A Deep CFHT Optical Search for a Counterpart to the Possible Neutron Star -- Black Hole Merger GW190814
Nicholas Vieira, John J. Ruan, Daryl Haggard, Maria R. Drout, Melania C. Nynka, Hope Boyce, Kristine Spekkens, Samar Safi-Harb, Raymond G. Carlberg, Rodrigo Fer… 展开作者
Nicholas Vieira, John J. Ruan, Daryl Haggard, Maria R. Drout, Melania C. Nynka, Hope Boyce, Kristine Spekkens, Samar Safi-Harb, Raymond G. Carlberg, Rodrigo Fernández, Anthony L. Piro, Niloufar Afsariardchi, Dae-Sik Moon
备注：
23 pages, 13 figures including appendices; accepted to ApJ with minor revisions
We present a wide-field optical imaging search for electromagnetic counterparts to the likely neutron star - black hole (NS-BH) merger GW190814/S190814bv. This compact binary merger was detected through gravitational waves by the LIGO/Virgo interferometers, with masses suggestive of a NS-BH merger. We imaged the LIGO/Virgo localization region using the MegaCam instrument on the Canada-France-Hawaii Telescope. We describe our hybrid observing strategy of both tiling and galaxy-targeted observations, as well as our image differencing and transient detection pipeline. Our observing campaign produced some of the deepest multi-band images of the region between 1.7 and 8.7 days post-merger, reaching a 5sigma depth of g > 22.8 (AB mag) at 1.7 days and i > 23.1 and i > 23.9 at 3.7 and 8.7 days, respectively. These observations cover a mean total integrated probability of 67.0% of the localization region. We find no compelling candidate transient counterparts to this merger in our images, which suggests that either the lighter object was tidally disrupted inside of the BH's innermost stable circular orbit, the transient lies outside of the observed sky footprint, or the lighter object is a low-mass BH. We use 5sigma source detection upper limits from our images in the NS-BH interpretation of this merger to constrain the mass of the kilonova ejecta to be Mej < 0.015Msun for a 'blue' (kappa = 0.5 cm^2 g^-1) kilonova, and Mej < 0.04Msun for a 'red' (kappa = 5-10 cm^2 g^-1) kilonova. Our observations emphasize the key role of large-aperture telescopes and wide-field imagers such as CFHT MegaCam in enabling deep searches for electromagnetic counterparts to gravitational wave events.
Despite world-wide ground, underground, and space based observations in search of anticipated electromagnetic and perhaps neutrino counterparts to the 29 compact binary merger events, which have been detected by the upgraded LIGO-Virgo gravitational wave detectors in the first half year of their observation period O3, no such counterparts were found. Although such a situation could be due to a poor localization of nearby merger events and/or a complex background of short extragalactic transients, it could be intrinsic. We show that, indeed, it is expected in the cannonball model of gamma ray b…
The recent observations of GW170817 and its electromagnetic (EM) counterparts show that double neutron star mergers could lead to rich and bright EM emissions. Recent numerical simulations suggest that neutron star and neutron star/black hole (NS-NS/BH) mergers would leave behind a central remnant surrounded by a mildly isotropic ejecta. The central remnant could launch a collimated jet and when the jet propagating through the ejecta, a mildly relativistic cocoon would be formed and the interaction between the cocoon and the ambient medium would accelerate electrons via external shock in a wid…
Mergers of compact objects are considered prime sources of gravitational waves (GW) and will soon be targets of GW observatories such as the Advanced-LIGO, VIRGO etc. Finding electromagnetic counterparts of these GW sources will be important to understand their nature. We discuss possible electromagnetic signatures of the mergers. We show that the BH-BH mergers could have luminosities which exceed Eddington luminosity from unity to several orders of magnitude depending on the masses of the merging BHs. As a result these mergers could be explosive, release up to $10^{51}$ erg of energy and shin…
Compact binary mergers, with neutron stars or neutron star and black-hole components, are thought to produce various electromagnetic counterparts: short gamma-ray bursts (GRBs) from ultra-relativistic jets followed by broadband afterglow; semi-isotropic kilonova from radioactive decay of r-process elements; and late time radio flares; etc. If the jets from such mergers follow a similar power-law distribution of Lorentz factors as other astrophysical jets then the population of merger jets will be dominated by low-Γ values. The prompt gamma-rays associated with short GRBs would be suppressed fo…
Multi-messenger astronomy combining Gravitational Wave (GW) and Electromagnetic Wave (EM) observation brings huge impact on physics, astrophysics and cosmology. However, the majority of sources to be detected with currently running ground-based GW observatories are binary black hole (BBH) mergers, which are expected disappointedly to have no EM counterparts. In this letter, we propose that if the BBH merger happens in a gaseous disk around a supermassive black hole, the merger can be accompanied by a transient radio flare alike a fast radio burst (FRB). We argue that the total mass and the eff…
The only binary neutron star merger gravitational wave event with detected electromagnetic counterparts recorded to date is GRB170817A. This merger occurred in a rarefied medium with a density smaller than $10^{-3}-10^{-2}~{\rm cm}^{-3}$. Since kicks are imparted to neutron star binaries upon formation, and due to their long delay times before merger, such low-density circum-merger media are generally expected. However, there is some indirect evidence for fast-merging or low-kick binaries, which would coalesce in denser environments. Nonetheless, present astronomical data are largely inconclus…
We propose a novel scenario for possible electromagnetic (EM) emission by compact binary mergers in the accretion disks of active galactic nuclei (AGNs). Nuclear star clusters in AGNs are a plausible formation site of compact-stellar binaries (CSBs) whose coalescences can be detected through gravitational waves (GWs). We investigate the accretion onto and outflows from CSBs embedded in AGN disks. We show that these outflows are likely to create outflow "cavities" in the AGN disks before the binaries merge, which makes EM or neutrino counterparts much less common than would otherwise be expecte…
The gravitational-wave event S190521g -- a likely binary black hole merger in the accretion disk of an active galactic nucleus -- was accompanied by an optical counterpart. Such dense environments around luminous energy release regions are favourable for high energy $γ$-ray production. We report on a search for high energy $γ$-rays from the direction of the candidate electromagnetic counterpart to the S190521g event using publicly-available data of the Fermi-LAT space $γ$-ray telescope. No significant signal was found. We present upper limits on the spectral energy distribution of the source i…
If at least one of the members of a compact binary coalescence is charged, the inspiral of the two members would generate a Poynting flux with an increasing power, giving rise to a brief electromagnetic counterpart temporally associated with the chirp signal of the merger (with possibly a small temporal offset), which we term as the {\em charged Compact Binary Coalescence} (cCBC) signal. We develop a general theory of cCBC for any mass and amount of charge for each member. Neutron stars (NSs), as spinning magnets, are guaranteed to be charged, so the cCBC signal should accompany all neutron st…
The first detection of a binary neutron star merger through gravitational waves and photons marked the dawn of multi-messenger astronomy with gravitational waves, and it greatly increased our insight in different fields of astrophysics and fundamental physics. However, many open questions on the physical process involved in a compact binary merger still remain and many of these processes concern plasma physics. With the second generation of gravitational wave interferometers approaching their design sensitivity, the new generation under design study, and new X-ray detectors under development, …
The recent discovery of electromagnetic signals in coincidence with gravitational waves from neutron-star mergers has solidified the importance of multimessenger campaigns for studying the most energetic astrophysical events. Pioneering multimessenger observatories, such as the LIGO/Virgo gravitational wave detectors and the IceCube neutrino observatory, record many candidate signals that fall short of the detection significance threshold. These sub-threshold event candidates are promising targets for multimessenger studies, as the information provided by these candidates may, when combined wi…
Short Gamma-Ray Bursts (SGRBs) are believed to arise from compact binary mergers (either neutron star-neutron star or black hole-neutron star). If so their jets must penetrate outflows that are ejected during the merger. As a jet crosses the ejecta it dissipates its energy, producing a hot cocoon which surrounds it. We present here 3D numerical simulations of jet propagation in mergers' outflows and we calculate the resulting emission. This emission consists of two components: the cooling emission, the leakage of the thermal energy of the hot cocoon, and the cocoon macronova that arises from t…
Electromagnetic observations of the first binary Neutron Star (BNS) merger GW170817 has established that relativistic jets can be successfully launched in BNS mergers. Typically, such jets produce emission in two phases: $γ$-ray prompt emission and multi-wavelength afterglow. Due to relativistic de-boosting, the detectability of both these counterparts is dependent on the angle ($θ_v$) between the observer's line of sight and the jet axis. We compare the detectability of prompt and afterglow emission from off-axis jets, assuming standard detector thresholds. We find that for top-hat jets, afte…
Unlike mergers of two compact objects containing a neutron star (NS), binary black hole (BBH) mergers are not accompanied by the production of tidally disrupted material, and hence lack the most direct source of accretion to power a jet and generate electromagnetic (EM) radiation. However, following a tentative detection by the Fermi GBM of a $γ$-ray counterpart to GW150914, several alternative ideas were proposed for driving a jet and producing EM radiation. {\em If} such jets were in fact produced, they would however lack the bright cocoon emission that makes jets from binary NSs bright also…
We present a sensitive search with the Karl G. Jansky Very Large Array (VLA) for the radio counterpart of the gravitational wave candidate S191216ap, classified as a binary black hole merger, and suggested to be a possible multi-messenger event, based on the detection of a high energy neutrino and a TeV photon. We carried out a blind search at C band (4--8 GHz) over 0.3 deg$^2$ of the gamma-ray counterpart of S191216ap reported by the High-Altitude Water Cherenkov Observatory (HAWC). Our search, spanning three epochs over 130 days post-merger and having mean source-detection threshold of 75$μ$…
Compact object mergers are promising candidates for the progenitor system of short gamma-ray bursts (GRBs). Using gravitational wave (GW) triggers to identify a merger, any electromagnetic (EM) counterparts from the jet can be used to constrain the dynamics and structure of short GRB jets. GW triggered searches could reveal a hidden population of optical transients associated with the short-lived jets from the merger object. If the population of merger-jets is dominated by low-Lorentz-factors, then a GW triggered search will reveal the on-axis orphan afterglows from these failed GRBs. By consi…
We present the properties of NGC 4993, the host galaxy of GW170817, the first gravitational wave (GW) event from the merger of a binary neutron star (BNS) system and the first with an electromagnetic (EM) counterpart. We use both archival photometry and new optical/near-IR imaging and spectroscopy, together with stellar population synthesis models to infer the global properties of the host galaxy. We infer a star formation history peaked at $\gtrsim 10$ Gyr ago, with subsequent exponential decline leading to a low current star formation rate of 0.01 M$_{\odot}$ yr$^{-1}$, which we convert into…
Recent detection of gravitational waves from a neutron star (NS) merger event GW170817 and identification of an electromagnetic counterpart provide a unique opportunity to study the physical processes in NS mergers. To derive properties of ejected material from the NS merger, we perform radiative transfer simulations of kilonova, optical and near-infrared emissions powered by radioactive decays of r-process nuclei synthesized in the merger. We find that the observed near-infrared emission lasting for > 10 days is explained by 0.03 Msun of ejecta containing lanthanide elements. However, the blu…
On 2019 August 14 the Laser Interferometer Gravitational Wave Observatory (LIGO) and the Virgo gravitational wave interferometer announced the detection of a binary merger, S190814bv, with a low false alarm rate (FAR) of about 1 in $1.6\times 10^{25}$ years, a distance of $267\pm 52$ Mpc, a 90\% (50\%) localization region of about 23 (5) deg$^2$, and a probability of being a neutron star--black hole (NS-BH) merger of $>99\%$. The LIGO/Virgo Collaboration (LVC) defines NS-BH such that the lighter binary member has a mass of $<3$ M$_\odot$ and the more massive one has $>5$ M$_\odot$, and this cl…
We present a systematic numerical relativity study of the mass ejection and the associated electromagnetic transients and nucleosynthesis from binary neutron star (NS) mergers. We find that a few $10^{-3}\, M_\odot$ of material are ejected dynamically during the mergers. The amount and the properties of these outflow depend on binary parameters and on the NS equation of state (EOS). A small fraction of these ejecta, typically ${\sim}10^{-6}\, M_\odot$, is accelerated by shocks formed shortly after merger to velocities larger than $0.6\, {\rm c}$ and produces bright radio flares on timescales o…
Binary black holes (BBHs) are one of the endpoints of isolated binary evolution, and their mergers a leading channel for gravitational wave events. Here, using the evolutionary code \textsc{StarTrack}, we study the statistical properties of the BBH population from isolated binary evolution for a range of progenitor star metallicities and BH natal kicks. We compute the mass function and the distribution of the primary BH spin $a$ as a result of mass accretion during the binary evolution, and find that this is not an efficient process to spin up BHs, producing an increase by at most $a\sim$~0.2-…
We report the results of our follow-up campaign for the neutron star - black hole (NSBH) merger GW200115 detected during the O3 run of the Advanced LIGO and Advanced Virgo detectors. We obtained wide-field observations with the Deca-Degree Optical Transient Imager (DDOTI) covering ~20% of the total probability area down to a limiting magnitude of $w$=20.5 AB at ~23 h after the merger. Our search for counterparts returns a single candidate (AT2020aeo), likely not associate to the merger. In total, only 25 sources of interest were identified by the community and later discarded as unrelated to t…
McFACTS. IV. Electromagnetic Counterparts to AGN-disk-embedded Binary Black Hole Mergers
Graduate Center, City University of New York（纽约市立大学研究生院）；Department of Astrophysics, American Museum of Natural History（美国自然历史博物馆天体物理系）；Department of Physics and Astronomy, Stony Brook University（石溪大学物理与天文系）；Department of Science, BMCC, City University of New York（纽约市立大学巴鲁克学院科学系）；Center for Computational Astrophysics, Flatiron Institute（平顿研究所计算天体物理中心）；New Mexico State University（新墨西哥州立大学）；Canadian Institute for Theoretical Astrophysics, University of Toronto（多伦多大学加拿大理论天体物理研究所）；Center for Computational Relativity and Gravitation, Rochester Institute of Technology（罗切斯特理工学院计算相对论与引力中心）；Data Science Institute, University of Chicago（芝加哥大学数据科学研究所）
Black hole-neutron star (BHNS) binaries are amongst promising candidates for the joint detection of electromagnetic (EM) signals with gravitational waves (GWs) and are expected to be detected in the near future. Here we study the effect of the BHNS binary parameters on the merger ejecta properties and associated EM signals. We estimate the remnant disk and unbound ejecta masses for BH mass and spin distributions motivated from the observations of transient low-mass X-ray binaries (LMXBs) and specific NS equation of state (EoS). The amount of r-process elements synthesised in BHNS mergers is es…
Detections of gravitational waves (GWs) may soon uncover the signal from the coalescence of a black hole - neutron star (BHNS) binary, that is expected to be accompanied by an electromagnetic (EM) signal. In this paper, we present a composite semi-analytical model to predict the properties of the expected EM counterpart from BHNS mergers, focusing on the kilonova emission and on the gamma-ray burst afterglow. Four main parameters rule the properties of the EM emission: the NS mass $M_\mathrm{NS}$, its tidal deformability $Λ_\mathrm{NS}$, the BH mass and spin. Only for certain combinations of t…
We present results from a search for a radio transient associated with the LIGO/Virgo source S190814bv, a likely neutron star-black hole (NSBH) merger, with the Australian Square Kilometre Array Pathfinder. We imaged a $30\,{\rm deg}^2$ field at $ΔT$=2, 9 and 33 days post-merger at a frequency of 944\,MHz, comparing them to reference images from the Rapid ASKAP Continuum Survey observed 110 days prior to the event. Each epoch of our observations covers $89\%$ of the LIGO/Virgo localisation region. We conducted an untargeted search for radio transients in this field, resulting in 21 candidates.…
Mergers of binaries consisting of two neutron stars, or a black hole and a neutron star, offer a unique opportunity to study a range of physical and astrophysical processes using two different and almost orthogonal probes - gravitational waves (GW) and electromagnetic (EM) emission. The GW signal probes the binary and the physical processes that take place during the last stages of the merger, while the EM emission provides clues to the material that is thrown out following the merger. The accurate localization, which only the EM emission can provide, also indicates the astrophysical setting i…
Recently, many gravitational wave events from compact binary mergers have been detected by LIGO. Determining the final mass and spin of the remnant black holes (RBHs) is a fundamental issue and is also important in astrophysics. In this paper, unified models for predicting the final mass and spin of the RBHs from compact binary mergers is proposed. The models achieve a good accuracy within the parameter range of interest. In addition, the rotational energy of the RBHs is also studied which is relevant to the electromagnetic counterparts of the mergers. It is found the distribution of the rotat…
On 2019 August 14, the Advanced LIGO and Virgo interferometers detected the high-significance gravitational wave (GW) signal S190814bv. The GW data indicated that the event resulted from a neutron star--black hole (NSBH) merger, or potentially a low-mass binary black hole merger. Due to the low false alarm rate and the precise localization (23 deg$^2$ at 90\%), S190814bv presented the community with the best opportunity yet to directly observe an optical/near-infrared counterpart to a NSBH merger. To search for potential counterparts, the GROWTH collaboration performed real-time image subtract…
By extrapolating the number of detections made during the first LIGO science run, tenths of gravitational wave signals from binary black hole mergers are anticipated in upcoming LIGO Virgo science runs. Finding an electromagnetic counterpart from compact binary merger events would be a capital achievement. We evaluate the ability of current wide-field X- and gamma-ray telescopes aboard INTEGRAL to find such counterparts thanks to an end-to-end simulation for estimating the fraction of the sources that can be followed up and/or detected.
LIGO/Virgo S190814bv is the first high-probability neutron star - black hole (NSBH) merger candidate, whose gravitational waves (GWs) triggered LIGO/Virgo detectors at 21:10:39.012957 UT, 14 August 2019. It has a probability $>99\%$ of being an NSBH merger, with a low false alarm rate (FAR) of 1 per 1.559e+25 years. For an NSBH merger, electromagnetic counterparts (especially short gamma-ray bursts (GRBs)) are generally expected. However, no electromagnetic counterpart has been found in the extensive follow-up observing campaign. In the present work, we propose a novel explanation to this null…
We propose a possibility of ultrarelativistic electromagnetic counterparts to gravitational waves from binary neutron star mergers at nearly all the viewing angles. Our proposed mechanism relies on the merger-shock propagation accelerating a smaller mass in the outer parts of the neutron star crust to a larger Lorentz factor $Γ$ with smaller energy $\sim 10^{47} Γ^{-1}$ erg. This mechanism is difficult to resolve by current 3D numerical simulations. The outflows emit synchrotron flares for seconds to days by shocking the ambient medium. Ultrarelativistic flares shine at an early time and in hi…
The Palomar Transient Factory (PTF) team recently reported the discovery of a rapidly fading optical transient source, PTF11agg. A long-lived scintillating radio counterpart was identified, but the search for a high energy counterpart showed negative results. The PTF team speculated that PTF11agg may represent a new class of relativistic outbursts. Here we suggest that a neutron star (NS)-NS merger system with a supra-massive magnetar central engine could be a possible source to power such a transient, if our line of sight is not on the jet axis direction of the system. These systems are also …
With the epochal first detection of gravitational waves from a binary neutron star (NS) merger with the GW170817 event, and its direct confirmation that NS-NS mergers are significant sources of the of the r-process nucleosynthesis of heavy elements, an immense new arena for prompt EM (X-rays through IR and radio) studies of fundamental physics has been opened. Over the next decade, GW observatories will expand in scale and sensitivity so the need for facilities that can provide prompt, high sensitivity, broad-band EM followup becomes more urgent. NS-NS or NS-black hole (BH) mergers will be ins…
Recent detection of gravitational waves from a binary-neutron star merger (GW170817) and the subsequent observations of electromagnetic counterparts provide a great opportunity to study the physics of compact binary mergers. The optical and near-infrared counterparts to GW170817 (SSS17a, also known as AT 2017gfo or DLT17ck) are found to be consistent with a kilonova/macronova scenario with red and blue components. However, in most of previous studies in which contribution from each ejecta component to the lightcurves is separately calculated and composited, the red component is too massive as …
We report on our observing campaign of the compact binary merger GW190814, detected by the Advanced LIGO and Advanced Virgo detectors on August 14th, 2019. This signal has the best localisation of any observed gravitational wave (GW) source, with a 90% probability area of 18.5 deg$^2$, and an estimated distance of ~ 240 Mpc. We obtained wide-field observations with the Deca-Degree Optical Transient Imager (DDOTI) covering 88% of the probability area down to a limiting magnitude of $w$ = 19.9 AB. Nearby galaxies within the high probability region were targeted with the Lowell Discovery Telescop…
We present Very Large Array (VLA) and Atacama Large Millimeter/sub-millimeter Array ALMA radio observations of GW\,170817, the first Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo gravitational wave (GW) event from a binary neutron star merger and the first GW event with an electromagnetic (EM) counterpart. Our data include the first observations following the discovery of the optical transient at both the centimeter ($13.7$ hours post merger) and millimeter ($2.41$ days post merger) bands. We detect faint emission at 6 GHz at 19.47 and 39.23 days after the merger, but not in…
The accretion disks of active galactic nuclei (AGN) are promising locations for the merger of compact objects detected by gravitational wave (GW) observatories. Embedded within a baryon-rich, high density environment, mergers within AGN are the only GW channel where an electromagnetic (EM) counterpart must occur (whether detectable or not). Considering AGN with unusual flaring activity observed by the Zwicky Transient Facility (ZTF), we describe a search for candidate EM counterparts to binary black hole (BBH) mergers detected by LIGO/Virgo in O3. After removing probable false positives, we fi…
During the final moments of a binary black hole (BH) merger, the gravitational wave (GW) luminosity of the system is greater than the combined electromagnetic output of the entire observable universe. However, the extremely weak coupling between GWs and ordinary matter makes these waves very difficult to detect directly. Fortunately, the inspiraling BH system will interact strongly--on a purely Newtonian level--with any surrounding material in the host galaxy, and this matter can in turn produce unique electromagnetic (EM) signals detectable at Earth. By identifying EM counterparts to GW sourc…
Long-lasting emission of short gamma-ray bursts (GRBs) is crucial to reveal the physical origin of the central engine as well as to detect electromagnetic (EM) counterparts to gravitational waves (GWs) from neutron star binary mergers. We investigate 65 X-ray light curves of short GRBs, which is six times more than previous studies, by combining both Swift/BAT and XRT data. The light curves are found to consist of two distinct components at $>5σ$ with bimodal distributions of luminosity and duration, i.e., extended (with timescale $\lesssim10^3$ s) and plateau emission (with timescale $\gtrsim…
We consider the question here whether the proposed electromagnetic counterpart of the gravitational wave signals in binary black hole coalescence may be due to the appearance of a `short lived' naked singularity during the merger. We point out that the change in topology that the spacetime undergoes during the merger can cause the appearance of a naked singularity. In case some matter, in the form of a small accretion disk, is present in the surroundings of the black hole system then the emitted luminosity during the merger would allow to distinguish the scenario where the naked singularity fo…
The electromagnetic counterparts to gravitational wave (GW) merger events are highly sought after, but difficult to find owing to large localization regions. In this study, we present a strategy to search for compact object merger radio counterparts in wide-field data collected by the Low-Frequency Array (LOFAR). In particular, we use multi-epoch LOFAR observations centred at 144 MHz spanning roughly 300 deg$^2$ at optimum sensitivity of a since retracted neutron star-black hole merger candidate detected during O2, the second Advanced Ligo-Virgo GW observing run. The minimum sensitivity of the…
The detection of the binary neutron star (BNS) merger, GW170817, was the first success story of multi-messenger observations of compact binary mergers. The inferred merger rate along with the increased sensitivity of the ground-based gravitational-wave (GW) network in the present LIGO/Virgo, and future LIGO/Virgo/KAGRA observing runs, strongly hints at detection of binaries which could potentially have an electromagnetic (EM) counterpart. A rapid assessment of properties that could lead to a counterpart is essential to aid time-sensitive follow-up operations, especially robotic telescopes. At …
We explore the electromagnetic counterparts that will associate with binary neutron star mergers for the case that remnant massive neutron stars survive for $\gtrsim 0.5\,$s after the merger. For this study, we employ the outflow profiles obtained by long-term general-relativistic neutrino-radiation magneto-hydrodynamics simulations with a mean field dynamo effect. We show that a synchrotron afterglow with high luminosity can be associated with the merger event if the magnetic fields of the remnant neutron stars are significantly amplified by the dynamo effect. We also perform a radiative tran…
Mergers of black hole (BH) and neutron star (NS) binaries are of interest since the emission of gravitational waves (GWs) can be followed by an electromagnetic (EM) counterpart, which could power short gamma-ray bursts. Until now, LIGO/Virgo has only observed a candidate BH-NS event, GW190426\_152155, which was not followed by any EM counterpart. We discuss how the presence (absence) of a remnant disk, which powers the EM counterpart, can be used along with spin measurements by LIGO/Virgo to derive a lower (upper) limit on the radius of the NS. For the case of GW190426\_152155, large measureme…
We present results from a search for the radio counterpart to the possible neutron star-black hole merger GW190814 with the Australian Square Kilometre Array Pathfinder. We have carried out 10 epochs of observation spanning 2-655 days post-merger at a frequency of 944 MHz. Each observation covered 30 deg$^2$, equivalent to 87% of the event localisation. We conducted an untargeted search for radio transients in the field, as well as a targeted search for transients associated with known galaxies. We find one radio transient, ASKAP J005022.3-230349, but conclude that it is unlikely to be associa…
We show the peak magnitude for orphan afterglows from the jets of gravitational wave (GW) detected black-hole/neutron star - neutron star (BH/NS-NS) mergers highly depends on the jet half-opening angle $θ_j$. Short $γ$-ray bursts (GRB) with a homogeneous jet structure and $θ_j>10^\circ$, the orphan afterglow viewed at the typical inclination for a GW detected event, 38$^\circ$, is brighter at optical frequencies than the comparable macronova emission. Structured jets, where the energetics and Lorentz factor $Γ$ vary with angle from the central axis, may have low-$Γ$ components where the prompt…
Neutron star binary mergers are strong sources of gravitational waves (GWs). Promising electromagnetic counterparts are short gamma-ray bursts (GRBs) but the emission is highly collimated. We propose that the scattering of the long-lasting plateau emission in short GRBs by the merger ejecta produces nearly isotropic emission for $\sim 10^4$ s with flux $10^{-13}-10^{-10}$ erg cm$^{-2}$ s$^{-1}$ at 100 Mpc in X-ray. This is detectable by Swift XRT and wide field X-ray detectors such as ISS-Lobster, Einstein Probe, eROSITA and WF-MAXI, which are desired by the infrared and optical follow-ups to …
We perform smoothed particle hydrodynamics (SPH) simulations for merging binary carbon-oxygen (CO) white dwarfs (WDs) with masses of $1.1$ and $1.0$ $M_\odot$, until the merger remnant reaches a dynamically steady state. Using these results, we assess whether the binary could induce a thermonuclear explosion, and whether the explosion could be observed as a type Ia supernova (SN Ia). We investigate three explosion mechanisms: a helium-ignition following the dynamical merger (`helium-ignited violent merger model'), a carbon-ignition (`carbon-ignited violent merger model'), and an explosion foll…
With the detection of gravitational wave (GW) GW170817 and its associated electromagnetic (EM) counterparts from a binary neutron star (NS) merger, the "standard siren" method for Hubble-constant measurements is expected to play a role in the Hubble-constant tension in the next few years. One intriguing proposal put forward in multiple studies is to use an NS merger's optical counterpart, known as a kilonova, as a standard candle, because its absolute magnitude can in principle be calculated from simulations. In this work, I detail the statistical framework for performing joint standard-candle…
Gravitational waves have been detected from a binary neutron star merger event, GW170817. The detection of electromagnetic radiation from the same source has shown that the merger occurred in the outskirts of the galaxy NGC 4993, at a distance of 40 megaparsecs from Earth. We report the detection of a counterpart radio source that appears 16 days after the event, allowing us to diagnose the energetics and environment of the merger. The observed radio emission can be explained by either a collimated ultra-relativistic jet viewed off-axis, or a cocoon of mildly relativistic ejecta. Within 100 da…
Electromagnetic Counterparts of Stellar-mass Binary Black Hole Mergers in AGN Accretion Disks: Theoretical Models and Observational Status
University of Science and Technology of China（中国科学技术大学）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；Guizhou University（贵州大学）
