arXiv subjects

E. A. M. Jensen

Publications and source records attributed to E. A. M. Jensen.

8 recordsLinked to original sources

arXiv2026

Precision $β$-delayed charged-particle emission spectroscopy at FRIB: Proof of principle with the $β$-decay of $^{25}\mathrm{Si}$

We report on the $β$-delayed proton and $γ$-ray emission from $^{25}\mathrm{Si}$, measured at the Facility for Rare Isotope Beams (FRIB). Low-energy $^{25}\mathrm{Si}$ ions extracted from the Advanced Cryogenic Gas Stopper were implanted into a thin carbon foil surrounded by a compact, highly segmented array of silicon detector telescopes and two high-purity germanium detectors. This setup provides high-resolution charged-particle spectroscopy, establishing a proof of principle for precision stopped-beam decay studies at FRIB. We reconstruct the $^{25}\mathrm{Si}$ decay scheme, resolving new high-energy proton transitions and determining the feeding to excited states in $^{24}\mathrm{Mg}$. The observation of spectral interference patterns enables firm spin and parity assignments for highly excited states in $^{25}\mathrm{Al}$. The $^{25}\mathrm{Si}$ $β$-strength distribution is extracted and compared with large-scale shell-model calculations.

nucl-ex↗

arXiv2026

The broad-lined type Ic supernova 2020lao experienced an energetic explosion with no central-engine signatures

We present infant-phase observations of the SN Ic-BL 2020lao, including optical spectroscopy beginning 48 hrs after explosion. The explosion time was constrained by power-law fits to the rising TESS and ZTF light curves, with the first ZTF detection occurring 27 hrs after explosion. The optical light curves show a rapid rise lasting 8.8 days and a peak luminosity typical of SNe Ic-BL (Mr=-18.5 mag). Unlike some engine-driven SN Ic-BL events, the light curve of SN 2020lao shows no evidence of an optical afterglow or excess emission, and the absence of shock-cooling in the TESS and ZTF data constrains the progenitor to a Wolf-Rayet-like star with radius less than a few times the solar radius, ruling out any extended envelope. The spectra resemble those of the X-ray-flash-associated SN 2006aj but with higher expansion velocities. From Arnett-type fits to the bolometric light curve and measured FeII velocities, we infer a Ni mass of 0.2 solar masses, an ejecta mass of 3.2 solar masses, and a kinetic energy of about 23x10^51 erg, corresponding to a specific kinetic energy of 7x10^51 erg per solar mass. Spectral synthesis modeling broadly reproduces the photospheric spectra of SN 2020lao and suggests a specific kinetic energy of 5x10^51 erg per solar mass. SN 2020lao and SN 2006aj synthesized comparable amounts of Ni, yet SN 2020lao exhibits specific kinetic energy values 5-10 times larger. VLA and Swift/XRT non-detections reveal no afterglow emission, allowing limits on relativistic ejecta and dense circumstellar material. Given that SN 2020lao reaches a specific kinetic energy typical of engine-driven SNe Ic-BL, the lack of an optical excess with the non-detections in the radio and X-ray bands suggests that if a relativistic jet was launched, it was either viewed far off axis or choked before breakout. If there was no relativistic jet, SN 2020lao would be an extreme nonrelativistic SN Ic-BL.

astro-ph.HE↗

arXiv2026

A ground state $^{22}$Al halo is unlikely

We report the decisive resolution of the ground state spin and parity of the proton-dripline nucleus $^{22}$Al, a prime candidate for a proton halo. The resolution stems from the first $β$-delayed charged particle emission experiment in the Gas Stopping Area at the Facility for Rare Isotope Beams (FRIB), leveraging high-intensity, low-energy beams extracted from the Advanced Cryogenic Gas Stopper (ACGS). The pristine beam quality from FRIB and the ACGS enabled a sensitive particle identification technique using thin silicon detectors, allowing for the suppression of the dominant proton background and the first observation of the weak $β$-delayed $α$ transition from the Isobaric Analog State in $^{22}$Mg to the $^{18}$Ne ground state. This observation uniquely fixes the $^{22}$Al ground state as $4^+$. The valence proton is confined by a dominant $d$-wave centrifugal barrier which, combined with the Coulomb repulsion, hinders the tunneling required for halo formation despite the exceptionally low proton separation energy of $^{22}$Al.

nucl-ex↗

arXiv2025

The Type Ia Supernova 2021hem: A 2003fg-like Event in an Apparently Hostless Environment

We report observations of Type Ia SN 2021hem, located in an apparently hostless environment. With a peak absolute B-band magnitude of -19.96 mag, and a lack of secondary maximum in near-infrared and i-band light curves make it resemble 2003fg-like events. The slowly evolving light curves, and the earliest spectrum showing CII absorption lines, further support this classification. Fireball model fit to early light curves yields a time of first light of -16.43 days relative to B-band maximum. The first detection occurs 1.51 days before the onset of the fireball-like flux rise. This early emission, and $(g - r)_0$ color, is inconsistent with circumstellar or companion interaction. Instead, shallow $^{56}$Ni mixing or an asymmetric $^{56}$Ni distribution offers a plausible explanation. SN2021hem is the fifth known 2003fg-like SN with early-time excess flux emission. The estimated mass of radioactive $^{56}$Ni in SN2021hem is $1.00\pm0.09 M_\odot$. Deep GTC imaging obtained 2.5 yr after the explosion (with $m_{lim,r}=24.4$ mag and $μ_{lim,r} = 26.3\rm~mag~arsec^{-2}$), reveals no coincident host, thereby ruling out most faint dwarf and UDGs. Alternatively, assuming the nearest plausible AGN host galaxy, at a distance of 104 kpc, implies a hyper-velocity progenitor ejected at $\sim$2200 km/s by AGN interaction. A faint diffuse feature ~6 kpc from the SN site has also been detected in the image, with its surface brightness of a UDGs. However, it is unclear whether it is a galaxy and is associated with SN2021hem. Considering its large normalized directional light distance ($d_{DLR}\sim3-4$) from SN, and its unusual elongation, it is a candidate of low probability to be the host galaxy of SN2021hem. These results identify SN2021hem as one of the strongest candidates for a hostless SN Ia, underscoring the diversity of luminous, slowly evolving, 2003fg-like explosions.

astro-ph.HE↗

arXiv2025

Extension of the particle x-ray coincidence technique: The lifetimes and branching ratios apparatus

The particle x-ray coincidence technique (PXCT) was originally developed to measure average lifetimes in the $10^{-17}-10^{-15}$~s range for proton-unbound states populated by electron capture (EC). We have designed and built the Lifetimes and Branching Ratios Apparatus (LIBRA) to be used in the stopped-beam area at the Facility for Rare Isotope Beams that extends PXCT to measure lifetimes and decay branching ratios of resonances populated by EC/$β^+$ decay. The first application of LIBRA aims to obtain essential nuclear data from $^{60}$Ga EC/$β^+$ decay to constrain the thermonuclear rates of the $^{59}$Cu$(p,γ)^{60}$Zn and $^{59}$Cu$(p,α)^{56}$Ni reactions, and in turn, the strength of the NiCu nucleosynthesis cycle, which is predicted to significantly impact the modeling of type I x-ray burst light curves and the composition of the burst ashes. Detailed theoretical calculations, Monte Carlo simulations, and performance tests with radioactive sources have been conducted to validate the feasibility of employing LIBRA for the $^{60}$Ga experiment. LIBRA can be utilized to measure most essential ingredients needed for charged-particle reaction rate calculations in a single experiment, in the absence of direct measurements, which are often impractical for radioactive reactants.

physics.ins-det↗

arXiv2025

Expanding the parameter space of 2002es-like type Ia supernovae: on the underluminous ASASSN-20jq / SN 2020qxp

We present optical photometric and spectroscopic observations of the peculiar Type Ia supernova ASASSN-20jq/SN 2020qxp. It is a low-luminosity object with a peak absolute magnitude of $M_B=-17.1\pm0.5$ mag. Despite its low luminosity, its post-peak light-curve decline rate ($Δm_{15}(B)=1.35\pm0.09$ mag) and color-stretch parameter (sBV>0.82) are similar to normal SNe Ia, making it an outlier in the luminosity-width and luminosity-color-stretch relations. Early light curves suggest a "bump" during the first 1.4 days of explosion. ASASSN-20jq synthesized a low radioactive $^{56}$Ni mass of $0.09\pm0.01M_\odot$. Near-maximum light spectra reveal strong Si II absorption lines, indicating a cooler photosphere than normal SNe Ia, but lack Ti II absorption lines. Unusually strong O I $λ$7773 and Ca II near-infrared triplet absorption features are present. Nebular spectra show a strong, narrow forbidden [Ca II] $λλ$7291,7324 doublet emission, rarely seen in SNe Ia except in some Type Iax events. Marginal detection of [O I] $λλ$6300,6364 doublet emission, which is extremely rare, is observed. Both [Ca II] and [O I] lines are redshifted by $\sim2000$ km/s. A strong [Fe II] $λ$7155 emission line with a tilted-top profile, identical to the [Fe II] $λ$16433 profile, is also observed. These asymmetric [Fe II] profiles and redshifted [Ca II] and [O I] emissions suggest a high central density white dwarf progenitor undergoing an off-center delayed-detonation explosion mechanism, producing roughly equal amounts of $^{56}$Ni in deflagration and detonation phases. This distinguishes ASASSN-20jq from normal and subluminous SNe Ia. ASASSN-20jq's light curve and spectra do not align with any single SNe Ia subclass but show similarities to 2002es-like objects. Thus, we add it as an extreme candidate within the heterogeneous parameter space of 2002es-like SNe Ia.

astro-ph.HE↗

arXiv2025

Beta-delayed particle emission and collective rotations

Beta-delayed proton emission in the lower half of the sd-shell will involve deformed nuclei. We derive the normalized matrix element connecting emission of one particle from an initial rotational nuclear state to another final rotating state, and we extract selection rules involving the $K$ quantum number. The initial state is approximated as having a core identical to the final nuclear state. The formalism is then directly applicable to $β^+$-delayed proton decays of even-$Z$, odd-$N$ nuclei or $β^-$-delayed neutron decays of odd-$Z$, even $N$ nuclei. These beta-decay results are compared to the outcomes of possible transfer reactions. As an example the beta-delayed proton emission of $^{21}$Mg is considered, where new quantum numbers can be assigned to several states in $^{21}$Na.

nucl-th↗

arXiv2024

Detailed study of the decay of $^{21}$Mg

Beta-delayed proton and gamma emission in the decay of $^{21}$Mg has been measured at ISOLDE, CERN with the ISOLDE Decay Station (IDS) set-up. The existing decay scheme is updated, in particular what concerns proton transitions to excited states in $^{20}$Ne. Signatures of interference in several parts of the spectrum are used to settle spin and parity assignments to highly excited states in $^{21}$Na. The previously reported $β$p$α$ branch is confirmed. A half-life of 120.5(4) ms is extracted for $^{21}$Mg. The revised decay scheme is employed to test mirror symmetry in the decay and to extract the beta strength distribution of $^{21}$Mg that is compared with theory.

nucl-ex↗