We describe and report first results from PALM-3000, the second-generation astronomical adaptive optics (AO) facility for the 5.1 m Hale telescope at Palomar Observatory. PALM-3000 has been ...engineered for high-contrast imaging and emission spectroscopy of brown dwarfs and large planetary mass bodies at near-infrared wavelengths around bright stars, but also supports general natural guide star use to V approx = 17. Using its unique 66 x 66 actuator deformable mirror, PALM-3000 has thus far demonstrated residual wave front errors of 141 nm rms under ~1" seeing conditions. PALM-3000 can provide phase conjugation correction over a 6".4 x 6".4 working region at lambda = 2.2 mu m, or full electric field (amplitude and phase) correction over approximately one-half of this field. With optimized back-end instrumentation, PALM-3000 is designed to enable 10 super(-7) contrast at 1" angular separation, including post-observation speckle suppression processing. While continued optimization of the AO system is ongoing, we have already successfully commissioned five back-end instruments and begun a major exoplanet characterization survey, Project 1640.
Abstract
While the vast majority of tidal disruption events (TDEs) have been identified by wide-field sky surveys in the optical and X-ray bands, recent studies indicate that a considerable fraction ...of TDEs may be dust obscured and thus preferentially detected in the infrared (IR) wave bands. In this Letter, we present the discovery of a luminous mid-IR nuclear flare (termed WTP14adbjsh), identified in a systematic transient search of archival images from the NEOWISE mid-IR survey. The source reached a peak luminosity of
L
≃ 10
43
erg s
−1
at 4.6
μ
m in 2015 before fading in the IR with a TDE-like
F
∝
t
−5/3
decline, radiating a total of more than 3 × 10
51
erg in the last 7 yr. The transient event took place in the nearby galaxy NGC 7392, at a distance of around 42 Mpc; yet, no optical or X-ray flare is detected. We interpret the transient as the nearest TDE candidate detected in the last decade, which was missed at other wavelengths due to dust obscuration, hinting at the existence of TDEs that have been historically overlooked. Unlike most previously detected TDEs, the transient was discovered in a star-forming galaxy, corroborating earlier suggestions that dust obscuration suppresses significantly the detection of TDEs in these environments. Our results demonstrate that the study of IR-detected TDEs is critical in order to obtain a complete understanding of the physics of TDEs and to conclude whether TDEs occur preferentially in a particular class of galaxies.
The Zwicky Transient Facility: Observing System Dekany, Richard; Smith, Roger M.; Riddle, Reed ...
Publications of the Astronomical Society of the Pacific,
03/2020, Volume:
132, Issue:
1009
Journal Article
Peer reviewed
Open access
The Zwicky Transient Facility (ZTF) Observing System (OS) is the data collector for the ZTF project to study astrophysical phenomena in the time domain. ZTF OS is based upon the 48 inch aperture ...Schmidt-type design Samuel Oschin Telescope at the Palomar Observatory in Southern California. It incorporates new telescope aspheric corrector optics, dome and telescope drives, a large-format exposure shutter, a flat-field illumination system, a robotic bandpass filter exchanger, and the key element: a new 47-square-degree, 600 megapixel cryogenic CCD mosaic science camera, along with supporting equipment. The OS collects and delivers digitized survey data to the ZTF Data System (DS). Here, we describe the ZTF OS design, optical implementation, delivered image quality, detector performance, and robotic survey efficiency.
Abstract
We present the discovery of a luminous X-ray transient, serendipitously detected by Swift’s X-ray Telescope on 2020 February 5, located in the nucleus of the galaxy SDSS J143359.16+400636.0 ...at
z
= 0.099 (luminosity distance
D
L
= 456 Mpc). The transient was observed to reach a peak luminosity of ∼10
44
erg s
−1
in the 0.3–10 keV X-ray band, which was ∼20 times more than the peak optical/UV luminosity. Optical, UV, and X-ray light curves from the Zwicky Transient Facility and Swift show a decline in flux from the source consistent with
t
−5/3
, and observations with NuSTAR and Chandra show a soft X-ray spectrum with photon index Γ = 2.9 ± 0.1. The X-ray/UV properties are inconsistent with well-known active galactic nucleus properties and have more in common with known X-ray tidal disruption events (TDEs), leading us to conclude that it was likely a TDE. The broadband spectral energy distribution can be described well by a disk blackbody model with an inner disk temperature of
K, with a large fraction (>40%) of the disk emission upscattered into the X-ray band. An optical spectrum taken with Keck/LRIS after the X-ray detection reveals LINER line ratios in the host galaxy, suggesting low-level accretion onto the supermassive black hole prior to the event, but no broad lines or other indications of a TDE were seen. The stellar velocity dispersion implies that the mass of the supermassive black hole powering the event is log(
M
BH
/
M
⊙
) = 7.41 ± 0.41, and we estimate that at peak the Eddington fraction of this event was ∼50%. This likely TDE was not identified by wide-field optical surveys or optical spectroscopy, indicating that more events like this would be missed without wide-field UV or X-ray surveys.
We present observations of ZTF18abfcmjw (SN2019dge), a helium-rich supernova with a fast-evolving light curve indicating an extremely low ejecta mass ( 0.33 M ) and low kinetic energy ( 1.3 × 1050 ...erg). Early-time (<4 days after explosion) photometry reveals evidence of shock cooling from an extended helium-rich envelope of ∼0.1 M located ∼1.2 × 1013 cm from the progenitor. Early-time He II line emission and subsequent spectra show signatures of interaction with helium-rich circumstellar material, which extends from 5 × 1013 cm to 2 × 1016 cm. We interpret SN2019dge as a helium-rich supernova from an ultra-stripped progenitor, which originates from a close binary system consisting of a mass-losing helium star and a low-mass main-sequence star or a compact object (i.e., a white dwarf, a neutron star, or a black hole). We infer that the local volumetric birth rate of 19dge-like ultra-stripped SNe is in the range of 1400-8200 Gpc − 3 yr − 1 (i.e., 2%-12% of core-collapse supernova rate). This can be compared to the observed coalescence rate of compact neutron star binaries that are not formed by dynamical capture.
ABSTRACT
The current generation of all-sky surveys is rapidly expanding our ability to study variable and transient sources. These surveys, with a variety of sensitivities, cadences, and fields of ...view, probe many ranges of time-scale and magnitude. Data from the Zwicky Transient Facility (ZTF) yields an opportunity to find variables on time-scales from minutes to months. In this paper, we present the codebase, ztfperiodic, and the computational metrics employed for the catalogue based on ZTF’s Second Data Release. We describe the publicly available, graphical-process-unit optimized period-finding algorithms employed, and highlight the benefit of existing and future graphical-process-unit clusters. We show how generating metrics as input to catalogues of this scale is possible for future ZTF data releases. Further work will be needed for future data from the Vera C. Rubin Observatory’s Legacy Survey of Space and Time.
Abstract
We present optical, radio, and X-ray observations of SN 2020bvc (=ASASSN-20bs, ZTF 20aalxlis), a nearby (
z
=
0.0252
;
d
= 114 Mpc) broad-line (BL) Type Ic supernova (SN) and the first ...double-peaked Ic-BL discovered without a gamma-ray burst (GRB) trigger. Our observations show that SN 2020bvc shares several properties in common with the Ic-BL SN 2006aj, which was associated with the low-luminosity gamma-ray burst (LLGRB) 060218. First, the 10 GHz radio luminosity (
L
radio
≈
10
37
erg
s
−
1
) is brighter than ordinary core-collapse SNe but fainter than LLGRB SNe such as SN 1998bw (associated with LLGRB 980425). We model our VLA observations (spanning 13–43 days) as synchrotron emission from a mildly relativistic (
v
≳ 0.3
c
) forward shock. Second, with Swift and Chandra, we detect X-ray emission (
L
X
≈ 10
41
erg
s
−
1
) that is not naturally explained as inverse Compton emission or part of the same synchrotron spectrum as the radio emission. Third, high-cadence (6× night
–1
) data from the Zwicky Transient Facility (ZTF) show a double-peaked optical light curve, the first peak from shock cooling of extended low-mass material (mass
M
e
<
10
−
2
M
⊙
at radius
R
e
> 10
12
cm) and the second peak from the radioactive decay of
56
Ni
. SN 2020bvc is the first double-peaked Ic-BL SN discovered without a GRB trigger, so it is noteworthy that it shows X-ray and radio emission similar to LLGRB SNe. For four of the five other nearby (
z
≲ 0.05) Ic-BL SNe with ZTF high-cadence data, we rule out a first peak like that seen in SN 2006aj and SN 2020bvc, i.e., that lasts ≈1 day and reaches a peak luminosity
M
≈ −18. Follow-up X-ray and radio observations of Ic-BL SNe with well-sampled early optical light curves will establish whether double-peaked optical light curves are indeed predictive of LLGRB-like X-ray and radio emission.
Abstract
We present visible and mid-infrared imagery and photometry of temporary Jovian co-orbital comet P/2019 LD
2
taken with Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3), Spitzer Space ...Telescope/Infrared Array Camera (Spitzer/IRAC), and the GROWTH telescope network, visible spectroscopy from Keck/Low-Resolution Imaging Spectrometer (LRIS), and archival Zwicky Transient Facility observations taken between 2019 April and 2020 August. Our observations indicate that the nucleus of LD
2
has a radius between 0.2 and 1.8 km assuming a 0.08 albedo and a coma dominated by ∼100
μ
m-scale dust ejected at ∼1 m s
−1
speeds with a ∼1′ jet pointing in the southwest direction. LD
2
experienced a total dust mass loss of ∼10
8
kg at a loss rate of ∼6 kg s
−1
with Af
ρ
/cross section varying between ∼85 cm/125 km
2
and ∼200 cm/310 km
2
from 2019 April 9 to 2019 November 8. If the increase in Af
ρ
/cross section remained constant, it implies LD
2
's activity began ∼2018 November when within 4.8 au of the Sun, implying the onset of H
2
O sublimation. We measure CO/CO
2
gas production of ≲10
27
mol s
−1
/≲10
26
mol s
−1
from our 4.5
μ
m Spitzer observations;
g
–
r
= 0.59 ± 0.03,
r
–
i
= 0.18 ± 0.05, and
i
–
z
= 0.01 ± 0.07 from GROWTH observations; and H
2
O gas production of ≲80 kg s
−1
scaling from our estimated
C
2
production of
mol s
−1
from Keck/LRIS spectroscopy. We determine that the long-term orbit of LD
2
is similar to Jupiter-family comets having close encounters with Jupiter within ∼0.5 Hill radius in the last ∼3 y and within 0.8 Hill radius in ∼9 y. Additionally, 78.8% of our orbital clones are ejected from the solar system within 1 × 10
6
yr, having a dynamical half-life of 3.4 × 10
5
yr.
Abstract
We observed the episodically active asteroid (6478) Gault in 2020 with multiple telescopes in Asia and North America and found that it is no longer active after its recent outbursts at the ...end of 2018 and the start of 2019. The inactivity during this apparition allowed us to measure the absolute magnitude of Gault of
H
r
= 14.63 ± 0.02,
G
r
= 0.21 ± 0.02 from our secular phase-curve observations. In addition, we were able to constrain Gault’s rotation period using time-series photometric lightcurves taken over 17 hr on multiple days in 2020 August, September, and October. The photometric lightcurves have a repeating ≲0.05 mag feature suggesting that (6478) Gault has a rotation period of ∼2.5 hr and may have a semispherical or top-like shape, much like the near-Earth asteroids Ryugu and Bennu. The rotation period of ∼2.5 hr is near the expected critical rotation period for an asteroid with the physical properties of (6478) Gault, suggesting that its activity observed over multiple epochs is due to surface mass shedding from its fast rotation spin-up by the Yarkovsky–O’Keefe–Radzievskii–Paddack effect.
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