arXiv subjects

Noémie Globus

Publications and source records attributed to Noémie Globus.

17 recordsLinked to original sources

arXiv2026

EP260119a: A High-Redshift Gamma-Ray Quiet Fast X-ray Transient Probing a Potentially Hidden Population of Relativistic Explosions

Gamma-ray quiet fast X-ray transients (FXTs) provide a new approach for studying relativistic explosions that evade traditional gamma-ray triggers. In this work, we present multi-wavelength observations and analysis of EP260119a, a high-$z$ FXT detected by Einstein Probe/WXT and followed up with COLIBRÍ, the Liverpool Telescope, and other facilities. Spectroscopy yields a redshift of $z = 5.47$, making EP260119a the most distant FXT detected by Einstein Probe to date. Despite its luminous X-ray and optical emission, no prompt gamma-ray counterpart was detected by SVOM/ECLAIRs, SVOM/GRM, Swift/BAT, or Konus/Wind, despite contemporaneous coverage. The broadband afterglow is well described by synchrotron emission from a uniform relativistic jet propagating into a shallowly stratified external medium close to the constant-density limit, indicating a standard relativistic explosion despite the absence of detectable gamma rays. Occupying the extreme high-$z$ end of the growing Einstein Probe FXT sample, EP260119a supports the possibility that soft X-ray surveys are uncovering relativistic transients that remain undetected by current gamma-ray instruments. Our results indicate that some explosions in the early Universe escape conventional gamma-ray surveys and demonstrate the value of combining sensitive soft X-ray discovery with rapid optical follow-up to obtain a more complete view of the high-$z$ transient population.

astro-ph.HE↗

arXiv2026

GRB 260310A / SN 2026fgk: A Multi-Wavelength Study of a Nearby Underluminous Long GRB and SN with a Complex Afterglow

We present a comprehensive multi-wavelength study of GRB 260310A / SN 2026fgk, a nearby ($z=0.153$), long-duration gamma-ray burst (GRB) with an exceptionally underluminous prompt $γ$-ray emission and a Comptonized spectrum. The burst occurred at the edge of a blue host galaxy at a projected distance of 15 kpc, which is one of the largest offsets reported for a long GRB. The bright optical afterglow, with dense coverage from COLIBRÍ, likely peaked at a few to several hours post-burst, followed by a shallow decay not expected from canonical afterglow models. Both the optical and X-ray light curves show a brief chromatic plateau from $4-7$ days. We show that the subsequent rebrightening observed at $\sim20$ days is best explained by the combined contribution of the associated Type Ic-BL supernova, identified in GTC spectra, and a late-time refreshed shock. The broadband optical to X-ray spectral energy distribution is well described by synchrotron emission from the forward shock, while the radio observations demand an additional emission component. We model the afterglow using (a) an on-axis uniform jet from a dirty fireball with late-time energy injection and (b) a misaligned jet with power-law angular structure, both having material emitting along our line-of-sight (LOS) moving with an initial Lorentz factor of $Γ_0\sim20-35$. We conclude that at more typical GRB distances ($z\gtrsim0.5$) the prompt $γ$-ray emission from this source would likely have escaped detection, whereas its optical afterglow would have remained observable, making the event appear as an orphan afterglow or a gamma-ray quiet fast X-ray transient.

astro-ph.HE↗

arXiv2026

Cosmogenic neutrinos from FRII galaxies as potential origin of the ultra-high-energy KM3-230213A event

Aim : We investigate whether the ultra-high-energy neutrino KM3-230213A can be interpreted as a cosmogenic neutrino produced by ultra-high-energy cosmic rays (UHECRs) accelerated in the lobes of FRII radio galaxies. Method : We model the UHECR, cosmogenic neutrino and photon fluxes expected at Earth using a recent luminosity-dependent density evolution of radio galaxies, empirical relations between radio luminosity and jet kinetic power, and standard assumptions for the UHECR output of FRII lobes. The FRII contribution to the UHECR population is derived self-consistently from the observed luminosity function, rather than imposed as a fixed normalization. The propagation of UHECRs and the production of secondary particles are computed with well-established numerical tools. Results : The predicted cosmogenic neutrino flux is compatible with that inferred from the detection of KM3-230213A, while remaining consistent with current UHECR and gamma-ray constraints. According to our models, the full GRAND observatory ($200\,000~\rm km^2$) should detect between $\sim50$ and $\sim135$ neutrinos above $10^{17}$~eV in ten years, allowing the diffuse UHE neutrino spectrum to be characterized. In contrast, the detection of individual FRII sources or statistically significant correlations with FRII catalogs is likely to remain challenging. At the highest energies, UHECR composition and anisotropy measurements, in particular those related to the nearby radio galaxy Cygnus~A, should provide complementary tests of this scenario. More generally, progress will likely rely on the combination of multimessenger observations with improved astrophysical constraints on particle acceleration and jet composition in FRII radio galaxies.

astro-ph.HE↗

arXiv2026

TEQUILA: Mechanism-free polarimetry for astronomy

TEQUILA (Transient Event $Q$, $U$, and $I$ Light Analyzer) is an optical imaging polarimeter developed for the second Nasmyth port of the 1.3-m COLIBRÍ altitude-azimuth telescope at Observatorio Astronómico Nacional in San Pedro Mártir, México (OAN-SPM). TEQUILA uses a CMOS sensor with an on-chip wire-grid micro-polarizer array to obtain simultaneous, single-exposure measurements of the Stokes parameters $I$, $Q$, and $U$ without moving optical components. This mechanism-free instrument, built entirely from commercial components, delivers seeing-limited imaging in a fixed optical band and is optimized for early-time follow-up of transient sources, including gamma-ray burst afterglows, blazars, and variable young stellar objects. In this paper, we describe the scientific motivation, the instrument design and implementation, the calibration, and initial science results. Sensor characterization reveals a polarimetric structure in the flat field and a low quantum efficiency, which we estimate to be approximately 17%, including losses introduced by the micro-polarizer array. For point sources, TEQUILA achieves absolute polarimetry with RMS uncertainties of 0.15% in pupil-tracking observations and 0.20% in field-tracking observations. In pupil-tracking mode, the observed RMS is fully explained by the measurement and standard-star uncertainties, with no evidence for an additional calibration term. In contrast, field-tracking observations require an additional calibration uncertainty of approximately 0.10%. Calibration for resolved-source polarimetry remains in progress.

astro-ph.IM↗

arXiv2026

Failed jet breakout in the metal-poor broad-lined type Ic supernova 2026gzf

A long-standing question in the death of massive stars is the role of relativistic jets. While many gamma-ray bursts and some fast X-ray transients seem to be associated with broad-lined type Ic supernovae, the opposite is not true. The lack of observable jet emission in those Ic-BL SNe can be explained by invoking off-axis jets, choked jets that inject all their energy into the stellar envelope, baryon-loaded jets for which the prompt high-energy emission is strongly suppressed, or non-jetted SNe. The lack of exact explosion time in the majority of SNe presents an obstacle to distinguish between these scenarios. Here we report the properties of SN 2026gzf associated with the X-ray thermal Einstein Probe shock-breakout EP260321a at z=0.0343. The absence of compelling shocked cocoon and radio emission up to 54 days, combined with initial expansion velocities of ~30,000 km/s and a circumstellar shell of ~0.07 M$_\odot$, favour a scenario for SN 2026gzf in which a jet was choked in the circumstellar shell. Our high-spatial resolution images of the SN environment show that the progenitor was located between two highly star-forming regions with a metallicity lower than any previously known Ic-BL SN. As the first case of a Ic-BL SN associated with high-energy prompt emission without the signature of a jet, SN 2026gzf provides a unique perspective to understand the successful launch of relativistic jets during the deaths of massive stars.

astro-ph.HE↗

arXiv2026

Fireballs' Whispers of Their Central Engine: Relativistic Filtering of Afterglow QPOs

Quasi-periodic oscillations (QPOs) in gamma-ray bursts (GRBs) afterglows have been suggested as probes of the central engine. Such interpretations generally assume that the observed modulation frequency directly corresponds to an intrinsic oscillation frequency of the source. We show that this assumption is not generally valid and that interpreting such features without accounting for relativistic propagation may lead to misleading inferences about the engine nature. We show that relativistic propagation effects - most importantly integration over equal-arrival-time surfaces - act as a frequency-dependent filter that can significantly modify or suppress intrinsic variability. In the constant-$Γ$ case, the angular kernel acts as a stationary low-pass filter that suppresses high-frequency variability without altering its frequency, whereas Blandford-McKee deceleration renders the filter time-dependent and manifests observationally as an apparent frequency drift.

astro-ph.HE↗

arXiv2026

A Hierarchical Shock Model of Ultra-High-Energy Cosmic Rays

We propose that a hierarchical shock model$\unicode{x2014}$including supernova remnant shocks, galactic wind termination shocks, and accretion shocks around cosmic filaments and galaxy clusters$\unicode{x2014}$can naturally explain the cosmic ray spectrum from ~1 GeV up to ~200 EeV. While this framework applies to the entire cosmic ray spectrum, in this work, we focus on its implications for ultra-high-energy cosmic rays (UHECRs). We perform a hydrodynamic cosmological simulation to investigate the power processed at shocks around clusters and filaments. The downstream flux from nearby shocks around the local filament accounts for the softer, lower-energy extragalactic component around the ankle, and the upstream escaping flux from nearby clusters accounts for the transition to a hard spectral component at the highest energies. This interpretation is in agreement with UHECR observations. We suggest that a combination of early-Universe galactic outflows, cosmic ray streaming instabilities, and a small-scale turbulent dynamo can increase magnetic fields enough to attain the required rigidities. Our simulation suggests that the available volume-averaged power density of accretion shocks exceeds the required UHECR luminosity density by three orders of magnitude. We show that microgauss magnetic fields at these shocks could explain both the origin of UHECRs and potentially contribute to the diffuse radio synchrotron background below 10 GHz. The shock-accelerated electrons produce a hard radio background without overproducing diffuse inverse Compton emission. These results motivate further observational tests with upcoming facilities to help distinguish accretion shocks from other UHECR sources.

astro-ph.HE↗

arXiv2026

Evidence of Energy Injection in the Short and Distant GRB 250221A in a High Density Environment

We present the photometric and spectroscopic analysis of the short-duration GRB 250221A ($T_{90}=1.80\pm0.32$ s), using a data set from the optical facilities COLIBRÍ, the Harlingten 50~cm Telescope, and the Very Large Telescope. We complement these observations with data from the Neil Gehrels Swift Observatory and the Einstein Probe, as well as radio observations from the Very Large Array. GRB 250221A is among the few short GRBs with direct afterglow spectroscopy, which gives a secure redshift determination of $z=0.768$ and allows the unambiguous identification of the host as a galaxy with a star-formation rate of $\sim3\,M_\odot\,{\rm yr}^{-1}$. The X-ray and optical light curves up to $T_0+3\times 10^4$ s (where $T_0$ refers to the GRB trigger time) are well described by forward-shock synchrotron emission in the slow-cooling regime within the standard fireball framework. However, at $T_0 \sim 5\times 10^4$ s, both the X-ray and optical bands exhibit an excess over the same interval, which we interpret as evidence of energy injection into a jet with a half-opening angle of $θ_j=11.5^{\circ}$ through a refreshed shock powered by late central engine activity or a radially stratified ejecta. The burst properties (duration, spectral hardness, peak energy, and location in the Amati plane) all favour a compact binary merger origin. However, our modelling of the afterglow suggests a dense circumburst medium ($n\sim80$ cm$^{-3}$), which is more typical of a collapsar environment.

astro-ph.HE↗

arXiv2025

Relativistic Jets and Winds in Radio-Identified Supermassive Black Hole Binary Candidates

Supermassive black hole binary systems (SMBHBs) are thought to emit the recently discovered nHz gravitational wave background; however, not a single individual nHz source has been confirmed to date. Long-term radio-monitoring at the Owens Valley Radio Observatory has revealed two potential SMBHB candidates: blazars PKS 2131-021 and PKS J0805-0111. These sources show periodic flux density variations across the electromagnetic spectrum, signaling the presence of a good clock. To explain the emission, we propose a generalizable jet model, where a mildly relativistic wind creates an outward-moving helical channel, along which the ultra-relativistic jet propagates. The observed flux variation from the jet is mostly due to aberration. The emission at lower frequency arises at larger radius and its variation is consequently delayed, as observed. Our model reproduces the main observable features of both sources and can be applied to other sources as they are discovered. We make predictions for radio polarization, direct imaging, and emission line variation, which can be tested with forthcoming observations. Our results motivate future numerical simulations of jetted SMBHB systems and have implications for the fueling, structure, and evolution of blazar jets.

astro-ph.HE↗

arXiv2025

HOLISMOKES XIX: SN 2025wny at $z=2$, the first strongly lensed superluminous supernova

We present imaging and spectroscopic observations of supernova SN 2025wny, associated with the lens candidate PS1 J0716+3821. Photometric monitoring from the Lulin and Maidanak observatories confirms multiple point-like images, consistent with SN 2025wny being strongly lensed by two foreground galaxies. Optical spectroscopy of the brightest image with the Nordic Optical Telescope and the University of Hawaii 88-inch Telescope allows us to determine the redshift to be z_s = 2.008 +- 0.001, based on narrow absorption lines originating in the interstellar medium of the supernova host galaxy. At this redshift, the spectra of SN 2025wny are consistent with those of superluminous supernovae of Type I. We find a high ejecta temperature and depressed spectral lines compared to other similar objects. We also measure, for the first time, the redshift of the fainter of the two lens galaxies (the "perturber") to be z_p = 0.375 +- 0.001, fully consistent with the DESI spectroscopic redshift of the main deflector at z_d = 0.3754. SN 2025wny thus represents the first confirmed galaxy-scale strongly lensed supernova with time delays likely in the range of days to weeks, as judged from the image separations. This makes SN 2025wny suitable for cosmography, offering a promising new system for independent measurements of the Hubble constant. Following a tradition in the field of strongly-lensed SNe, we give SN 2025wny the nickname SN Winny.

astro-ph.CO↗

arXiv2025

Ultra High Energy Cosmic Rays

Ultra High Energy Cosmic Rays, UHECR, are charged particles with energies between $\sim10^{18}\,{\rm eV}$ and $\sim3\times10^{20}\,{\rm eV}\sim50\,{\rm J}$. They exhibit fundamental physics at energies inaccessible to terrestrial accelerators, challenge experimental physics and connect strongly to astronomical observations through electromagnetic, neutrino and even gravitational wave channels. There has been much theoretical and observational progress in the sixty years that have elapsed since the discovery of UHECR, to divine their nature and identify their sources. The highest energy UHECR appear to be heavy nuclei with rigidity extending up to $\sim10\,{\rm EV}$; A significant ($6.9σ$) dipole anisotropy has been measured but our poor understanding of the Galactic magnetic fields makes this hard to interpret; The UHECR luminosity density is $\sim 10^{44}$ erg Mpc$^{-3}$ yr$^{-1}$ which constrains explanations of their origin; The most promising acceleration mechanisms involve diffusive shock acceleration and unipolar induction; The most promising sources include intergalactic accretion shocks, and relativistic jets from stellar-mass or supermassive black holes. We explore the prospects for using the highest energy events, combined with multimessenger astronomy, to help us solve the riddle of UHECR.

astro-ph.HE↗

arXiv2025

Neutrino anisotropy as a probe of extreme astrophysical accelerators

We predict that neutrino sources following the matter distribution of the universe result in an anisotropy in the neutrino sky imprinted by the local large-scale structure. We calculate the level of this anisotropy and explore how it depends on the cosmological evolution of neutrino sources. We show how the level of anisotropy can be amplified when a cutoff in the neutrino spectrum is considered, introducing an effective neutrino horizon. This effect might allow for future neutrino detectors to measure a neutrino anisotropy associated with the local large-scale structure. Measurement of the level of this anisotropy along with features of the neutrino spectrum will allow observers to constrain the cosmological evolution of neutrino sources, which at ultrahigh energies (UHEs) are also expected to be the sources of UHE cosmic rays.

astro-ph.HE↗

arXiv2025

Life in the Bubble: How a Nearby Supernova Left Ephemeral Footprints on the Cosmic-Ray Spectrum and Indelible Imprints on Life

The Earth sits inside a 300pc-wide void that was carved by a series of supernova explosions that went off tens of millions of years ago, pushing away interstellar gas and creating a bubble-like structure. The $^{60}$Fe peak deposits found in the deep-sea crust have been interpreted by the imprints left by the ejecta of supernova explosions occurring about 2-3 and 5-6 Myr ago. It is likely that the $^{60}$Fe peak at about 2-3 Myr originated from a supernova occurring in the Upper Centaurus Lupus association in Scorpius Centaurus ($\approx$140 pc) or the Tucana Horologium association ($\approx$70 pc). Whereas, the $\approx$ 5-6 Myr peak is likely attributed to the solar system's entrance into the bubble. In this {\it Letter}, we show that the supernova source responsible for synthesizing the $^{60}$Fe peak deposits $\approx$ 2-3 Myr ago can consistently explain the cosmic-ray spectrum and the large-scale anisotropy between 100 TeV and 100 PeV. The cosmic-ray knee could then potentially be attributed entirely to a single nearby "Pevatron" source. Matching the intensity and shape of the cosmic-ray spectrum allows us to place stringent constraints on the cosmic-ray energy content from the supernova as well as on the cosmic-ray diffusion coefficient. Making use of such constraints we provide a robust estimate of the temporal variation of terrestrial ionizing cosmic radiation levels and discuss their implications in the development of early life on Earth by plausibly influencing the mutation rate and, as such, conceivably assisting in the evolution of complex organisms.

astro-ph.HE↗

arXiv2023

A Hierarchical Framework for explaining the Cosmic Ray Spectrum using Diffusive Shock Acceleration

The hypothesis that the entire cosmic ray spectrum, from $\lesssim1\,{\rm GeV}$ to $\gtrsim100\,{\rm EeV}$ energy, can be accounted for by diffusive shock acceleration on increasingly large scales is critically examined. Specifically, it is conjectured that Galactic cosmic rays, up to $\sim3\,{\rm PeV}$, are mostly produced by local supernova remnants, from which they escape upstream. These cosmic rays initiate a powerful magnetocentrifugal wind, removing disk mass and angular momentum before passing through the Galactic Wind Termination Shock at a radius $\sim200\,{\rm kpc}$, where they can be re-accelerated to account for observed cosmic rays up to $\sim30\,{\rm PeV}$. The cosmic rays transmitted downstream from more powerful termination shocks associated with other galaxies can be further accelerated at Intergalactic Accretion Shocks to the highest energies observed. In this interpretation, the highest rigidity observed particles are protons; the highest energy particles are heavy nuclei, such as iron. A universal "bootstrap" prescription, coupling the energy density of the magnetic turbulence to that of the resonant cosmic rays, is proposed, initially for the highest energy particles escaping far ahead of the shock front and then scattering, successively, lower energy particles downstream. Observable implications of this general scheme relate to the spectrum, composition and sky distribution of Ultra-High-Energy Cosmic Rays, the extragalactic radio background, the Galactic halo magnetic field and Pevatrons.

astro-ph.HE↗

arXiv2023

Probing extreme astrophysical accelerators through neutrino anisotropy

We present the extent to which anisotropies in the ultrahigh energy neutrino sky can probe the distribution of extreme astrophysical accelerators in the universe. In this talk, we discuss the origin of an anisotropic neutrino sky and show how observers can use this anisotropy to measure the evolution of ultrahigh energy neutrino sources - and therefore, the sources of ultrahigh energy cosmic rays - for the very first time.

astro-ph.HE↗

arXiv2023

Extreme Energy Cosmic Rays "Treasure Maps": a new methodology to unveil the nature of cosmic accelerators

Extreme Energy Cosmic Rays, EECRs -- cosmic rays with energies beyond the GZK cutoff (i.e. greater than 100 EeV) are scarce. Only a few of such events have been detected by air shower experiments and the nature of the primary particles are still unknown. Individual EECRs sources become more prominent, relative to the background, as the horizon diminishes. We show that an event-by-event, composition-dependent observatory would allow us to limit the character of the sources and learn about the intervening magnetic fields, as the deflections in the intervening Galactic and extragalactic magnetic fields depend on the nature of the particle. A major goal here is to provide a methodology to distinguish between steady and transient sources.

astro-ph.HE↗

arXiv2018

Cosmic-Ray Anisotropy from Large Scale Structure and the effect of magnetic horizons

Motivated by the ~7 % dipole anisotropy in the distribution of ultra-high energy cosmic-rays (UHECRs) above 8 EeV, we explore the anisotropy induced by the large scale structure, using constrained simulations of the local Universe and taking into account the effect of magnetic fields. The value of the intergalactic magnetic field (IGMF) is critical as it determines the UHECR cosmic horizon. We calculate the UHECR sky maps for different values of the IGMF variance and show the effect of the UHECR horizon on the observed anisotropy. The footprint of the local ($\lesssim350$ Mpc) Universe on the UHECR background, a small angular scale enhancement in the Northern Hemisphere, is seen. At 11.5 EeV (the median value of the energy bin at which the dipole has been reported), the LSS-induced dipole amplitude is $A_1\sim10\%$, for IGMF in the range [0.3-3] nG for protons, helium and nitrogen, compatible with the rms value derived from the cosmic power spectrum. However at these energies the UHECRs are also influenced by the Galactic Magnetic Field (GMF) and we discuss its effect on the LSS-induced anisotropy.

astro-ph.HE↗