arXiv subjects

E. Waxman

Publications and source records attributed to E. Waxman.

At least 19 recordsLinked to original sources

arXiv2026

Composite sub-micron solid particles engineered to enable safe, controllable, efficient, and practical SAI

The properties of candidate particles for solar radiation management (SRM) through stratospheric aerosol injection (SAI) should comply with safety, controllability, and functionality requirements. Following the proposal in arXiv:2604.02283 of safety and controllability requirements, we define here a set of functionality requirements on the particles' properties -- optical properties, stratospheric residence time, scalable manufacturing compatibility, and aerial dispersion compatibility -- that, if met, ensure the feasibility of practical implementation, providing reflection of $\sim1$% of the solar flux. We then present design principles and fabrication methods for sub-micron solid particles that may enable satisfying the combined requirements. These requirements do not identify a unique solution, but favor sub-micron particles with tightly controlled size distributions and stable properties over their stratospheric lifetime, and motivate a composite design where the bulk core composition is selected primarily for optimal radiative properties and the outer shell surface is engineered to control atmospheric chemistry and aging, and enhance aerial dispersion compatibility. We present two specific particle designs that are viable for meeting the coupled requirements: amorphous silica spheres and calcium-carbonate cores surrounded by spherical silica shells (both with appropriate surface treatment). The former is at an advanced stage of experimental verification (described in detail in a companion paper) of meeting all requirements, provides a practical platform for surface engineering, and will enable reaching a substantial fraction of $\sim\!1$% solar flux reflection. The latter is under development and will enable reaching $>1$\% reflection.

physics.ao-ph↗

arXiv2026

A proposal for the safety and controllability requirements that SRM systems should meet

Solar Radiation Modification (SRM) may be the only way to limit global warming in the coming decades, leading to increased interest in the subject and to the expansion of related research & development (R&D) activity. Defining the safety and controllability requirements that any SRM system should meet is crucial for directing R&D activities and enabling governments to make informed decisions on the development and possible implementation of such systems. We present an initial proposal for this set of requirements, which also guides Stardust's R&D, as a basis for further discussion and consideration. While we focus on SRM systems based on Stratospheric Aerosol Injection (SAI), the proposed principles may be applicable more broadly.

physics.ao-ph↗

arXiv2024

Shock breakouts from compact CSM surrounding core-collapse SN progenitors may contribute significantly to the observed $\gtrsim10$ TeV neutrino background

Growing observational evidence suggests that enhanced mass loss from the progenitors of core-collapse supernovae (SNe) is common during $\sim1$ yr preceding the explosion, creating an optically thick circum-stellar medium (CSM) shell at $\sim10^{14.5}$ cm radii. We show that if such mass loss is indeed common, then the breakout of the SN shock through the dense CSM shell produces a neutrino flux that may account for a significant fraction of the observed $\gtrsim10$ TeV neutrino background. The neutrinos are created within a few days from the explosion, during and shortly after the shock breakout, which produces also large UV (and later X-ray) luminosity. The compact size and large UV luminosity imply a pair production optical depth of $\sim10^4$ for $>100$ GeV photons, naturally accounting for the lack of a high-energy gamma-ray background accompanying the neutrino background. SNe producing $>1$ neutrino event in a 1 km$^2$ detector are expected at a rate of $\lesssim0.1$/yr. A quantitative theory describing the evolution of the electromagnetic spectrum during a breakout, as the radiation-mediated shock is transformed into a collisionless one, is required to enable (i) using data from upcoming surveys that will systematically detect large numbers of young, $<1$ d old SNe, to determine the pre-explosion mass loss history of the SN progenitor population, and (ii) a quantitative determination of the neutrino luminosity and spectrum.

astro-ph.HE↗

arXiv2024

Shock cooling emission from explosions of massive stars: III. Blue Super Giants

Light emission in the first hours and days following core-collapse supernovae is dominated by the escape of photons from the expanding shock-heated envelope. In preceding papers, we provided a simple analytic description of the time-dependent luminosity, $L$, and color temperature, $T_{\rm col}$, as well as of the small ($\simeq10\%$) deviations of the spectrum from blackbody at low frequencies, $hν< 3T_{\rm col}$, and of `line dampening' at $hν> 3T_{\rm col}$, for explosions of red supergiants (RSGs) with convective polytropic envelopes (without significant circum-stellar medium). Here, we extend our work to provide similar analytic formulae for explosions of blue supergiants with radiative polytropic envelopes. The analytic formulae are calibrated against a large set of spherically symmetric multi-group (frequency-dependent) calculations for a wide range of progenitor parameters (mass, radius, core/envelope mass ratios) and explosion energies. In these calculations we use the opacity tables we constructed (and made publicly available), that include the contributions of bound-bound and bound-free transitions. They reproduce the numeric $L$ and $T_{\rm col}$ to within 10\% and 5\% accuracy, and the spectral energy distribution to within $\sim20-40\%$. The accuracy is similar to that achieved for RSG explosions.

astro-ph.HE↗

arXiv2023

UV to near-IR observations of the DART-Dimorphos collision

The impact of the Double Asteroid Redirection Test (DART) spacecraft with Dimorphos allows us to study asteroid collision physics, including momentum transfer, the ejecta properties, and the visibility of such events in the Solar System. We report observations of the DART impact in the ultraviolet (UV), visible light, and near-infrared (IR) wavelengths. The observations support the existence of at least two separate components of the ejecta: a fast and a slow component. The fast-ejecta component is composed of a gaseous phase, moving at about 1.6 km/s with a mass of <10^4 kg. The fast ejecta is detected in the UV and visible light, but not in the near-IR $z$-band observations. Fitting a simplified optical thickness model to these observations allows us to constrain some of the properties of the fast ejecta, including its scattering efficiency and the opacity of the gas. The slow ejecta component is moving at typical velocities of up to about 10 m/s. It is composed of micrometer-size particles, that have a scattering efficiency, at the direction of the observer, of the order of 10^-3 and a total mass of about 10^6 kg. The larger particles in the slow ejecta, whose size is bound to be in the range between ~1 mm to ~1 m, likely have a scattering efficiency larger than that of the pre-impact Didymos system.

astro-ph.EP↗

arXiv2023

Photometric prioritization of neutron star merger candidates

Rapid identification of the optical counterparts of Neutron Star (NS) merger events discovered by gravitational wave detectors may require observing a large error region and sifting through a large number of transients to identify the object of interest. Given the expense of spectroscopic observations, a question arises: How can we utilize photometric observations for candidate prioritization, and what kinds of photometric observations are needed to achieve this goal? NS merger kilonova exhibits low ejecta mass (~5x10^-2 solar mass) and a rapidly evolving photospheric radius (with a velocity ~0.2c). As a consequence, these sources display rapid optical-flux evolution. Indeed, selection based on fast flux variations is commonly used for young supernovae and NS mergers. In this study, we leverage the best currently available flux-limited transient survey - the Zwicky Transient Facility Bright Transient Survey - to extend and quantify this approach. We focus on selecting transients detected in a 3-day cadence survey and observed at a one-day cadence. We explore their distribution in the phase space defined by g-r, g-dot, and r-dot. Our analysis demonstrates that for a significant portion of the time during the first week, the kilonova AT 2017gfo stands out in this phase space. It is important to note that this investigation is subject to various biases and challenges; nevertheless, it suggests that certain photometric observations can be leveraged to identify transients with the highest probability of being fast-evolving events. We also find that a large fraction (~0.75) of the transient candidates with |g-dot|>0.7 mag/day, are cataclysmic variables or active galactic nuclei with radio counterparts.

astro-ph.HE↗

arXiv2023

ULTRASAT: A wide-field time-domain UV space telescope

The Ultraviolet Transient Astronomy Satellite (ULTRASAT) is scheduled to be launched to geostationary orbit in 2026. It will carry a telescope with an unprecedentedly large field of view (204 deg$^2$) and NUV (230-290nm) sensitivity (22.5 mag, 5$σ$, at 900s). ULTRASAT will conduct the first wide-field survey of transient and variable NUV sources and will revolutionize our ability to study the hot transient universe: It will explore a new parameter space in energy and time-scale (months long light-curves with minutes cadence), with an extra-Galactic volume accessible for the discovery of transient sources that is $>$300 times larger than that of GALEX and comparable to that of LSST. ULTRASAT data will be transmitted to the ground in real-time, and transient alerts will be distributed to the community in $<$15 min, enabling a vigorous ground-based follow-up of ULTRASAT sources. ULTRASAT will also provide an all-sky NUV image to $>$23.5 AB mag, over 10 times deeper than the GALEX map. Two key science goals of ULTRASAT are the study of mergers of binaries involving neutron stars, and supernovae: With a large fraction ($>$50%) of the sky instantaneously accessible, fast (minutes) slewing capability and a field-of-view that covers the error ellipses expected from GW detectors beyond 2025, ULTRASAT will rapidly detect the electromagnetic emission following BNS/NS-BH mergers identified by GW detectors, and will provide continuous NUV light-curves of the events; ULTRASAT will provide early (hour) detection and continuous high (minutes) cadence NUV light curves for hundreds of core-collapse supernovae, including for rarer supernova progenitor types.

astro-ph.IM↗

arXiv2023

The Large Array Survey Telescope -- System Overview and Performances

The Large Array Survey Telescope (LAST) is a wide-field visible-light telescope array designed to explore the variable and transient sky with a high cadence. LAST will be composed of 48, 28-cm f/2.2 telescopes (32 already installed) equipped with full-frame backside-illuminated cooled CMOS detectors. Each telescope provides a field of view (FoV) of 7.4 deg^2 with 1.25 arcsec/pix, while the system FoV is 355 deg^2 in 2.9 Gpix. The total collecting area of LAST, with 48 telescopes, is equivalent to a 1.9-m telescope. The cost-effectiveness of the system (i.e., probed volume of space per unit time per unit cost) is about an order of magnitude higher than most existing and under-construction sky surveys. The telescopes are mounted on 12 separate mounts, each carrying four telescopes. This provides significant flexibility in operating the system. The first LAST system is under construction in the Israeli Negev Desert, with 32 telescopes already deployed. We present the system overview and performances based on the system commissioning data. The Bp 5-sigma limiting magnitude of a single 28-cm telescope is about 19.6 (21.0), in 20 s (20x20 s). Astrometric two-axes precision (rms) at the bright-end is about 60 (30)\,mas in 20\,s (20x20 s), while absolute photometric calibration, relative to GAIA, provides ~10 millimag accuracy. Relative photometric precision, in a single 20 s (320 s) image, at the bright-end measured over a time scale of about 60 min is about 3 (1) millimag. We discuss the system science goals, data pipelines, and the observatory control system in companion publications.

astro-ph.IM↗

arXiv2021

AT2018lqh and the nature of the emerging population of day-scale duration optical transients

We report on the discovery of AT2018lqh (ZTF18abfzgpl) -- a rapidly-evolving extra-galactic transient in a star-forming host at 242 Mpc. The transient g-band light curve's duration above half-maximum light is about 2.1 days, where 0.4/1.7 days are spent on the rise/decay, respectively. The estimated bolometric light curve of this object peaked at about 7x10^42 erg/s -- roughly seven times brighter than AT2017gfo. We show that this event can be explained by an explosion with a fast (v~0.08 c) low-mass (~0.07 Msun) ejecta, composed mostly of radioactive elements. For example, ejecta dominated by Ni-56 with a time scale of t_0=1.6 days for the ejecta to become optically thin for gamma-rays fits the data well. Such a scenario requires burning at densities that are typically found in the envelopes of neutron stars or the cores of white dwarfs. A combination of circumstellar material (CSM) interaction power at early times and shock cooling at late times is consistent with the photometric observations, but the observed spectrum of the event may pose some challenges for this scenario. The observations are not consistent with a shock breakout from a stellar envelope, while a model involving a low-mass ejecta ramming into low-mass CSM cannot explain both the early- and late-time observations.

astro-ph.HE↗

arXiv2020

High-energy particles and radiation in star-forming regions

Non-thermal particles and high-energy radiation can play a role in the dynamical processes in star-forming regions and provide an important piece of the multiwavelength observational picture of their structure and components. Powerful stellar winds and supernovae in compact clusters of massive stars and OB associations are known to be favourable sites of high-energy particle acceleration and sources of non-thermal radiation and neutrinos. Namely, young massive stellar clusters are likely sources of the PeV (petaelectronvolt) regime cosmic rays (CRs). They can also be responsible for the cosmic ray composition, e.g., 22Ne/20Ne anomalous isotopic ratio in CRs. Efficient particle acceleration can be accompanied by super-adiabatic amplification of the fluctuating magnetic fields in the systems converting a part of kinetic power of the winds and supernovae into the magnetic energy through the CR-driven instabilities. The escape and CR propagation in the vicinity of the sources are affected by the non-linear CR feedback. These effects are expected to be important in starburst galaxies, which produce high-energy neutrinos and gamma-rays. We give a brief review of the theoretical models and observational data on high-energy particle acceleration and their radiation in star-forming regions with young stellar population.

astro-ph.HE↗

arXiv2015

The origin of IceCube's neutrinos: Cosmic ray accelerators embedded in star forming calorimeters

The IceCube collaboration reports a detection of extra-terrestrial neutrinos. The isotropy and flavor content of the signal, and the coincidence, within current uncertainties, of the 50 TeV to 2 PeV flux and the spectrum with the Waxman-Bahcall bound, suggest a cosmological origin of the neutrinos, related to the sources of ultra-high energy, $>10^{10}$ GeV, cosmic-rays (UHECR). The most natural explanation of the UHECR and neutrino signals is that both are produced by the same population of cosmological sources, producing CRs (likely protons) at a similar rate, $E^2d\dot{n}/dE\propto E^{0}$, over the [$1$ PeV,$10^{11}$ GeV] energy range, and residing in "calorimetric" environments, like galaxies with high star formation rate, in which $E/Z<100$ PeV CRs lose much of their energy to pion production. A tenfold increase in the effective mass of the detector at $\gtrsim100$ TeV is required in order to significantly improve the accuracy of current measurements, to enable the detection of a few bright nearby starburst "calorimeters", and to open the possibility of identifying the CR sources embedded within the calorimeters, by associating neutrinos with photons accompanying transient events responsible for their generation. Source identification and a large neutrino sample may enable one to use astrophysical neutrinos to constrain new physics models.

astro-ph.HE↗

arXiv2013

IceCube's Neutrinos: The beginning of extra-Galactic neutrino astrophysics?

The flux, spectrum and angular distribution of the excess neutrino signal detected by IceCube between 50TeV and 2PeV are inconsistent with those expected for Galactic sources. The coincidence of the excess, $E_ν^2Φ_ν=3.6\pm1.2\times10^{-8}(GeV/ cm^2 sr s)$, with the Waxman-Bahcall (WB) bound, $E_ν^2Φ_{WB}=3.4\times10^{-8}(GeV/cm^2 sr s)$, is probably a clue to the origin of IceCube's neutrinos. The most natural explanation of this coincidence is that both the neutrino excess and the ultra-high energy, $>10^{19}$ eV, cosmic-ray (UHECR) flux are produced by the same population of cosmologically distributed sources, producing CRs, likely protons, at a similar rate, $E^2 dQ/dE=0.5\times10^{44}(erg/Mpc^3yr)$ (at z=0), across a wide range of energies, from $10^{15}$ eV to $>10^{20}$ eV, and residing in environments (such as starburst galaxies) in which CRs of rigidity $E/Z< 10^{17}$ eV lose much of their energy to pion production. Identification of the neutrino sources will allow one to identify the UHECR accelerators, to resolve open questions related to the accelerator models, and to study neutrino properties (related e.g. to flavor oscillations and coupling to gravity) with an accuracy many orders of magnitude better than is currently possible. The most promising method for identifying the sources is by association of a neutrino with an electromagnetic signal accompanying a transient event responsible for its generation. The neutrino flux that is produced within the sources, and that may thus be directly associated with transient events, may be significantly lower than the total observed neutrino flux, which may be dominated by neutrino production at the environment in which the sources reside.

astro-ph.HE↗

arXiv2013

Multimessenger astronomy with gravitational waves and high-energy neutrinos

Many of the astrophysical sources and violent phenomena observed in our Universe are potential emitters of gravitational waves (GW) and high-energy neutrinos (HEN). Both GWs and HENs may escape very dense media and travel unaffected over cosmological distances, carrying information from the innermost regions of the astrophysical engines. Such messengers could also reveal new, hidden sources that have not been observed by conventional photon-based astronomy. Coincident observation of GWs and HENs may thus play a critical role in multimessenger astronomy. This is particularly true at the present time owing to the advent of a new generation of dedicated detectors: IceCube, ANTARES, VIRGO and LIGO. Given the complexity of the instruments, a successful joint analysis of this data set will be possible only if the expertise and knowledge of the data is shared between the two communities. This review aims at providing an overview of both theoretical and experimental state-of-the-art and perspectives for such a GW+HEN multimessenger astronomy.

astro-ph.HE↗

arXiv2013

Science with a wide-field UV transient explorer

The time-variable electromagnetic sky has been well-explored at a wide range of wavelengths. Numerous high-energy space missions take advantage of the dark Gamma-ray and X-ray sky and utilize very wide field detectors to provide almost continuous monitoring of the entire celestial sphere. In visible light, new wide-field ground-based surveys cover wide patches of sky with ever decreasing cadence, progressing from monthly-weekly time scale surveys to sub-night sampling. In the radio, new powerful instrumentation offers unprecedented sensitivity over wide fields of view, with pathfinder experiments for even more ambitious programs underway. In contrast, the ultra-violet (UV) variable sky is relatively poorly explored, even though it offers exciting scientific prospects. Here, we review the potential scientific impact of a wide-field UV survey on the study of explosive and other transient events, as well as known classes of variable objects, such as active galactic nuclei and variable stars. We quantify our predictions using a fiducial set of observational parameters which are similar to those envisaged for the proposed ULTRASAT mission. We show that such a mission would be able to revolutionize our knowledge about massive star explosions by measuring the early UV emission from hundreds of events, revealing key physical parameters of the exploding progenitor stars. Such a mission would also detect the UV emission from many tens of tidal-disruption events of stars by super massive black holes at galactic nuclei and enable a measurement of the rate of such events. The overlap of such a wide-field UV mission with existing and planned gravitational-wave and high-energy neutrino telescopes makes it especially timely.

astro-ph.CO↗

arXiv2011

Relativistic Jet Dynamics and Calorimetry of Gamma-Ray Bursts

We present numerical solutions of the 2D relativistic hydrodynamics equations describing the deceleration and expansion of highly relativistic conical jets, of opening angles 0.05 R/c the emission of radiation from the jet blast wave is similar to that of a spherical blast wave carrying the same energy. Thus, the total (calorimetric) energy of GRB blast waves may be estimated with only a small fractional error based on t>R/c observations.

astro-ph.HE↗

arXiv2011

High energy cosmic ray and neutrino astronomy

Cosmic-rays with energies exceeding 10^{19} eV are referred to as Ultra High Energy Cosmic Rays (UHECRs). The sources of these particles and their acceleration mechanism are unknown, and for many years have been the issue of much debate. The first part of this review describes the main constraints, that are implied by UHECR observations on the properties of candidate UHECR sources, the candidate sources, and the related main open questions. In order to address the challenges of identifying the UHECR sources and of probing the physical mechanisms driving them, a "multi-messenger" approach will most likely be required, combining electromagnetic, cosmic-ray and neutrino observations. The second part of the review is devoted to a discussion of high energy neutrino astronomy. It is shown that detectors, which are currently under construction, are expected to reach the effective mass required for the detection of high energy extra-Galactic neutrino sources, and may therefore play a key role in the near future in resolving the main open questions. The detection of high energy neutrinos from extra-Galactic sources will not only provide constraints on the identity and underlying physics of UHECR sources, but may furthermore provide information on fundamental neutrino properties.

astro-ph.HE↗

arXiv2010

Supernova PTF 09uj: A possible shock breakout from a dense circumstellar wind

Type-IIn supernovae (SNe), which are characterized by strong interaction of their ejecta with the surrounding circumstellar matter (CSM), provide a unique opportunity to study the mass-loss history of massive stars shortly before their explosive death. We present the discovery and follow-up observations of a Type IIn SN, PTF 09uj, detected by the Palomar Transient Factory (PTF). Serendipitous observations by GALEX at ultraviolet (UV) wavelengths detected the rise of the SN light curve prior to the PTF discovery. The UV light curve of the SN rose fast, with a time scale of a few days, to a UV absolute AB magnitude of about -19.5. Modeling our observations, we suggest that the fast rise of the UV light curve is due to the breakout of the SN shock through the dense CSM (n~10^10 cm^-3). Furthermore, we find that prior to the explosion the progenitor went through a phase of high mass-loss rate (~0.1 solar mass per year) that lasted for a few years. The decay rate of this SN was fast relative to that of other SNe IIn.

astro-ph.HE↗

arXiv2009

Long duration radio transients lacking optical counterparts are possibly Galactic Neutron Stars

(abridged) Recently, a new class of radio transients in the 5-GHz band was detected by Bower et al. We present new deep near-Infrared (IR) observations of the field containing these transients, and find no counterparts down to a limiting magnitude of K=20.4 mag. We argue that the bright (>1 Jy) radio transients recently reported by Kida et al. are consistent with being additional examples of the Bower et al. transients. We refer to these groups of events as "long-duration radio transients". The main characteristics of this population are: time scales longer than 30 minute but shorter than several days; rate, ~10^3 deg^-2 yr^-1; progenitors sky surface density of >60 deg^-2 (95% C.L.) at Galactic latitude ~40 deg; 1.4-5 GHz spectral slopes, f_ν~ ν^alpha, with alpha>0; and most notably the lack of any counterparts in quiescence in any wavelength. We rule out an association with many types of objects. Galactic brown-dwarfs or some sort of exotic explosions remain plausible options. We argue that an attractive progenitor candidate for these radio transients is the class of Galactic isolated old neutron stars (NS). We confront this hypothesis with Monte-Carlo simulations of the space distribution of old NSs, and find satisfactory agreement for the large areal density. Furthermore, the lack of quiescent counterparts is explained quite naturally. In this framework we find: the mean distance to events in the Bower et al. sample is of order kpc; the typical distance to the Kida et al. transients are constrained to be between 30 pc and 900 pc (95% C.L.); these events should repeat with a time scale of order several months; and sub-mJy level bursts should exhibit Galactic latitude dependence. We discuss possible mechanisms giving rise to the observed radio emission.

astro-ph.HE↗