arXiv subjects

Keiichi Maeda

Publications and source records attributed to Keiichi Maeda.

At least 19 recordsLinked to original sources

arXiv2026

A Unified Timescale Relation for Quasi-Periodic Eruptions and Repeated Nuclear Transients

Quasi-periodic eruptions (QPEs) and recurrent nuclear transients (RNTs) exhibit recurrent high-amplitude flares from galactic nuclei, yet their characteristic timescales remain poorly understood. In this work, we compile a sample of these systems and investigate empirical scaling relations between flare timescales and black hole masses. We find that the recurrence timescale exhibits a positive but highly scattered dependence on black hole mass in the combined QPE and RNT sample, approximately following $t_{\rm rec}\propto M_{\rm BH}^{1.19^{+0.52}_{-0.47}}$ with an intrinsic scatter of 0.95 dex. Remarkably, we uncover a tight nearly linear relation between recurrence time and flare timescale for QPEs and RNTs, described by $t_{\rm rec}\propto t_{\rm rise}^{1.00\pm0.07}$ with an intrinsic scatter of 0.29 dex. This relation extends across timescales from hours for QPEs to months and years for nuclear transients. We further find that QPEs and RNTs approximately follow a common empirical relation between recurrence time and flare rise time, although the physical origin of this relation remains uncertain. Our findings reveal a common phenomenological timescale link across RNTs, providing a practical framework for characterizing their temporal behavior.

astro-ph.HE↗

arXiv2026

SN 2023gfo: A Peculiar Type IIP Supernova with High Luminosity and Normal Plateau Duration

We present near-infrared (NIR) and optical observations of the highly reddened Type IIP supernova (SN) 2023gfo in the nearby galaxy NGC 4995 ($d = 26.4 \pm 3.2$ Mpc), which reached a high peak luminosity of $M_V = -18.6$ mag. The SN was initially detected as a faint red event, with $B-V = 0.8$ mag at the beginning of the plateau phase. By comparison with template, we estimate a total extinction of $A_V = 2.1$ mag. After correcting for this extinction, we derive a peak quasi-bolometric luminosity of $(5.9 \pm 1.5)\times10^{42}$ erg s$^{-1}$, placing this event among the most luminous SNe IIP, while its plateau duration remains within the normal range. The early-phase optical spectrum exhibits a P-Cygni profile of H$\alpha$, with a broad absorption of $V$ = $13{,}800$ km s$^{-1}$, which is among the highest observed for SNe IIP at comparable epochs. The high luminosity and the normal plateau duration suggest that this event represents an outlier. Applying an analytical model, we infer an unusually large progenitor radius. This may indicate that the progenitor experienced an extreme energy injection from the core to the envelope shortly before explosion, resulting in a substantially inflated radius. While ejecta-circumstellar matter (CSM) interaction could in principle account for the high luminosity, we find no observational evidence supporting strong interaction.

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arXiv2026

JWST Spectroscopy of Type Ia Supernova 2025rbs from Maximum Light to the Nebular Phase

We present JWST observations of the Type Ia supernova (SN Ia) 2025rbs ($D=$14.5 Mpc) at +1, +23, and +84 days after B-band maximum, spanning peak light through a wavelength-dependent transition toward the nebular phase. Combined with ground-based optical and near-infrared (NIR) data, our panchromatic spectra (0.4-14 $\mu$m) include the first maximum-light mid-infrared (MIR) spectrum and the earliest MIR spectroscopic sequence of an SN Ia to date. At peak light, the MIR spectrum exhibits a continuum with permitted and forbidden features, including Si II, Ni II, and early-emerging [Ni III-IV] and [Ar II-III]. By +23 days the MIR is dominated by forbidden lines with a weak continuum, and by +84 days it is fully nebular, whereas the optical/NIR spectra remain transitional. The nebular spectrum reveals strongly stratified ejecta, with stable Ni concentrated at the lowest velocities, radioactive Co at intermediate velocities but absent within ~2000 km s$^{-1}$, and Ar occupying an outer shell. We detect small-scale substructure in [Ca IV] 3.21 $\mu$m with fractional amplitudes of a few percent and a characteristic velocity scale of ~800 km s$^{-1}$, which may reflect compositional structure, ionization variations, or both. Radiative-transfer calculations substantially underpredict these MIR Mg II features despite approximately reproducing the NIR Mg II 1.0927 $\mu$m line, suggesting that the relative strengths of these transitions are sensitive to the treatment of Mg ionization and excitation. These observations demonstrate that MIR spectroscopy beginning near maximum light simultaneously probes the emerging inner ejecta and rapidly fading outer burning products, providing new constraints for explosion and radiative-transfer models.

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arXiv2026

Radio Constraints on the Circumstellar Environment of the Type IIb Supernova SN 2024iss

Type~IIb supernovae exhibit diverse progenitor properties, and radio observations offer a unique probe of their mass-loss histories shortly before the explosion. We present Japanese VLBI Network single-baseline monitoring of the nearby Type IIb SN 2024iss at 6.9 and 8.4 GHz, spanning approximately one year after its discovery. Our radio observations have detected its emission at 10 and 23 days after the explosion, with subsequent epochs yielding non-detections. Based on the peak radio luminosity and peak time, SN 2024iss exhibits radio properties highly comparable to those of compact-envelope events. Using a synchrotron self-absorption (SSA) modeling, we estimate a progenitor mass-loss rate of $\dot{M} \approx 2.5 \times 10^{-6}\>M_{\odot}\>{\rm yr^{-1}}$ for a compact progenitor wind velocity of $100 \>{\rm km\>s^{-1}}$. Furthermore, our SSA analysis yields a mean expansion velocity of $V_{\rm sh} \approx 3.3 \times 10^4\>{\rm km\>s^{-1}}$, which exceeds the theoretical shock velocity derived from the self-similar solution by a factor of $\sim 2.4$. Even for the conservative upper-bound peak time, the SSA-derived velocity remains larger than the theoretical expectation by a factor of $\gtrsim 1.7$. To explain this velocity excess, we propose the presence of a confined, dense circumstellar matter (CSM) surrounding the progenitor. The shock emergence from this confined CSM may have accelerated the forward shock, pointing to a highly complex and non-steady mass-loss history shortly before the explosion.

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arXiv2026

Shock breakout from mildly relativistic ejecta in a dense wind: the case of EP260321a/SN~2026gzf

We present shock breakout (SBO) modeling of the recently discovered X-ray transient EP260321a detected by the \textit{Einstein Probe} mission. Our semi-analytic model, based on our previous work, follows the interaction between a supernova ejecta with a mildly relativistic outer envelope and a dense, wind-like circumstellar medium (CSM) by using a thin-shell approximation that incorporates relativistic effects. We find that the observed properties of the X-ray emission are well explained by the breakout emission powered by a high-velocity envelope with a kinetic energy of $\sim3.5\times10^{49}\,\mathrm{erg}$ (excluding the supernova ejecta) and a dense wind characterized by a mass-loss rate of $\dot{M}\simeq1.2\times 10^{-3}(v_\mathrm{w}/10^3\,\mathrm{km\,s}^{-1})\,M_\odot\,\mathrm{yr}^{-1}$, where $v_\mathrm{w}$ is the wind velocity. The observed burst duration requires the dense CSM to extend up to $\sim350\,R_\odot$, corresponding to a CSM mass of $\sim 10^{-5}\,M_\odot$. These results demonstrate that SBO observations provide a sensitive probe of mass loss from stripped-envelope supernova progenitors shortly before core collapse.

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arXiv2026

Dust Without Na I D Trace: The Case of Highly Attenuated Type Ib SN 2024vjc

Understanding dust attenuation toward extragalactic transients is critical for recovering their intrinsic properties and probing the local environments of distant galaxies. A popular diagnostic is the Na I D absorption equivalent width widely applied to extragalactic transients. In this paper, we present early-time optical and near-infrared observations of the Type Ib supernova (SN) SN 2024vjc, followed for $\sim$130 days post-explosion. SN~2024vjc exhibits only weak Na~I~D absorption, indicating only a modest host attenuation with $E (B-V)_{\rm host} \sim 0.18$ mag; if this argument were applied, SN~2024vjc would be a peculiar, faint, and red SN Ib while showing the light-curve shape and spectral evolution broadly consistent with those of canonical SNe Ib. We show that this is not the case; SN-based diagnostics (intrinsic color templates, color-curve evolution, and spectral dereddening) together with the Balmer decrement indicate substantial attenuation, $E(B-V) \sim 0.45$ $-$ $0.8$\,mag. The weak Na I D absorption may result from photoionization of neutral sodium by the intense radiation field of a young H$_{2}$ region at the explosion site; this scenario is directly supported by the detection of narrow H$_{\alpha}$, [N$_{2}$], and H$_{\beta}$ emission lines and a blue continuum excess in late-time spectroscopy. SN~2024vjc represents a clear counterexample to the commonly assumption that weak or absent Na I D absorption implies negligible host-galaxy attenuation, and highlights the importance of employing multiple, independent attenuation diagnostics.

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arXiv2026

VENUS: an ultra-faint galaxy hosting the metal-poor type II supernova at $z=5.13$ Witnessing the initial metal enrichment with extremely frequent core-collapse supernovae?

We present the first characterization of the host galaxy of a recently discovered type IIP SN at $z=5.13$ (SN Eos). SN Eos and its host galaxy are gravitationally lensed and multiply imaged. The total magnification $\mu\sim53$ enables spatially resolving the system, allowing us to localize the core-collapse supernova (CCSN) position and to characterize its local environment within an early galaxy. Our observation reveals that the host is an ultra-faint ($M_{\rm UV}=-14.4\pm0.3$ mag) Lyman-$\alpha$ emitter with a very high equivalent width. The host galaxy also shows very weak [O iii]4959,5007 lines despite an H$\alpha$ line detection ([O iii]5007/H$\beta <0.7$ with case B recombination). Assuming that the weak [O iii] is due to low gas-phase metallicity given the low-metallicity of SN Eos itself, SN Eos plausibly marks the formation and explosion of a metal-poor star in an extremely metal-poor environment ($<1\ \%\ Z_\odot$), facilitating the initial stages of the chemical enrichment of the host. Finding the CCSN in such an ultra-faint galaxy at $z=5.13$ also indicates that the SN rate could be considerably higher in high-$z$, metal-poor environments, potentially implying e.g., a $Z$-dependent IMF, $Z$-dependent massive star explodability, or runaway stellar collisions in dense star clusters. Without lensing, only SN Eos would be detectable and the host would be below the detection limit in any NIRCam surveys ever performed. The Eos host galaxy can thus be representative of the origin of {\it hostless} supernovae frequently found in JWST blank field surveys.

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arXiv2026

Radio and X-ray Observations of the Transitional Supernova 2019yvr: Insights into the Progenitor Mass-Loss History

The final life stages of the massive star progenitors of stripped-envelope supernovae (SESNe) are still an open question, especially when it comes to the timing and magnitude of the progenitor stripping. Observing SESNe across the electromagnetic spectrum allows for the most direct constraints on mass loss in the final stages of progenitor evolution. In this work, we present radio (GMRT+VLA) and X-ray (Swift+Chandra) observations of SN 2019yvr obtained from 18-1784 days post-explosion. SN 2019yvr was a type Ib supernova (SN Ib, with strong helium but no or little optical hydrogen features) that transitioned into a type IIn supernova (SN IIn, with shock-driven hydrogen features) at $\sim$ 100 days post-explosion. The radio evolution is best-fit by a synchrotron self-absorbed model with a $\rho \propto r^{-1.65 \pm 0.25}$ CSM density profile, suggesting a decreasing mass-loss rate from the progenitor in the years leading up to the explosion. The radio-derived shock speed is high, more than 30,000 km/s at early times, suggesting a compact progenitor star. The combined radio and X-ray data probe CSM that extends from less than $10^{16}$ cm up to $\sim$ 20$\times10^{16}$ cm and was created by mass-loss from $\sim 1-3 \times10^{-5} \rm{M_{\odot} yr^{-1}} $ (assuming a CSM speed of 100 km/s). The combined dataset rules out any dramatic jump in CSM density (which was seen in the optical analog SN 2014C) associated with the emergence of optical hydrogen emission in SN 2019yvr. We place SN 2019yvr in context with similar transitional SNe and discuss implications for the progenitor.

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arXiv2026

VLBI Astrometry of Magnetars

The origin of the strongest magnetic fields in the Universe, i.e., the origin of magnetars, is a longstanding question. An enhanced dynamo effect in an irregular supernova explosion is a possible origin, which implies a stronger kick velocity and a higher proper motion of the magnetar compared to those of ordinary pulsars as well as an irregular morphology of the host supernova remnant (SNR). However, this hypothesis is not well studied yet, because there is a lack of precise measurement of the proper motion of magnetar and of identification of the host SNR. VLBI astrometry of magnetars is a unique tool to examine the hypothesis. In this chapter, we introduce the MONSTER (Monitoring Observations of the Neutron Stars That Evolve Rapidly) Project. SKA-VLBI's unprecedented sensitivity and the highest angular resolution will allow us to dramatically expand the survey volume in which we can measure the proper motion of magnetars within a radio outburst period of a few months.

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arXiv2026

Two years of shock interaction tracing three phases of evolution: the explosion of a Type IIn supernova, SN 2019vxm

We present multi-wavelength photometric and optical spectroscopic observations of the long-lived interacting supernova SN 2019vxm, spanning more than two years after the explosion. SN 2019vxm is a slowly rising (rise time ~ 45.9 days in the R-band), slowly declining supernova reaching an R-band peak absolute magnitude of ~-20.3 mag. The SN light curve post-maximum shows a shallow decline, followed by a secondary, steeper decline in the optical (0.01 mag/day), with late-time IR brightening. The total radiated luminosity is 5x10^50 erg, placing it among the energetic class of its type. We estimated a CSM mass of 3-8 M_sun through light-curve modeling (independent of the CSM density profile) and by comparison with theoretical models. We estimate a minimum ejecta mass of ~ 3.88 M_sun from the broad H-alpha component, consistent with the ejecta mass obtained from the light curve models. The solely interaction-dominated initial epochs are later accompanied by photon-scattering signatures, leading to asymmetric line profiles with symmetric wings. The late phase, characterized by enhanced brightness at longer wavelengths and a stronger asymmetric line profile with the red side flux strongly suppressed, indicates the influence of pre-existing or newly formed dust with temperatures ~ 1500 K at ~4x10^16 cm. Even in the late phases, no nebular lines are present in the spectra, indicating dense or obscured ejecta.

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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

A Multi-Wavelength View of the First Type Ic-BL Supernova with an Einstein Probe X-ray Shock Breakout

In March 2026, the Einstein Probe (EP) discovered its most nearby (z = 0.0343) Fast X-ray Transient (FXT), EP260321a, the first EP FXT to provide a strong match to expectations for X-ray "shock breakout'" (SBO) emission. Here, we present our multi-wavelength follow-up campaign of EP260321a and its broad-line Type Ic (Ic-BL) supernova (SN) counterpart, SN2026gzf. We show that our radio follow-up extending over 5.8 - 54.5 days post-FXT rules out an on-axis jet counterpart of isotropic-equivalent kinetic energy $E_{K} \gtrsim 10^{49}$ erg for circumburst densities $n > 10^{-2}~{\rm cm}^{-3}$ and assuming microphysical parameters $\epsilon_e = \epsilon_B = 0.1$. Our radio data also constrains a median mass-loss rate of $\dot{M} \lesssim 1.2 \times 10^{-5} M_{\odot}~{\rm yr}^{-1}$ for a Wolf-Rayet progenitor. In addition, we derive SN2026gzf's properties, including $^{56}$Ni mass, diffusion timescale, and expansion velocities, from our $\sim$nightly-cadence optical data and compare them with those of optically discovered Type Ic-BL SNe, finding that SN 2026gzf is well within the 90\% confidence interval across all properties. We further fit SN2026gzf's light curve and determine that combined emission from both interaction with CSM and $^{56}$Ni radioactive decay provides the best fit with plausible model parameters. Finally, using the rate of Ic-BL SNe from the ZTF Bright Transient Survey and assuming all Type Ic-BL SNe produce EP260321a-like FXTs, we infer an expected rate of EP-detected SBOs of 4.4 - 16 year$^{-1}$. This is inconsistent at the 90% confidence level with current EP detection rates, potentially indicating that most Type Ic-BL SNe produce less luminous X-ray SBO signals compared to EP260321a.

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arXiv2026

Constraints on the Metallicity-dependent Explodability of Massive Stars from Galactic Chemical Evolution: Toward Alleviating the Red Supergiant Problem

The explodability of massive stars, namely whether they undergo core-collapse supernovae (CCSNe) or form black holes (BHs), strongly influences galactic chemical evolution (GCE). Details of the explodability are still controversial, but realistic predictions including metallicity-dependence are becoming available through stellar-evolution and explosion calculations. In the present work, we implement recently-proposed metallicity-dependent explodability prescriptions into a GCE framework. We show that the physics-motivated explodability prescriptions reproduce the key observed abundance trends. Further, within uncertainties of the explodability models, the GCE model provides important constraints on the region of the BH formation in the mass-metallicity space. Guided by these findings, we further construct a simplified form of the metallicity-dependent explodability designed to alleviate the red supergiant (RSG) problem and explore its compatibility with GCE constraints. We find that such a solution exists, if (1) the net outflows from the system are negligible/absent, and (2) the transition of the explodability takes place at sub-solar metallicity. These results demonstrate that GCE can provide meaningful constraints on massive-star explodability and that explodability prescriptions capable of addressing the RSG problem can be constructed without violating chemical-evolution observables. We also show that a metallicity-dependent initial mass function can improve agreement with observations; this effect becomes important once coupled with the metallicity-dependent explodability.

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arXiv2026

Interacting Binary Stars as Progenitors for Interacting Supernovae

Dense, compact circumstellar media (CSM) are required to power strongly interacting supernovae, yet their physical origin remains uncertain. We present a systematic study of binary stellar evolution models computed with MESA, demonstrating that Case C mass transfer, initiated after core helium ignition, can naturally produces the dense, nearby CSM inferred in interacting events. Across a grid of binary models, we find that donors of 10--20 solar masses in binaries with separations of approximately 1000--2700 solar radius undergo late-stage Roche-lobe overflow within ~10^3 yr prior to core collapse, ejecting ~0.01--0.2 solar masses and forming CSM extending to ~10^16--10^18 cm. Our results suggest that the Case C mass transfer may account for ~13% of all core-collapse supernova (CCSN) progenitors, rather than representing a rare channel. A subset of these Case C binaries produces CSM properties that are quantitatively in agreement with those inferred for interacting supernovae such as SN 2014C. In contrast to earlier binary interactions or single-star mass loss, Case C transfer operates at the right time and scale to shape the immediate pre-supernova environment without requiring ad hoc eruptive mechanisms. Our results identify late-stage binary interaction as a robust and physically motivated channel for producing the dense CSM that powers interacting supernovae.

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arXiv2026

JWST Nebular Spectroscopy of SN 2023qov: Circumstellar Dust Emission in a Normal Type Ia Supernova

We present panchromatic observations of the Type Ia supernova (SN Ia) 2023qov, ranging from $\sim$2 weeks before to $\sim$1 year after maximum light. \textit{JWST} near- and mid-infrared spectra at $+$276 and $+$363~days show $\sim$400 K dust emission that cools by $\sim$75 K between epochs, the first unambiguous spectroscopic detection of dust emission in a normal SN Ia. We find that the emission is well described by models of carbonaceous dust placed within $\sim$1 light year of the SN, with a dust mass of $\sim$$10^{-4}$ M$_{\odot}$. We do not see evidence of active dust creation, suggesting an infrared light echo by pre-existing circumstellar dust as the likely source of the emission. The \textit{JWST} nebular line profiles suggest asymmetric, stratified ejecta, similar to other normal SNe Ia, though a slight double-horn structure in the argon lines indicate a toroidal enhancement. SN 2023qov exhibits a slightly red, fast-declining early light curve ($\Delta m_{15}(B) = 1.47 \pm 0.05$ mag), from which we determine a $^{56}$Ni mass of $M_{56} = 0.21 \pm 0.04$ M$_{\odot}$, and a distance of $d = 36.0 \pm 1.8$ Mpc to the SN and its host, NGC 7029.

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arXiv2026

Single vs. Binary Origin: The Diversity of Stripped-Envelope Supernova Remnants

Core-collapse supernova remnants (CCSNRs) are crucial for understanding the final stages of massive star evolution, as they reflect the imprints of their progenitors' pre-explosion activities. However, the evolution of CCSNRs, particularly those originating from progenitors with high mass-loss rates -- known as stripped-envelope SNRs (SESNRs) -- remains poorly understood. This is largely due to the lack of comprehensive numerical models connecting progenitor stars to their remnants, especially in the context of binarity. In this study, we perform self-consistent simulations of CCSNRs from both single and binary progenitors, utilizing mass-loss histories and supernova ejecta profiles directly derived from stellar evolution and explosion calculations. Our models reveal significant differences in the circumstellar medium (CSM) structures between single and binary progenitors, which drive distinct SNR dynamics and spectral characteristics. We find that binary-stripped progenitors tend to produce SNRs with more monotonic CSM profiles, resulting in smoother shock dynamics and less pronounced X-ray luminosity peaks compared to their single-star counterparts. Additionally, we introduce a new characteristic timescale, $t_{\rm CSM}$, defined by the total mass lost by the progenitor. This timescale effectively scales the evolutionary phases of CCSNRs in complex CSM environments, thereby facilitating the comparison of SESNRs. Given that observed elemental abundances in SNRs reflect the nucleosynthesis yields of the progenitor, our results highlight the importance of considering the dynamical state of SNRs when interpreting observed abundances. This work provides a fiducial framework for future observational and theoretical studies of CCSNRs, particularly regarding the impact of binary evolution.

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arXiv2026

Angular momentum transport in the convection zone of a 3D MHD simulation of a rapidly rotating core-collapse progenitor

Rotation and magnetic fields in the cores of evolved massive stars in their final phase are thought to play an important role in the subsequent supernova explosion and the formation of a compact object, especially in hyperenergetic explosions. However, the interplay between rotation, magnetic fields, and convection up to the final collapse is a nonlinear, multidimensional effect that is difficult to capture with standard one-dimensional (1D) stellar evolution models. We quantify the magnetic angular momentum (AM) transport in the convective oxygen burning shell in a three-dimensional (3D) rotating core-collapse progenitor model. We find that the radial direction of magnetic AM transport is directly related to the Rossby number of the convective oxygen shell. We also analyze the magnetic energy, which sets the amplitude of the magnetic AM flux. The magnetic energy is determined both by rotation and the nuclear energy generation rate analogously to low-mass stars like the Sun. Based on these results, we construct a 1D model of magnetic AM transport in the convection zone for the first time in terms of properties of a given stellar evolution model. This model successfully reproduces the AM transport in the 3D model when the convective dynamo is in a quasi-steady state. Notably, our model for radial AM transport is the first to account for inward AM flux. This may result in interesting differences compared to the conventional treatment of magnetic AM transport in stellar evolution models, which assume AM is transported outward by a purely diffusive process.

astro-ph.SR↗

arXiv2026

An investigation on the FWHM of absorption features of type Ia supernovae

We present an investigation of the full width at half maximum (FWHM, or {\gamma}) of absorption features of Type Ia supernova (SNe Ia). We found that, the average value of FWHM can be well predicted with the rest wavelength ({\lambda}). The velocity also plays an important role, as objects with a higher velocity tend to have a larger FWHM. Temperature may be the third factor, as we found that, at the same velocity (but different phases), a normal-velocity (NV) object tends to have a larger FWHM than high-velocity (HV) object. Also, 1991T/1999aa-like objects that are believed to have relatively high temperatures show the largest FWHMs if compared at the same velocity. Generally speaking, FWHM evolves very slowly with time and shows no correlation with {\Delta}m15, but 1991T/1999aa-like objects are characterized by relatively fast decreasing FWHM. On the other hand, we found that, objects with relatively small FWHMs shows a tighter correlation between absorption depth (A) and {\Delta}m15, possibly a sign of higher degree of homogeneity. We also found that A/{\gamma} of Si II {\lambda}5972 has a strong correlation with {\Delta}m15, and more importantly, a relatively slow time evolution, making it a useful luminosity estimator even in the absence of phase information.

astro-ph.HE↗