Abstract
Luminous red novae (LRNe) are transients characterized by low luminosities and expansion velocities, and they 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 they are generally believed to be either electron-capture supernovae in super-asymptotic giant branch stars or outbursts in dusty luminous blue variables (LBVs). In this paper, we present a systematic sample of eight LRNe and eight 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
−
3.7
+
6.5
×
10
−
5
Mpc
−3
yr
−1
in the luminosity range −16 ≤
M
r
≤ −11 mag. We find that, in this luminosity range, the LRN rate scales as
dN
/
dL
∝
L
−
2.5
±
0.3
—significantly steeper than the previously derived scaling of
L
−1.4±0.3
for lower-luminosity LRNe (
M
V
≥ −10 mag). 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
≤ −13 mag) are consistent with a significant fraction of them being progenitors of double compact objects that merge within a Hubble time. For ILRTs, we derive a volumetric rate of
2.6
−
1.4
+
1.8
×
10
−
6
Mpc
−3
yr
−1
for
M
r
≤ −13.5 mag, which scales as
dN
/
dL
∝
L
−
2.5
±
0.5
. This rate is ∼1%–5% of the local core-collapse supernova rate and is consistent with theoretical ECSN rate estimates.
We present a public catalog of transients from the Zwicky Transient Facility (ZTF) Bright Transient Survey, a magnitude-limited (m < 19 mag in either the g or r filter) survey for extragalactic ...transients in the ZTF public stream. We introduce cuts on survey coverage, sky visibility around peak light, and other properties unconnected to the nature of the transient, and show that the resulting statistical sample is spectroscopically 97% complete at <18 mag, 93% complete at <18.5 mag, and 75% complete at <19 mag. We summarize the fundamental properties of this population, identifying distinct duration-luminosity correlations in a variety of supernova (SN) classes and associating the majority of fast optical transients with well-established spectroscopic SN types (primarily SN Ibn and II/IIb). We measure the Type Ia SN and core-collapse (CC) SN rates and luminosity functions, which show good consistency with recent work. About 7% of CC SNe explode in very low-luminosity galaxies (Mi > −16 mag), 10% in red-sequence galaxies, and 1% in massive ellipticals. We find no significant difference in the luminosity or color distributions between the host galaxies of SNe Type II and SNe Type Ib/c, suggesting that line-driven wind stripping does not play a major role in the loss of the hydrogen envelope from their progenitors. Future large-scale classification efforts with ZTF and other wide-area surveys will provide high-quality measurements of the rates, properties, and environments of all known types of optical transients and limits on the existence of theoretically predicted but as yet unobserved explosions.
We present preliminary results from a study exploring the origin of Milky Way substructures, and show initial evidence of a common “kicked-out” formation mechanism for two low-latitude substructures. ...In this scenario, stars in these substructures formed in the disk and were subsequently “kicked-out” by an external perturbation, such as the merger of an accreted satellite, which created an oscillation in the Galactic disk. To test this origin scenario, we found the fraction of different stellar populations – M giants and RR Lyrae stars – in the Monoceros Ring (also known as GASS) and A13, supplementing a study of stellar populations in the Triangulum-Andromeda cloud. This work provides: (1) the first analysis of the GASS and A13 features based upon their stellar populations; and (2) preliminary evidence of disk stars in the Milky Way that have been relocated to the disk-halo interface due to vertical oscillations of the Milky Way’s disk.
We report the serendipitous discovery of Gaia17bpp/2MASS J19372316+1759029, a star with a deep single large-amplitude dimming event of \(\sim\)4.5 magnitudes that lasted over 6.5 years. Using the ...optical to IR spectral energy distribution (SED), we constrain the primary star to be a cool giant M0-III star with effective temperature \(T_{\text{eff}}\)=3,850 K and radius R=58 R\(_{\odot}\). Based on the SED fitting, we obtained a bimodal posterior distribution of primary stellar masses at 1.5 M\({\odot}\) and 3.7 M\({\odot}\). Within the last 66 years of photometric coverage, no other significant dimming events of this depth and duration were identified in the optical light curves. Using a Gaussian Process, we fit a high-order Gaussian model to the optical and IR light curves and conclude the dimming event exhibits moderate asymmetries from optical to IR. At the minimum of the dimming event, the (W\(_{1}\)-W\(_{2}\)) color was bluer by \(\sim\)0.2 mag relative to the primary star outside the dimming event. The ingress and egress colors show a shallow reddening profile. We suggest that the main culprit of the dimming event is likely due to the presence of a large, optically thick disk transiting the primary giant star. By fitting a monochromatic transit model of an oblate disk transiting a star, we found good agreement with a slow-moving, 0.005 km sec\(^{-1}\), disk with a \(\sim\)1.4 AU radius. We propose that Gaia17bpp belongs to a rare binary star population similar to the Epsilon Aurigae system, which consists of a secondary star enshrouded by an optically thick debris disk.
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.
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 -- including 18 observed with the Zwicky Transient Facility and 7 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 find 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.
SN 1987A was an unusual hydrogen-rich core-collapse supernova originating from a blue supergiant star. Similar blue supergiant explosions remain a small family of events, and are broadly ...characterized by their long rises to peak. The Zwicky Transient Facility (ZTF) Census of the Local Universe (CLU) experiment aims to construct a spectroscopically complete sample of transients occurring in galaxies from the CLU galaxy catalog. We identify 13 long-rising (>40 days) Type II supernovae from the volume-limited CLU experiment during a 3.5 year period from June 2018 to December 2021, approximately doubling the previously known number of these events. We present photometric and spectroscopic data of these 13 events, finding peak r-band absolute magnitudes ranging from -15.6 to -17.5 mag and the tentative detection of Ba II lines in 9 events. Using our CLU sample of events, we derive a long-rising Type II supernova rate of \(1.37^{+0.26}_{-0.30}\times10^{-6}\) Mpc\(^{-3}\) yr\(^{-1}\), \(\approx\)1.4% of the total core-collapse supernova rate. This is the first volumetric rate of these events estimated from a large, systematic, volume-limited experiment.
The new generation of wide-field time-domain surveys has made it feasible to study the clustering of supernova (SN) host galaxies in the large-scale structure (LSS) for the first time. We investigate ...the LSS environment of SN populations, using 106 dark matter density realisations with a resolution of \(\sim\) 3.8 Mpc, constrained by the 2M++ galaxy survey. We limit our analysis to redshift \(z<0.036\), using samples of 498 thermonuclear and 782 core-collapse SNe from the Zwicky Transient Facility's Bright Transient Survey and Census of the Local Universe catalogues. We detect clustering of SNe with high significance; the observed clustering of the two SNe populations is consistent with each other. Further, the clustering of SN hosts is consistent with that of the Sloan Digital Sky Survey (SDSS) Baryon Oscillation Spectroscopic Survey (BOSS) DR12 spectroscopic galaxy sample in the same redshift range. Using a tidal shear classifier, we classify the LSS into voids, sheets, filaments and knots. We find that both SNe and SDSS galaxies are predominantly found in sheets and filaments. SNe are significantly under-represented in voids and over-represented in knots compared to the volume fraction in these structures. This work opens the potential for using forthcoming wide-field deep SN surveys as a complementary LSS probe.
We present optical, radio and X-ray observations of a rapidly-evolving transient AT2019wxt (PS19hgw), discovered during the search for an electromagnetic (EM) counterpart to the gravitational-wave ...(GW) trigger S191213g (LIGO Scientific Collaboration & Virgo Collaboration 2019a). Although S191213g was not confirmed as a significant GW event in the off-line analysis of LIGO-Virgo data, AT2019wxt remained an interesting transient due its peculiar nature. The optical/NIR light curve of AT2019wxt displayed a double-peaked structure evolving rapidly in a manner analogous to currently know ultra-stripped supernovae (USSNe) candidates. This double-peaked structure suggests presence of an extended envelope around the progenitor, best modelled with two-components: i) early-time shock-cooling emission and ii) late-time radioactive \(^{56}\)Ni decay. We constrain the ejecta mass of AT2019wxt at \(M_{ej} \approx{0.20 M_{\odot}}\) which indicates a significantly stripped progenitor that was possibly in a binary system. We also followed-up AT2019wxt with long-term Chandra and Jansky Very Large Array observations spanning \(\sim\)260 days. We detected no definitive counterparts at the location of AT2019wxt in these long-term X-ray and radio observational campaigns. We establish the X-ray upper limit at \(9.93\times10^{-17}\) erg cm\(^{-2}\) s\(^{-1}\) and detect an excess radio emission from the region of AT2019wxt. However, there is little evidence for SN1993J- or GW170817-like variability of the radio flux over the course of our observations. A substantial host galaxy contribution to the measured radio flux is likely. The discovery and early-time peak capture of AT2019wxt in optical/NIR observation during EMGW follow-up observations highlights the need of dedicated early, multi-band photometric observations to identify USSNe.
Eruptive mass loss of massive stars prior to supernova (SN) explosion is key to understanding their evolution and end fate. An observational signature of pre-SN mass loss is the detection of an ...early, short-lived peak prior to the radioactive-powered peak in the lightcurve of the SN. This is usually attributed to the SN shock passing through an extended envelope or circumstellar medium (CSM). Such an early peak is common for double-peaked Type IIb SNe with an extended Hydrogen envelope but is uncommon for normal Type Ibc SNe with very compact progenitors. In this paper, we systematically study a sample of 14 double-peaked Type Ibc SNe out of 475 Type Ibc SNe detected by the Zwicky Transient Facility. The rate of these events is ~ 3-9 % of Type Ibc SNe. A strong correlation is seen between the peak brightness of the first and the second peak. We perform a holistic analysis of this sample's photometric and spectroscopic properties. We find that six SNe have ejecta mass less than 1.5 Msun. Based on the nebular spectra and lightcurve properties, we estimate that the progenitor masses for these are less than ~ 12 Msun. The rest have an ejecta mass > 2.4 Msun and a higher progenitor mass. This sample suggests that the SNe with low progenitor masses undergo late-time binary mass transfer. Meanwhile, the SNe with higher progenitor masses are consistent with wave-driven mass loss or pulsation-pair instability-driven mass loss simulations.
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