分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Luminous red novae (LRNe) are transients characterized by low luminosities and expansion velocities, and are associated with mergers or common envelope ejections in stellar binaries. Intermediate-luminosity red transients (ILRTs) are an observationally similar class with unknown origins, but generally believed to either be electron capture supernovae (ECSN) in super-AGB stars, or outbursts in dusty luminous blue variables (LBVs). In this paper, we present a systematic sample of 8 LRNe and 8 ILRTs detected as part of the Census of the Local Universe (CLU) experiment on the Zwicky Transient Facility (ZTF). The CLU experiment spectroscopically classifies ZTF transients associated with nearby ($<150$ Mpc) galaxies, achieving 80% completeness for m$_{r}<20$\,mag. Using the ZTF-CLU sample, we derive the first systematic LRNe volumetric-rate of 7.8$^{+6.5}_{-3.7}\times10^{-5}$ Mpc$^{-3}$ yr$^{-1}$ in the luminosity range $-16\leq$M$_{\rm{r}}$$\leq -11$ mag. We find that in this luminosity range, the LRN rate scales as dN/dL $\propto L^{-2.5\pm0.3}$ - significantly steeper than the previously derived scaling of $L^{-1.4\pm0.3}$ for lower luminosity LRNe (M$_{V}\geq-10$). The steeper power law for LRNe at high luminosities is consistent with the massive merger rates predicted by binary population synthesis models. We find that the rates of the brightest LRNe (M$_{r}\leq-13$ mag) are consistent with a significant fraction of them being progenitors of double compact objects (DCOs) that merge within a Hubble time. For ILRTs, we derive a volumetric rate of $2.6^{+1.8}_{-1.4}\times10^{-6}$ Mpc$^{-3}$yr$^{-1}$ for M$_{\rm{r}}\leq-13.5$, that scales as dN/dL $\propto L^{-2.5\pm0.5}$. This rate is $\approx1-5\%$ of the local core-collapse supernova rate, and is consistent with theoretical ECSN rate estimates.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: A rare class of supernovae (SNe) is characterized by strong interaction between the ejecta and several solar masses of circumstellar matter (CSM) as evidenced by strong Balmer-line emission. Within the first few weeks after the explosion, they may display spectral features similar to overluminous Type Ia SNe, while at later phase their observation properties exhibit remarkable similarities with some extreme case of Type IIn SNe that show strong Balmer lines years after the explosion. We present polarimetric observations of SN2018evt obtained by the ESO Very Large Telescope from 172 to 219 days after the estimated time of peak luminosity to study the geometry of the CSM. The nonzero continuum polarization decreases over time, suggesting that the mass loss of the progenitor star is aspherical. The prominent H$\alpha$ emission can be decomposed into a broad, time-evolving component and an intermediate-width, static component. The former shows polarized signals, and it is likely to arise from a cold dense shell (CDS) within the region between the forward and reverse shocks. The latter is significantly unpolarized, and it is likely to arise from shocked, fragmented gas clouds in the H-rich CSM. We infer that SN2018evt exploded inside a massive and aspherical circumstellar cloud. The symmetry axes of the CSM and the SN appear to be similar. SN\,2018evt shows observational properties common to events that display strong interaction between the ejecta and CSM, implying that they share similar circumstellar configurations. Our preliminary estimate also suggests that the circumstellar environment of SN2018evt has been significantly enriched at a rate of $\sim0.1$ M$_\odot$ yr$^{-1}$ over a period of $>100$ yr.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: UVEX is a proposed medium class Explorer mission designed to provide crucial missing capabilities that will address objectives central to a broad range of modern astrophysics. The UVEX design has two co-aligned wide-field imagers operating in the FUV and NUV and a powerful broadband medium resolution spectrometer. In its two-year baseline mission, UVEX will perform a multi-cadence synoptic all-sky survey 50/100 times deeper than GALEX in the NUV/FUV, cadenced surveys of the Large and Small Magellanic Clouds, rapid target of opportunity followup, as well as spectroscopic followup of samples of stars and galaxies. The science program is built around three pillars. First, UVEX will explore the low-mass, low-metallicity galaxy frontier through imaging and spectroscopic surveys that will probe key aspects of the evolution of galaxies by understanding how star formation and stellar evolution at low metallicities affect the growth and evolution of low-metallicity, low-mass galaxies in the local universe. Such galaxies contain half the mass in the local universe, and are analogs for the first galaxies, but observed at distances that make them accessible to detailed study. Second, UVEX will explore the dynamic universe through time-domain surveys and prompt spectroscopic followup capability will probe the environments, energetics, and emission processes in the early aftermaths of gravitational wave-discovered compact object mergers, discover hot, fast UV transients, and diagnose the early stages of stellar explosions. Finally, UVEX will become a key community resource by leaving a large all-sky legacy data set, enabling a wide range of scientific studies and filling a gap in the new generation of wide-field, sensitive optical and infrared surveys provided by the Rubin, Euclid, and Roman observatories. This paper discusses the scientific potential of UVEX, and the broad scientific program.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The fate of stars in the zero-age main-sequence (ZAMS) range $\approx 8-12$ Msun is unclear. They could evolve to form white dwarfs or explode as electron-capture supernovae (SNe) or iron core-collapse SNe (CCSNe). Even though the initial mass function indicates that this mass range should account for over 40% of all CCSNe progenitors, few have been observationally confirmed, likely owing to the faintness and rapid evolution of these transients. In this paper, we present a sample of nine Ca-rich/O-poor Type IIb SNe detected by the Zwicky Transient Facility with progenitors likely in this mass range. We perform a holistic analysis of the spectroscopic and photometric properties of the sample. These sources have a flux ratio of [Ca II] $\lambda \lambda$7291, 7324 to [O I] $\lambda \lambda$6300, 6364 of $\gtrsim$ 2 in their nebular spectra. Comparing the measured [O I] luminosity ($\lesssim 10^{39} \mathrm{erg\ s^{-1}}$) and derived oxygen mass ($\lesssim 0.1$ Msun) with theoretical models, we infer that the progenitor ZAMS mass for these explosions is less than 12 Msun. These correspond to He-stars with core masses less than around 3 Msun. We find that the ejecta properties (Mej $\lesssim 1$ Msun) are also consistent with those expected for such low mass He-stars. The low ejecta mass of these sources indicates a class of strongly-stripped SNe that is a transition between the regular stripped-envelope SNe and ultra-stripped SNe. The progenitor could be stripped by a main sequence companion and result in the formation of a neutron star $-$ main sequence binary. Such binaries have been suggested to be progenitors of neutron star $-$ white dwarf systems that could merge within a Hubble time, and be detectable with LISA.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The dividing line between gamma-ray bursts (GRBs) and ordinary stripped-envelope core-collapse supernovae (SNe) is yet to be fully understood. Observationally mapping the variety of ejecta outcomes (ultra-relativistic, mildly-relativistic or non-relativistic) in SNe of Type Ic with broad lines (Ic-BL) can provide a key test to stellar explosion models. However, this requires large samples of the rare Ic-BL events with follow-up observations in the radio, where fast ejecta can be probed largely free of geometry and viewing angle effects. Here, we present the results of a radio (and X-ray) follow-up campaign of 16 SNe Ic-BL detected by the Zwicky Transient Facility (ZTF). Our radio campaign resulted in 4 counterpart detections and 12 deep upper limits. None of the events in our sample is as relativistic as SN 1998bw and we constrain the fraction of SN 1998bw-like explosions to $< 19\%$ (3$\sigma$ Gaussian equivalent), a factor of $\approx 2$ smaller than previously established. We exclude relativistic ejecta with radio luminosity densities in between $\approx 5\times10^{27}$ erg s$^{-1}$ Hz$^{-1}$ and $\approx 10^{29}$ erg s$^{-1}$ Hz$^{-1}$ at $t\gtrsim 20$ d since explosion for $\approx 60\%$ of the events in our sample. This shows that SNe Ic-BL similar to the GRB-associated SN 1998bw, SN 2003lw, SN 2010dh, or to the relativistic SN 2009bb and iPTF17cw, are rare. Our results also exclude an association of the SNe Ic-BL in our sample with largely off-axis GRBs with energies $E\gtrsim 10^{50}$ erg. The parameter space of SN2006aj-like events (faint and fast-peaking radio emission) is, on the other hand, left largely unconstrained and systematically exploring it represents a promising line of future research.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: One of the open questions following the discovery of GW170817 is whether neutron star mergers are the only astrophysical sites capable of producing r-process elements. Simulations have shown that 0.01-0.1M$_\odot$ of r-process material could be generated in the outflows originating from the accretion disk surrounding the rapidly rotating black hole that forms as a remnant to both neutron star mergers and collapsing massive stars associated with long-duration gamma-ray bursts (collapsars). The hallmark signature of r-process nucleosynthesis in the binary neutron star merger GW170817 was its long-lasting near-infrared emission, thus motivating a systematic photometric study of the light curves of broadlined stripped-envelope (Ic-BL) supernovae (SNe) associated with collapsars. We present the first systematic study of 25 SNe Ic-BL -- discovered with the Zwicky Transient Facility and from the literature -- in the optical/near-infrared bands to determine what quantity of r-process material, if any, is synthesized in these explosions. Using semi-analytic models designed to account for r-process production in SNe Ic-BL, we perform light curve fitting to derive constraints on the r-process mass for these SNe. We also perform independent light curve fits to models without r-process. We find that the r-process-free models are a better fit to the light curves of the objects in our sample. Thus we conclude that there is no compelling evidence of r-process enrichment in any of our objects. Further high-cadence infrared photometric studies and nebular spectroscopic analysis would be sensitive to smaller quantities of r-process ejecta mass or indicate whether all collapsars are completely devoid of r-process nucleosynthesis.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: We demonstrate a fully-integrated multipurpose microwave frequency identification system on silicon-on-insulator platform. Thanks to its multipurpose features, the chip is able to identify different types of microwave signals, including single-frequency, multiple-frequency, chirped and frequency-hopping microwave signals, as well as discriminate instantaneous frequency variation among the frequency-modulated signals. This demonstration exhibits fully integrated solution and fully functional microwave frequency identification, which can meet the requirements in reduction of size, weight and power for future advanced microwave photonic processor.