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 considering the EM counterparts from a jet, with or without the prompt GRB, the jet structure and dynamics can be constrained. By modelling the afterglow of various jet structures with viewing angle, we provide observable predictions for the on- and off- axis EM jet counterparts. The predictions provide an indication for the various features expected from the proposed jet structure models.

The identification of the electromagnetic(EM) counterpart of gravitational wave(GW) trigger in the sky localization is a very difficult task because of the large uncertainty. Two complementary approaches are used in order to search for EM counterpart of GW signal with a typical large sky localization uncertainty: wide-field tilling search on high probability GW region, e.g. Gravitational Wave Inaf Team(GRAWITA) project or pointed search of selected galaxies in high probability GW region, e.g. Distance Less Than 40 Mpc survey(DLT40) project.

We report our investigations on the host galaxy properties of stellar binary black holes (SBBHs) by implementing simple recipes for SBBH formation and merger into cosmological galaxy formation model. If the time delay between SBBH formation and merger ranges from Gyr to the Hubble time, SBBH mergers at redshift z < 0.3 occur preferentially in big galaxies with stellar mass M* > 2 × 1010M⊙ and metallicities Z peaking around ~0.6Z⊙. However, the host galaxy stellar mass distribution of heavy SBBH mergers (with total black hole mass >50M⊙) is bimodal with one peak at ~109M⊙ and the other peak at ~2 × 1010M⊙. The contribution fraction from metal-poor host galaxies (Z < 0.2Z⊙) to heavy mergers is much larger than that to less heavy mergers. If SBBHs were formed in the early universe, their mergers detected at z < 0.3 occur preferentially in even more massive galaxies with M* > 3 × 1010M⊙ and in galaxies with metallicities mostly >0.2Z⊙ and peaking at Z ~ 0.6Z⊙.

We present a critical reanalysis of the black-hole binary coalescences detected during LIGO’s first observing run under different Bayesian prior assumptions. We summarize the main findings of Vitale et al. (2017) and show additional marginalized posterior distributions for some of the binaries’ intrinsic parameters.

These findings were presented at IAU Symposium 338, held on October 16-19, 2017 in Baton Rouge, LA, USA.

Blazar OJ287 exhibits large thermal flares at least twice every 12 years. The times of these flares have been predicted successfully using the model of a quasi-Keplerian eccentric black hole binary where the secondary impacts the accretion disk of the primary, creating the thermal flares. New measurements of the historical light curve have been combined with the observations of the 2015 November/December flare to identify the impact record since year 1886, and to constrain the orbit of the binary. The orbital solution shows that the binary period, now 12.062 years, is decreasing at the rate of 36 days per century. This corresponds to an energy loss to gravitational waves that is 6.5 ± 4 % less than the rate predicted by the standard quadrupolar gravitational wave (GW) emission. We show that the difference is due to higher order gravitational radiation reaction terms that include the dominant order tail contributions.

The paper presents a proof of concept method of background rejection based on convolutional neural networks (CNN). The method was tested on simulated data and achieved very high accuracy (100%). What is more, method based on CNN is very fast and could be easily applied to wide field surveys. Since early stage results suggest method is very accurate and robust, it could be helpful in creating very low-latency pipelines for EM Follow-up purposes, which will be needed in LIGO-Virgo O3 EM Follow-up.

The LIGO/Virgo detections of gravitational waves from merging black holes of ≃ 30 solar mass suggest progenitor stars of low metallicity (Z/Z⊙ ≲ 0.3). In this talk I will provide constrains on where the progenitors of GW150914 and GW170104 may have formed, based on advanced models of galaxy formation and evolution combined with binary population synthesis models. First I will combine estimates of galaxy properties (star-forming gas metallicity, star formation rate and merger rate) across cosmic time to predict the low redshift BBH merger rate as a function of present day host galaxy mass, formation redshift of the progenitor system and different progenitor metallicities. I will show that the signal is dominated by binaries formed at the peak of star formation in massive galaxies with and binaries formed recently in dwarf galaxies. Then, I will present what very high resolution hydrodynamic simulations of different galaxy types can learn us about their black hole populations.

We conducted a systematic search for periodically varying quasars, which are predicted manifestations of sub-pc supermassive black hole binaries (SMBHBs), in the Pan-STARRS1 Medium Deep Survey (PS1 MDS). Since the normal variability of quasars can also mimic periodicity over a small number of cycles, we have extended the temporal baseline by monitoring the candidates with the Discovery Channel Telescope and the Las Cumbres Observatory telescopes. We have also adopted a more rigorous method to evaluate the significance of the periodic candidates, by considering in the light curves a “red noise” background modeled as the Damped Random Walk process. While none of the candidates can be resolved by the current pulsar timing arrays (PTAs) as individual gravitational wave sources, the Large Synoptic Survey Telescope is capable of finding more periodic candidates, some of which are likely to be detected by the PTA experiment with the Square Kilometre Array.

Swift’s rapid slewing, flexible planning, and multi-wavelength instruments make it the most capable space-based follow-up engine for finding poorly localized sources. During O1 and O2 Swift successfully tiled hundreds of square-degrees of sky in the LVC localization regions, searching for, and identifying, possible X-ray and UV/O transients in the field. Swift made important contributions to the discovery and characterization of the kilonova AT 2017gfo, discovering the UV emission and providing the deepest X-ray upper limits in the first 24 hours after the trigger, strongly constraining the dynamics and geometry of the counterpart. Swift tiled 92% of the galaxy convolved error region down to average X-ray flux sensitivities of 10−12 erg cm−2 s−1, significantly increasing our confidence that AT 2017gfo is indeed the counterpart to GW 170817 and sGRB 170817. However, there remains significant room for improvement of Swift’s follow-up in preparation for O3. This will take the form of both revised observation strategy based on detailed analysis of the results from O2, and significant changes to Swift’s operational capabilities. These improvements are necessary both for maximizing the likelihood that Swift finds a counterpart, and minimizing the impact that follow-up activities have on other Swift science priorities. We outline areas of improvement to the observing strategy itself for optimal tiling of the LVC localization regions. We also discuss ongoing work on operational upgrades that will decrease latency in our response time, and minimize impact on pre-planned observations, while maintaining spacecraft health and safety.

The DESGW program is a collaboration between members of the Dark Energy Survey, the wider astronomical community, and the LIGO-Virgo Collaboration to search for optical counterparts of gravitational wave events, such as those expected from binary neutron star mergers or neutron star-black hole mergers. While binary black hole (BBH) events are not expected to produce an electromagnetic (EM) signature, emission is certainly not impossible. The DESGW program has performed follow-up observations of four BBH events detected by LIGO in order to search for any possible EM counterpart. Failure to find such counterparts is still relevant in that it produces limits on optical emission from such events. This is a review of follow-up results from O1 BBH events and a discussion of the status of ongoing uniform re-analysis of all BBH events that DESGW has followed up to date.

Motivated by the prospect of the wealth of data arising from the inauguration of the era of gravitational wave detection by ground-based interferometers the DES collaboration, in partnership with members of the LIGO collaboration and members of the astronomical community at large, have established a research program to search for their optical counterparts and to explore their use as cosmological probes. In this talk we present the status of our program and discuss prospects for establishing this new probe as part of the portfolio of the Dark Energy research program in the future, in particular for the next generation survey, LSST.

On August 17, 2017 LIGO/Virgo detected a binary neutron star via gravitational waves. We observed 70 sq-degrees in the LIGO/Virgo spatial localization with the DECam on the 4m Blanco telescope covering 80% of the final map. Our group independently discovered an optical counterpart in NGC 4993. We searched our entire imaged region: the object in NGC 4993 was the only viable candidate. Our observations of NGC4993 show complicated morphology but simple star formation history. Our x-ray and radio observations indicate an off-axis jet as afterglow. Our high-cadence optical and infrared spectra show a source that must be described by at least two components, one of which is dominated by the r-process nucleosynthesis elements characteristic of a kilonova. Our modeling of the light curve demonstrates such a model in which 0.05 M⊙ of material is ejected from the system. Finally, we discuss the first standard siren measurement of H0.

We present the results of prompt optical follow-up of the electromagnetic counterpart of GW170817 by the Transient Optical Robotic Observatory of the South Collaboration (TOROS). We detected highly significant dimming in the light curves of the counterpart over the course of only 80 minutes of observations obtained ~35 hr after the trigger with the T80-South telescope. A second epoch of observations, obtained ~59 hr after the event with the EABA 1.5m telescope, confirms the fast fading nature of the transient. The observed colors of the counterpart suggest that this event was a “blue kilonova” relatively free of lanthanides.

AGILE is a space mission of the Italian Space Agency dedicated to γ-ray astrophysics, launched in 2007. AGILE performed dedicated real-time searches for possible γ-ray counterparts of gravitational wave (GW) events detected by the LIGO-Virgo scientific Collaboration (LVC) during the O2 observation run. We present a review of AGILE observations of GW events, starting with the first, GW150914, which was a test case for future searches. We focus here on the main characteristics of the observations of the most important GW events detected in 2017, i.e. GW170104 and GW170817. In particular, for the former event we published γ-ray upper limits (ULs) in the 50 MeV – 10 GeV energy band together with a detailed analysis of a candidate precursor event in the Mini-Calorimeter data. As for GW170817, we published a set of constraining γ-ray ULs obtained for integrations preceding and following the event time. These results allow us to establish important constraints on the γ-ray emission from a possible magnetar-like remnant in the first ~1000 s following T0. AGILE is a major player in the search of electromagnetic counterparts of GW events, and its enhanced detection capabilities in hard X-ray/MeV/GeV ranges will play a crucial role in the future O3 observing run.

The LIGO detectors have just completed a successful and exciting observation run. Both facilities are now undergoing upgrades and commissioning, including doubling the circulating power in the interferometer which will increase LIGO’s sensitivity above 100 Hz. This paper motivates the power increase and discusses the problems in general that arise with higher power and the progress to date with addressing them. Topics include input power noise coupling, parametric instability, and thermal effects.

Discovery of strongly-lensed gravitational wave (GW) sources will unveil binary compact objects at higher redshifts and lower intrinsic luminosities than is possible without lensing. Such systems will yield unprecedented constraints on the mass distribution in galaxy clusters, measurements of the polarization of GWs, tests of General Relativity, and constraints on the Hubble parameter. Excited by these prospects, and intrigued by the presence of so-called “heavy black holes” in the early detections by LIGO-Virgo, we commenced a search for strongly-lensed GWs and possible electromagnetic counterparts in the latter stages of the second LIGO observing run (O2). Here, we summarise our calculation of the detection rate of strongly-lensed GWs, describe our review of BBH detections from O1, outline our observing strategy in O2, summarize our follow-up observations of GW170814, and discuss the future prospects of detection.

The LIGO direct-detection of gravitational waves arriving from cosmic sources—now, happily including (as of this meeting!) the merging of two neutron stars—opens a new chapter in our understanding of physics itself: for General Relativity, conceptually so extremely simple, has robustly produced predictions that have invariably been found to be correct when tested. My poster (page 3 of this paper) is intended for high school students who have just learned simple algebra. My derivation of the famous E = mc2 from the Pythagorean Theorem necessarily requires an algebraic expansion that is due to Newton, but apart from that it is simplicity itself: a transparent introduction to what all of physics is today: the construction of mathematics that, miraculously, reproduces our observations of the world—and which also successfully predicts the results of future observations—as so magnificently demonstrated at this glorious Symposium!