which originates from the progenitor's late-phase mass loss. Cas A, the youngest known Galactic core-collapse SNR, was studied to analyze the spatial distribution of Si and S radial velocities using two high-spectral resolution observations from the XRISM-Resolve imaging spectrometer.Resolve's capabilities enabled the detailed characterization of Si XIII, Si XIV, S XV, and S XVI lines, whose line shapes can be resolved and modeled using Gaussian radial-velocity components. The radial velocities measured generally align with previous CCD-based results, confirming that they were not artifacts caused by blended lines or ionization variations. Modeling line profiles with two-component Gaussians improved fits in some regions, revealing distinct redshifted (backside) and blueshifted (frontside) components only in a few specific areas. In most regions, however, both components were either both redshifted (northwest) or both blueshifted (southeast), consistent with the patchy ejecta shell morphology seen in optically emitting fast-moving knots. The individual line components revealed a line broadening ranging from $\sigma_v \approx 200$ to $\sigma_v \approx 2000$ km/s. Components with $1000 \lesssim \sigma_v \lesssim 2000$km/s are consistent with previously determined reverse shock velocities, suggesting non-equilibrated or partially equilibrated ion temperatures. Narrow components with small radial velocities found near Cas A's projected center likely originate from shocked CSM plasma. But the low radial velocity and small $\sigma_v$ defies identifying these components with either the frontside or backside of the SNR, or both. less
By: W. V. Jacobson-Galán, L. Dessart, K. W. Davis, K. A. Bostroem, C. D. Kilpatrick, R. Margutti, A. V. Filippenko, R. J. Foley, R. Chornock, G. Terreran, D. Hiramatsu, M. Newsome, E. Padilla Gonzalez, C. Pellegrino, D. A. Howell, J. P. Anderson, C. R. Angus, K. Auchettl, T. G. Brink, R. Cartier, D. A. Coulter, T. de Boer, M. R. Drout, N. Earl, K. Ertini, J. R. Farah, D. Farias, C. Gall, H. Gao, M. A. Gerlach, F. Guo, A. Haynie, G. Hosseinzadeh, A. L. Ibik, S. W. Jha, D. O. Jones, D. Langeroodi, N LeBaron, E. A. Magnier, A. L. Piro, S. I. Raimundo, A. Rest, S. Rest, R. Michael Rich, C. Rojas-Bravo, H. Sears, K. Taggart, V. A. Villar, R. J. Wainscoat, X-F. Wang, A. R. Wasserman, S. Yan, Y. Yang, J. Zhang, W. Zheng
We present analysis of the plateau and late-time phase properties of a sample of 39 Type II supernovae (SNe II) that show narrow, transient, high-ionization emission lines (i.e., "IIn-like") in their early-time spectra from interaction with confined, dense circumstellar material (CSM). Originally presented by Jacobson-Gal\'an et al 2024a, this sample also includes multicolor light curves and spectra extending to late-time phases of 35 SNe w... more
We present analysis of the plateau and late-time phase properties of a sample of 39 Type II supernovae (SNe II) that show narrow, transient, high-ionization emission lines (i.e., "IIn-like") in their early-time spectra from interaction with confined, dense circumstellar material (CSM). Originally presented by Jacobson-Gal\'an et al 2024a, this sample also includes multicolor light curves and spectra extending to late-time phases of 35 SNe with no evidence for IIn-like features at <2 days after first light. We measure photospheric phase light-curve properties for the distance-corrected sample and find that SNe II with IIn-like features have significantly higher luminosities and decline rates at +50 days than the comparison sample, which could be connected to inflated progenitor radii, lower ejecta mass, and/or persistent CSM interaction. However, we find no statistical evidence that the measured plateau durations and $^{56}$Ni masses of SNe II with and without IIn-like features arise from different distributions. We estimate progenitor zero-age main sequence (ZAMS) masses for all SNe with nebular spectroscopy through spectral model comparisons and find that most objects, both with and without IIn-like features, are consistent with progenitor masses <12.5 M$_{\odot}$. Combining progenitor ZAMS masses with CSM densities inferred from early-time spectra suggests multiple channels for enhanced mass loss in the final years before core collapse such as a convection-driven chromosphere or binary interaction. Finally, we find spectroscopic evidence for ongoing ejecta-CSM interaction at radii $>10^{16}$ cm, consistent with substantial progenitor mass-loss rates of $\sim 10^{-4}$--$10^{-5}$ M$_{\odot}$ yr$^{-1}$ ($v_w < 50$ km/s) in the final centuries to millennia before explosion. less
By: Ian Holst, Yoann Génolini, Pasquale Dario Serpico
We revisit the problem of the capture of a primordial black hole (PBH) by a neutron star, accounting for the tidal perturbation from a nearby star or planet. For asteroid-mass PBHs, which could constitute all of the dark matter in the universe, a weakly bound post-capture orbit could be tidally disturbed to the point of preventing the PBH from settling in the neutron star and consuming it within a cosmologically short timescale. We show how... more
We revisit the problem of the capture of a primordial black hole (PBH) by a neutron star, accounting for the tidal perturbation from a nearby star or planet. For asteroid-mass PBHs, which could constitute all of the dark matter in the universe, a weakly bound post-capture orbit could be tidally disturbed to the point of preventing the PBH from settling in the neutron star and consuming it within a cosmologically short timescale. We show how this effect depends on environmental parameters and can weaken the proposed constraints based on observations of old neutron stars in high-density dark matter environments for PBH masses $\lesssim 10^{22}\,$g. We also provide approximate analytical formulae for the capture rates. less
Exploring the Formation Mechanisms of Double Neutron Star Systems: An Analytical Perspective
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By: Ali Taani, Mohammed Abu-Saleem, Mohammad Mardini, Hussam Aljboor, Mohammad Tayem
Double Neutron Stars (DNSs) are unique probes to study various aspects of modern astrophysics. Recent discoveries have confirmed direct connections between DNSs and supernova explosions. This provides valuable information about the evolutionary history of these systems, especially regarding whether the second-born Neutron Star (NS) originated from either a Core-Collapse ($CC$) or Electron-Capture Supernovae ($ECSNe$) event. The provided sca... more
Double Neutron Stars (DNSs) are unique probes to study various aspects of modern astrophysics. Recent discoveries have confirmed direct connections between DNSs and supernova explosions. This provides valuable information about the evolutionary history of these systems, especially regarding whether the second-born Neutron Star (NS) originated from either a Core-Collapse ($CC$) or Electron-Capture Supernovae ($ECSNe$) event. The provided scale diagram illustrates the distribution of different types of DNSs on the basis of their orbital parameters and other factors, including mass loss. As a result, the physical processes in DNSs vary depending on the formation mechanisms of the second-born NS and characteristics of the systems. $ECSNe$ processes are typically associated with merging systems ($e\times{P_{orb}}< 0.05$), while $CC$ processes are more commonly linked to non-merging systems ($e\times{P_{orb}}> 0.05$). Our results suggest a critical mass threshold of 1.30$M_\odot \pm 0.22M_\odot$ (critical value) for the $ECSNe$ process to form an NS, while $CC$ processes might occur at higher masses. Examining the orbital parameters of DNSs in a known gravitational potential can enhance our understanding of the theoretical predictions for DNS progenitor characteristics. It turns out that the $ECSNe$ process predominantly produces DNS systems with short orbital ($P_{orb} \leq 0.25 d$), nearly circular orbits ($e\simeq 0.2$), accompanied by minimal kick velocities imparted on the proto-NS and significant mass loss. In contrast, their orbital dynamics in a known gravitational potential plays a crucial role in enhancing our understanding of the SNe geometry and the formation and evolution processes among different NS samples. less
By: I. A. Mereminskiy IKI RAS, Moscow, Russia, A. S. Gorban IKI RAS, Moscow, Russia HSE University, Moscow, Russia, Yu. S. Klein HSE University, Moscow, Russia IKI RAS, Moscow, Russia, E. A. Ushakova HSE University, Moscow, Russia IKI RAS, Moscow, Russia, A. N. Semena IKI RAS, Moscow, Russia, A. A. Lutovinov IKI RAS, Moscow, Russia, A. Yu. Tkachenko IKI RAS, Moscow, Russia, S. V. Molkov IKI RAS, Moscow, Russia
Using the Mikhail Pavlinsky ART-XC onboard the SRG observatory we have detected, for the first time, X-ray pulsations with a period of ~106 s from the poorly-studied high-mass X-ray binary RX J0535.0-6700 located in the Large Magellanic Cloud (LMC), thus proving that the accretor is a neutron star with strong magnetic field. Pulsations with similar period were also found in archival archival data from Chandra and XMM-Newton telescopes. Usin... more
Using the Mikhail Pavlinsky ART-XC onboard the SRG observatory we have detected, for the first time, X-ray pulsations with a period of ~106 s from the poorly-studied high-mass X-ray binary RX J0535.0-6700 located in the Large Magellanic Cloud (LMC), thus proving that the accretor is a neutron star with strong magnetic field. Pulsations with similar period were also found in archival archival data from Chandra and XMM-Newton telescopes. Using photometry from WISE we shown that the source demonstrate significant variability in IR during the last twenty years, which could be caused by a secular evolution of the decretion disk. This discovery makes RX J0535.0-6700 another member of the large family of X-ray pulsars with Be-type companions in the LMC. less
By: Helena Ubach, Mark Gieles, Jordi Miralda-Escudé
Gravitational waves (GWs) from coalescing binary black holes (BBHs) can come from different environments. GWs interact gravitationally with astrophysical objects, which makes it possible to use gravitational lensing by nearby objects (self-lensing) to learn about their environments. We quantify the probability of self-lensing through the optical depth $\tau$ for the main channels of detectable GWs at frequencies $f_{\rm GW}\sim (1-10^3)\,{\... more
Gravitational waves (GWs) from coalescing binary black holes (BBHs) can come from different environments. GWs interact gravitationally with astrophysical objects, which makes it possible to use gravitational lensing by nearby objects (self-lensing) to learn about their environments. We quantify the probability of self-lensing through the optical depth $\tau$ for the main channels of detectable GWs at frequencies $f_{\rm GW}\sim (1-10^3)\,{\rm Hz}$. We then analyze the detectability of the lensing effect (imprint). In star clusters, the probability of self-lensing by stellar-mass black holes (BHs) is low ($\tau\simeq10^{-7}$), even when taking into account nearby BHs in resonant interactions ($\tau\simeq 10^{-5}$). Additionally, the lensing imprint of a stellar-mass lens (diffraction and interference) is too marginal to be detectable by the LIGO-Virgo-KAGRA detectors and most Einstein Telescope signals. For a massive BH lens in the center of a cluster, the probability can reach $\tau\simeq 10^{-4}$ either via von Zeipel-Lidov-Kozai induced mergers of BBHs orbiting a central massive BH or BBHs formed as GW captures in single-single interactions in the Bahcall-Wolf cusp of a nuclear cluster, likely eccentric. For self-lensing by a supermassive BH for BBHs in the migration trap of an AGN (active galactic nucleus) disk, $\tau \simeq 10^{-2}$. The imprint of these massive lenses are two images that are easily detectable already in current detectors. Moreover, AGN disk merger signals have a distinct linear $h_+$ polarization. The probability depends on the extent of the detectability through the threshold impact parameter $y_{\rm max}$, which can increase for future detectors. We conclude that constraining the environment of BBHs is possible by combining self-lensing imprints with other waveform signatures such as eccentricity and polarization. less
Variabilities of Gamma-ray Bursts from the Dynamics of Fallback Material after Tidal Disruption
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By: Yun-Peng Li, Da-Bin Lin, Guo-Yu Li, Zi-Min Zhou, En-Wei Liang
The gamma-ray burst (GRB) GRB 211211A and GRB 060614, believed to originate from the merger of compact objects, exhibit similarities to the jetted tidal disruption event (TDE) Sw J1644+57, by showing violent variabilities in the light-curve during the decay phase. Previous studies suggest that such fluctuations in TDE may arise from the fallback of tidal disrupted debris. In this paper, we introduce the fluctuations of the mass distribution... more
The gamma-ray burst (GRB) GRB 211211A and GRB 060614, believed to originate from the merger of compact objects, exhibit similarities to the jetted tidal disruption event (TDE) Sw J1644+57, by showing violent variabilities in the light-curve during the decay phase. Previous studies suggest that such fluctuations in TDE may arise from the fallback of tidal disrupted debris. In this paper, we introduce the fluctuations of the mass distribution ${\rm d}M/{\rm d}E$ for the debris ejected during the tidal disruption (with energy $E$) and study their impact on jet power. Turbulence induced by tidal force and the self-gravity of the debris may imprint variabilities in ${\rm d}M/{\rm d}E$ during fallback. We model these fluctuations with a power density spectrum $\propto f_{\rm E}^{\beta}$, where $f_{\rm E} = 1/E$ and $\beta$ is the power-law index. We find that the resulting light curve can preserve the fluctuation characteristics from ${\rm d}M/{\rm d}E$. In addition, the observed fluctuations in the light-curves can be reproduced for a given suitable $\beta$. Based on the observations, we find that the value of $\beta$ should be around $-1$. less
By: I. M. Khamitov, I. F. Bikmaev, M. R. Gilfanov, R. A. Sunyaev, P. S. Medvedev
Using data from the SRG/eROSITA all-sky X-ray survey and the GAIA-based catalog of 2,209 members of the Pleiades open star cluster, we found 850 X-ray sources associated with the cluster stars. Over 650 of them were detected in X-rays for the first time. At the distance of the Pleiades, the nominal sensitivity of eROSITA corresponds to a luminosity of $L_X \sim 1.6 \cdot 10^{28}$ erg/s in the 0.3-2.3 keV band. The eROSITA sources associated... more
Using data from the SRG/eROSITA all-sky X-ray survey and the GAIA-based catalog of 2,209 members of the Pleiades open star cluster, we found 850 X-ray sources associated with the cluster stars. Over 650 of them were detected in X-rays for the first time. At the distance of the Pleiades, the nominal sensitivity of eROSITA corresponds to a luminosity of $L_X \sim 1.6 \cdot 10^{28}$ erg/s in the 0.3-2.3 keV band. The eROSITA sources associated with Pleiades stars have a total luminosity of $L_{X,tot} \sim 1.3 \cdot 10^{32}$ erg/s , a million times greater than the X-ray luminosity of the quiet Sun. Strong X-ray variability, more than 10 times, was recorded for 27 sources. Most of them are known as eruptive optical variables of the dM class. The value of $R_X=log(L_X/L_{bol})$ increases with decreasing effective temperature of the star from $R_X\approx -5$ to $R_X\approx -2$. The distribution of stars over $R_X$ is bimodal, with the left peak at $R_X\sim-4.3$ being formed by stars of FGK classes, and the right peak at $R_X\sim-3.1$ being mainly populated by M-stars. The relation between $R_X$ and the Rossby number $Ro$ depends on the spectral class. For K- and M- stars, at low Rossby numbers $R_X\sim -3$ and depends weakly on $Ro$. At $Ro \gt 0.25$, a rapid drop in $R_X$ is observed for K stars, while in our sample there are no M stars with large Rossby number. Most of F- and G- stars appear to have smaller $R_X\sim -4.5$, however, our sample size is insufficient for a more detailed characterization of their $R_X-Ro$ dependence. less
By: Yaowei Li, Lin Wang, Lei Qian, Liyun Zhang, Yujie Chen, Dejiang Yin, Baoda Li, Yinfeng Dai, Ralph P. Eatough, Wenze Li, Dongyue Jiang, Xingnan Zhang, Minghui Li, Yujie Lian, Yuxiao Wu, Tong Liu, Kuo Liu, Zhichen Pan
We employed the Fast Folding Algorithm (FFA) on L-Band Globular Cluster (GC) observations taken with Five-hundred-meter Aperture Spherical radio Telescope (FAST) to search for new pulsars, especially those with a long rotational period. We conducted a search across 16 GCs that collectively host 93 known pulsars, as well as 14 GCs that do not contain any known pulsars. The majority of these known pulsars were successfully re-detected in our ... more
We employed the Fast Folding Algorithm (FFA) on L-Band Globular Cluster (GC) observations taken with Five-hundred-meter Aperture Spherical radio Telescope (FAST) to search for new pulsars, especially those with a long rotational period. We conducted a search across 16 GCs that collectively host 93 known pulsars, as well as 14 GCs that do not contain any known pulsars. The majority of these known pulsars were successfully re-detected in our survey. The few non-detections could be attributed to the high accelerations of these pulsars. Additionally, we have discovered a new binary millisecond pulsar, namely M13I (or PSR J1641+3627I) in GC M13 (or NGC 6205), and obtained its phase-coherent timing solution using observations spanning 6 years. M13I has a spin period of 6.37 ms, and an orbital period of 18.23 days. The eccentricity of the binary orbit is 0.064, with a companion mass range of approximately 0.45 to 1.37 M$_{\odot}$. The orbital properties of M13I are remarkably different from those of the other known pulsars in M13, indicating that this pulsar has undergone a different evolutionary path compared to the rest. less