Peak Luminosity Research Articles

Study on background full simulation and implementation for Super Tau-Charm Facility

The Super Tau-Charm Facility is a new generation high luminosity electron-positron collider designed to operate in the tau-charm energy region. With the designed peak luminosity of at least 0.5 × 1035 cm-2s-1, the background full simulation and implementation would be an important part in the detector study. Based on Offline Software of Super Tau-Charm Facility, the software platform for STCF, the spectrometer structure modeling, simulation for both luminosity-related and beam-related background sources, the random mixing algorithm of signal and background are carried out. The simulation result indicates that the highest TID in STCF detector is 4700 Gy/y, the highest NIEL damage is below 1011 1 MeV neutron·cm-2y-1 except MDC, and the highest SEEs is below 2 kHz/cm2. The cross check with FLUKA also indicates a similar magnitude for both the TID and NIEL damage simulation result, except MDC NIEL damage due to the (n, p) reaction was not considered in FLUKA. The highest background total count rate is hundreds of MHz for most of detectors, the highest count rate per channel is approximately 720 kHz/channel in ITKW and 580 kHz/channel in ECAL. This work presents a systematic background evaluation route based on GEANT4, which is easy to combine with the further detector performance study. These simulation results indicate that all the systems can tolerate the background with the newly developed detector and electronics technologies. Moreover, the further optimization of STCF lattice design, the shield in MDI and detector systems are still required to suppress the background to an even lower level for a better detector performance. Meanwhile, the physics signal can be well mixed with the randomly sampled background data at the level of GEANT4 steps, aiming to simulate the realistic situation of the detector and providing necessary database for detector performance optimization and physics study.

The high-energy cyclotron line in 2S 1417-624 discovered with Insight-HXMT during the 2018 outburst

We report a detailed timing and spectral analysis of the X-ray pulsar 2S 1417-624 using the data from Insight-HXMT during the 2018 outburst. The pulse profiles are highly variable with respect to both unabsorbed flux and energy. A double-peaked pulse profile from the low flux evolved to a multi-peaked shape in the high-flux state. The pulse fraction is negatively correlated to the source flux in the range of sim (1--6)$\ $ erg cm$^ $ s$^ $, consistent with Rossi X-ray Timing Explorer (RXTE) studies during the 2009 giant outburst. The energy-resolved pulse profiles around the peak outburst showed a four-peak shape in the low-energy bands and gradually evolved to triple peaks at higher energies. The continuum spectrum is well described by typical phenomenological models, such as the cut-off power law and the power law with high-energy cut-off models. Notably, we discovered high-energy cyclotron resonant scattering features (CRSFs) for the first time, which are around 100 keV with a statistical significance of sim 7sigma near the peak luminosity of the outburst. This CRSF line is significantly detected with different continuum models and provides very robust evidence for its presence. Furthermore, pulse-phase-resolved spectroscopy confirmed the presence of the line, whose energy varied from 97 to 107 keV over the pulse phase and appeared to have a maximum value at the narrow peak phase of the profiles.

A Gamma-Ray Flare from TXS 1508+572: Characterizing the Jet of a z = 4.31 Blazar in the Early Universe

Blazars can be detected from very large distances due to their high luminosity. However, the detection of γ-ray emission of blazars beyond z = 3 has only been confirmed for a small number of sources. Such observations probe the growth of supermassive black holes close to the peak of star formation in the history of galaxy evolution. As a result from a continuous monitoring of a sample of 80 z > 3 blazars with the Fermi Large Area Telescope (Fermi-LAT), we present the first detection of a γ-ray flare from the z = 4.31 blazar TXS 1508+572. This source showed high γ-ray activity from 2022 February to August, reaching a peak luminosity comparable to the most luminous flares ever detected with Fermi-LAT. We conducted a multiwavelength observing campaign involving XMM-Newton, the Neil Gehrels Swift Observatory, the Effelsberg 100 m radio telescope, and the Very Long Baseline Array. In addition, we make use of the monitoring programs by the Zwicky Transient Facility and the Near-Earth Object Wide-field Infrared Survey Explorer at optical and infrared wavelengths, respectively. We find that the source is particularly variable in the infrared band on daily timescales. The spectral energy distribution collected during our campaign is well described by a one-zone leptonic model, with the γ-ray flare originating from an increase of external Compton emission as a result of a fresh injection of accelerated electrons.

Late Jets, Early Sparks: Illuminating the Premaximum Bumps in Superluminous Supernovae

Superluminous supernovae (SLSNe) radiate ≳10–100 times more energy than ordinary stellar explosions, implicating a novel power source behind these enigmatic events. One frequently discussed source, particularly for hydrogen-poor (Type I) SLSNe, is a central engine such as a millisecond magnetar or accreting black hole. Both black hole and magnetar engines are expected to channel a fraction of their luminosity into a collimated relativistic jet. Using 3D relativistic hydrodynamical simulations, we explore the interaction of a relativistic jet, endowed with a luminosity L j ≈ 1045.5 erg s−1 and duration t eng ≈ 10 days compatible with those needed to power SLSNe, launched into the envelope of the exploding star. The jet successfully breaks through the expanding ejecta, and its shocked cocoon powers ultraviolet/optical emission lasting several days after the explosion and reaching a peak luminosity ≳1044 erg s−1, corresponding to a sizable fraction of L j . This high radiative efficiency is the result of the modest adiabatic losses the cocoon experiences owing to the low optical depths of the enlarged ejecta at these late times, e.g., compared to the more compact stars in gamma-ray bursts. The luminosity and temperature of the cocoon emission match those of the “bumps” in SLSN light curves observed weeks prior to the optical maximum in many SLSNe. Confirmation of jet breakout signatures by future observations (e.g., days-long to weeks-long internal X-ray emission from the jet for on-axis observers, spectroscopy confirming large photosphere velocities v/c ≳ 0.1, or detection of a radio afterglow) would offer strong evidence for central engines powering SLSNe.

Research progress on long lifetime MCP-PMT for the DTOF detector in STCF

The Super Tau Charm Facility (STCF) is a state-of-the-art electron-positron collider operating in the center-of-mass energy range of 2–7[Formula: see text]GeV and achieving a peak luminosity of more than [Formula: see text][Formula: see text]cm−2s−1, which is pivotal for advancing particle physics research. The DIRC-like time-of-flight (DTOF) detector is one of the crucial components of the STCF, designed to identify high-momentum charged particles with high precision. A significant element of the DTOF is the microchannel plate photomultiplier tube (MCP-PMT), known for its exceptional time resolution in the detection of Cherenkov light. With the STCF expected to operate for over a decade, stringent requirements are imposed on the MCP-PMT, requiring an integrated anode charge (IAC) in excess of 10[Formula: see text]C/cm2. In this paper, the lifetime of the single anode MCP-PMT prototypes is investigated and a multi-anode MCP-PMT design is presented. The results show that the lifetime of the single anode MCP-PMT is greater than 11[Formula: see text]C/cm2 when a 6 nm-thick ALD layer is deposited on the inner surface of the MCP and an electron scrubbing dosage of 0.75[Formula: see text][Formula: see text]A[Formula: see text][Formula: see text][Formula: see text]h/cm2 is applied to the MCP. The lifetime is expected to be further improved by increasing the electron scrubbing dosage and optimizing the ALD layer. The studies on the single anode MCP-PMTs will be applied to the development of the long-life multi-anode MCP-PMT.

A 9 Month Hubble Space Telescope Near-UV Survey of M87. II. A Strongly Enhanced Nova Rate near the Jet of M87

The 135 classical novae that we have discovered in M87 with two Hubble Space Telescope imaging surveys appear to be strongly concentrated along that galaxy’s jet. Detailed simulations show that the likelihood that this distribution occurred by chance is of order 0.3%. The novae near the jet display outburst characteristics (peak luminosities, colors, and decline rates) that are indistinguishable from novae far from the jet. We explore whether the remarkable nova distribution could be caused by the jet’s irradiation of the hydrogen-rich donors in M87's cataclysmic binaries. This explanation, and others extant in the literature that rely on increased binary mass transfer rates, fail by orders of magnitude in explaining the enhanced nova rate near the jet. An alternate explanation is the presence of a genuine surplus of nova binary systems near the jet, perhaps due to jet-induced star formation. This explanation fails to explain the lack of nova enhancement along M87's counterjet. The enhanced rate of novae along M87's jet is now firmly established, and unexplained.

Effects of nucleon-nucleon short-range correlation and symmetry energy on the evolution of newly born magnetars

Abstract Millisecond magnetars are widely suggested as the central engines powering hydrogen-poor superluminous supernovae (SLSNe). These magnetars primarily lose huge rotational energy through gravitational wave radiation (GWR) and magnetic dipole radiation (MDR), with MDR serving as an energy source for SLSNe. We study the evolution of the magnetar spin, magnetic inclination angle, and the resulting thermal radiative luminosity of the SLSNe, where the impacts of the nucleon-nucleon short-range correlation, the mass and initial spin of the magnetar, and the density-dependent symmetry energy of the dense nuclear matter on the evolution are discussed. The relativistic mean-field theory is employed to calculate the nuclear matter properties, and we particularly concentrate on the time- and space-dependent bulk viscosity which is crucial for the magnetic inclination angle evolution. It is found that the nucleon-nucleon short-range correlation weakens the damping of bulk viscosity of dense matter and therefore inhibits the growth of magnetic inclination angle, and it reduces the MDR (GWR) peak luminosity of a canonical magnetar by several times while it raises the peak thermal radiation luminosity of SLSNe by several times. For magnetars with nonrotating mass obviously lower than the $1.4 \, \rm M_\odot$ with slow initial rotation, the magnetic inclination angle is more likely to evolve towards 0 degrees quickly, and these magnetars are not suitable as the central engine for SLSNe. Within the ‘family’ of FSUGarnet interaction, a stiffer symmetry energy gives a lower threshold of direct Urca process and hence gives a much larger bulk viscosity coefficient, and thus it promotes the growth of the magnetic inclination angle and the GWR for canonical stars but reduces the peak brightness of SLSNe significantly.

New results on the gamma-ray burst variability--luminosity relation

At the dawn of the gamma--ray burst (GRB) afterglow era, a Cepheid-like correlation was discovered between the time variability $V$ and the isotropic-equivalent peak luminosity $L_ iso $ of the prompt emission of about a dozen long GRBs with measured redshift available at that time. Soon afterwards, the correlation was confirmed in a sample of about 30 GRBs, even though it was affected by significant scatter. Unlike the minimum variability timescale (MVT), $V$ measures the relative power of short-to-intermediate timescales. We aim to test the correlation using about 200 long GRBs with spectroscopically measured redshift, detected by Swift Fermi and Konus/ WIND for which both observables can be accurately estimated. The variability for all selected GRBs was calculated according to the original definition using the 64 ms background-subtracted light curves of Swift /BAT ( Fermi /GBM) in the 15--150 (8--900) keV energy passband. Peak luminosities were either taken from the literature or derived from modelling broad-band spectra acquired with either Konus/ WIND or Fermi /GBM. The statistical significance of the correlation has weakened to $ 2$<!PCT!>, mostly due to the appearance of a number of smooth and luminous GRBs that are characterised by a relatively small $V$. At odds with most long GRBs, three out of four long-duration merger candidates have high $V$ and low iso The luminosity is more tightly connected with shortest timescales measured by MVT than the short to intermediate timescales measured by $V$. We discuss the implications for internal dissipation models and the role of the $e^ pm $ photosphere. We identified a few smooth GRBs with a single broad pulse and low $V$ that might have an external shock origin, in contrast with most GRBs. The combination of high variability $(V 0.1)$, low luminosity iso $ erg s$^ $, and short MVT ($ 0.1$ s) could be a good indicator for a compact binary merger origin.

Energetic explosions from collisions of stars at relativistic speeds in galactic nuclei

Aims. We investigated collisions that could occur between stars moving near the speed of light around supermassive black holes (SMBHs) with mass M• ≳ 108 M⊙, without being tidally disrupted. Within this approximate SMBH mass range, for sun-like stars, the tidal-disruption radius is smaller than the SMBH’s event horizon; therefore we did not anticipate tidal disruption events (TDEs). Methods. Differential collision rates were calculated by defining probability distribution functions for various parameters of interest, such as the impact parameter, distance from the SMBH at the time of the collision, the relative velocity between the two colliding stars, and the masses of the two colliding stars. The relative velocity parameter was drawn from an appropriate distribution function for SMBHs. We integrated over all these parameters to arrive at a total collision rate for a galaxy with a specific SMBH mass. We then considered how the stellar population in the vicinity of the SMBH was depleted and replenished over time, and calculated the effect this can have on the collision rate over time. We further calculated the differential collision rate as a function of the total energy released, the energy released per unit mass lost, and the galactocentric radius. Results. The overall rate for collisions taking place within the inner ∼1 pc of galaxies with M• = 108, 109, and 1010 M⊙ are Γ ∼ 2.2 × 10−3, 2.2 × 10−4, and 4.7 × 10−5 yr−1, respectively. The most common collisions would release energies on the order of ∼1049 − 1051 ergs, with the energy distribution peaking at higher energies in galaxies with more massive SMBHs. In addition, we examined sample light curves for collisions with varying parameters, and find that the peak luminosity could reach or even exceed that of superluminous supernovae (SLSNe), albeit in the case of light curves with much shorter durations. Conclusions. Weaker events may initially be mistaken for low-luminosity supernovae. In addition, we note that these events would likely create streams of debris that would accrete onto the SMBH, potentially creating accretion flares that may resemble TDEs.

SN 2022oqm: A Bright and Multipeaked Calcium-rich Transient

We present the photometric and spectroscopic evolution of SN 2022oqm, a nearby multipeaked hydrogen- and helium-weak calcium-rich transient (CaRT). SN 2022oqm was detected 13.1 kpc from its host galaxy, the face-on spiral galaxy NGC 5875. Extensive spectroscopic coverage reveals an early hot (T ≥ 40,000 K) continuum and carbon features observed ∼1 day after discovery, SN Ic-like photospheric-phase spectra, and strong forbidden calcium emission starting 38 days after discovery. SN 2022oqm has a relatively high peak luminosity (M B = −17 mag) for CaRTs, making it an outlier in the population. We determine that three power sources are necessary to explain the light curve (LC), with each corresponding to a distinct peak. The first peak is powered by an expanding blackbody with a power-law luminosity, suggesting shock cooling by circumstellar material (CSM). Subsequent LC evolution is powered by a double radioactive decay model, consistent with two sources of photons diffusing through optically thick ejecta. From the LC, we derive an ejecta mass and 56Ni mass of ∼0.6 M ⊙ and ∼0.09 M ⊙. Spectroscopic modeling ∼0.6 M ⊙ of ejecta, and with well-mixed Fe-peak elements throughout. We discuss several physical origins for SN 2022oqm and find either a surprisingly massive white dwarf progenitor or a peculiar stripped envelope model could explain SN 2022oqm. A stripped envelope explosion inside a dense, hydrogen- and helium-poor CSM, akin to SNe Icn, but with a large 56Ni mass and small CSM mass could explain SN 2022oqm. Alternatively, helium detonation on an unexpectedly massive white dwarf could also explain SN 2022oqm.

Spectral evolution of RX J0440.9+4431 during the 2022–2023 giant outburst observed with Insight-HXMT

In 2022–2023, the Be/X-ray binary X-ray pulsar RX J0440.9+4431 underwent a Type II giant outburst, reaching a peak luminosity of LX ∼ × 1037 erg s−1. In this work, we utilized Insight-HXMT data to analyze the spectral evolution of RX J0440.9+4431 during the giant outburst. By analyzing the variation in the X-ray spectrum during the outburst using standard phenomenological models, we find that as the luminosity approaches the critical luminosity, the spectrum becomes flatter, with the photon enhancement predominantly concentrated around ∼2 keV and 20–40 keV. The same behavior has also been noted in Type II outbursts from other sources. While the phenomenological models provide good fits to the spectrum, it is sometimes difficult to gain insight into details of the fundamental accretion physics using this approach. Hence, we also analyzed spectra obtained during high and low phases of the outburst using a new, recently developed physics-based theoretical model that allows us to study the variations in the physical parameters during the outburst, such as the temperature, density, and magnetic field strength. Application of the theoretical model reveals that the observed spectrum is dominated by Comptonized bremsstrahlung emission emitted from the column walls in both the high and low states. We show that the spectral flattening observed at high luminosities results from a decrease in the electron temperature, combined with a compactification of the emission zone, which reduces the efficiency of bulk Comptonization. We also demonstrate that when the source is at maximum luminosity, the spectrum tends to harden around the peak of the pulse profile, and we discuss possible theoretical explanations for this behavior. We argue that the totality of the behavior in this source can be explained if the accretion column is in a quasi-critical state at the time of maximum luminosity during the outburst.

The Intrinsic Correlations between Prompt Emission and X-ray Flares of Gamma-Ray Bursts

X-ray flare (XRF) is a common phenomenon in the X-ray afterglow of gamma-ray bursts (GRBs). Although it is commonly believed that XRFs may share a common origin with prompt emission, i.e., the “internal” origin, the origin of XRFs is still unknown. In this work, we compile a GRB sample containing 31 GRBs with a single XRF, a well-measured spectrum, and a redshift, and investigate the intrinsic properties and correlations between prompt emission and the XRFs of these events. We find that the distributions of main physical parameters of prompt emission and XRFs are basically log-normal. The median value of the rise time is shorter than the decay time for all flares, with a ratio of about 1:2, which is similar to the fast rise and exponential decay structure of prompt emission pulses. We also find that the prompt emission energy (Eiso) and peak luminosity (Liso) have tight correlations with XRF energy (EX,iso) and peak luminosity (LX,p), Eiso∝EX,iso0.74 (LX,p0.62) and Liso∝EX,iso0.85 (LX,p0.68). However, the durations of prompt emissions are independent of the temporal properties of XRFs. Furthermore, we also analyze the three-parameter correlations between prompt emissions and XRFs, and find that there are tight correlations among the XRF peak time (Tp,z), LX,p, and Eiso/Liso, LX,p∝Tp,z−1.08Eiso0.84 and LX,p∝Tp,z−1.09Liso0.71. Interestingly, these results are very similar to the properties of an X-ray plateau in GRBs, which indicates that X-ray flares and plateaus may have the same physical origin, and strongly supports that the two emission components originate from the late-time activity of the central engine.

Discovery of a Relativistic Stripped-envelope Type Ic-BL Supernova at z = 2.83 with JWST

Abstract We present James Webb Space Telescope (JWST) NIRCam and NIRSpec observations of a Type Ic supernova (SN Ic) and its host galaxy (JADES-GS+53.13533-27.81457) at z = 2.83. This SN (named SN 2023adta) was identified in deep JWST/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Follow-up observations with JWST/NIRSpec provided a spectroscopic redshift of z = 2.83 and the classification as an SN Ic-BL. The light curve of SN 2023adta matches well with other stripped-envelope SNe, and we find a high peak luminosity, M V = −19.0 ± 0.2 mag, based on the distribution of best-fit SNe. The broad absorption features in its spectrum are consistent with other SNe Ic-BL 1–3 weeks after peak brightness. We measure a Ca ii near-IR triplet expansion velocity of 29,000 ± 2000 km s−1. The host galaxy of SN 2023adta is irregular, and modeling of its spectral energy distribution indicates a metallicity of Z = 0.35 − 0.08 + 0.16 Z ⊙ . This environment is consistent with the population of low-z SNe Ic-BL that prefer lower metallicities relative to other stripped-envelope SNe and track long-duration γ-ray burst environments. We do not identify any γ-ray bursts that are coincident with SN 2023adta. Given the rarity of SNe Ic-BL in the local Universe, the detection of an SN Ic-BL at z = 2.83 could indicate that their rates are enhanced at high redshift.

STELLA Lightcurves of Energetic Pair-instability Supernovae in the Context of SN2018ibb

SN2018ibb is a recently observed hydrogen-poor superluminous supernova that appears to be powered by the decay of 30 M ⊙ of radioactive nickel. This supernova has been suggested to show hybrid signatures of a pair-instability supernova and an interacting supernova. In a previous paper, we found that rotating, metal-enriched pair-instability supernova progenitors appeared to check both of these boxes. In this paper, we model the lightcurves of the pair-instability supernovae using STELLA. We find that the STELLA models can explain the overall shape of the bolometric lightcurve of SN2018ibb, though not specific morphological features such as the luminosity peak or the bump at roughly 300 days after the peak. We also estimate the contribution from interaction and find that with relatively low wind velocities, the circumstellar medium originating from the stellar winds is consistent with the evidence for interaction in the spectra. The observed values of the photosphere velocity in the 100 days after peak luminosity are similar to the STELLA models, but the deceleration is lower. This leads to the biggest inconsistency, which is the blackbody temperature of SN2018ibb being much hotter than any of the STELLA models. We note that this high temperature (and the flat velocity) may be difficult to reconcile with the long rise time of SN2018ibb, but nevertheless conclude that if it is accurate, this discrepancy represents a challenge for SN2018ibb being a robust PISN candidate. This result is noteworthy given the lack of other scenarios for this supernova.

Effect of Methyl Butyrate blending on soot formation in Jet A laminar diffusion flame

To investigate the effect of methyl butyrate (MB) blending on soot formation in a Jet A laminar diffusion flame, laser-induced incandescence (LII) and laser-induced fluorescence (LIF) techniques were employed to assess the distributions of soot-LII signal and polycyclic aromatic hydrocarbons (PAH) signal in Jet A with varying MB blending ratios from 0% to 80%. The experimental results revealed that an increase in the MB blending ratio resulted in decreased flame height, reduced radially integrated natural luminosity peak signal, and lower the total spatially integrated natural luminosity, while the flame base height increased. The starting position of soot-LII signal moved downstream gradually, and the peak signal magnitude on the axis decreased. The addition of MB effectively reduced the soot-LII signal in Jet A. Compared to pure Jet A, the average soot-LII signal for MB20, MB40, MB60, and MB80 decreased by 18.9%, 79.6%, 85.3%, and 94.2%, respectively. The maximum soot-LII signal decreased by 18.2%, 68.3%, 76.0%, and 93.5%, respectively. Furthermore, the PAH-LIF signal gradually decreased as the MB blending ratio increased. Moreover, the MB-Jet A-PAH mechanism was constructed, and the formation pathways of the soot precursor based on a diffusion flame model were calculated. The kinetic results indicate that an increase in the MB blending ratio reduces the rates of different reactions involved in the generation of A1, leading to a reduction in A1. The dilution of PBZ in Jet A by MB is identified as the primary factor for the reduction in soot.

Revisiting the concordance ΛCDM model using Gamma-Ray Bursts together with supernovae Ia and Planck data

The Hubble constant, H0, tension is the tension among the local probes, Supernovae Ia, and the Cosmic Microwave Background Radiation. This tension has persisted for decades and continues to puzzle the community. Here, we add intermediate redshift probes, such as Gamma-Ray Bursts (GRB) and Quasars (QS0s), to check if and to what extent these higher redshift probes can reduce this tension. We use the three-dimensional fundamental plane relation among the prompt peak luminosity, the luminosity at the end of the plateau emission, and its rest frame duration. We find similar trend in GRB intrinsic parameters as previously seen in Pantheon-Plus intrinsic parameters. We find an apparent 3.14σ tension for the GRB intrinsic parameter b. Indeed, this tension disappears and the parameters are actually compatible within 2.26σ. Another interesting point is that the 3D relation plays an important role in conjunction with Supernovae data with Pantheon Plus and that this apparent discrepancy shows the importance of the correction for selection biases and redshift evolution. The incorporation of redshift evolution correction results in a reduction of the GRB tension to 2.26σ when adjusting correction parameters. We envision that with more data this indication of tension will possibly disappear when the evolutionary parameters of GRBs are computed with increased precision.

The Unluckiest Star: A Spectroscopically Confirmed Repeated Partial Tidal Disruption Event AT 2022dbl

The unluckiest star orbits a supermassive black hole elliptically. Every time it reaches the pericenter, it shallowly enters the tidal radius and gets partially tidally disrupted, producing a series of flares. Confirmation of a repeated partial tidal disruption event (pTDE) requires not only evidence to rule out other types of transients but also proof that only one star is involved, as TDEs from multiple stars can also produce similar flares. In this Letter, we report the discovery of a repeated pTDE, AT 2022dbl. In a quiescent galaxy at z = 0.0284, two separate optical/UV flares have been observed in 2022 and 2024 with no bright X-ray, radio, or mid-infrared counterparts. Compared to the first flare, the second flare has a similar blackbody temperature of ∼26,000 K, slightly lower peak luminosity, and slower rise and fall phases. Compared to the Zwicky Transient Facility TDEs, their blackbody parameters and light-curve shapes are all similar. The spectra taken during the second flare show a steeper continuum than the late-time spectra of the previous flare, consistent with a newly risen flare. More importantly, the possibility of two independent TDEs can be largely ruled out because the optical spectra taken around the peak of the two flares exhibit highly similar broad Balmer, N iii, and possible He ii emission lines, especially the extreme ∼4100 Å emission lines. This represents the first robust spectroscopic evidence for a repeated pTDE, which can soon be verified by observing the third flare, given its short orbital period.

Final Moments. II. Observational Properties and Physical Modeling of Circumstellar-material-interacting Type II Supernovae

We present ultraviolet/optical/near-infrared observations and modeling of Type II supernovae (SNe II) whose early time (δ t < 2 days) spectra show transient, narrow emission lines from shock ionization of confined (r < 1015 cm) circumstellar material (CSM). The observed electron-scattering broadened line profiles (i.e., IIn-like) of H i, He i/ii, C iv, and N iii/iv/v from the CSM persist on a characteristic timescale (t IIn) that marks a transition to a lower-density CSM and the emergence of Doppler-broadened features from the fast-moving SN ejecta. Our sample, the largest to date, consists of 39 SNe with early time IIn-like features in addition to 35 “comparison” SNe with no evidence of early time IIn-like features, all with ultraviolet observations. The total sample includes 50 unpublished objects with a total of 474 previously unpublished spectra and 50 multiband light curves, collected primarily through the Young Supernova Experiment and Global Supernova Project collaborations. For all sample objects, we find a significant correlation between peak ultraviolet brightness and both t IIn and the rise time, as well as evidence for enhanced peak luminosities in SNe II with IIn-like features. We quantify mass-loss rates and CSM density for the sample through the matching of peak multiband absolute magnitudes, rise times, t IIn, and optical SN spectra with a grid of radiation hydrodynamics and non-local thermodynamic equilibrium radiative-transfer simulations. For our grid of models, all with the same underlying explosion, there is a trend between the duration of the electron-scattering broadened line profiles and inferred mass-loss rate: tIIn≈3.8[Ṁ/ (0.01 M ⊙ yr−1)] days.

Evidence for a Cyclotron Absorption Line and Spectral Transition in EXO 2030+375 during the 2021 Giant Outburst

Based on Insight-HXMT observations of EXO 2030+375 during its 2021 giant outburst, we report the analysis of pulse variations and the broadband X-ray spectrum, and find the presence of a potential cyclotron resonant scattering feature (CRSF) with the fundamental line at ∼47 keV from both average spectra and phase-resolved spectroscopy. During the outburst, the source reached an X-ray luminosity of ∼1038 erg s−1 from 2 to 105 keV at a distance of 7.1 kpc. The X-ray pulsar at the spin period of 41.27 ± 0.61 s exhibits complex timing and spectral variations with both energy and luminosity during the outburst. The shapes of the pulse profiles show the single main peak above ∼20 keV, while appearing to exhibit multipeak patterns in low-energy bands, and the transition of the 10–20 keV pulse profiles from multipeak to single peak is observed at ∼0.8 × 1038 erg s−1, which suggests the evolution from the subcritical luminosity (pencil-beam dominated) to the supercritical luminosity (fan-beam dominated) regime. A dip structure before the energy of the CRSFs is found in the pulse fraction–energy relation of EXO 2030+375 near the peak luminosity. A detailed analysis of spectral parameters showed that the power-law photon index exhibits three distinct trends as luminosity increases, and these spectral changes also signify a spectral transition from subcritical to supercritical regimes. The critical luminosity infers a magnetic field of ∼(4.8−6.0) × 1012 G, which supports the presence of the cyclotron line at ∼47 keV. A Comptonization model applied for the broad X-ray spectra during the outburst also suggests the surface magnetic field ranging from ∼(5−9) × 1012 G.

ALMA-IMF

Context. A crucial aspect in addressing the challenge of measuring the core mass function (CMF), that is pivotal for comprehending the origin of the initial mass function (IMF), lies in constraining the temperatures of the cores. Aims. We aim to measure the luminosity, mass, column density and dust temperature of star-forming regions imaged by the ALMA-IMF large program. These fields were chosen to encompass early evolutionary stages of massive protoclusters. High angular resolution mapping is required to capture the properties of protostellar and pre-stellar cores within these regions, and to effectively separate them from larger features, such as dusty filaments. Methods. We employed the point process mapping (PPMAP) technique, enabling us to perform spectral energy distribution fitting of far-infrared and submillimeter observations across the 15 ALMA-IMF fields, at an unmatched 2.5″ angular resolution. By combining the modified blackbody model with near-infrared data, we derived bolometric luminosity maps. We estimated the errors impacting values of each pixel in the temperature, column density, and luminosity maps. Subsequently, we employed the extraction algorithm getsf on the luminosity maps in order to detect luminosity peaks and measure their associated masses. Results. We obtained high-resolution constraints on the luminosity, dust temperature, and mass of protoclusters, that are in agreement with previously reported measurements made at a coarser angular resolution. We find that the luminosity-to-mass ratio correlates with the evolutionary stage of the studied regions, albeit with intra-region variability. We compiled a PPMAP source catalog of 313 luminosity peaks using getsf on the derived bolometric luminosity maps. The PPMAP source catalog provides constraints on the mass and luminosity of protostars and cores, although one source may encompass several objects. Finally, we compare the estimated luminosity-to-mass ratio of PPMAP sources with evolutionary tracks and discuss the limitations imposed by the 2.5″ beam.