Late-time Observations Research Articles

Primordial black hole dark matter from inflation: The reverse engineering approach

Constraining the inflationary epoch is one of the aims of modern cosmology. In order to fully exploit current and future small-scale observations, it is necessary to devise tools to directly relate them to the early Universe's dynamics. We present here a novel reverse engineering approach able to connect fundamental late-time observables to consistent inflationary dynamics and, eventually, to the inflaton potential. Employing this procedure, we are able to describe which conditions can give rise to a raised plateau in the power spectrum of curvature perturbations at small scales, which are not constrained by CMB observations. Within this new phenomenologically driven approach, we find that inflation can generate a raised plateau in the spectrum of curvature perturbations that potentially connects three fundamental observables; a dominant component of the dark matter in the form of asteroid-mass/atomic-size primordial black holes, detectable signals in stochastic gravitational waves, and a subdominant fraction of stellar-mass primordial black holes mergers.

Multiwavelength study of the luminous GRB 210619B observed with Fermi and ASIM

ABSTRACT We report on detailed multiwavelength observations and analysis of the very bright and long GRB 210619B, detected by the Atmosphere-Space Interactions Monitor installed on the International Space Station and the Gamma-ray Burst Monitor (GBM) on-board the Fermi mission. Our main goal is to understand the radiation mechanisms and jet composition of GRB 210619B. With a measured redshift of z = 1.937, we find that GRB 210619B falls within the 10 most luminous bursts observed by Fermi so far. The energy-resolved prompt emission light curve of GRB 210619B exhibits an extremely bright hard emission pulse followed by softer/longer emission pulses. The low-energy photon index (αpt) values obtained using the time-resolved spectral analysis of the burst suggest a transition between the thermal (during harder pulse) to non-thermal (during softer pulse) outflow. We examine the correlation between spectral parameters and find that both peak energy and αpt exhibit the flux tracking pattern. The late time broad-band photometric data set can be explained within the framework of the external forward shock model with νm < νc < νx (where νm, νc, and νx are the synchrotron peak, cooling-break, and X-ray frequencies, respectively) spectral regime supporting a rarely observed hard electron energy index (p < 2). We find moderate values of host extinction of E(B − V) = 0.14 ± 0.01 mag for the small magellanic cloud extinction law. In addition, we also report late-time optical observations with the 10.4 m Gran Telescopio de Canarias placing deep upper limits for the host galaxy (z = 1.937), favouring a faint, dwarf host for the burst.

Field-based physical inference from peculiar velocity tracers

ABSTRACT We present a proof-of-concept Bayesian hierarchical modelling approach to reconstruct the initial cosmic matter density field constrained by peculiar velocity observations. Using a model for the gravitational evolution of dark matter to connect the initial conditions to late-time observations, it reconstructs the late-time density and velocity fields as natural byproducts. We implement this field-based physical inference approach by adapting the Bayesian Origin Reconstruction from Galaxies ($\small {\rm BORG}$) algorithm, which explores the high-dimensional posterior through the use of Hamiltonian Monte Carlo sampling. We test the self-consistency of the method using random sets of tracers, and assess its accuracy in a more complex scenario where peculiar velocity tracers are mock haloes drawn from $\small {\rm GADGET2}$ N-body simulations. We find that our framework self-consistently infers the initial conditions, density and velocity fields, and shows some robustness to model mis-specification. Compared with the approach of constrained Gaussian random fields/Wiener filtering, the hierarchical model produces more accurate final density and velocity field reconstructions. It also allows us to constrain the initial conditions by peculiar velocity observations, complementing in this aspect other field-based approaches based on alternative cosmological observables such as galaxy clustering or weak lensing.

Supernova double-peaked light curves from double-nickel distribution

Among supernovae (SNe) of different luminosities, many double-peaked light curves (LCs) have been observed, representing a broad morphological variety. In this work, we investigate which of these can be modelled by assuming a double-peaked distribution of their radioactive material, as originally proposed for SN2005bf. The inner zone corresponds to the regular explosive nucleosynthesis and extends outwards, according to the usual scenario of mixing. The outer 56Ni-rich shell may be related to the effect of jet-like outflows that have interacted with more distant portions of the star before the arrival of the SN shock. As the outer layer is covered by matter that is optically less thick, its energy emerges earlier and generates a first peak of radiation. To investigate this scenario in more detail, we have applied our hydrodynamic code that follows the shock propagation through the progenitor star and takes into account the effect of the γ-ray photons produced by the decay of the radioactive isotopes. We present a simple parametric model for the 56Ni abundance profile and explore the consequences on the LC of individually varying the quantities that define this distribution, setting our focus onto the stripped-envelope progenitors. In this first study, we are interested in the applicability of this model to SNe that have not been classified as superluminous, thus, we have selected our parameter space accordingly. Then, within the same mathematical prescription for the 56Ni -profile, we revisited the modelling process for a series of objects: SN2005bf, PTF2011mnb, SN2019cad, and SN2008D. In some cases, a decrease in the gamma ray opacity is required to fit the late time observations. We also discuss the other cases in which this scenario might be likely to explain the LC morphology. A steep initial decline in the observed bolometric LC within less than few days after the explosion becomes less feasible for this model, because it requires a large abundance of 56Ni near the stellar surface, indicating a strongly inverted distribution. An initial bolometric rise before the two peaks seems more favourable for the double-nickel case, particularly as it can be difficult to explain through other scenarios, unless a combination of power sources is invoked.

Probing parity violation with the four-point correlation function of BOSS galaxies

Parity-violating physics in the early Universe can leave detectable traces in late-time observables. Whilst vector- and tensor-type parity-violation can be observed in the $B$-modes of the cosmic microwave background, scalar-type signatures are visible only in the four-point correlation function (4PCF) and beyond. This work presents a blind test for parity-violation in the 4PCF of the BOSS CMASS sample, considering galaxy separations in the range $[20,160]h^{-1}\mathrm{Mpc}$. The parity-odd 4PCF contains no contributions from standard $\Lambda$CDM physics and can be efficiently measured using recently developed estimators. Data are analyzed using both a non-parametric rank test (comparing the BOSS 4PCFs to those of realistic simulations) and a compressed $\chi^2$ analysis, with the former avoiding the assumption of a Gaussian likelihood. These find similar results, with the rank test giving a detection probability of $99.6\%$ ($2.9\sigma$). This provides significant evidence for parity-violation, either from cosmological sources or systematics. We perform a number of systematic tests: although these do not reveal any observational artefacts, we cannot exclude the possibility that our detection is caused by the simulations not faithfully representing the statistical properties of the BOSS data. Our measurements can be used to constrain physical models of parity-violation. As an example, we consider a coupling between the inflaton and a $U(1)$ gauge field and place bounds on the latter's energy density, which are several orders of magnitude stronger than those previously reported. Upcoming probes such as DESI and Euclid will reveal whether our detection of parity-violation is due to new physics, and strengthen the bounds on a variety of models.

Updated Photometry of the Yellow Supergiant Progenitor and Late-time Observations of the Type IIb Supernova SN 2016gkg

We present Hubble Space Telescope (HST) observations of the Type IIb supernova (SN) SN 2016gkg at 652, 1698, and 1795 days from explosion with the Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3). Comparing to pre-explosion imaging from 2001 obtained with the Wide Field Planetary Camera 2, we demonstrate that SN 2016gkg is now fainter than its candidate counterpart in the latest WFC3 imaging, implying that the counterpart has disappeared and confirming that it was the SN progenitor star. We show the latest light curve and Keck spectroscopy of SN 2016gkg, which imply that SN 2016gkg is declining more slowly than the expected rate for 56Co decay during its nebular phase. We find that this emission is too luminous to be powered by other radioisotopes and infer that SN 2016gkg is entering a new phase in its evolution where it is powered primarily by interaction with circumstellar matter. Finally, we reanalyze the progenitor star spectral energy distribution and late-time limits in the context of binary evolution models. Including emission from a potential companion star, we find that all such predicted companion stars would be fainter than our limiting magnitudes.

Tale of GRB 171010A/SN 2017htp and GRB 171205A/SN 2017iuk: Magnetar origin?

We present late-time optical follow-up observations of GRB 171010A/SN 2017htp (z = 0.33) and low-luminosity GRB 171205A/SN 2017iuk (z = 0.037) acquired using the 4K×4K CCD Imager mounted at the 3.6 m Devasthal Optical Telescope (3.6 m DOT) along with the prompt emission data analysis of these two interesting bursts. The prompt characteristics (other than brightness) such as spectral hardness, T90, and minimum variability time-scale are comparable for both the bursts. The isotropic X-ray and kinetic energies of the plateau phase of GRB 171205A are found to be less than the maximum energy budget of magnetars, supporting magnetar as a central engine powering source. The new optical data of SN 2017htp and SN 2017iuk presented here, along with published ones, indicate that SN 2017htp is one of the brightest and SN 21017iuk is among the faintest GRB associated SNe (GRB–SNe). Semi-analytical light-curve modelling of SN 2017htp, SN 2017iuk and only known GRB associated superluminous supernova (SLSN 2011kl) are performed using the MINIM code. The model with a spin-down millisecond magnetar as a central engine powering source nicely reproduced the bolometric light curves of all three GRB–SNe mentioned above. The magnetar central engines for SN 2017htp, SN 2017iuk, and SLSN 2011kl exhibit values of initial spin periods higher and magnetic fields closer to those observed for long GRBs and H-deficient SLSNe. Detection of these rare events at such late epochs also demonstrates the capabilities of the 3.6 m DOT for deep imaging considering longitudinal advantage in the era of time-domain astronomy.

The late-time light curves of Type Ia supernovae: confronting models with observations

ABSTRACT Type Ia supernovae (SNe Ia) play a crucial role as standardizable candles in measurements of the Hubble constant and dark energy. Increasing evidence points towards multiple possible explosion channels as the origin of normal SNe Ia, with possible systematic effects on the determination of cosmological parameters. We present, for the first time, a comprehensive comparison of publicly available SN Ia model nucleosynthetic data with observations of late-time light curve observations of SN Ia events. These models span a wide range of white dwarf (WD) progenitor masses, metallicities, explosion channels, and numerical methodologies. We focus on the influence of 57Ni and its isobaric decay product 57Co in powering the late-time (t > 1000 d) light curves of SNe Ia. 57Ni and 57Co are neutron-rich relative to the more abundant radioisotope 56Ni, and are consequently a sensitive probe of neutronization at the higher densities of near-Chandrashekhar (near-MCh) progenitor WDs. We demonstrate that observations of one SN Ia event, SN 2015F is only consistent with a sub-Chandrasekhar (sub-MCh) WD progenitor. Observations of four other events (SN 2011fe, SN 2012cg, SN 2014J, and SN2013aa) are consistent with both near-MCh and sub-MCh progenitors. Continued observations of late-time light curves of nearby SNe Ia will provide crucial information on the nature of the SN Ia progenitors.

Late-time X-ray observations of the transient source Cygnus A-2

ABSTRACT We examine Chandra observations of the powerful Fanaroff–Riley class II (FR II) radio galaxy Cygnus A for an X-ray counterpart to the radio transient Cygnus A-2 that was first detected in 2011. Observations are performed using the High-Resolution Camera (HRC) instrument in order to spatially resolve Cygnus A-2 and the central active galactic nucleus (AGN) at a separation of 0.′′42. Simulated images are generated of the emission region, and radial profiles for the region of interest are extracted. A comparison between the simulations and observations reveals no X-ray detection of Cygnus A-2 to a 0.5–7.0 keV flux upper limit of $1.04 \times 10^{-12}\rm \, erg\, cm^{-2}\, s^{-1}$, or a rest-frame 2–10 keV luminosity of $8.6\times 10^{42}\rm \, erg\, s^{-1}$. We estimate the black hole mass of Cygnus A-2 based on our X-ray flux limit and find it to be consistent with a flaring black hole rather than a steadily accreting source. The HRC observations are additionally compared with archival Advanced CCD Imaging Spectrometer (ACIS) data from 2016 to 2017, and both the overall morphology and the flux limits of the AGN complex agree between the two data sets. This consistency is despite the pile-up effect in ACIS which was previously considered to bias the observed morphology of the AGN. The agreement between the data sets demonstrates the viability of utilizing the archival Chandra data of Cygnus A to analyse its AGN at an unprecedented level of precision.

Light-curve Evolution of the Nearest Tidal Disruption Event: A Late-time, Radio-only Flare

Abstract Tidal disruption events (TDEs) occur when a star passes close enough to a galaxy’s supermassive black hole to be disrupted by tidal forces. We discuss new observations of IGRJ12580+0134, a TDE observed in NGC 4845 (d = 17 Mpc) in 2010 November, with the Karl G. Jansky Very Large Array (VLA 9 9 The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. ). We also discuss a reanalysis of 2010–2011 Swift and XMM-Newton observations, as well as new, late-time Swift observations. Our JVLA observations show a decay of the nuclear radio flux until 2015, when a plateau was seen, and then a significant (factor ∼3) radio flare during 2016. The 2016 radio flare was also accompanied by radio spectral changes, but was not seen in the X-rays. We model the flare as resulting from the interaction of the nuclear jet with a cloud in the interstellar medium. This is distinct from late-time X-ray flares in a few other TDEs where changes in the accretion state and/or a fallback event were suggested, neither of which appears possible in this case. Our reanalysis of the Swift and XMM-Newton data from 2011 shows significant evidence for thermal emission from a disk, as well as a very soft power law. This, in addition to the extreme X-ray flux increase seen in 2010 (a factor of >100) bolsters the identification of IGRJ12580+0134 as a TDE, not an unusual active galactic nucleus variability event.

Still Brighter than Pre-explosion, SN 2012Z Did Not Disappear: Comparing Hubble Space Telescope Observations a Decade Apart

Abstract Type Iax supernovae (SNe Iax) represent the largest class of peculiar white dwarf supernovae. The type Iax SN 2012Z in NGC 1309 is the only white dwarf supernova with a detected progenitor system in pre-explosion observations. Deep Hubble Space Telescope (HST) images taken before SN 2012Z show a luminous, blue source that we have interpreted as a helium-star companion (donor) to the exploding white dwarf. We present here late-time HST observations taken ∼1400 days after the explosion to test this model. We find the SN light curve can empirically be fit by an exponential-decay model in magnitude units. The fitted asymptotic brightness is within 10% of our latest measurements and approximately twice the brightness of the pre-explosion source. The decline of the light curve is too slow to be powered by 56Co or 57Co decay: if radioactive decay is the dominate power source, it must be from longer half-life species like 55Fe. Interaction with circumstellar material may contribute to the light curve, as may shock heating of the companion star. Companion-star models underpredict the observed flux in the optical, producing most of their flux in the UV at these epochs. A radioactively heated bound remnant, left after only a partial disruption of the white dwarf, is also capable of producing the observed excess late-time flux. Our analysis suggests that the total ejecta + remnant mass is consistent with the Chandrasekhar mass for a range of SNe Iax.

Nebular-phase spectra of Type Ia supernovae from the Las Cumbres Observatory Global Supernova Project

ABSTRACT The observed diversity in Type Ia supernovae (SNe Ia) – the thermonuclear explosions of carbon–oxygen white dwarf stars used as cosmological standard candles – is currently met with a variety of explosion models and progenitor scenarios. To help improve our understanding of whether and how often different models contribute to the occurrence of SNe Ia and their assorted properties, we present a comprehensive analysis of seven nearby SNe Ia. We obtained one to two epochs of optical spectra with Gemini Observatory during the nebular phase (>200 d past peak) for each of these events, all of which had time series of photometry and spectroscopy at early times (the first ∼8 weeks after explosion). We use the combination of early- and late-time observations to assess the predictions of various models for the explosion (e.g. double-detonation, off-centre detonation, stellar collisions), progenitor star (e.g. ejecta mass, metallicity), and binary companion (e.g. another white dwarf or a non-degenerate star). Overall, we find general consistency in our observations with spherically symmetric models for SN Ia explosions, and with scenarios in which the binary companion is another degenerate star. We also present an in-depth analysis of SN 2017fzw, a member of the subgroup of SNe Ia which appear to be transitional between the subluminous ‘91bg-like’ events and normal SNe Ia, and for which nebular-phase spectra are rare.

Mass assembly history of dark matter haloes in the light of H0 tension

ABSTRACT The Hubble tension may introduce a new course of action to revise the standard Lambda cold dark matter (ΛCDM) model to unravel dark energy and dark matter physics. The Hubble parameter can be reconstructed by late-time observations of the background evolution model independently. We relate the reconstructed Hubble parameter to the structure formation and large-scale structure observables in this work. We use excursion set theory to calculate the number density of dark matter haloes and the mass function of progenitors. We obtain results for both the Markov and non-Markov extensions of excursion set theory in the context of spherical and ellipsoidal collapse. We show that the number density of dark matter haloes in the reconstructed model has ∼2σ difference in comparison with the Planck 2018 ΛCDM in the mass range M ≳ 1012 M⊙. We also compare the dark matter halo progenitor mass function with the pair-galaxy statistics and their mass assembly history from observational data of the Hubble Space Telescope Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey. Due to complications in distinguishing the ratio of accretion and merger in mass assembly, our result on the pair fraction is for illustration only. However, the ∼5 times more accurate observations will be promising for distinguishing the reconstructed model and the Planck 2018 ΛCDM.

The Late-Time Light Curves of Type Ia Supernovae: Confronting Models with Observations

Type Ia supernovae (SNe Ia) play a crucial role as standardizable candles in measurements of the Hubble constant and dark energy. Increasing evidence points towards multiple possible explosion channels as the origin of normal SNe Ia, with possible systematic effects on the determination of cosmological parameters. We present, for the first time, a comprehensive comparison of publicly-available SN Ia model nucleosynthetic data with observations of late-time light curve observations of SN Ia events. These models span a wide range of white dwarf (WD) progenitor masses, metallicities, explosion channels, and numerical methodologies. We focus on the influence of $^{57}$Ni and its isobaric decay product $^{57}$Co in powering the late-time ($t > 1000$ d) light curves of SNe Ia. $^{57}$Ni and $^{57}$Co are neutron-rich relative to the more abundant radioisotope $^{56}$Ni, and are consequently a sensitive probe of neutronization at the higher densities of near-Chandrashekhar (near-$M_{\rm Ch}$) progenitor WDs. We demonstrate that observations of one SN Ia event, SN 2015F is only consistent with a sub-$M_{\rm Ch}$ WD progenitor. Observations of four other events (SN 2011fe, SN 2012cg, SN 2014J, SN2013aa) are consistent with both near-$M_{\rm Ch}$ and sub-$M_{\rm Ch}$ progenitors. Continued observations of late-time light curves of nearby SNe Ia will provide crucial information on the nature of the SN Ia progenitors.

AT 2018lqh and the Nature of the Emerging Population of Day-scale Duration Optical Transients

Abstract We report on the discovery of AT 2018lqh (ZTF 18abfzgpl)—a rapidly evolving extragalactic transient in a star-forming host at 242 Mpc. The transient g-band light curve’s duration above a half-maximum light is about 2.1 days, where 0.4/1.7 days are spent on the rise/decay, respectively. The estimated bolometric light curve of this object peaked at about 7 × 1042erg s−1—roughly 7 times brighter than the neutron star (NS)–NS merger event AT 2017gfo. We show that this event can be explained by an explosion with a fast (v ∼ 0.08 c) low-mass (≈0.07 M ⊙) ejecta, composed mostly of radioactive elements. For example, ejecta dominated by 56Ni with a timescale of t 0 ≅ 1.6 days for the ejecta to become optically thin for γ-rays fits the data well. Such a scenario requires burning at densities that are typically found in the envelopes of neutron stars or the cores of white dwarfs. A combination of circumstellar material (CSM) interaction power at early times and shock cooling at late times is consistent with the photometric observations, but the observed spectrum of the event may pose some challenges for this scenario. We argue that the observations are not consistent with a shock breakout from a stellar envelope, while a model involving a low-mass ejecta ramming into low-mass CSM cannot explain both the early- and late-time observations.

Late-time Hubble Space Telescope Observations of a Hydrogen-poor Superluminous Supernova Reveal the Power-law Decline of a Magnetar Central Engine

Abstract The light-curve diversity of hydrogen-poor superluminous supernovae (SLSNe) has kept open the possibility that multiple power sources account for the population. Specifically, pair-instability explosions (PISNe), which produce large masses of 56Ni, have been argued as the origin of some slowly-evolving SLSNe. Here we present detailed observations of SN 2016inl (=PS16fgt), a slowly-evolving SLSN at z = 0.3057, whose unusually red spectrum matches PS1-14bj, an SLSN with an exceptionally long rise time consistent with a PISN. Ground-based and Hubble Space Telescope data, spanning about 800 rest-frame days, reveal a significant light-curve flattening, similar to that seen in SN 2015bn and much slower than the decline rate expected from radioactive decay of 56Co. We therefore conclude that despite its slow evolution, SN 2016inl is inconsistent with a PISN. Instead, the light-curve evolution matches the expected power-law spindown of a magnetar central engine, but with a shallower power law (L ∝ t −2.8) compared to that in SN 2015bn, indicating a possible difference in the γ-ray opacity between the two events. Analytical modeling indicates typical magnetar engine parameters, but one of the highest ejecta masses (≈20 M ⊙) inferred for an SLSN. Our results indicate that monitoring the late-time light-curve evolution of SLSNe provides a powerful diagnostic of their energy source.

Multi-interacting dark energy and its cosmological implications

In the effort to define the main features a successful solution to the Hubble tension should have, growing evidence has emerged pointing to the need for models able to modify the expansion (and possibly thermal) history of the universe both prior and after recombination, and that could thereby restore the overall concordance between early- and late-time observations without introducing nor worsening other cosmological tensions in the process. In precisely this spirit, here we consider a multi-interacting dark energy model with two complementary interaction channels: one with the dark matter and one with the photons. The former most significantly affects the matter dominated epoch as well as the very late universe, and has been shown to be able to significantly resolve the $S_8$ tension. The latter has been introduced in this work to allow for a larger and natural time dependence of the evolution of the universe since it mostly impacts the radiation dominated epoch as well as the temperature scaling of the photons, as extensively explained in the text. As a result, considering data from Planck+BAO+Pantheon+KV450+DES (which can be combined since the $S_8$ value is lowered even neglecting the weak lensing data) we find that the significance of the $H_0$ tension only reduces to about 3.5$\sigma$, while that of the $S_8$ tension falls below the 2$\sigma$ level. Also, the statistical analysis we perform strongly favors $\Lambda$CDM in all considered cases. Overall, we conclude that the specific multi-interacting dark energy model considered here, despite its broad generality and very rich cosmological phenomenology, cannot successfully restore the aforementioned overall concordance between early- and late-time observations.

Blast from the past: constraining progenitor models of SN 1972E

ABSTRACT We present a novel technique to study Type Ia supernovae (SNe Ia) by constraining surviving companions of historical extragalactic SN by combining archival photographic plates and Hubble Space Telescope(HST) imaging. We demonstrate this technique for Supernova 1972E, the nearest known SN Ia in 125 yr. Some models of SNe Ia describe a white dwarf with a non-degenerate companion that donates enough mass to trigger thermonuclear detonation. Hydrodynamic simulations and stellar evolution models show that these donor stars will survive the explosion, and show increased luminosity for at least a 1000 yr. Thus, late-time observations of the exact location of a supernova can constrain the presence of a surviving donor star and progenitor models. We find the explosion site of SN 1972E by analysing 17 digitized photographic plates taken with the European Southern Observatory 1-m Schmidt and 1 plate taken with the Cerro Tololo Inter-American Observatory 1.5-m telescope. Using the Gaia eDR3 catalogue to determine Supernova 1972E’s location yields: α = 13h39m52${_{.}^{\rm s}}$708 ± 0${_{.}^{\rm s}}$004 and δ = −31°40’9${_{.}^{\prime\prime}}$00 ± 0${_{.}^{\prime\prime}}$04 (ICRS). In 2005, HST/ACS imaged the host galaxy of SN 1972E with the F435W, F555W, and F814W filters covering the explosion site. The nearest detected source is offset by 3.0 times our positional precision, and is inconsistent with the colours expected of a surviving donor star. Thus, the limiting magnitude of the HST observation (F555W > 28 mag) rules out all He star companion models and the most luminous main-sequence companion model currently in the literature. The remaining main-sequence companion models could be tested with a 10 orbit HST exposure in the F606W filter.

Cutting cosmological correlators

The initial conditions of our universe appear to us in the form of a classical probability distribution that we probe with cosmological observations. In the current leading paradigm, this probability distribution arises from a quantum mechanical wavefunction of the universe. Here we ask what the imprint of quantum mechanics is on the late time observables. We show that the requirement of unitary time evolution, colloquially the conservation of probabilities, fixes the analytic structure of the wavefunction and of all the cosmological correlators it encodes. In particular, we derive in perturbation theory an infinite set of single-cut rules that generalize the Cosmological Optical Theorem and relate a certain discontinuity of any tree-level n-point function to that of lower-point functions. Our rules are closely related to, but distinct from the recently derived Cosmological Cutting Rules. They follow from the choice of the Bunch-Davies vacuum and a simple property of the (bulk-to-bulk) propagator and are astoundingly general: we prove that they are valid for fields with a linear dispersion relation and any mass, any integer spin and arbitrary local interactions with any number of derivatives. They also apply to general FLRW spacetimes admitting a Bunch-Davies vacuum, including de Sitter, slow-roll inflation, power-law cosmologies and even resonant oscillations in axion monodromy. We verify the single-cut rules in a number of non-trivial examples, including four massless scalars exchanging a massive scalar, as relevant for cosmological collider physics, four gravitons exchanging a graviton, and a scalar five-point function.

Late-time radio observations of the short GRB 200522A: constraints on the magnetar model

ABSTRACT GRB 200522A is a short duration gamma-ray burst (GRB) at redshift z= 0.554 characterized by a bright infrared counterpart. A possible, although not unambiguous, interpretation of the observed emission is the onset of a luminous kilonova powered by a rapidly rotating and highly magnetized neutron star, known as magnetar. A bright radio flare, arising from the interaction of the kilonova ejecta with the surrounding medium, is a prediction of this model. Whereas the available data set remains open to multiple interpretations (e.g. afterglow, r-process kilonova, magnetar-powered kilonova), long-term radio monitoring of this burst may be key to discriminate between models. We present our late-time upper limit on the radio emission of GRB 200522A, carried out with the Karl G. Jansky Very Large Array at 288 d after the burst. For kilonova ejecta with energy Eej $\approx 10^{53}\, \rm erg$, as expected for a long-lived magnetar remnant, we can already rule out ejecta masses $M_{\rm ej}\lesssim 0.03\, \mathrm{M}_\odot$ for the most likely range of circumburst densities n ≳ 10−3 cm−3. Observations on timescales of ≈ 3–10 yr after the merger will probe larger ejecta masses up to Mej ∼ 0.1 M⊙, providing a robust test to the magnetar scenario.