arXiv subjects

Nanda Rea

Publications and source records attributed to Nanda Rea.

At least 37 records · Page 2Linked to original sources

arXiv2025

A binary model of long period radio transients and white dwarf pulsars

Long-period radio transients (LPTs) represent a recently uncovered class of Galactic radio sources exhibiting minute-to-hour periodicities and highly polarised pulses of second-to-minute duration. Their phenomenology does not fit exactly in any other class, although it might resemble that of radio magnetars or white dwarf (WD) radio emitting binary systems. Notably, two LPTs with confirmed multi-wavelength counterparts have been identified as WD -- M dwarf binaries. Meanwhile, systems such as AR Scorpii and J1912-44 exhibit short-period pulsations in hrs-tight orbits, with polarised radio emission proposed to be generated by the interaction of the WD magnetosphere with the low-mass companion wind. Here, we investigate the longest-lived LPT known, GPM J1839-10, demonstrating that it has a ~8.75 hr orbital period. We show that its radio pulses can be modelled in the same geometric framework as WD binary pulsars, in which radio emission is triggered when the magnetic axis of a rotating WD intersects its companion's wind in the binary orbital plane. We use a 36-year timing baseline to infer the orbital period and binary geometry from radio data alone. The model naturally predicts its intermittent emission and double-pulse structure. Crucially, we show that the beat period between the spin and the orbit matches the observed pulse substructure and polarisation signatures, providing strong support for the model. Applying it to the WD pulsar J1912-44, it successfully reproduces the emission profile and geometry as well. Our results suggest analogous emission-site geometries in these related classes of binary system -- a possibility we extend to the broader LPT / WD pulsar population.

astro-ph.HE↗

arXiv2025

ASKAP J144834-685644: a newly discovered long period radio transient detected from radio to X-rays

Long-period radio transients (LPTs) are an emerging group of radio transients that show periodic polarized radio bursts with periods varying from a few minutes to a few hours. Fewer than a dozen LPTs have been detected so far, and their origin (source and emission mechanism) remains unclear. Here, we report the discovery of a 1.5 h LPT, ASKAP J144834-685644, adding to the current sample of sources. ASKAP J144834-685644 is one of the very few LPTs that has been detected from X-rays to radio. It shows a steep radio spectrum and polarized radio bursts, which resemble the radio emission in known LPTs. In addition, it also shows highly structured and periodic narrow-band radio emission. Multiwavelength properties suggest that the spectral energy distribution (SED) peaks at near ultraviolet wavelengths, indicating the presence of a hot magnetic source. Combining multiwavelength information, we infer that ASKAP J144834-685644 may be a near edge-on magnetic white dwarf binary (MWD), although we cannot fully rule out ASKAP J144834-685644 being an isolated white dwarf pulsar or even a transitional millisecond pulsar (despite the lack of radio pulsations). If ASKAP J144834-685644 is a MWD binary, the observed broad-band SED can be explained by emission from an accretion disc. This hints that some fraction of optically bright LPTs may be accreting binaries with the radio period being the orbital period. It might further suggest a connection between optically bright synchronized WD binaries, such as polars, and non-accreting asynchronous WD pulsars, such as AR Sco and J1912-4410.

astro-ph.HE↗

arXiv2025

Dense Matter in Neutron Stars with eXTP

In this White Paper, we present the potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission to constrain the equation of state of dense matter in neutron stars, exploring regimes not directly accessible to terrestrial experiments. By observing a diverse population of neutron stars - including isolated objects, X-ray bursters, and accreting systems - eXTP's unique combination of timing, spectroscopy, and polarimetry enables high-precision measurements of compactness, spin, surface temperature, polarimetric signals, and timing irregularity. These multifaceted observations, combined with advances in theoretical modeling, pave the way toward a comprehensive description of the properties and phases of dense matter from the crust to the core of neutron stars. Under development by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Sciences, the eXTP mission is planned to be launched in early 2030.

astro-ph.HE↗

arXiv2025

Probing multi-band variability and mode switching in the candidate transitional millisecond pulsar 3FGL J1544.6-1125

We present the most extensive high-time resolution multi-band campaign to date on the candidate transitional millisecond pulsar (tMSP) 3FGL J1544.6-1125 in the sub-luminous disk state, with coordinated observations from the radio to the X-ray band. While XMM-Newton and NuSTAR X-ray light curves exhibit the characteristic high- and low-mode bimodality, the source faintness prevents firm evidence for similar bimodality in the ultraviolet and near-infrared light curves, presented here for the first time. A re-analysis of archival XMM-Newton/OM data reveals an optical flare without an X-ray counterpart, likely originating from the outer accretion disk or the companion star. During our observations, no radio emission was detected, with a 3$σ$ flux density upper limit of 8 $μ$Jy at 6 GHz. While past works have already reported radio variability in the source, this limit is a factor of 3.5 below the average value measured in 2019 in similar conditions, underscoring significant radio variability despite the relatively stable X-ray flux. Simultaneous optical light curves in five filters with GTC/HiPERCAM revealed flickering and dipping activities that resemble the observed X-ray variability, along with a reddening trend at lower fluxes. The latter is consistent with discrete mass ejections that disrupt the inner flow and reduce both X-ray and optical fluxes, thereby driving the high-to-low-mode switches. This suggests a common origin for most optical and X-ray emission at the boundary region between the pulsar wind and the inner disk, as also supported by our modelling of the spectral energy distribution in the high mode. Overall, our findings reinforce the mini-pulsar nebula picture for tMSPs in the sub-luminous state and demonstrate how coordinated, high-time resolution, multi-wavelength campaigns are essential to probe the processes governing rapid mode switches in these systems.

astro-ph.HE↗

arXiv2025

A sample of ionised Fe line-emitting X-ray sources in the inner Galactic disc

Previous studies suggest that the Galactic diffuse X-ray emission is composed of unresolved point sources, primarily mCVs. However, nearby mCVs have a much lower 6.7 keV line equivalent width ($\rm EW_{6.7}$) compared to the diffuse X-ray emission. Therefore, the primary contributors to the unresolved X-ray emission remain unclear. We detected a total of 859 sources in the 6.5-7 keV band using XMM-Newton observations of the inner Galactic disc, of which 72 sources show significant iron line emission at 6.7 keV. The distribution of spectral index $Γ$ for these 72 sources is bimodal, with peaks at $Γ=0.5\pm0.4$ and $1.8\pm0.3$, suggesting two populations of sources. The soft X-ray sources have significantly larger $\rm EW_{6.7}$ than the hard X-ray sources. Furthermore, 18 of the 32 hard sources are associated with previously known CVs. We identify CV candidates in our sample as those with spectral index $Γ<1.25$. The line ratio, 2-10 keV luminosity, and previous detection of spin period suggest that most of these hard sources are mCVs. The distribution of the $\rm EW_{6.7}$ line for the combined sample of previously identified and candidate CVs has a mean value of <$\rm EW_{6.7}$>$=415\pm39$ eV. Furthermore, we computed the stacked spectra of all sources detected in the 6.5-7 keV band for different flux groups, and we find evidence in the stacked spectra of hard sources that the $\rm EW_{6.7}$ increases with decreasing flux. The soft X-ray sources have <$\rm EW_{6.7}$>$=1.1\pm0.1$ keV. We identified 13 of the 30 soft sources associated with active stars, young stellar objects, and active binaries of RS CVn type. The <$\rm EW_{6.7}$> of our CV candidate sample is more than twice as large as the typical $\rm EW_{6.7}$ found in mCVs within 500 pc, and the <$\rm EW_{6.7}$> of our CV candidate sample is close to the $\rm EW_{6.7}$ value of Galactic diffuse X-ray emission.

astro-ph.HE↗

arXiv2025

New X-ray Supernova Remnants in NGC 7793

This work focuses on the detection of X-ray Supernova Remnants (SNRs) in the galaxy NGC 7793 and the study of their properties. X-ray SNRs in galaxies beyond the Local Group are rare, mainly due to the limited sensitivity of current X-ray instruments. Additionally, their identification requires an optical counterpart, making incomplete optical identification methods an extra challenge. Detecting X-ray SNRs in other galaxies is crucial for understanding their feedback in different evolutionary phases and gaining insights into their local interstellar medium. In NGC 7793, only one X-ray SNR was previously known, while a recent study reported nearly 240 optical SNRs. The discovery of a new, larger optical SNR sample motivated a re-examination of the X-ray SNR population by comparing optical SNRs with X-ray sources. To identify X-ray SNRs, we utilised Chandra's spatial resolution and analysed all available archival data of NGC 7793, totaling 229.9 ks over 19 years. After data reduction, we performed source detection and analysis, searching for X-ray sources coinciding with optical SNRs. We also used XMM-Newton for spectral analysis of the confirmed and candidate SNRs. We detected 58 X-ray sources down to an observed luminosity of $\sim 1.5\times 10^{36}\, erg\, s^{-1}$. Among them, five X-ray counterparts to optical SNRs were identified, all presenting soft emission (<1.2 keV) with no short- or long-term variability. One corresponds to the previously known X-ray SNR, while four are newly detected. Spectral modeling of two SNRs shows thermal spectra exceeding 2.5 million K, with strong OVII, OVIII, and NeIX emission lines. A correlation between density, X-ray luminosity, and source softness was observed. We also report X-ray emission from supernova 2008bk, refining its position, and suggest two candidate X-ray SNRs with soft, non-variable spectra, one resembling the identified X-ray SNRs.

astro-ph.HE↗

arXiv2025

Radio pulsar population synthesis with consistent flux measurements using simulation-based inference

The properties of the entire neutron star population can be inferred by modeling their evolution, from birth to the present, through pulsar population synthesis. This involves simulating a mock population, applying observational filters, and comparing the resulting sources to the limited subset of detected pulsars. We specifically focus on the magneto-rotational properties of Galactic isolated neutron stars and provide new insights into the intrinsic radio luminosity law by combining pulsar population synthesis with a simulation-based inference (SBI) technique called truncated sequential neural posterior estimation (TSNPE). We employ TSNPE to train a neural density estimator on simulated pulsar populations to approximate the posterior distribution of the underlying parameters. This technique efficiently explores the parameter space by concentrating on regions that are most likely to match the observed data thus allowing a significant reduction in training dataset size. We demonstrate the efficiency of TSNPE over standard neural posterior estimation (NPE), achieving robust inferences of magneto-rotational parameters consistent with previous studies using only around 4% of the simulations required by NPE approaches. Moreover, for the first time, we incorporate data from the Thousand Pulsar Array (TPA) program on MeerKAT, the largest unified sample of neutron stars with consistent fluxes measurement to date, to help constrain the stars' intrinsic radio luminosity. We find that adding flux information as an input to the neural network largely improves the constraints on the pulsars' radio luminosity, as well as improving the estimates on other input parameters.

astro-ph.HE↗

arXiv2025

Magnetars

Magnetars are the most magnetic objects in the Universe, serving as unique laboratories to test physics under extreme magnetic conditions that cannot be replicated on Earth. They were discovered in the late 1970s through their powerful X-ray flares, and were subsequently identified as neutron stars characterized by steady and transient emission across the radio, infrared, optical, X-ray, and gamma-ray bands. In this chapter, we summarize the current state of our experimental and theoretical knowledge on magnetars, as well as briefly discussing their relationship with supernovae, gamma-ray bursts, fast radio bursts, and the transient multi-band sky at large.

astro-ph.HE↗

arXiv2025

IXPE detection of highly polarized X-rays from the magnetar 1E 1841-045

The Imaging X-ray Polarimetry Explorer (IXPE) observed for the first time highly polarized X-ray emission from the magnetar 1E 1841-045, targeted after a burst-active phase in August 2024. To date, IXPE has observed four other magnetars during quiescent periods, highlighting substantially different polarization properties. 1E 1841-045 exhibits a high, energy-dependent polarization degree, which increases monotonically from ~15% at 2-3 keV up to ~55% at 5.5-8 keV, while the polarization angle, aligned with the celestial North, remains fairly constant. The broadband spectrum (2-79 keV) obtained by combining simultaneous IXPE and NuSTAR data is well modeled by a blackbody and two power-law components. The unabsorbed 2-8 keV flux (~2E-11 erg/cm2/s) is about 10% higher than that obtained from archival XMM-Newton and NuSTAR observations. The polarization of the soft, thermal component does not exceed ~25%, and may be produced by a condensed surface or a bombarded atmosphere. The intermediate power law is polarized at around 30%, consistent with predictions for resonant Compton scattering in the star magnetosphere; while, the hard power law exhibits a polarization degree exceeding 65%, pointing to a synchrotron/curvature origin.

astro-ph.HE↗

arXiv2025

Science objectives of the Einstein Probe mission

The Einstein Probe (EP) is an interdisciplinary mission of time-domain and X-ray astronomy. Equipped with a wide-field lobster-eye X-ray focusing imager, EP will discover cosmic X-ray transients and monitor the X-ray variability of known sources in 0.5-4 keV, at a combination of detecting sensitivity and cadence that is not accessible to the previous and current wide-field monitoring missions. EP can perform quick characterisation of transients or outbursts with a Wolter-I X-ray telescope onboard. In this paper, the science objectives of the Einstein Probe mission are presented. EP is expected to enlarge the sample of previously known or predicted but rare types of transients with a wide range of timescales. Among them, fast extragalactic transients will be surveyed systematically in soft X-rays, which include γ-ray bursts and their variants, supernova shock breakouts, and the predicted X-ray transients associated with binary neutron star mergers. EP will detect X-ray tidal disruption events and outbursts from active galactic nuclei, possibly at an early phase of the flares for some. EP will monitor the variability and outbursts of X-rays from white dwarfs, neutron stars and black holes in our and neighbouring galaxies at flux levels fainter than those detectable by the current instruments, and is expected to discover new objects. A large sample of stellar X-ray flares will also be detected and characterised. In the era of multi-messenger astronomy, EP has the potential of detecting the possible X-ray counterparts of gravitational wave events, neutrino sources, and ultra-high energy γ-ray and cosmic ray sources. EP is expected to help advance the studies of extreme objects/phenomena and their underlying physical processes revealed in the dynamic X-ray universe, as well as studies in other areas of X-ray astronomy.

astro-ph.HE↗

arXiv2025

The NewAthena mission concept in the context of the next decade of X-ray astronomy

Large X-ray observatories such as Chandra and XMM-Newton have been delivering scientific breakthroughs in research fields as diverse as our Solar System, the astrophysics of stars, stellar explosions and compact objects, accreting super-massive black holes, and large-scale structures traced by the hot plasma permeating and surrounding galaxy groups and clusters. The recently launched observatory XRISM is opening in earnest the new observational window of non-dispersive high-resolution spectroscopy. However, several quests are left open, such as the effect of the stellar radiation field on the habitability of nearby planets, the Equation-of-State regulating matter in neutron stars, the origin and distribution of metals in the Universe, the processes driving the cosmological evolution of the baryons locked in the gravitational potential of Dark Matter and the impact of supermassive black hole growth on galaxy evolution, just to mention a few. Furthermore, X-ray astronomy is a key player in multi-messenger astrophysics. Addressing these quests experimentally requires an order-of-magnitude leap in sensitivity, spectroscopy and survey capabilities with respect to existing X-ray observatories. This paper succinctly summarizes the main areas where high-energy astrophysics is expected to contribute to our understanding of the Universe in the next decade and describes a new mission concept under study by the European Space Agency, the scientific community worldwide and two International Partners (JAXA and NASA), designed to enable transformational discoveries: NewAthena. This concept inherits its basic payload design from a previous study carried out until 2022, Athena.

astro-ph.IM↗

arXiv2024

Detection of X-ray Emission from a Bright Long-Period Radio Transient

Recently, a class of long-period radio transients (LPTs) has been discovered, exhibiting emission on timescales thousands of times longer than radio pulsars. Several models had been proposed implicating either a strong magnetic field neutron star, isolated white dwarf pulsar, or a white dwarf binary system with a low-mass companion. While several models for LPTs also predict X-ray emission, no LPTs have been detected in X-rays despite extensive searches. Here we report the discovery of an extremely bright LPT (10-20 Jy in radio), ASKAP J1832-0911, which has coincident radio and X-ray emission, both with a 44.2-minute period. The X-ray and radio luminosities are correlated and vary by several orders of magnitude. These properties are unique amongst known Galactic objects and require a new explanation. We consider a $\gtrsim0.5$ Myr old magnetar with a $\gtrsim 10^{13}$ G crustal field, or an extremely magnetised white dwarf in a binary system with a dwarf companion, to be plausible explanations for ASKAP J1832-0911, although both explanations pose significant challenges to formation and emission theories. The X-ray detection also establishes a new class of hour-scale periodic X-ray transients of luminosity $\sim10^{33}$ erg/s associated with exceptionally bright coherent radio emission.

astro-ph.HE↗

arXiv2024

Einstein Probe discovery of EP240408a: a peculiar X-ray transient with an intermediate timescale

We report the discovery of a peculiar X-ray transient, EP240408a, by Einstein Probe (EP) and follow-up studies made with EP, Swift, NICER, GROND, ATCA and other ground-based multi-wavelength telescopes. The new transient was first detected with Wide-field X-ray Telescope (WXT) on board EP on April 8th, 2024, manifested in an intense yet brief X-ray flare lasting for 12 seconds. The flare reached a peak flux of 3.9x10^(-9) erg/cm2/s in 0.5-4 keV, about 300 times brighter than the underlying X-ray emission detected throughout the observation. Rapid and more precise follow-up observations by EP/FXT, Swift and NICER confirmed the finding of this new transient. Its X-ray spectrum is non-thermal in 0.5-10 keV, with a power-law photon index varying within 1.8-2.5. The X-ray light curve shows a plateau lasting for about 4 days, followed by a steep decay till becoming undetectable about 10 days after the initial detection. Based on its temporal property and constraints from previous EP observations, an unusual timescale in the range of 7-23 days is found for EP240408a, which is intermediate between the commonly found fast and long-term transients. No counterparts have been found in optical and near-infrared, with the earliest observation at 17 hours after the initial X-ray detection, suggestive of intrinsically weak emission in these bands. We demonstrate that the remarkable properties of EP240408a are inconsistent with any of the transient types known so far, by comparison with, in particular, jetted tidal disruption events, gamma-ray bursts, X-ray binaries and fast blue optical transients. The nature of EP240408a thus remains an enigma. We suggest that EP240408a may represent a new type of transients with intermediate timescales of the order of about 10 days. The detection and follow-ups of more of such objects are essential for revealing their origin.

astro-ph.HE↗

arXiv2024

Long-term study of the 2020 magnetar-like outburst of the young pulsar PSRJ1846-0258 in Kes 75

Magnetar-like activity has been observed in a large variety of neutron stars. PSR J1846-0258 is a young 327 ms radio-quiet pulsar with a large rotational power ($\sim 8 \times 10^{36}$ erg s$^{-1}$), and resides at the center of the supernova remnant Kes 75. It is one of the rare examples of a high magnetic field pulsar showing characteristics both of magnetars and radio pulsars, and can thus provide important clues on the differences in the emission mechanisms between these two classes. In 2006, PSR J1846-0258 was detected to undergo an outburst for the first time, accompanied by a large flux increase, millisecond X-ray bursts, significant spectral changes and a large timing glitch. In the period between May-June 2020, after fourteen years of quiescent stable emission, the source underwent a second magnetar-like outburst, which was followed up with several observations by NICER, XMM-Newton, NuSTAR and Swift. In this work, we report on the long-term timing and X-ray spectral properties of the source following the 2020 outburst, and place upper limits on any source activity at radio wavelengths. We demonstrate that the pulsed flux increased by a factor $> 6$ during the outburst, followed by non-trivial variability in the spin-down rate. Our timing analysis shows that the spin frequency and its derivative are clearly affected by magnetospheric activity due to the outburst. We find hints for an oscillation in the frequency derivative with a timescale of 50-60 days, recovering later on to stable quiescence.

astro-ph.HE↗

arXiv2024

3D code for MAgneto-Thermal evolution in Isolated Neutron Stars, MATINS: thermal evolution and lightcurves

The thermal evolution of isolated neutron stars is a key element in unraveling their internal structure and composition and establishing evolutionary connections among different observational subclasses. Previous studies have predominantly focused on one-dimensional or axisymmetric two-dimensional models. In this study, we present the thermal evolution component of the novel three-dimensional magnetothermal code MATINS (MAgneto-Thermal evolution of Isolated Neutron Star). MATINS employs a finite volume scheme and integrates a realistic background structure, along with state-of-the-art microphysical calculations for the conductivities, neutrino emissivities, heat capacity, and superfluid gap models. This paper outlines the methodology employed to solve the thermal evolution equations in MATINS, along with the microphysical implementation which is essential for the thermal component. We test the accuracy of the code and present simulations with non-evolving magnetic fields of different configurations (all with electrical currents confined to the crust and a magnetic field that does not thread the core), to produce temperature maps of the neutron star surface. Additionally, for a specific magnetic field configuration, we show one fully coupled evolution of magnetic field and temperature. Subsequently, we use a ray-tracing code to link the neutron star surface temperature maps obtained by MATINS with the phase-resolved spectra and pulsed profiles that would be detected by distant observers. This study, together with our previous article focused on the magnetic formalism, presents in detail the most advanced evolutionary code for isolated neutron stars, with the aim of comparison with their timing properties, thermal luminosities and the associated X-ray light curves.

astro-ph.HE↗

arXiv2024

XMM-Newton and NuSTAR discovery of a likely IP candidate XMMU J173029.8-330920 in the Galactic Disk

We aim at characterizing the population of low-luminosity X-ray sources in the Galactic plane by studying their X-ray spectra and periodic signals in the light curves. We are performing an X-ray survey of the Galactic disk using XMM-Newton, and the source XMMU J173029.8-330920 was serendipitously discovered in our campaign. We performed a follow-up observation of the source using our pre-approved NuSTAR target of opportunity time. We used various phenomenological models in xspec for the X-ray spectral modeling. We also computed the Lomb-Scargle periodogram to search for X-ray periodicity. A Monte Carlo method was used to simulate 1000 artificial light curves to estimate the significance of the detected period. We also searched for X-ray, optical, and infrared counterparts of the source in various catalogs. The spectral modeling indicates the presence of an intervening cloud with $N_{\rm H}\sim(1.5-2.3)\times10^{23}\ \rm cm^{-2}$ that partially absorbs the incoming X-ray photons. The X-ray spectra are best fit by a model representing emission from a collisionally ionized diffuse gas with plasma temperature $kT=26^{+11}_{-5}$ keV. Furthermore, an Fe $K_α$ line at $6.47^{+0.13}_{-0.06}$ keV was detected with an equivalent width of the line of $312\pm104$ eV. We discovered a coherent pulsation with a period of $521.7\pm0.8$ s. The 3-10 keV pulsed fraction of the source is around $\sim$50-60\%. The hard X-ray emission with plasma temperature $kT=26^{+11}_{-5}$ keV, iron $K_α$ emission at 6.4 keV and a periodic behavior of $521.7\pm0.8$ s suggest XMMU J173029.8-33092 to be an intermediate polar. We estimated the mass of the central white dwarf to be $0.94-1.4\ M_{\odot}$ by assuming a distance to the source of $\sim1.4-5$ kpc.

astro-ph.HE↗

arXiv2024

Isolated pulsar population synthesis with simulation-based inference

We combine pulsar population synthesis with simulation-based inference (SBI) to constrain the magnetorotational properties of isolated Galactic radio pulsars. We first develop a framework to model neutron star birth properties and their dynamical and magnetorotational evolution. We specifically sample initial magnetic field strengths, $B$, and spin periods, $P$, from lognormal distributions and capture the late-time magnetic field decay with a power law. Each lognormal is described by a mean, $μ_{\log B}, μ_{\log P}$, and standard deviation, $σ_{\log B}, σ_{\log P}$, while the power law is characterized by the index, $a_{\rm late}$. We subsequently model the stars' radio emission and observational biases to mimic detections with three radio surveys, and we produce a large database of synthetic $P$--$\dot{P}$ diagrams by varying our five magnetorotational input parameters. We then follow an SBI approach that focuses on neural posterior estimation and train deep neural networks to infer the parameters' posterior distributions. After successfully validating these individual neural density estimators on simulated data, we use an ensemble of networks to infer the posterior distributions for the observed pulsar population. We obtain $μ_{\log B} = 13.10^{+0.08}_{-0.10}$, $σ_{\log B} = 0.45^{+0.05}_{-0.05}$ and $μ_{\log P} = -1.00^{+0.26}_{-0.21}$, $σ_{\log P} = 0.38^{+0.33}_{-0.18}$ for the lognormal distributions and $a_{\rm late} = -1.80^{+0.65}_{-0.61}$ for the power law at the $95\%$ credible interval. We contrast our results with previous studies and highlight uncertainties of the inferred $a_{\rm late}$ value. Our approach represents a crucial step toward robust statistical inference for complex population synthesis frameworks and forms the basis for future multiwavelength analyses of Galactic pulsars.

astro-ph.HE↗

arXiv2024

Constraints on the dense matter equation of state from young and cold isolated neutron stars

Neutron stars are the dense and highly magnetic relics of supernova explosions of massive stars. The quest to constrain the Equation of State (EoS) of ultra-dense matter and thereby probe the behavior of matter inside neutron stars, is one of the core goals of modern physics and astrophysics. A promising method involves investigating the long-term cooling of neutron stars, and comparing theoretical predictions with various sources at different ages. However, limited observational data, and uncertainties in source ages and distances, have hindered this approach. In this work, re-analyzing XMM-Newton and Chandra data from dozens of thermally emitting isolated neutron stars, we have identified three sources with unexpectedly cold surface temperatures for their young ages. To investigate these anomalies, we conducted magneto-thermal simulations across diverse mass and magnetic fields, considering three different EoS. We found that the "minimal" cooling model, failed to explain the observations, regardless the mass and the magnetic field, as validated by a machine learning classification method. The existence of these young cold neutron stars suggests that any dense matter EoS must be compatible with a fast cooling process at least in certain mass ranges, eliminating a significant portion of current EoS options according to recent meta-modelling analysis.

astro-ph.HE↗