The Astrophysical Journal Letters最新文献

{"title":"Quantitative Exploration of the Similarity of Gamma-Ray Pulsar Light Curves","authors":"C. R. García and Diego F. Torres","doi":"10.3847/2041-8213/adbf0f","DOIUrl":"https://doi.org/10.3847/2041-8213/adbf0f","url":null,"abstract":"We introduce and apply a methodology based on dynamic time warping to compare the whole set of gamma-ray light curves reported in the Third Fermi-Large Area Telescope Pulsar Catalogue. Our method allows us to quantitatively measure the degree of global similarity between two light curves beyond comparing indicators such as how many peaks there are, what their separation is, and their width and height. Once the morphology of the light curve is showcased via background subtraction, min-max scaler normalization and rotations are considered to take into account that phase 0 is arbitrary, and the level of detail with which light curves of different pulsars appear is revealed. In many cases, their similarity is striking and occurs disregarding any other timing, physical, or spectral property. In particular, some millisecond pulsars and young pulsars share detailed light-curve morphology.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"35 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143723330","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}

{"title":"Single-pulse-based Interstellar Scintillation Studies of RRATs","authors":"Zi-wei Wu, Wei-wei Zhu, Zi-yao Fang, Qiu-yang Fu, Ji-guang Lu, Ling-qi Meng, Chen-Chen Miao, Xue-li Miao, Jia-rui Niu, Rukeya Rejiefu, Xun Shi, Chao Wang, Meng-yao Xue, Mao Yuan, You-ling Yue, Chun-feng Zhang, Zhen Zhang, Shi-jun Dang and Yu-lan Liu","doi":"10.3847/2041-8213/adc25c","DOIUrl":"https://doi.org/10.3847/2041-8213/adc25c","url":null,"abstract":"The nature of irregularly spaced pulses of rotating radio transients (RRATs) complicates interstellar scintillation studies. In this Letter, we report the primary scintillation parameters of a sample of RRATs using pairwise correlations of pulse spectra. Moreover, from the measured scintillation velocities, we constrain their transverse velocities. We also find a reduced modulation index, m = 0.13 ± 0.01, for RRAT J1538+2345. Several possible explanations are discussed. Furthermore, the single-pulse-based interstellar scintillation technique is applicable to other pulsar populations, including nulling pulsars and those with short scintillation timescales, and fast radio bursts.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"183 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143723332","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}

{"title":"A New Approach to the Low-frequency Stochastic Gravitational-wave Background: Constraints from Quasars and the Astrometric Hellings–Downs Curve","authors":"Jeremy Darling","doi":"10.3847/2041-8213/adbf0d","DOIUrl":"https://doi.org/10.3847/2041-8213/adbf0d","url":null,"abstract":"We present new astrometric constraints on the stochastic gravitational-wave background and construct the first astrometric Hellings–Downs curve using quasar proper motions. From quadrupolar vector spherical harmonic fits to the Gaia proper motions of 1,108,858 quasars, we obtain a frequency-integrated upper limit on the gravitational-wave energy density, (95% confidence limit), for frequencies between 11.2 nHz and 3.1 × 10−9 nHz (1.33/t0). However, from the astrometric Hellings–Downs curve that describes the correlated proper motions between 2,104,609,881 quasar pairs as a function of their angular separation, we find a stronger constraint: a characteristic strain of hc ≤ 2.7 × 10−12 for fref = 1 yr−1 and at 95% confidence. We probe down to ±0.005 μas2 yr−2 in correlated power and obtain the lowest astrometric limit to date. This is also the first time that optical wavelength astrometry surpasses limits from radio-frequency interferometry. This astrometric analysis does not yet reach the sensitivity needed to detect the pulsar timing–based red gravitational-wave spectrum extrapolated to the quasar gravitational-wave sensitivity window, assuming that the turnover in the spectrum occurs at ∼1 nHz for massive black hole binaries. The limits presented here may exclude some exotic interpretations of the stochastic gravitational-wave background.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"41 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143723334","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}

{"title":"The Einstein Probe Transient EP240414a: Linking Fast X-Ray Transients, Gamma-Ray Bursts, and Luminous Fast Blue Optical Transients","authors":"Joyce N. D. van Dalen, Andrew J. Levan, Peter G. Jonker, Daniele Bjørn Malesani, Luca Izzo, Nikhil Sarin, Jonathan Quirola-Vásquez, Daniel Mata Sánchez, Antonio de Ugarte Postigo, Agnes P. C. van Hoof, Manuel A. P. Torres, Steve Schulze, Stuart P. Littlefair, Ashley Chrimes, Maria E. Ravasio, Franz E. Bauer, Antonio Martin-Carrillo, Morgan Fraser, Alexander J. van der Horst, Pall Jakobsson, Paul O’Brien, Massimiliano De Pasquale, Giovanna Pugliese, Jesper Sollerman, Nial R. Tanvir, Tayyaba Zafar, Joseph P. Anderson, Lluís Galbany, Avishay Gal-Yam, Mariusz Gromadzki, Tomás E. Müller-Bravo, Fabio Ragosta and Jacco H. Terwel","doi":"10.3847/2041-8213/adbc7e","DOIUrl":"https://doi.org/10.3847/2041-8213/adbc7e","url":null,"abstract":"Detections of fast X-ray transients (FXTs) have accrued over the last few decades. However, their origin has remained mysterious. Rapid progress is now being made thanks to timely discoveries and localizations with the Einstein Probe mission. Early results indicate that FXTs may frequently, but not always, be associated with gamma-ray bursts (GRBs). Here, we report on the multiwavelength counterpart of FXT EP240414a, which has no reported gamma-ray counterpart. The transient is located 25.7 kpc in projection from a massive galaxy at z = 0.401. We perform comprehensive photometric and spectroscopic follow-up. The optical light curve shows at least three distinct emission episodes with timescales of ~1, 4, and 15 days and peak absolute magnitudes of MR ∼ −20, –21, and –19.5, respectively. The optical spectrum at early times is extremely blue, inconsistent with afterglow emission. It may arise from the interaction of both jet and supernova (SN) shock waves with the stellar envelope and a dense circumstellar medium, as has been suggested for some luminous fast blue optical transients (LFBOTs). At late times, the spectrum evolves to a broad-lined Type Ic SN, similar to those seen in collapsar long GRBs. This implies that the progenitor of EP240414a is a massive star creating a jet-forming SN inside a dense envelope, resulting in an X-ray outburst with a luminosity of ~1048 erg s−1 and the complex observed optical/IR light curves. If correct, this argues for a causal link between the progenitors of long GRBs, FXTs, and LFBOTs.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"30 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143723333","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}

{"title":"Inhomogeneous Dust Biases Photometric Redshifts and Stellar Masses for LSST","authors":"ChangHoon Hahn and Peter Melchior","doi":"10.3847/2041-8213/adbe5e","DOIUrl":"https://doi.org/10.3847/2041-8213/adbe5e","url":null,"abstract":"Spectral energy distribution (SED) modeling is one of the main methods to estimate galaxy properties, such as photometric redshifts, z, and stellar masses, M*, for extragalactic imaging surveys. SEDs are currently modeled as light from a composite stellar population attenuated by a geometrically homogeneous foreground dust screen. This is despite evidence from simulations and observations that find large spatial variations in dust attenuation due to the detailed geometry of stars and gas within galaxies. In this work, we examine the impact of this simplistic dust assumption on inferred z and M* for Rubin LSST. We first construct synthetic LSST-like observations (ugrizy magnitudes) from the Numerical Investigation of Hundred Astrophysical Objects (NIHAO)-SKIRT catalog, which provides SEDs from high-resolution hydrodynamic simulations using 3D Monte Carlo radiative transfer. We then infer z and M* from the synthetic observations using the PROVABGS Bayesian SED modeling framework. Overall, the homogeneous dust screen assumption biases both z and M* in galaxies, consistently and significantly for galaxies with dust attenuation AV ≳ 0.5, and likely below. The biases depend on the orientation in which the galaxies are observed. At z = 0.4, z is overestimated by ∼0.02 for face-on galaxies and M* is underestimated by ∼0.4 dex for edge-on galaxies. The bias in photo-z is equivalent to the desired redshift precision level of the LSST “gold sample” and will be larger at higher redshifts. Our results underscore the need for SED models with additional flexibility in the dust parameterization to mitigate significant systematic biases in cosmological analyses with LSST.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"215 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143702877","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}

{"title":"Multipoint Observations of Magnetic Reconnection in the Martian Magnetotail Triggered by an Interplanetary Magnetic Field Rotation","authors":"Yuanzheng Wen, Jasper S. Halekas, Han-Wen Shen, Abigail R. Azari, David A. Brain, Yaxue Dong, David L. Mitchell, Christian X. Mazelle, Jared R. Espley and James P. McFadden","doi":"10.3847/2041-8213/adbf10","DOIUrl":"https://doi.org/10.3847/2041-8213/adbf10","url":null,"abstract":"The induced magnetosphere of Mars is highly dynamic, driven by both the upstream solar wind and the planet’s crustal magnetic fields. This variability can occur on timescales much shorter than a single spacecraft orbit, making it difficult to distinguish between spatial and temporal variations in the induced magnetosphere. In this study, we utilize simultaneous multipoint observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) and Tianwen-1 missions to investigate how the induced magnetosphere responds to dynamic changes in the solar wind. We report a magnetic reconnection event observed by MAVEN in the Martian magnetotail, occurring a few minutes after an interplanetary magnetic field (IMF) rotation observed by Tianwen-1 in the upstream solar wind. This reconnection event is characterized by clear Hall magnetic field signatures and high-speed ion jets, indicating the presence of a diffusion region. Our analysis of the change in the magnetic field morphology suggests that this reconnection was likely triggered by this IMF rotation, occurring during the resulting reconfiguration of the induced magnetosphere. This multipoint study demonstrates the important role of dynamic upstream solar wind conditions, particularly IMF rotations, in driving the plasma processes in the Martian magnetotail, contributing to our understanding of solar wind energy and momentum transfer and their roles in ion escape in Mars’s hybrid magnetosphere.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"99 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143703335","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}

{"title":"Streams, Shells, and Substructures in the Accretion-built Stellar Halo of NGC 300","authors":"Catherine E. Fielder, David J. Sand, Michael G. Jones, Denija Crnojević, Alex Drlica-Wagner, Paul Bennet, Jeffrey L. Carlin, William Cerny, Amandine Doliva-Dolinsky, Laura C. Hunter, Ananthan Karunakaran, Guilherme Limberg, Burçin Mutlu-Pakdil, Andrew B. Pace, Sarah Pearson, Adam Smercina, Kristine Spekkens, Tjitske Starkenburg, Jay Strader, Guy S. Stringfellow, Erik Tollerud, Clecio R. Bom, Julio A. Carballo-Bello, Astha Chaturvedi, Yumi Choi, David J. James, Clara E. Martínez-Vázquez, Alexander H. Riley, Joanna Sakowska and Kathy Vivas","doi":"10.3847/2041-8213/adbf17","DOIUrl":"https://doi.org/10.3847/2041-8213/adbf17","url":null,"abstract":"We present deep optical observations of the stellar halo of NGC 300, an LMC-mass galaxy, acquired with the DEEP subcomponent of the DECam Local Volume Exploration survey using the 4 m Blanco Telescope. Our resolved star analysis reveals a large, low surface brightness stellar stream (MV ∼ −8.5; [Fe/H] = −1.4 ± 0.15) extending more than 40 kpc north from the galaxy’s center. We also find other halo structures, including potentially an additional stream wrap to the south, which may be associated with the main stream. The morphology and derived low metallicities of the streams and shells discovered surrounding NGC 300 are highly suggestive of a past accretion event. Assuming a single progenitor, the accreted system is approximately Fornax-like in luminosity, with an inferred mass ratio to NGC 300 of approximately 1:15. We also present the discovery of a metal-poor globular cluster (GC) (Rproj = 23.3 kpc; MV = −8.99 ± 0.16; [Fe/H] ≈ −1.6 ± 0.6) in the halo of NGC 300, the furthest identified GC associated with NGC 300. The stellar structures around NGC 300 represent the richest features observed in a Magellanic Cloud analog to date, strongly supporting the idea that accretion and subsequent disruption is an important mechanism in the assembly of dwarf galaxy stellar halos.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"28 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143702878","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}

{"title":"A Recent Supermassive Black Hole Binary in the Galactic Center Unveiled by the Hypervelocity Stars","authors":"Chunyang Cao, F. K. Liu, Shuo Li, Xian Chen and Ke Wang","doi":"10.3847/2041-8213/adbbf2","DOIUrl":"https://doi.org/10.3847/2041-8213/adbbf2","url":null,"abstract":"When a binary of early-type stars from the young stellar populations in the Galactic center (GC) region is scattered to the vicinity of the supermassive black hole (SMBH) Sgr A*, one of the components would be tidally ejected as an early-type hypervelocity star (HVS) and the counterpart would be captured on a tight orbit around Sgr A*. Dozens of B-type HVSs moving faster than the Galactic escape speed have been discovered in the Galactic halo and are produced most likely by the SMBH Sgr A*. However, the velocity distribution and in particular the deficit of the HVSs above 700 km s−1 is seriously inconsistent with the expectations of the present models. Here we show that the high-velocity deficit is due to the deficiency in close interactions of stars with the SMBH Sgr A*, because an orbiting intermediate-mass black hole (IMBH) of about 15,000 Solar mass kicked away slowly approaching stars 50–250 million years ago. The SMBH–IMBH binary formed probably after the merger of the Milky Way with the Gaia-Sausage-Enceladus dwarf galaxy, and coalesced about 10 million years ago, leading to a gravitational recoil of Sgr A* at a velocity of 0.3–0.5 km s−1 and to a change of the HVS ejection scenarios. The SMBH–IMBH binary scenario predicts the formation of the S-star cluster at the GC with the distribution of the orbital size and stellar ages that are well consistent with the observations.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"93 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143713005","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}

{"title":"Cross Helicity and the Helium Abundance as an In Situ Metric of Solar Wind Acceleration","authors":"B. L. Alterman and Raffaella D’Amicis","doi":"10.3847/2041-8213/adb48e","DOIUrl":"https://doi.org/10.3847/2041-8213/adb48e","url":null,"abstract":"The two-state solar wind paradigm is based on observations showing that slow and fast solar wind have distinct properties like helium abundances, kinetic signatures, elemental composition, and charge-state ratios. Nominally, the fast wind originates from solar sources that are continuously magnetically open to the heliosphere like coronal holes while the slow wind is from solar sources that are only intermittently open to the heliosphere like helmet streamers and pseudostreamers. The Alfvénic slow wind is an emerging third class of solar wind that challenges the two-state fast/slow paradigm. It has slow wind speeds but is highly Alfvénic, i.e., has a high correlation between velocity and magnetic field fluctuations along with low compressibility typical of Alfvén waves, which is typically observed in fast wind. Its other properties are also more similar to the fast than slow wind. From 28 yr of Wind observations at 1 au, we derive the solar wind helium abundance (AHe), Alfvénicity (∣σc∣), and solar wind speed (vsw). Characterizing vsw as a function of ∣σc∣ and AHe, we show that the maximum solar wind speed for plasma accelerated in source regions that are intermittently open is faster than the minimum solar wind speed for plasma accelerated in continuously open regions. We infer that the Alfvénic slow wind is likely solar wind originating from open field regions with speeds below the maximum solar wind speed for plasma from intermittently open regions. We then discuss possible implications for solar wind acceleration. Finally, we utilize the combination of helium abundance and normalized cross helicity to present a novel solar wind categorization scheme that illustrates the transition in observations of solar wind at 1 au from magnetically closed to magnetically open sources.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"72 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143713004","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}

{"title":"Density Fluctuation–Mach Number Scaling in Compressible, High Plasma Beta Turbulence: In Situ Space Observations and High-Reynolds Number Simulations","authors":"Riddhi Bandyopadhyay, James R. Beattie and Amitava Bhattacharjee","doi":"10.3847/2041-8213/adbe3b","DOIUrl":"https://doi.org/10.3847/2041-8213/adbe3b","url":null,"abstract":"Understanding the nature of compressible fluctuations in a broad range of turbulent plasmas, from the intracluster medium to the solar wind, has been an active field of research in the past decades. Theoretical frameworks for weakly compressible magnetohydrodynamical turbulence in an inhomogeneous background magnetic field predict a linear scaling of the normalized mass density fluctuation (δρ/ρ0), as a function of the turbulent Mach number ( ), . However, so far, the scaling relation has been tested only using moderate to low plasma beta (β ≲ 1) solar wind observational data, where the compressibility is weak δρ/ρ0 ∼ 0.1. Here, we combine NASA’s Magnetospheric Multiscale Mission data in Earth’s magnetosheath, where β ∼ 10 is high, and β ∼ 1/8 highly compressible magnetohydrodynamic turbulence simulations at unprecedented resolutions. Both show that holds across a broad range of δρ/ρ0, , and β, demonstrating that is a robust compressible turbulence relation, going beyond the asymptotics of the weakly compressible theory. We discuss the findings in the context of understanding the nature of strongly compressible turbulent fluctuations and the driving parameter in astrophysical and space plasmas.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"99 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143702875","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}