We report observations of the optical counterpart of the long gamma-ray burst (LGRB) GRB 230812B, and its associated supernova (SN) SN 2023pel. The proximity (\(z = 0.36\)) and high energy ...(\(E_{\gamma, \rm{iso}} \sim 10^{53}\) erg) make it an important event to study as a probe of the connection between massive star core-collapse and relativistic jet formation. With a phenomenological power-law model for the optical afterglow, we find a late-time flattening consistent with the presence of an associated SN. SN 2023pel has an absolute peak \(r\)-band magnitude of \(M_r = -19.46 \pm 0.18\) mag (about as bright as SN 1998bw) and evolves on quicker timescales. Using a radioactive heating model, we derive a nickel mass powering the SN of \(M_{\rm{Ni}} = 0.38 \pm 0.01\) \(\rm{M_\odot}\), and a peak bolometric luminosity of \(L_{\rm{bol}} \sim 1.3 \times 10^{43}\) \(\rm{erg}\) \(\rm{s^{-1}}\). We confirm SN 2023pel's classification as a broad-lined Type Ic SN with a spectrum taken 15.5 days after its peak in \(r\) band, and derive a photospheric expansion velocity of \(v_{\rm{ph}} = 11,300 \pm 1,600\) \(\rm{km}\) \(\rm{s^{-1}}\) at that phase. Extrapolating this velocity to the time of maximum light, we derive the ejecta mass \(M_{\rm{ej}} = 1.0 \pm 0.6\) \(\rm{M_\odot}\) and kinetic energy \(E_{\rm{KE}} = 1.3^{+3.3}_{-1.2} \times10^{51}\) \(\rm{erg}\). We find that GRB 230812B/SN 2023pel has SN properties that are mostly consistent with the overall GRB-SN population. The lack of correlations found in the GRB-SN population between SN brightness and \(E_{\gamma, \rm{iso}}\) for their associated GRBs, across a broad range of 7 orders of magnitude, provides further evidence that the central engine powering the relativistic ejecta is not coupled to the SN powering mechanism in GRB-SN systems.
The observation of a compact object with a mass of \(2.50-2.67M_{\odot}\) on August 14, 2019, by the LIGO Scientific and Virgo collaborations (LVC) has the potential to improve our understanding of ...the supranuclear equation of state. While the gravitational-wave analysis of the LVC suggests that GW190814 likely was a binary black hole system, the secondary component could also have been the heaviest neutron star observed to date. We use our previously derived nuclear-physics-multimessenger astrophysics framework to address the nature of this object. Based on our findings, we determine GW190814 to be a binary black hole merger with a probability of \(>99.9\%\). Even if we weaken previously employed constraints on the maximum mass of neutron stars, the probability of a binary black hole origin is still \(\sim 81\%\). Furthermore, we study the impact that this observation has on our understanding of the nuclear equation of state by analyzing the allowed region in the mass-radius diagram of neutron stars for both a binary black hole or neutron star--black hole scenario. We find that the unlikely scenario in which the secondary object was a neutron star requires rather stiff equations of state with a maximum speed of sound \(c_s\geq \sqrt{0.6}\) times the speed of light, while the binary black hole scenario does not offer any new insight.
The Hubble diagram of type-Ia supernovae (SNe-Ia) provides cosmological constraints on the nature of dark energy with an accuracy limited by the flux calibration of currently available ...spectrophotometric standards. The StarDICE experiment aims at establishing a 5-stage metrology chain from NIST photodiodes to stars, with a targeted accuracy of \SI{1}{mmag} in \(griz\) colors. We present the first two stages, resulting in the calibration transfer from NIST photodiodes to a demonstration \SI{150}{Mpixel} CMOS sensor (Sony IMX411ALR as implemented in the QHY411M camera by QHYCCD). As a side-product, we provide full characterization of this camera. A fully automated spectrophotometric bench is built to perform the calibration transfer. The sensor readout electronics is studied using thousands of flat-field images from which we derive stability, high resolution photon transfer curves and estimates of the individual pixel gain. The sensor quantum efficiency is then measured relative to a NIST-calibrated photodiode. Flat-field scans at 16 different wavelengths are used to build maps of the sensor response. We demonstrate statistical uncertainty on quantum efficiency below \SI{0.001}{e^-/\gamma} between \SI{387}{nm} and \SI{950}{nm}. Systematic uncertainties in the bench optics are controlled at the level of \SI{1e-3}{e^-/\gamma}. Uncertainty in the overall normalization of the QE curve is 1\%. Regarding the camera we demonstrate stability in steady state conditions at the level of \SI{32.5}{ppm}. Homogeneity in the response is below \SI{1}{\percent} RMS across the entire sensor area. Quantum efficiency stays above \SI{50}{\percent} in most of the visible range, peaking well above \SI{80}{\percent} between \SI{440}{nm} and \SI{570}{nm}. Differential non-linearities at the level of \SI{1}{\percent} are detected. A simple 2-parameter model is proposed to mitigate the effect.
Observations of neutron-star mergers based on distinct messengers, including gravitational waves and electromagnetic signals, can be used to study the behavior of matter denser than an atomic ...nucleus, and to measure the expansion rate of the Universe described by the Hubble constant. We perform a joint analysis of the gravitational-wave signal GW170817 with its electromagnetic counterparts AT2017gfo and GRB170817A, and the gravitational-wave signal GW190425, both originating from neutron-star mergers. We combine these with previous measurements of pulsars using X-ray and radio observations, and nuclear-theory computations using chiral effective field theory to constrain the neutron-star equation of state. We find that the radius of a \(1.4\) solar mass neutron star is \(11.75^{+0.86}_{-0.81}\ \rm km\) at \(90\%\) confidence and the Hubble constant is \(66.2^{+4.4}_{-4.2}\ \rm km \,Mpc^{-1}\, s^{-1}\) at \(1\sigma\) uncertainty.
PNAS 121 (18) e2316474121 (2024) Multi-messenger searches for BNS and NSBH mergers are currently one of the
most exciting areas of astronomy. The search for joint electromagnetic and
neutrino ...counterparts to GWs has resumed with 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. In
preparation for O4, we have conducted a study using a simulated population of
compact binaries and a 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. We present an overview of the low-latency infrastructure and the
performance of the data products that are now being released during O4 based on
the MDC. We report the expected median latency for the preliminary alert of
full bandwidth searches (29.5s) and show consistency and accuracy of released
data products using the MDC. For the first time, we report the expected median
latency for triggers from early warning searches (-3.1s), which are new in O4
and target neutron star mergers during inspiral phase. This paper provides a
performance overview for LVK low-latency alert infrastructure and data products
using the MDC and serves as a useful reference for the interpretation of O4
detections.
GW170817 showed that neutron star mergers not only emit gravitational waves but also can release electromagnetic signatures in multiple wavelengths. Within the first half of the third observing run ...of the Advanced LIGO and Virgo detectors, there have been a number of gravitational wave candidates of compact binary systems for which at least one component is potentially a neutron star. In this article, we look at the candidates S190425z, S190426c, S190510g, S190901ap, and S190910h, predicted to have potentially a non-zero remnant mass, in more detail. All these triggers have been followed up with extensive campaigns by the astronomical community doing electromagnetic searches for their optical counterparts; however, according to the released classification, there is a high probability that some of these events might not be of extraterrestrial origin. Assuming that the triggers are caused by a compact binary coalescence and that the individual source locations have been covered during the EM follow-up campaigns, we employ three different kilonova models and apply them to derive possible constraints on the matter ejection consistent with the publicly available gravitational-wave trigger information and the lack of a kilonova detection. These upper bounds on the ejecta mass can be related to limits on the maximum mass of the binary neutron star candidate S190425z and to constraints on the mass-ratio, spin, and NS compactness for the potential black hole-neutron star candidate S190426c. Our results show that deeper electromagnetic observations for future gravitational wave events near the horizon limit of the advanced detectors are essential.
Kilonovae produced by the coalescence of compact binaries with at least one neutron star are promising standard sirens for an independent measurement of the Hubble constant (\(H_0\)). Through their ...detection via follow-up of gravitational-wave (GW), short gamma-ray bursts (sGRBs) or optical surveys, a large sample of kilonovae (even without GW data) can be used for \(H_0\) contraints. Here, we show measurement of \(H_0\) using light curves associated with four sGRBs, assuming these are attributable to kilonovae, combined with GW170817. Including a systematic uncertainty on the models that is as large as the statistical ones, we find \(H_0 = 73.8^{+6.3}_{-5.8}\)\,\(\mathrm{km}\) \(\mathrm{s}^{-1}\) \(\mathrm{Mpc}^{-1}\) and \(H_0 = 71.2^{+3.2}_{-3.1}\)\,\(\mathrm{km}\) \(\mathrm{s}^{-1}\) \(\mathrm{Mpc}^{-1}\) for two different kilonova models that are consistent with the local and inverse-distance ladder measurements. For a given model, this measurement is about a factor of 2-3 more precise than the standard-siren measurement for GW170817 using only GWs.
Nature Commun. 14 (2023) 1, 8352 The multi-messenger detection of the gravitational-wave signal GW170817, the
corresponding kilonova AT2017gfo and the short gamma-ray burst GRB170817A, as
well as the ...observed afterglow has delivered a scientific breakthrough. For an
accurate interpretation of all these different messengers, one requires robust
theoretical models that describe the emitted gravitational-wave, the
electromagnetic emission, and dense matter reliably. In addition, one needs
efficient and accurate computational tools to ensure a correct
cross-correlation between the models and the observational data. For this
purpose, we have developed the Nuclear-physics and Multi-Messenger Astrophysics
framework NMMA. The code allows incorporation of nuclear-physics constraints at
low densities as well as X-ray and radio observations of isolated neutron
stars. In previous works, the NMMA code has allowed us to constrain the
equation of state of supranuclear dense matter, to measure the Hubble constant,
and to compare dense-matter physics probed in neutron-star mergers and in
heavy-ion collisions, and to classify electromagnetic observations and perform
model selection. Here, we show an extension of the NMMA code as a first attempt
of analyzing the gravitational-wave signal, the kilonova, and the gamma-ray
burst afterglow simultaneously. Incorporating all available information, we
estimate the radius of a $1.4M_\odot$ neutron star to be
$R=11.98^{+0.35}_{-0.40}$km.
Joint multi-messenger observations with gravitational waves and electromagnetic data offer new insights into the astrophysical studies of compact objects. The third Advanced LIGO and Advanced Virgo ...observing run began on April 1, 2019; during the eleven months of observation, there have been 14 compact binary systems candidates for which at least one component is potentially a neutron star. Although intensive follow-up campaigns involving tens of ground and space-based observatories searched for counterparts, no electromagnetic counterpart has been detected. Following on a previous study of the first six months of the campaign, we present in this paper the next five months of the campaign from October 2019 to March 2020. We highlight two neutron star - black hole candidates (S191205ah, S200105ae), two binary neutron star candidates (S191213g and S200213t) and a binary merger with a possible neutron star and a "MassGap" component, S200115j. Assuming that the gravitational-wave candidates are of astrophysical origin and their location was covered by optical telescopes, we derive possible constraints on the matter ejected during the events based on the non-detection of counterparts. We find that the follow-up observations during the second half of the third observing run did not meet the necessary sensitivity to constrain the source properties of the potential gravitational-wave candidate. Consequently, we suggest that different strategies have to be used to allow a better usage of the available telescope time. We examine different choices for follow-up surveys to optimize sky localization coverage vs.\ observational depth to understand the likelihood of counterpart detection.
The rise of multi-messenger astronomy has brought with it the need to exploit all available data streams and learn more about the astrophysical objects that fall within its breadth. One possible ...avenue is the search for serendipitous optical/near-infrared counterparts of gamma-ray bursts (GRBs) and gravitational-wave (GW) signals, known as kilonovae. With surveys such as the Zwicky Transient Facility (ZTF), which observes the sky with a cadence of ~ three days, the existing counterpart locations are likely to be observed; however, due to the significant amount of sky to explore, it is difficult to search for these fast-evolving candidates. Thus, it is beneficial to optimize the survey cadence for realtime kilonova identification and enable further photometric and spectroscopic observations. We explore how the cadence of wide field-of-view surveys like ZTF can be improved to facilitate such identifications. We show that with improved observational choices, e.g., the adoption of three epochs per night on a ~ nightly basis, and the prioritization of redder photometric bands, detection efficiencies improve by about a factor of two relative to the nominal cadence. We also provide realistic hypothetical constraints on the kilonova rate as a form of comparison between strategies, assuming that no kilonovae are detected throughout the long-term execution of the respective observing plan. These results demonstrate how an optimal use of ZTF increases the likelihood of kilonova discovery independent of GWs or GRBs, thereby allowing for a sensitive search with less interruption of its nominal cadence through Target of Opportunity programs.
