58 research outputs found
The Impact of Initial-Final Mass Relations on Black Hole Microlensing
Uncertainty in the initial-final mass relation (IFMR) has long been a problem
in understanding the final stages of massive star evolution. One of the major
challenges of constraining the IFMR is the difficulty of measuring the mass of
non-luminous remnant objects (i.e. neutron stars and black holes).
Gravitational wave detectors have opened the possibility of finding large
numbers of compact objects in other galaxies, but all in merging binary
systems. Gravitational lensing experiments using astrometry and photometry are
capable of finding compact objects, both isolated and in binaries, in the Milky
Way. In this work we improve the PopSyCLE microlensing simulation code in order
to explore the possibility of constraining the IFMR using the Milky Way
microlensing population. We predict that the Roman Space Telescope's
microlensing survey will likely be able to distinguish different IFMRs based on
the differences at the long end of the Einstein crossing time distribution and
the small end of the microlensing parallax distribution, assuming the small
() microlensing parallaxes characteristic of black hole
lenses are able to be measured accurately. We emphasize that future
microlensing surveys need to be capable of characterizing events with small
microlensing parallaxes in order to place the most meaningful constraints on
the IFMR.Comment: 24 pages, 17 figures Accepted to Ap
Gravitational Microlensing Event Statistics for the Zwicky Transient Facility
Microlensing surveys have discovered thousands of events with almost all
events discovered within the Galactic bulge or toward the Magellanic clouds.
The Zwicky Transient Facility (ZTF), while not designed to be a microlensing
campaign, is an optical time-domain survey that observes the entire northern
sky every few nights including the Galactic plane. ZTF observes
stars in g-band and r-band and can significantly contribute to the observed
microlensing population. We predict that ZTF will observe 1100
microlensing events in three years of observing within degrees
latitude of the Galactic plane, with 500 events in the outer Galaxy
(). This yield increases to 1400 (800) events
by combining every three ZTF exposures, 1800 (900) events if ZTF
observes for a total of five years, and 2400 (1300) events for a
five year survey with post-processing image stacking. Using the microlensing
modeling software PopSyCLE, we compare the microlensing populations in the
Galactic bulge and the outer Galaxy. We also present an analysis of the
microlensing event ZTF18abhxjmj to demonstrate how to leverage these population
statistics in event modeling. ZTF will constrain Galactic structure, stellar
populations, and primordial black holes through photometric microlensing.Comment: 19 pages, 13 figures, 5 tables, accepted to ApJ (6/4/2020),
microlensing simulation catalogs available at
https://portal.nersc.gov/project/uLens/Galactic_Microlensing_Distribution
A Reanalysis of Public Galactic Bulge Gravitational Microlensing Events from OGLE-III and IV
Modern surveys of gravitational microlensing events have progressed to
detecting thousands per year. Surveys are capable of probing Galactic
structure, stellar evolution, lens populations, black hole physics, and the
nature of dark matter. One of the key avenues for doing this is studying the
microlensing Einstein radius crossing time distribution (). However,
systematics in individual light curves as well as over-simplistic modeling can
lead to biased results. To address this, we developed a model to simultaneously
handle the microlensing parallax due to Earth's motion, systematic instrumental
effects, and unlensed stellar variability with a Gaussian Process model. We
used light curves for nearly 10,000 OGLE-III and IV Milky Way bulge
microlensing events and fit each with our model. We also developed a forward
model approach to infer the timescale distribution by forward modeling from the
data rather than using point estimates from individual events. We find that
modeling the variability in the baseline removes a source of significant bias
in individual events, and previous analyses over-estimated the number of long
timescale ( days) events due to their over simplistic models ignoring
parallax effects and stellar variability. We use our fits to identify hundreds
of events that are likely black holes.Comment: Submitted version, in review, 33 pages, 18 figures, MCMC posterior
samples available by publisher after acceptanc
GROWTH on S190510g: DECam Observation Planning and Follow-Up of a Distant Binary Neutron Star Merger Candidate
The first two months of the third Advanced LIGO and Virgo observing run (2019 April–May) showed that distant gravitational-wave (GW) events can now be readily detected. Three candidate mergers containing neutron stars (NS) were reported in a span of 15 days, all likely located more than 100 Mpc away. However, distant events such as the three new NS mergers are likely to be coarsely localized, which highlights the importance of facilities and scheduling systems that enable deep observations over hundreds to thousands of square degrees to detect the electromagnetic counterparts. On 2019 May 10 02:59:39.292 UT the GW candidate S190510g was discovered and initially classified as a binary neutron star (BNS) merger with 98% probability. The GW event was localized within an area of 3462 deg^2, later refined to 1166 deg^2 (90%) at a distance of 227 ± 92 Mpc. We triggered Target-of-Opportunity observations with the Dark Energy Camera (DECam), a wide-field optical imager mounted at the prime focus of the 4 m Blanco Telescope at Cerro Tololo Inter-American Observatory in Chile. This Letter describes our DECam observations and our real-time analysis results, focusing in particular on the design and implementation of the observing strategy. Within 24 hr of the merger time, we observed 65% of the total enclosed probability of the final skymap with an observing efficiency of 94%. We identified and publicly announced 13 candidate counterparts. S190510g was reclassified 1.7 days after the merger, after our observations were completed, with a "BNS merger" probability reduced from 98% to 42% in favor of a "terrestrial classification
Simultaneous Observations of the Northern TESS Sectors by the Zwicky Transient Facility
The Transiting Exoplanet Survey Satellite (TESS) (Schliegel 2017) is a powerful facility for studying a broad range of astrophysical objects. The Zwicky Transient Facility (ZTF) (Bellm et al. 2019; Graham et al. 2019; Masci et al. 2019) is conducting a nightly public survey of all 13 TESS northern sectors in 2019–2020. ZTF will observe the portions of the current TESS sector visible from Palomar Observatory each night. Each ZTF pointing will have one exposure each with g and r filters, totaling two images per night. The first northern sector, Sector 14, was observed from 2019 July 18 to August 15. The observations of the second northern sector, Sector 15, began on 2019 August 15. The majority of Sectors 14 and 15 have been covered by ZTF, except for a portion of TESS Camera 4, due to the visibility limits. ZTF is also making additional nightly g- and r-band observations of denser stellar regions (e.g., near the Galactic Plane) to better facilitate variability studies of Galactic objects
Long-rising Type II Supernovae in the Zwicky Transient Facility Census of the Local Universe
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 Mpc yr,
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.Comment: 32 pages, 17 figures, 5 tables. Submitted to Ap
A Search for Extragalactic Fast Blue Optical Transients in ZTF and the Rate of AT2018cow-like Transients
We present a search for extragalactic fast blue optical transients (FBOTs)
during Phase I of the Zwicky Transient Facility (ZTF). We identify 38
candidates with durations above half-maximum light 1 d < t1/2 < 12 d, of which
28 have blue (g-r<-0.2 mag) colors at peak light. Of the 38 transients (28
FBOTs), 19 (13) can be spectroscopically classified as core-collapse supernovae
(SNe): 11 (8) H- or He-rich (Type II/IIb/Ib) SNe, 6 (4) interacting (Type
IIn/Ibn) SNe, and 2 (1) H&He-poor (Type Ic/Ic-BL) SNe. Two FBOTs (published
previously) had high-S/N predominantly featureless spectra and luminous radio
emission: AT2018lug and AT2020xnd. Seven (five) did not have a definitive
classification: AT 2020bdh showed tentative broad H in emission, and AT
2020bot showed unidentified broad features and was 10 kpc offset from the
center of an early-type galaxy. Ten (six) have no spectroscopic observations or
redshift measurements. We present multiwavelength (radio, millimeter, and/or
X-ray) observations for five FBOTs (three Type Ibn, one Type IIn/Ibn, one Type
IIb). Additionally, we search radio-survey (VLA and ASKAP) data to set limits
on the presence of radio emission for 22 of the transients. All X-ray and radio
observations resulted in non-detections; we rule out AT2018cow-like X-ray and
radio behavior for five FBOTs and more luminous emission (such as that seen in
the Camel) for four additional FBOTs. We conclude that exotic transients
similar to AT2018cow, the Koala, and the Camel represent a rare subset of
FBOTs, and use ZTF's SN classification experiments to measure the rate to be at
most 0.1% of the local core-collapse SN rate.Comment: Replaced following peer-review process. 46 pages, 20 figures.
Accepted for publication in Ap
GROWTH on S190510g: DECam Observation Planning and Follow-Up of a Distant Binary Neutron Star Merger Candidate
The first two months of the third Advanced LIGO and Virgo observing run (2019 April–May) showed that distant gravitational-wave (GW) events can now be readily detected. Three candidate mergers containing neutron stars (NS) were reported in a span of 15 days, all likely located more than 100 Mpc away. However, distant events such as the three new NS mergers are likely to be coarsely localized, which highlights the importance of facilities and scheduling systems that enable deep observations over hundreds to thousands of square degrees to detect the electromagnetic counterparts. On 2019 May 10 02:59:39.292 UT the GW candidate S190510g was discovered and initially classified as a binary neutron star (BNS) merger with 98% probability. The GW event was localized within an area of 3462 deg^2, later refined to 1166 deg^2 (90%) at a distance of 227 ± 92 Mpc. We triggered Target-of-Opportunity observations with the Dark Energy Camera (DECam), a wide-field optical imager mounted at the prime focus of the 4 m Blanco Telescope at Cerro Tololo Inter-American Observatory in Chile. This Letter describes our DECam observations and our real-time analysis results, focusing in particular on the design and implementation of the observing strategy. Within 24 hr of the merger time, we observed 65% of the total enclosed probability of the final skymap with an observing efficiency of 94%. We identified and publicly announced 13 candidate counterparts. S190510g was reclassified 1.7 days after the merger, after our observations were completed, with a "BNS merger" probability reduced from 98% to 42% in favor of a "terrestrial classification
Neutrino follow-up with the Zwicky Transient Facility: Results from the first 24 campaigns
The Zwicky Transient Transient Facility (ZTF) performs a systematic neutrino
follow-up program, searching for optical counterparts to high-energy neutrinos
with dedicated Target-of-Opportunity (ToO) observations. Since first light in
March 2018, ZTF has taken prompt observations for 24 high-quality neutrino
alerts from the IceCube Neutrino Observatory, with a median latency of 12.2
hours from initial neutrino detection. From two of these campaigns, we have
already reported tidal disruption event (TDE) AT2019dsg and likely TDE
AT2019fdr as probable counterparts, suggesting that TDEs contribute >7.8% of
the astrophysical neutrino flux. We here present the full results of our
program through to December 2021. No additional candidate neutrino sources were
identified by our program, allowing us to place the first constraints on the
underlying optical luminosity function of astrophysical neutrino sources.
Transients with optical absolutes magnitudes brighter that -21 can contribute
no more than 87% of the total, while transients brighter than -22 can
contribute no more than 58% of the total, neglecting the effect of extinction.
These are the the first observational constraints on the neutrino emission of
bright populations such as superluminous supernovae. None of the neutrinos were
coincident with bright optical AGN flares comparable to that observed for TXS
0506+056/IC170922A, suggesting that most astrophysical neutrinos are not
produced during such optical flares. We highlight the outlook for
electromagnetic neutrino follow-up programs, including the expected potential
for the Rubin Observatory.Comment: To be submitted to MNRAS, comments welcome
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