18 research outputs found
Performance of the low-latency GstLAL inspiral search towards LIGO, Virgo, and KAGRA's fourth observing run
GstLAL is a stream-based matched-filtering search pipeline aiming at the
prompt discovery of gravitational waves from compact binary coalescences such
as the mergers of black holes and neutron stars. Over the past three
observation runs by the LIGO, Virgo, and KAGRA (LVK) collaboration, the GstLAL
search pipeline has participated in several tens of gravitational wave
discoveries. The fourth observing run (O4) is set to begin in May 2023 and is
expected to see the discovery of many new and interesting gravitational wave
signals which will inform our understanding of astrophysics and cosmology. We
describe the current configuration of the GstLAL low-latency search and show
its readiness for the upcoming observation run by presenting its performance on
a mock data challenge. The mock data challenge includes 40 days of LIGO
Hanford, LIGO Livingston, and Virgo strain data along with an injection
campaign in order to fully characterize the performance of the search. We find
an improved performance in terms of detection rate and significance estimation
as compared to that observed in the O3 online analysis. The improvements are
attributed to several incremental advances in the likelihood ratio ranking
statistic computation and the method of background estimation.Comment: 19 pages, 21 figure
Daksha: On Alert for High Energy Transients
We present Daksha, a proposed high energy transients mission for the study of
electromagnetic counterparts of gravitational wave sources, and gamma ray
bursts. Daksha will comprise of two satellites in low earth equatorial orbits,
on opposite sides of earth. Each satellite will carry three types of detectors
to cover the entire sky in an energy range from 1 keV to >1 MeV. Any transients
detected on-board will be announced publicly within minutes of discovery. All
photon data will be downloaded in ground station passes to obtain source
positions, spectra, and light curves. In addition, Daksha will address a wide
range of science cases including monitoring X-ray pulsars, studies of
magnetars, solar flares, searches for fast radio burst counterparts, routine
monitoring of bright persistent high energy sources, terrestrial gamma-ray
flashes, and probing primordial black hole abundances through lensing. In this
paper, we discuss the technical capabilities of Daksha, while the detailed
science case is discussed in a separate paper.Comment: 9 pages, 3 figures, 1 table. Additional information about the mission
is available at https://www.dakshasat.in
Low-latency gravitational wave alert products and their performance in anticipation of the fourth LIGO-Virgo-KAGRA observing run
Multi-messenger searches for binary neutron star (BNS) and neutron star-black
hole (NSBH) mergers are currently one of the most exciting areas of astronomy.
The search for joint electromagnetic and neutrino counterparts to gravitational
wave (GW)s has resumed with Advanced LIGO (aLIGO)'s, Advanced Virgo (AdVirgo)'s
and KAGRA's fourth observing run (O4). To support this effort, public
semi-automated data products are sent in near real-time and include
localization and source properties to guide complementary observations.
Subsequent refinements, as and when available, are also relayed as updates. In
preparation for O4, we have conducted a study using a simulated population of
compact binaries and a Mock Data Challenge (MDC) in the form of a real-time
replay to optimize and profile the software infrastructure and scientific
deliverables. End-to-end performance was tested, including data ingestion,
running online search pipelines, performing annotations, and issuing alerts to
the astrophysics community. In this paper, we present an overview of the
low-latency infrastructure as well as an overview of the performance of the
data products to be released during O4 based on a MDC. We report on expected
median latencies for the preliminary alert of full bandwidth searches (29.5 s)
and for the creation of early warning triggers (-3.1 s), and show consistency
and accuracy of released data products using the MDC. This paper provides a
performance overview for LVK low-latency alert structure and data products
using the MDC in anticipation of O4
Science with the Daksha High Energy Transients Mission
We present the science case for the proposed Daksha high energy transients
mission. Daksha will comprise of two satellites covering the entire sky from
1~keV to ~MeV. The primary objectives of the mission are to discover and
characterize electromagnetic counterparts to gravitational wave source; and to
study Gamma Ray Bursts (GRBs). Daksha is a versatile all-sky monitor that can
address a wide variety of science cases. With its broadband spectral response,
high sensitivity, and continuous all-sky coverage, it will discover fainter and
rarer sources than any other existing or proposed mission. Daksha can make key
strides in GRB research with polarization studies, prompt soft spectroscopy,
and fine time-resolved spectral studies. Daksha will provide continuous
monitoring of X-ray pulsars. It will detect magnetar outbursts and high energy
counterparts to Fast Radio Bursts. Using Earth occultation to measure source
fluxes, the two satellites together will obtain daily flux measurements of
bright hard X-ray sources including active galactic nuclei, X-ray binaries, and
slow transients like Novae. Correlation studies between the two satellites can
be used to probe primordial black holes through lensing. Daksha will have a set
of detectors continuously pointing towards the Sun, providing excellent hard
X-ray monitoring data. Closer to home, the high sensitivity and time resolution
of Daksha can be leveraged for the characterization of Terrestrial Gamma-ray
Flashes.Comment: 19 pages, 7 figures. Submitted to ApJ. More details about the mission
at https://www.dakshasat.in
Kilonova Luminosity Function Constraints Based on Zwicky Transient Facility Searches for 13 Neutron Star Merger Triggers during O3
We present a systematic search for optical counterparts to 13 gravitational wave (GW) triggers involving at least one neutron star during LIGO/Virgo's third observing run (O3). We searched binary neutron star (BNS) and neutron star black hole (NSBH) merger localizations with the Zwicky Transient Facility (ZTF) and undertook follow-up with the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration. The GW triggers had a median localization area of 4480 deg², a median distance of 267 Mpc, and false-alarm rates ranging from 1.5 to 10⁻²⁵ yr⁻¹. The ZTF coverage in the g and r bands had a median enclosed probability of 39%, median depth of 20.8 mag, and median time lag between merger and the start of observations of 1.5 hr. The O3 follow-up by the GROWTH team comprised 340 UltraViolet/Optical/InfraRed (UVOIR) photometric points, 64 OIR spectra, and three radio images using 17 different telescopes. We find no promising kilonovae (radioactivity-powered counterparts), and we show how to convert the upper limits to constrain the underlying kilonova luminosity function. Initially, we assume that all GW triggers are bona fide astrophysical events regardless of false-alarm rate and that kilonovae accompanying BNS and NSBH mergers are drawn from a common population; later, we relax these assumptions. Assuming that all kilonovae are at least as luminous as the discovery magnitude of GW170817 (−16.1 mag), we calculate that our joint probability of detecting zero kilonovae is only 4.2%. If we assume that all kilonovae are brighter than −16.6 mag (the extrapolated peak magnitude of GW170817) and fade at a rate of 1 mag day⁻¹ (similar to GW170817), the joint probability of zero detections is 7%. If we separate the NSBH and BNS populations based on the online classifications, the joint probability of zero detections, assuming all kilonovae are brighter than −16.6 mag, is 9.7% for NSBH and 7.9% for BNS mergers. Moreover, no more than 10⁻⁴, or φ > 30° to be consistent with our limits. We look forward to searches in the fourth GW observing run; even 17 neutron star mergers with only 50% coverage to a depth of −16 mag would constrain the maximum fraction of bright kilonovae to <25%
GROWTH on S190425z: Searching Thousands of Square Degrees to Identify an Optical or Infrared Counterpart to a Binary Neutron Star Merger with the Zwicky Transient Facility and Palomar Gattini-IR
The third observing run by LVC has brought the discovery of many compact binary coalescences. Following the detection of the first binary neutron star merger in this run (LIGO/Virgo S190425z), we performed a dedicated follow-up campaign with the Zwicky Transient Facility (ZTF) and Palomar Gattini-IR telescopes. The initial skymap of this single-detector gravitational wave (GW) trigger spanned most of the sky observable from Palomar Observatory. Covering 8000 deg2 of the initial skymap over the next two nights, corresponding to 46% integrated probability, ZTF system achieved a depth of ≈21 m AB in g- and r-bands. Palomar Gattini-IR covered 2200 square degrees in J-band to a depth of 15.5 mag, including 32% integrated probability based on the initial skymap. The revised skymap issued the following day reduced these numbers to 21% for the ZTF and 19% for Palomar Gattini-IR. We narrowed 338,646 ZTF transient "alerts" over the first two nights of observations to 15 candidate counterparts. Two candidates, ZTF19aarykkb and ZTF19aarzaod, were particularly compelling given that their location, distance, and age were consistent with the GW event, and their early optical light curves were photometrically consistent with that of kilonovae. These two candidates were spectroscopically classified as young core-collapse supernovae. The remaining candidates were ruled out as supernovae. Palomar Gattini-IR did not identify any viable candidates with multiple detections only after merger time. We demonstrate that even with single-detector GW events localized to thousands of square degrees, systematic kilonova discovery is feasible
GROWTH on GW190425: Searching thousands of square degrees to identify an optical or infrared counterpart to a binary neutron star merger with the Zwicky Transient Facility and Palomar Gattini IR
The beginning of the third observing run by the network of gravitational-wave
detectors has brought the discovery of many compact binary coalescences.
Prompted by the detection of the first binary neutron star merger in this run
(GW190425 / LIGO/Virgo S190425z), we performed a dedicated follow-up campaign
with the Zwicky Transient Facility (ZTF) and Palomar Gattini-IR telescopes. As
it was a single gravitational-wave detector discovery, the initial skymap
spanned most of the sky observable from Palomar Observatory, the site of both
instruments. Covering 8000 deg of the inner 99\% of the initial skymap over
the next two nights, corresponding to an integrated probability of 46\%, the
ZTF system achieved a depth of \,21 in - and
-bands. Palomar Gattini-IR covered a total of 2200 square degrees in
-band to a depth of 15.5\,mag, including 32\% of the integrated probability
based on the initial sky map. However, the revised skymap issued the following
day reduced these numbers to 21\% for the Zwicky Transient Facility and 19\%
for Palomar Gattini-IR. Out of the 338,646 ZTF transient "alerts" over the
first two nights of observations, we narrowed this list to 15 candidate
counterparts. Two candidates, ZTF19aarykkb and ZTF19aarzaod were particularly
compelling given that their location, distance, and age were consistent with
the gravitational-wave event, and their early optical lightcurves were
photometrically consistent with that of kilonovae. These two candidates were
spectroscopically classified as young core-collapse supernovae. The remaining
candidates were photometrically or spectroscopically ruled-out as supernovae.
Palomar Gattini-IR identified one fast evolving infrared transient after the
merger, PGIR19bn, which was later spectroscopically classified as an M-dwarf
flare. [abridged
Observation of gravitational waves from the coalescence of a 2.5−4.5 M⊙ compact object and a neutron star
Ultralight vector dark matter search using data from the KAGRA O3GK run
Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM