Abstract
SX Phoenicis (SXP) variables are short-period pulsating stars that exhibit a period–luminosity (PL) relation. We derived the
gri
-band PL and extinction-free period–Wesenheit (PW) relations, ...as well as the period-color and reddening-free period-Q-index relations for 47 SXP stars located in 21 globular clusters, using the optical light curves taken from Zwicky Transient Facility. These empirical relations were derived for the first time in the
gri
filters except for the
g
-band PL relation. We used our
gi
-band PL and PW relations to derive a distance modulus to Crater II dwarf spheroidal which hosts one SXP variable. Assuming that the fundamental and first-overtone pulsation mode for the SXP variable in Crater II, we found distance moduli of 20.03 ± 0.23 mag and 20.37 ± 0.24 mag, respectively, using the PW relation, where the latter is in excellent agreement with independent RR Lyrae based distance to Crater II dwarf galaxy.
Abstract
Based on 14 Miras located in seven globular clusters, we derived the first
gr
-band period–luminosity (PL) at maximum light for the large-amplitude Mira variables using the multiyear ...light-curve data collected from the Zwicky Transient Facility (ZTF). Since Miras are red variables, we applied a color-term correction to subsets of ZTF light curves, and found that such corrections do not have a large impact on period determinations. We applied our derived PL relations to the known extragalactic Miras in five local galaxies (Sextans, Leo I, Leo II, NGC 6822 and IC 1613), and determined their Mira-based distances. We demonstrated that our PL relations can be applied to short-period (≲300 days) Miras, including those in the two most distant galaxies (NGC 6822 and IC 1613) in our sample even when only a portion of the light curves around maximum light have detections. We have also shown that the long-period extragalactic Miras do not follow the PL relations extrapolated to longer periods. Hence, our derived PL relations are only applicable to the short-period Miras, which will be discovered in abundance in local galaxies within the era of Vera C. Rubin Observatory’s Legacy Survey of Space and Time.
Abstract
We present observations of SN 2022joj, a peculiar Type Ia supernova discovered by the Zwicky Transient Facility. SN 2022joj exhibits an unusually red
g
ZTF
−
r
ZTF
color at early times and a ...rapid blueward evolution afterward. Around maximum brightness, SN 2022joj shows a high luminosity (
M
g
ZTF
,
max
≃
−
19.7
mag), a blue broadband color (
g
ZTF
−
r
ZTF
≃ −0.2 mag), and shallow Si
ii
absorption lines, consistent with those of overluminous, SN 1991T-like events. The maximum-light spectrum also shows prominent absorption around 4200 Å, which resembles the Ti
ii
features in subluminous, SN 1991bg-like events. Despite the blue optical-band colors, SN 2022joj exhibits extremely red ultraviolet minus optical colors at maximum luminosity (
u
−
v
≃ 0.6 mag and
uvw
1 −
v
≃ 2.5 mag), suggesting a suppression of flux at ∼2500–4000 Å. Strong C
ii
lines are also detected at peak. We show that these unusual spectroscopic properties are broadly consistent with the helium-shell double detonation of a sub-Chandrasekhar mass (
M
≃ 1
M
⊙
) carbon/oxygen white dwarf from a relatively massive helium shell (
M
s
≃ 0.04–0.1
M
⊙
), if observed along a line of sight roughly opposite to where the shell initially detonates. None of the existing models could quantitatively explain all the peculiarities observed in SN 2022joj. The low flux ratio of Ni
ii
λ
7378 to Fe
ii
λ
7155 emission in the late-time nebular spectra indicates a low yield of stable Ni isotopes, favoring a sub-Chandrasekhar mass progenitor. The significant blueshift measured in the Fe
ii
λ
7155 line is also consistent with an asymmetric chemical distribution in the ejecta, as is predicted in double-detonation models.
Abstract The classification of variable objects provides insight into a wide variety of astrophysics ranging from stellar interiors to galactic nuclei. The Zwicky Transient Facility (ZTF) provides ...time-series observations that record the variability of more than a billion sources. The scale of these data necessitates automated approaches to make a thorough analysis. Building on previous work, this paper reports the results of the ZTF Source Classification Project ( SCoPe ), which trains neural network and XGBoost (XGB) machine-learning (ML) algorithms to perform dichotomous classification of variable ZTF sources using a manually constructed training set containing 170,632 light curves. We find that several classifiers achieve high precision and recall scores, suggesting the reliability of their predictions for 209,991,147 light curves across 77 ZTF fields. We also identify the most important features for XGB classification and compare the performance of the two ML algorithms, finding a pattern of higher precision among XGB classifiers. The resulting classification catalog is available to the public, and the software developed for SCoPe is open source and adaptable to future time-domain surveys.
Abstract We present the discovery and analysis of SN 2022oqm, a Type Ic supernova (SN) detected <1 day after the explosion. The SN rises to a blue and short-lived (2 days) initial peak. Early-time ...spectral observations of SN 2022oqm show a hot (40,000 K) continuum with high ionization C and O absorption features at velocities of 4000 km s −1 , while its photospheric radius expands at 20,000 km s −1 , indicating a pre-existing distribution of expanding C/O material. After ∼2.5 days, both the spectrum and light curves evolve into those of a typical SN Ic, with line velocities of ∼10,000 km s −1 , in agreement with the evolution of the photospheric radius. The optical light curves reach a second peak at t ≈ 15 days. By t = 60 days, the spectrum of SN 2022oqm becomes nearly nebular, displaying strong Ca ii and Ca ii emission with no detectable O i , marking this event as Ca-rich. The early behavior can be explained by 10 −3 M ⊙ of optically thin circumstellar material (CSM) surrounding either (1) a massive compact progenitor such as a Wolf–Rayet star, (2) a massive stripped progenitor with an extended envelope, or (3) a binary system with a white dwarf. We propose that the early-time light curve is powered by both the interaction of the ejecta with the optically thin CSM and shock cooling (in the massive star scenario). The observations can be explained by CSM that is optically thick to X-ray photons, is optically thick in the lines as seen in the spectra, and is optically thin to visible-light continuum photons that come either from downscattered X-rays or from the shock-heated ejecta. Calculations show that this scenario is self-consistent.
Abstract Multipeaked supernovae with precursors, dramatic light-curve rebrightenings, and spectral transformation are rare, but are being discovered in increasing numbers by modern night-sky ...transient surveys like the Zwicky Transient Facility. Here, we present the observations and analysis of SN 2023aew, which showed a dramatic increase in brightness following an initial luminous (−17.4 mag) and long (∼100 days) unusual first peak (possibly precursor). SN 2023aew was classified as a Type IIb supernova during the first peak but changed its type to resemble a stripped-envelope supernova (SESN) after the marked rebrightening. We present comparisons of SN 2023aew’s spectral evolution with SESN subtypes and argue that it is similar to SNe Ibc during its main peak. P-Cygni Balmer lines are present during the first peak, but vanish during the second peak’s photospheric phase, before H α resurfaces again during the nebular phase. The nebular lines (O i , Ca ii , Mg i , H α ) exhibit a double-peaked structure that hints toward a clumpy or nonspherical ejecta. We analyze the second peak in the light curve of SN 2023aew and find it to be broader than that of normal SESNe as well as requiring a very high 56 Ni mass to power the peak luminosity. We discuss the possible origins of SN 2023aew including an eruption scenario where a part of the envelope is ejected during the first peak and also powers the second peak of the light curve through interaction of the SN with the circumstellar medium.
Abstract We present SN 2023zaw—a subluminous ( M r = −16.7 mag) and rapidly evolving supernova ( t 1/2, r = 4.9 days), with the lowest nickel mass (≈0.002 M ⊙ ) measured among all stripped-envelope ...supernovae discovered to date. The photospheric spectra are dominated by broad He i and Ca near-infrared emission lines with velocities of ∼10,000−12,000 km s −1 . The late-time spectra show prominent narrow He i emission lines at ∼1000 km s −1 , indicative of interaction with He-rich circumstellar material. SN 2023zaw is located in the spiral arm of a star-forming galaxy. We perform radiation-hydrodynamical and analytical modeling of the lightcurve by fitting with a combination of shock-cooling emission and nickel decay. The progenitor has a best-fit envelope mass of ≈0.2 M ☉ and an envelope radius of ≈50 R ⊙ . The extremely low nickel mass and low ejecta mass (≈0.5 M ⊙ ) suggest an ultrastripped SN, which originates from a mass-losing low-mass He-star (zero-age main-sequence mass < 10 M ⊙ ) in a close binary system. This is a channel to form double neutron star systems, whose merger is detectable with LIGO. SN 2023zaw underscores the existence of a previously undiscovered population of extremely low nickel mass (<0.005 M ☉ ) stripped-envelope supernovae, which can be explored with deep and high-cadence transient surveys.
Abstract
Jupiter-family comet (JFC) P/2021 HS (PANSTARRS) only exhibits a coma within a few weeks of its perihelion passage at 0.8 au, which is atypical for a comet. Here we present an investigation ...into the underlying cause using serendipitous survey detections and targeted observations. We find that the detection of the activity is caused by an extremely faint coma being enhanced by the forward scattering effect owing to the comet reaching a phase angle of ∼140°. The coma morphology is consistent with sustained, sublimation-driven activity produced by a small active area, ∼700 m
2
, one of the smallest values ever measured on a comet. The phase function of the nucleus shows a phase coefficient of 0.035 ± 0.002 mag deg
−1
, implying an absolute magnitude of
H
= 18.31 ± 0.04 and a phase slope of
G
= − 0.13, with color consistent with typical JFC nuclei. Thermal observations suggest a nucleus diameter of 0.6–1.1 km, implying an optical albedo of 0.04–0.23, which is higher than typical cometary nuclei. An unsuccessful search for dust trail and meteor activity confirms minimal dust deposit along the orbit, totaling ≲10
8
kg. As P/2021 HS is dynamically unstable, similar to typical JFCs, we speculate that it has an origin in the trans-Neptunian region and that its extreme depletion of volatiles is caused by a large number of previous passages to the inner solar system. The dramatic discovery of the cometary nature of P/2021 HS highlights the challenges of detecting comets with extremely low activity levels. Observations at high phase angle, where forward scattering is pronounced, will help identify such comets.
Abstract
SkyPortal
is an open-source software package designed to discover interesting transients efficiently, manage follow-up, perform characterization, and visualize the results. By enabling fast ...access to archival and catalog data, crossmatching heterogeneous data streams, and the triggering and monitoring of on-demand observations for further characterization, a
SkyPortal
-based platform has been operating at scale for >2 yr for the Zwicky Transient Facility Phase II community, with hundreds of users, containing tens of millions of time-domain sources, interacting with dozens of telescopes, and enabling community reporting. While
SkyPortal
emphasizes rich user experiences across common front-end workflows, recognizing that scientific inquiry is increasingly performed programmatically,
SkyPortal
also surfaces an extensive and well-documented application programming interface system. From back-end and front-end software to data science analysis tools and visualization frameworks, the
SkyPortal
design emphasizes the reuse and leveraging of best-in-class approaches, with a strong extensibility ethos. For instance,
SkyPortal
now leverages ChatGPT large language models to generate and surface source-level human-readable summaries automatically. With the imminent restart of the next generation of gravitational-wave detectors,
SkyPortal
now also includes dedicated multimessenger features addressing the requirements of rapid multimessenger follow-up: multitelescope management, team/group organizing interfaces, and crossmatching of multimessenger data streams with time-domain optical surveys, with interfaces sufficiently intuitive for newcomers to the field. This paper focuses on the detailed implementations, capabilities, and early science results that establish
SkyPortal
as a community software package ready to take on the data science challenges and opportunities presented by this next chapter in the multimessenger era.
ABSTRACT
Rapid identification of the optical counterparts of neutron star (NS) merger events discovered by gravitational wave detectors may require observing a large error region and sifting through ...a large number of transients to identify the object of interest. Given the expense of spectroscopic observations, a question arises: How can we utilize photometric observations for candidate prioritization, and what kinds of photometric observations are needed to achieve this goal? NS merger kilonova exhibits low ejecta mass (∼5 × 10−2 M⊙) and a rapidly evolving photospheric radius (with a velocity ∼0.2c). As a consequence, these sources display rapid optical-flux evolution. Indeed, selection based on fast flux variations is commonly used for young supernovae and NS mergers. In this study, we leverage the best currently available flux-limited transient survey – the Zwicky Transient Facility Bright Transient Survey – to extend and quantify this approach. We focus on selecting transients detected in a 3-day cadence survey and observed at a one-day cadence. We explore their distribution in the phase space defined by g–r, $\dot{g}$, and $\dot{r}$. Our analysis demonstrates that for a significant portion of the time during the first week, the kilonova AT 2017gfo stands out in this phase space. It is important to note that this investigation is subject to various biases and challenges; nevertheless, it suggests that certain photometric observations can be leveraged to identify transients with the highest probability of being fast-evolving events. We also find that a large fraction (≈75 per cent) of the transient candidates with $\vert\dot{g}\vert>0.7$ mag d−1, are cataclysmic variables or active galactic nuclei with radio counterparts.
