41 research outputs found
Processing Images from the Zwicky Transient Facility
The Zwicky Transient Facility is a new robotic-observing program, in which a
newly engineered 600-MP digital camera with a pioneeringly large field of view,
47~square degrees, will be installed into the 48-inch Samuel Oschin Telescope
at the Palomar Observatory. The camera will generate ~petabyte of raw
image data over three years of operations. In parallel related work, new
hardware and software systems are being developed to process these data in real
time and build a long-term archive for the processed products. The first public
release of archived products is planned for early 2019, which will include
processed images and astronomical-source catalogs of the northern sky in the
and bands. Source catalogs based on two different methods will be
generated for the archive: aperture photometry and point-spread-function
fitting.Comment: 6 pages, 4 figures, submitted to RTSRE Proceedings (www.rtsre.org
Providing comprehensive and consistent access to astronomical observatory archive data: the NASA archive model
Since the turn of the millennium a constant concern of astronomical archives have begun providing data to the public through standardized protocols unifying data from disparate physical sources and wavebands across the electromagnetic spectrum into an astronomical virtual observatory (VO). In October 2014, NASA began support for the NASA Astronomical Virtual Observatories (NAVO) program to coordinate the efforts of NASA astronomy archives in providing data to users through implementation of protocols agreed within the International Virtual Observatory Alliance (IVOA). A major goal of the NAVO collaboration has been to step back from a piecemeal implementation of IVOA standards and define what the appropriate presence for the US and NASA astronomy archives in the VO should be. This includes evaluating what optional capabilities in the standards need to be supported, the specific versions of standards that should be used, and returning feedback to the IVOA, to support modifications as needed.
We discuss a standard archive model developed by the NAVO for data archive presence in the virtual observatory built upon a consistent framework of standards defined by the IVOA. Our standard model provides for discovery of resources through the VO registries, access to observation and object data, downloads of image and spectral data and general access to archival datasets. It defines specific protocol versions, minimum capabilities, and all dependencies. The model will evolve as the capabilities of the virtual observatory and needs of the community change
The Early Ultraviolet Light-Curves of Type II Supernovae and the Radii of Their Progenitor Stars
We present a sample of 34 normal SNe II detected with the Zwicky Transient
Facility, with multi-band UV light-curves starting at days after
explosion, as well as X-ray detections and upper limits. We characterize the
early UV-optical colors and provide prescriptions for empirical host-extinction
corrections. We show that the days UV-optical colors and the blackbody
evolution of the sample are consistent with the predictions of spherical phase
shock-cooling (SC), independently of the presence of `flash ionization"
features. We present a framework for fitting SC models which can reproduce the
parameters of a set of multi-group simulations without a significant bias up to
20% in radius and velocity. Observations of about half of the SNe II in the
sample are well-fit by models with breakout radii cm. The other
half are typically more luminous, with observations from day 1 onward that are
better fit by a model with a large cm breakout radius. However,
these fits predict an early rise during the first day that is too slow. We
suggest these large-breakout events are explosions of stars with an inflated
envelope or a confined CSM with a steep density profile, at which breakout
occurs. Using the X-ray data, we derive constraints on the extended
( cm) CSM density independent of spectral modeling, and find most
SNe II progenitors lose a few years before
explosion. This provides independent evidence the CSM around many SNe II
progenitors is confined. We show that the overall observed breakout radius
distribution is skewed to higher radii due to a luminosity bias. We argue that
the of red supergiants (RSG) explode as SNe II with breakout
radii consistent with the observed distribution of field RSG, with a tail
extending to large radii, likely due to the presence of CSM.Comment: Submitted to ApJ. Comments are welcome at [email protected] or
[email protected]
Searching for late-time interaction signatures in Type Ia supernovae from the Zwicky Transient Facility
The nature of the progenitor systems and explosion mechanisms that give rise
to Type Ia supernovae (SNe Ia) are still debated. The interaction signature of
circumstellar material (CSM) being swept up by expanding ejecta can constrain
the type of system from which it was ejected. Most previous studies have
focused on finding CSM ejected shortly before the SN Ia explosion still
residing close to the explosion site, resulting in short delay times until the
interaction starts. We use a sample of 3627 SNe Ia from the Zwicky Transient
Facility discovered between 2018 and 2020 and search for interaction signatures
over 100 days after peak brightness. By binning the late-time light curve data
to push the detection limit as deep as possible, we identify potential
late-time rebrightening in 3 SNe Ia (SN 2018grt, SN 2019dlf, SN 2020tfc). The
late-time detections occur between 550 and 1450 d after peak brightness, have
mean absolute -band magnitudes of -16.4 to -16.8 mag and last up to a few
hundred days, significantly brighter than the late-time CSM interaction
discovered in the prototype SN 2015cp. The late-time detections all occur
within 0.8 kpc of the host nucleus and are not easily explained by nuclear
activity, another transient at a similar sky position, or data quality issues.
This suggests environment or specific progenitor characteristics playing a role
in producing potential CSM signatures in these SNe Ia. By simulating the ZTF
survey we estimate that <0.5 per cent of normal SNe Ia display late-time strong
H -dominated CSM interaction. This is equivalent to an absolute rate of
to Gpc yr assuming a constant SN
Ia rate of Mpc yr for . Weaker
interaction signatures, more similar to the strength seen in SN 2015cp, could
be more common but are difficult to constrain with our survey depth.Comment: 24 pages, 13 figures, 6 tables, A&A accepte
SN 2020jgb: A Peculiar Type Ia Supernova Triggered by a Massive Helium-Shell Detonation in a Star-Forming Galaxy
The detonation of a thin () helium shell
(He-shell) atop a white dwarf (WD) is a promising
mechanism to explain normal Type Ia supernovae (SNe Ia), while thicker
He-shells and less massive WDs may explain some recently observed peculiar SNe
Ia. We present observations of SN 2020jgb, a peculiar SN Ia discovered by the
Zwicky Transient Facility (ZTF). Near maximum light, SN 2020jgb is slightly
subluminous (ZTF -band absolute magnitude between and
mag depending on the amount of host galaxy extinction) and shows an unusually
red color ( between 0.4 and 0.2 mag) due to
strong line-blanketing blueward of 5000 . These properties
resemble those of SN 2018byg, a peculiar SN Ia consistent with a thick He-shell
double detonation (DDet) SN. Using detailed radiative transfer models, we show
that the optical spectroscopic and photometric evolution of SN 2020jgb are
broadly consistent with a (C/O core + He-shell;
up to depending on the total host extinction)
progenitor ignited by a thick () He-shell. We
detect a prominent absorption feature at 1 in the
near-infrared (NIR) spectrum of SN 2020jgb, which could originate from unburnt
helium in the outermost ejecta. While the sample size is limited, similar 1
features have been detected in all the thick He-shell DDet
candidates with NIR spectra obtained to date. SN 2020jgb is also the first
subluminous, thick He-shell DDet SN discovered in a star-forming galaxy,
indisputably showing that He-shell DDet objects occur in both star-forming and
passive galaxies, consistent with the normal SN Ia population.Comment: 23 pages, 10 figures. Updated to accepted version (ApJ
SN 2020udy: a SN Iax with strict limits on interaction consistent with a helium-star companion
Early observations of transient explosions can provide vital clues to their
progenitor origins. In this paper we present the nearby Type Iax (02cx-like)
supernova (SN), SN 2020udy that was discovered within hours (7 hr) of
estimated first light. An extensive dataset of ultra-violet, optical, and
near-infrared observations was obtained, covering out to 150 d after
explosion. SN 2020udy peaked at -17.860.43 mag in the r band and evolved
similarly to other 'luminous' SNe Iax, such as SNe 2005hk and 2012Z. Its
well-sampled early light curve allows strict limits on companion interaction to
be placed. Main-sequence companion stars with masses of 2 and 6 M are
ruled out at all viewing angles, while a helium-star companion is allowed from
a narrow range of angles (140-180 away from the companion). The spectra
and light curves of SN2020udy are in good agreement with those of the 'N5def'
deflagration model of a near Chandrasekhar-mass carbon-oxygen white dwarf.
However, as has been seen in previous studies of similar luminosity events, SN
2020udy evolves slower than the model. Broad-band linear polarisation
measurements taken at and after peak are consistent with no polarisation, in
agreement with the predictions of the companion-star configuration from the
early light curve measurements. The host galaxy environment is low metallicity
and is consistent with a young stellar population. Overall, we find the most
plausible explosion scenario to be the incomplete disruption of a CO white
dwarf near the Chandrasekhar-mass limit, with a helium-star companion.Comment: 18 pages, 14 figures, submitted to MNRA
Tidal Disruption Event Demographics with the Zwicky Transient Facility: Volumetric Rates, Luminosity Function, and Implications for the Local Black Hole Mass Function
We conduct a systematic tidal disruption event (TDE) demographics analysis
using the largest sample of optically selected TDEs. A flux-limited,
spectroscopically complete sample of 33 TDEs is constructed using the Zwicky
Transient Facility over three years (from October 2018 to September 2021). We
infer the black hole (BH) mass () with host galaxy scaling
relations, showing that the sample ranges from
to . We developed a survey efficiency corrected maximum
volume method to infer the rates. The rest-frame -band luminosity function
(LF) can be well described by a broken power-law of , with . In the BH mass regime of , the TDE mass function follows
, which favors a flat local BH mass
function (). We confirm
the significant rate suppression at the high-mass end (), which is consistent with theoretical predictions
considering direct capture of hydrogen-burning stars by the event horizon. At a
host galaxy mass of , the average optical TDE
rate is . We constrain
the optical TDE rate to be [3.7, 7.4, and 1.6 in galaxies with red, green, and blue colors.Comment: Replaced following peer-review process. 38 pages, 23 figures.
Accepted for publication in ApJ
SN 2021zny: an early flux excess combined with late-time oxygen emission suggests a double white dwarf merger event
We present a photometric and spectroscopic analysis of the ultra-luminous and
slowly evolving 03fg-like Type Ia SN 2021zny. Our observational campaign starts
from hours after explosion (making SN 2021zny one of the earliest
observed members of its class), with dense multi-wavelength coverage from a
variety of ground- and space-based telescopes, and is concluded with a nebular
spectrum months after peak brightness. SN 2021zny displayed several
characteristics of its class, such as the peak brightness ( mag),
the slow decline ( mag), the blue early-time colours,
the low ejecta velocities and the presence of significant unburned material
above the photosphere. However, a flux excess for the first days
after explosion is observed in four photometric bands, making SN 2021zny the
third 03fg-like event with this distinct behavior, while its d spectrum
shows prominent [O I] lines, a very unusual characteristic of thermonuclear
SNe. The early flux excess can be explained as the outcome of the interaction
of the ejecta with of H/He-poor circumstellar
material at a distance of cm, while the low ionization state of
the late-time spectrum reveals low abundances of stable iron-peak elements. All
our observations are in accordance with a progenitor system of two
carbon/oxygen white dwarfs that undergo a merger event, with the disrupted
white dwarf ejecting carbon-rich circumstellar material prior to the primary
white dwarf detonation.Comment: 19 pages, 16 figures, accepted for publication in MNRA
Probing pre-supernova mass loss in double-peaked Type Ibc supernovae from the Zwicky Transient Facility
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.Comment: Submitted to ApJ. Comments are welcome. arXiv admin note: text
overlap with arXiv:2210.0572
The Zwicky Transient Facility: Science Objectives
The Zwicky Transient Facility (ZTF), a public–private enterprise, is a new time-domain survey employing a dedicated camera on the Palomar 48-inch Schmidt telescope with a 47 deg2 field of view and an 8 second readout time. It is well positioned in the development of time-domain astronomy, offering operations at 10% of the scale and style of the Large Synoptic Survey Telescope (LSST) with a single 1-m class survey telescope. The public surveys will cover the observable northern sky every three nights in g and r filters and the visible Galactic plane every night in g and r. Alerts generated by these surveys are sent in real time to brokers. A consortium of universities that provided funding (“partnership”) are undertaking several boutique surveys. The combination of these surveys producing one million alerts per night allows for exploration of transient and variable astrophysical phenomena brighter than r∼20.5 on timescales of minutes to years. We describe the primary science objectives driving ZTF, including the physics of supernovae and relativistic explosions, multi-messenger astrophysics, supernova cosmology, active galactic nuclei, and tidal disruption events, stellar variability, and solar system objects. © 2019. The Astronomical Society of the Pacific