Abstracts of Interest
Selected by:
Rami Alsulami
Abstract: 2208.11597
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Title:VERITAS highlights of observations and results
Download PDFAbstract: Located in southern Arizona, VERITAS is amongst the most sensitive detectors for astrophysical very high energy (VHE; E>100 GeV) gamma rays and has been operational since April 2007. We highlight some recent results from VERITAS observations. These include the long-term observations of the gamma-ray binaries HESS J0632+057 and LS I +61° 303, the observations of the Galactic Center region, and of the supernova remnant Cas~A. We discuss the results from a decade of multi-wavelength observations of the blazar 1ES 1215+303, the EHT 2017 campaign on the M87 galaxy, the discovery of 3C 264 in VHE, and the observation of three flaring quasars. Brief highlights of the indirect dark matter searches and targets-of-opportunity (ToO) observations are also discussed. The ToO observations allow for rapid follow-up of multi-messenger alerts and astrophysical transients.
Abstract: 2208.11968
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Title:X-ray view of a merging supermassive black hole binary candidate SDSSJ1430+2303: results from the first ~200 days observations
Download PDFAbstract: Recently we discovered an unprecedented supermassive black hole binary (SMBHB) candidate in the nearby Seyfert galaxy SDSS J1430+2303, predicted to merge within three years. X-ray spectroscopy may bring unique kinematic evidence for the last inspiraling stage, when the binary is too close to allow each of them to hold an individual broad line region. We try to confirm the unique SMBHB merger event and understand the associated high-energy processes from a comprehensive X-ray view. We observed SDSS J1430+2303 with XMM-Newton, NuSTAR}, Chandra and Swift spanning the first $\sim200$ days since its discovery. X-ray variability, up to a factor of 7, has been detected on a time scale of a few days. The broad band spectrum from 0.2-70 keV can be well fitted with a model consisting of a powerlaw and a relativistic reflection covered by a warm absorber. The properties of the warm absorber changed dramatically, e.g., with a decrease of the line-of-sight velocity from ~0.2c to ~0.02c, between the two XMM-Newton observations separated by only 19 days, which can be naturally understood in the context of the SMBHB although the clumpy wind scenario can not be completely excluded. Broad Fe K$\alpha$ emission has been robustly detected though its velocity shift or profile change is not yet measurable. Further longer X-ray observations are highly encouraged to detect the expected orbital motion of the binary.
Abstract: 2208.12075
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Title:Two-dimensional particle simulation of the boundary between a hot pair plasma and magnetized electrons and protons: out-of-plane magnetic field
Download PDFAbstract: By means of a particle-in-cell (PIC) simulation, we study the interaction between a uniform magnetized ambient electron-proton plasma at rest and an unmagnetized pair plasma, which we inject at one simulation boundary with a mildly relativistic mean speed and temperature. The magnetic field points out of the simulation plane. The injected pair plasma expels the magnetic field and piles it up at its front. It traps ambient electrons and drags them across the protons. An electric field grows, which accelerates protons into the pair cloud's expansion direction. This electromagnetic pulse separates the pair cloud from the ambient plasma. Electrons and positrons, which drift in the pulse's nonuniform field, trigger an instability that disrupts the current sheet ahead of the pulse. The wave vector of the growing perturbation is orthogonal to the magnetic field direction and magnetic tension cannot stabilize it. The electromagnetic pulse becomes permeable for pair plasma, which forms new electromagnetic pulses ahead of the initial one. A transition layer develops with a thickness of a few proton skin depths, in which protons and positrons are accelerated by strong electromagnetic fields. Protons form dense clumps surrounded by a strong magnetic field. The thickness of the transition layer grows less rapidly than we would expect from the typical speeds of the pair plasma particles and the latter transfer momentum to protons; hence, the transition layer acts as a discontinuity, separating the pair plasma from the ambient plasma. Such a discontinuity is an important building block for astrophysical pair plasma jets.
Abstract: 2208.11137
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Full Text: [ PostScript, PDF]
Title:Properties of shocked dust grains in supernova remnants
Download PDFAbstract: Shockwaves driven by supernovae both destroy dust and reprocess the surviving grains, greatly affecting the resulting dust properties of the interstellar medium (ISM). While these processes have been extensively studied theoretically, observational constraints are limited. We use physically-motivated models of dust emission to fit the infrared (IR) spectral energy distributions of seven Galactic supernova remnants, allowing us to determine the distribution of dust mass between diffuse and dense gas phases, and between large and small grain sizes. We find that the dense ($\sim 10^3 \,{\rm cm}^{-3}$), relatively cool ($\sim 10^3 \, {\rm K}$) gas phase contains $>90\%$ of the dust mass, making the warm dust located in the X-ray emitting plasma ($\sim 1 \,{\rm cm}^{-3}$/$10^6 \, {\rm K}$) a negligible fraction of the total, despite dominating the mid-IR emission. The ratio of small ($\lesssim 10 \, {\rm nm}$) to large ($\gtrsim 0.1 \, {\rm \mu m}$) grains in the cold component is consistent with that in the ISM, and possibly even higher, whereas the hot phase is almost entirely devoid of small grains. This suggests that grain shattering, which processes large grains into smaller ones, is ineffective in the low-density gas, contrary to model predictions. Single-phase models of dust destruction in the ISM, which do not account for the existence of the cold swept-up material containing most of the dust mass, are likely to greatly overestimate the rate of dust destruction by supernovae.
Abstract: 2208.11704
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Title:Weighing the Local Interstellar Medium using Gamma Rays and Dust
Download PDFAbstract: Cold gas forms a significant mass fraction of the Milky Way disk, but is its most uncertain baryonic component. The density and distribution of cold gas is of critical importance for Milky Way dynamics, as well as models of stellar and galactic evolution. Previous studies have used correlations between gas and dust to obtain high-resolution measurements of cold gas, but with large normalization uncertainties. We present a novel approach that uses Fermi-LAT $\gamma$-ray data to measure the total gas density, achieving a similar precision as previous works, but with independent systematic uncertainties. Notably, our results have sufficient precision to distinguish between the tension in current world-leading experiments.
Abstract: 2208.12030
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Title:Catastrophic Cooling in Superwinds. III. Non-equilibrium Photoionization
Download PDFAbstract: Observations of some starburst-driven galactic superwinds suggest that strong radiative cooling could play a key role in the nature of feedback and the formation of stars and molecular gas in star-forming galaxies. These catastrophically cooling superwinds are not adequately described by adiabatic fluid models, but they can be reproduced by incorporating non-equilibrium radiative cooling functions into the fluid model. In this work, we have employed the atomic and cooling module MAIHEM implemented in the framework of the FLASH hydrodynamics code to simulate the formation of radiatively cooling superwinds as well as their corresponding non-equilibrium ionization (NEI) states for various outflow parameters, gas metallicities, and ambient densities. We employ the photoionization program CLOUDY to predict radiation- and density-bounded photoionization for these radiatively cooling superwinds, and we predict UV and optical line emission. Our non-equilibrium photoionization models built with the NEI states demonstrate the enhancement of C IV, especially in metal-rich, catastrophically cooling outflows, and O VI in metal-poor ones.
Abstract: 2208.12193
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Title:Dropouts of Fully Stripped Ions in the Solar Wind: A Diagnostic for Wave Heating versus Reconnection
Download PDFAbstract: The SWICS instrument aboard the ACE satellite has detected frequent intervals in the slow solar wind and interplanetary coronal mass ejections (ICMEs) in which C6+ and other fully stripped ions are strongly depleted, though the ionization states of elements such as Si and Fe indicate that those ions should be present. It has been suggested that these outlier or dropout events can be explained by the resonant cyclotron heating process, because these ions all have the same cyclotron frequency as He2+. We investigate the region in the corona where these outlier events form. It must be above the ionization freeze-in height and the transition to collisionless plasma conditions, but low enough that the wind still feels the effects of solar gravity. We suggest that the dropout events correspond to relatively dense blobs of gas in which the heating is reduced because local variations in the Alfven speed change the reflection of Alfven waves and the turbulent cascade. As a result, the wave power at the cyclotron frequency of the fully stripped ions is absorbed by He2+ and may not be able to heat the other fully-stripped ions enough to overcome solar gravity. If this picture is borne out, it may help to discriminate between resonant cyclotron heating and stochastic heating models of the solar wind.
Abstract: 2208.11871
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Full Text: [ PostScript, PDF]
Title:Tight Constraint on the Maximum Mass of Stellar-origin Binary Black Holes and Evidence for Hierarchical Mergers in Gravitational Wave Observations
Download PDFAbstract: The origins of the coalescing binary black holes (BBHs) detected by the advanced LIGO/Virgo are still under debate, and clues may present in the joint mass-spin distribution of these merger events. Here we construct phenomenological models to investigate the BBH population detected in gravitational observations. The data can be well explained by the members originated from two different channels: one is the evolution of field binaries, and the other is the dynamical assembly. We obtain a tight constraint on the maximum mass for events of the stellar-origin, which is $m_{\rm max}=39.4^{+2.6}_{-2.5}M_{\odot}$ at 90\% credibility. This mass cutoff likely arises from the (pulsational) pair-instability supernova explosion and/or stellar winds. We also find that a fraction of $4-17\%$ of dynamical events were hierarchical mergers, and these BHs had an average spin magnitude significantly larger than the first-generation mergers, with ${\rm d}\mu_{\rm a} > 0.4 $ at $99\%$ credibility.
Abstract: 2208.13997
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Title:Discovery of Peculiar Radio Morphologies with ASKAP using Unsupervised Machine Learning}
Download PDFAbstract: We present a set of peculiar radio sources detected using an unsupervised machine learning method. We use data from the Australian Square Kilometre Array Pathfinder (ASKAP) telescope to train a self-organizing map (SOM). The radio maps from three ASKAP surveys, Evolutionary Map of Universe pilot survey (EMU-PS), Deep Investigation of Neutral Gas Origins pilot survey (DINGO) and Survey With ASKAP of GAMA-09 + X-ray (SWAG-X), are used to search for the rarest or unknown radio morphologies. We use an extension of the SOM algorithm that implements rotation and flipping invariance on astronomical sources. The SOM is trained using the images of all "complex" radio sources in the EMU-PS which we define as all sources catalogued as "multi-component". The trained SOM is then used to estimate a similarity score for complex sources in all surveys. We select 0.5\% of the sources that are most complex according to the similarity metric, and visually examine them to find the rarest radio morphologies. Among these, we find two new odd radio circle (ORC) candidates and five other peculiar morphologies. We discuss multiwavelength properties and the optical/infrared counterparts of selected peculiar sources. In addition, we present examples of conventional radio morphologies including: diffuse emission from galaxy clusters, and resolved, bent-tailed, and FR-I and FR-II type radio galaxies. We discuss the overdense environment that may be the reason behind the circular shape of ORC candidates.
Abstract: 2208.14240
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Title:CORSIKA 8 -- the next-generation air shower simulation framework
Download PDFAbstract: For more than 20 years, the community has heavily relied on CORSIKA for the simulation of extensive air showers, their Cherenkov light emission and their radio signals. While tremendously successful, the Fortran-based monolithic design of CORSIKA up to version 7 limits adaptation to new experimental needs, for example in complex scenarios where showers transition from air into dense media, and to new computing paradigms such as the use of multi-core and GPU parallelization. With CORSIKA 8, we have reimplemented the core functionality of CORSIKA in a modern, modular, C++-based simulation framework, and successfully validated it against CORSIKA 7. Here, we discuss the philosophy of CORSIKA 8, showcase some example applications, and present the current state of implementation as well as the plans for the future.
Abstract: 2208.14258
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Full Text: [ PostScript, PDF]
Title:Reconstructing inclined extensive air showers from radio measurements
Download PDFAbstract: We present a reconstruction algorithm for extensive air showers with zenith angles between 65$^\circ$ and 85$^\circ$ measured with radio antennas in the 30-80 MHz band. Our algorithm is based on a signal model derived from CoREAS simulations which explicitly takes into account the asymmetries introduced by the superposition of charge-excess and geomagnetic radiation as well as by early-late effects. We exploit correlations among fit parameters to reduce the dimensionality and thus ensure stability of the fit procedure. Our approach reaches a reconstruction efficiency near 100% with an intrinsic resolution for the reconstruction of the electromagnetic energy of well below 5\%. It can be employed in upcoming large-scale radio detection arrays using the 30-80 MHz band, in particular the AugerPrime Radio detector of the Pierre Auger Observatory, and can likely be adapted to experiments such as GRAND operating at higher frequencies.
Abstract: 2208.14186
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Title:Updated constraints on WIMP dark matter by radio observations of M31 -- other annihilation channels
Download PDFAbstract: This brief paper generalizes dark matter (DM) constraints recently derived in [A.E.Egorov, Phys. Rev. D 106, 023023 (2022)] by radio observations of M31 to all possible annihilation channels (except the cases of neutrinos and photons as primary annihilation products). All the methodology here exactly repeats that in the mentioned paper, where only two representative and popular annihilation channels - $\chi\chi \rightarrow b\overline{b}$ and $\chi\chi \rightarrow \tau^+\tau^-$ - were considered. It is confirmed here, that in the case of light primary annihilation products $\chi\chi \rightarrow \tau^+\tau^-, \mu^+\mu^-,gg,c\overline{c},u\overline{u},d\overline{d},s\overline{s},e^+e^-,b\overline{b}$ (and an arbitrary combination of them) the fiducial (averaged over uncertainties) lower mass limit for the thermal weakly interacting massive particle (WIMP) is confined in the range $\approx$(40-70) GeV, which is bounded by $\chi\chi \rightarrow b\overline{b},\tau^+\tau^-$ cases. Heavier WIMP, which can annihilate to $W^+W^-,Z^0Z^0,t\overline{t},hh$; can not be probed at the level of thermal cross section, unless one assumes the optimistic cases of DM density and magnetic field distributions in M31. In conclusion, $m_x \gtrsim 40$ GeV represents the fiducial channel-independent mass limit for the thermal WIMP with the full uncertainty range estimated to be $\approx$(20-90) GeV.
Abstract: 2208.13794
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Title:Seeking dark matter with $γ$-ray attenuation
Download PDFAbstract: The flux of high-energy astrophysical $\gamma$ rays is attenuated by the production of electron-positron pairs from scattering off of extragalactic background light (EBL). We use the most up-to-date information on galaxy populations to compute their contributions to the pair-production optical depth. We find that the optical depth inferred from $\gamma$-ray measurements exceeds that expected from galaxies at the $\sim2\sigma$ level. If the excess is modeled as a frequency-independent re-scaling of the standard contribution to the EBL from galaxies, then it is detected at the $2.7\sigma$ level (an overall $14-30\%$ increase of the EBL). If the frequency dependence of the excess is instead modeled as a two-photon decay of a dark-matter axion, then the excess is favored over the null hypothesis of no excess at the $2.1\sigma$ confidence level. While we find no evidence for a dark-matter signal, the analysis sets the strongest current bounds on the photon-axion coupling over the $8-25$ eV mass range.
Abstract: 2208.13999
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Title:Exploiting the Einstein Telescope to solve the Hubble tension
Download PDFAbstract: We probe four cosmological models which, potentially, can solve the Hubble tension according to the dark energy equation of state. In this context, we demonstrate that the Einstein Telescope is capable of achieving a relative accuracy below $1\%$ on the Hubble constant independently of the specific dark energy model. We firstly build mock catalogs containing gravitational wave events for one, five and ten years of observations, and above Signal-to-Noise Ratio equal to nine. From these catalogs, we extract the events which are most likely associated with possible electromagnetic counterpart detected by THESEUS. Finally, we select four dark energy models, namely a non-flat $\omega$CDM, an interacting dark energy, an emergent dark energy, and a time varying gravitational constant model, to forecast the precision down to which the Einstein Telescope can bound the corresponding cosmological parameters. We foresee that the Hubble constant is always constrained with less than $1\%$ uncertainty, thereby offering a potential solution to the Hubble tension. The accuracy on the other cosmological parameters is at most comparable with the one currently obtained using multiple probes, except for the emergent dark energy model for which the Einstein Telescope alone will be able to improve the current limits by more than one order of magnitude.
Abstract: 2208.13222
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Title:Rapid decline in the lightcurves of luminous supernovae by jet-driven bipolar explosions
Download PDFAbstract: We calculate the lightcurves of jet-driven bipolar core collapse supernova (CCSN) explosions into a bipolar circumstellar mater (CSM) and show that an equatorial observer finds the lightcurves to possess a rapid, and even an abrupt, drop. The scenario that might lead to such an explosion morphology is a common envelope evolution (CEE) where shortly before the CCSN explosion the RSG progenitor interacts with a more compact companion that spirals-in and spins-up the core. The companion can be a main sequence star, a neutron star, or a black hole. The binary interaction ejects a shell through an intensive wind and the CEE ejects a denser gas in the equatorial plane. We assume that the companion accretes mass and launches jets. We conduct three-dimensional (3D) hydrodynamical simulations where we launch weak jets, the shaping jets, into the dense shell and show that the interaction forms a bipolar CSM. As a result of the rapid pre-collapse core rotation jets drive the CCSN explosion. We simulate the interaction of the jets with the bipolar CSM and use a simple scheme to calculate the lightcurves. We show that the abrupt drop in the lightcurve of an observer not too close to the polar directions can account for the lightcurve of the hydrogen poor luminous supernova (LSN) SN 2018don. Our study strengthens the claim that jet-driven explosions account for many, even most, CCSNe.
Abstract: 2208.13792
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Full Text: [ PostScript, PDF]
Title:Neutrino search from γ-ray bursts during the prompt and X-ray afterglow phases using 10 years of IceCube public data
Download PDFAbstract: Neutrino emission from gamma-ray bursts (GRBs) has been sought for a long time, and stringent limits on the most accredited GRB emission models have been obtained from IceCube. Multi-wavelength GRB observations of the last decades improved our knowledge of the GRB emission parameters, such as the Lorentz factor and the luminosity, which can vary from one GRB to another by several orders of magnitude. Empirical correlations among such parameters have been identified during the prompt phase, with direct implications on GRB models. In this work, we use the PSLab open-access code, developed for IceCube data analyses, to search for individual neutrino emission from the prompt and afterglow phases of selected GRBs, and for stacking emission from the ensemble of such GRBs. For the afterglow phase, we focus in particular on GRBs with X-ray flares and plateaus. While past stacking searches assumed the same GRB fluence at Earth, we present a stacking scheme based on physically motivated GRB weights. Moreover, we conceive a new methodology for the prompt phase that uses the empirical correlations to infer the GRB luminosity and Lorentz factor, when redshift measurements are not available. We do not observe any significant neutrino excess. Hence, we set constraints on the GRB neutrino fluxes and on relevant GRB parameters, including the magnetic field in the jet. Notably, the baryon loading is found to be <10 for typical GRB prompts, thus disfavoring a baryonic-dominated origin of the GRB ejecta.
Abstract: 2208.14245
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Title:The all-particle energy spectrum of cosmic rays from 10 TeV to 1 PeV measured with HAWC
Download PDFAbstract: The HAWC observatory is an air-shower detector, which is designed to study both astrophysical gamma-rays in the TeV region and galactic cosmic rays in the energy interval from 1 TeV to 1 PeV. This energy regime is quite interesting for cosmic ray research, since indirect observations overlap with direct measurements, which offers the opportunity for cross calibration and studies of experimental systematic errors in both techniques. One quantity that could help for this purpose is the all-particle energy spectrum of cosmic rays. In this work, we present an update of HAWC measurements on the total cosmic-ray energy spectrum between 10 TeV and 1 PeV. The spectrum was obtained from an unfolding analysis of almost two years of HAWC's data, which was collected from January, 2018 to December, 2019. For the energy estimation, we employed the high-energy hadronic interaction model QGSJET-II-04. The results show the presence of a knee-like structure around tens of TeVs, which was previously reported by the HAWC collaboration in 2017.
Abstract: 2208.14300
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Full Text: [ PostScript, PDF]
Title:Results on high energy galactic cosmic rays from the DAMPE space mission
Download PDFAbstract: DAMPE (Dark Matter Particle Explorer) is a satellite-born experiment launched in 2015 in a sun-synchronous orbit at 500 km altitude, and it has been taking data in stable conditions ever since. Its main goals include the spectral measurements of cosmic electrons and positrons, protons, nuclei and gamma rays, up to very high energies. The detector's main features include the 32 radiation lengths deep calorimeter and large geometric acceptance, making DAMPE one of the most powerful space instruments in operation, covering with high statistics and small systematics the high energy frontier up to several hundreds TeV. The results of different species spectral measurements will be shown and discussed.
Abstract: 2208.14320
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Full Text: [ PostScript, PDF]
Title:Expanding Fireball in Magnetar Bursts and Fast Radio Bursts
Download PDFAbstract: A fireball of radiation plasma created near the surface of a neutron star (NS) expands under its own pressure along magnetic field lines, and produces photon emission and relativistic matter outflow. We comprehensively classify the expanding fireball evolution into five cases and obtain the photospheric luminosity and the kinetic energy of the outflow, taking into account key processes; lateral diffusion of photons escaping from a magnetic flux tube, effects of strong magnetic field, baryon loading from the NS surface, and radiative acceleration via cyclotron resonant scattering, some of which have not been considered in the context of gamma-ray bursts. Applying our model to magnetar bursts with fast radio bursts (FRBs), in particular the X-ray short bursts from SGR 1935+2154 associated with the Galactic FRB 20200428A, we show that the burst radiation can accelerate the outflow to high Lorentz factor with sufficient energy to power FRBs.
Abstract: 2208.14333
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Full Text: [ PostScript, PDF]
Title:Detection of GeV emission from an ultra-long gamma-ray burst with the Fermi Large Area Telescope
Download PDFAbstract: GRB 220627A, detected by Fermi GBM, shows two episodes of gamma-ray emission, which are separated by a {$\sim$700} s-long quiescent phase. Due to similar temporal shapes and spectra in the two episodes, GRB 220627A is speculated to be a gravitationally-lensed GRB. We analyze the Fermi-LAT data and find that about 49 gamma-ray photons above 100 MeV come from the GRB during the first episode, while there is no GeV photons detected in the second episode. Based on the broad-band spectral study of the two episodes, the gravitationally-lensing scenario can be ruled out at a high confidence level and we thus conclude that GRB 220627A is an intrinsically ultra-long GRB with the prompt burst emission lasting longer than 1000 s. It is then the first case that GeV emission is detected from an ultra-long GRB. We find that a short spike seen in the LAT light curve is also present in GBM detectors that see the burst, suggesting a common internal region of emission across the entire Fermi energy range. The detection of a 15.7-GeV photon during the early prompt phase places a lower limit of $\Gamma\ge300$ on the bulk Lorentz factor of the GRB ejecta. The constraint on the bulk Lorentz factor could shed light on the origin of ultra-long GRBs.
Abstract: 2208.11794
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Full Text: [ PostScript, PDF]
Title:Climate Change and Astronomy: A Look at Long-Term Trends on Maunakea
Download PDFAbstract: Maunakea is one of the world's primary sites for astronomical observing, with multiple telescopes operating over sub-millimeter to optical wavelengths. With its summit higher than 4200 meters above sea level, Maunakea is an ideal location for astronomy with an historically dry, stable climate and minimal turbulence above the summit. Under a changing climate, however, we ask how the (above-) summit conditions may have evolved in recent decades since the site was first selected as an observatory location, and how future-proof the site might be to continued change. We use data from a range of sources, including in-situ meteorological observations, radiosonde profiles, and numerical reanalyses to construct a climatology at Maunakea over the previous 40 years. We are interested in both the meteorological conditions (e.g., wind speed and humidity), and the image quality (e.g., seeing). We find that meteorological conditions were, in general, relatively stable over the period with few statistically significant trends and with quasi-cyclical inter-annual variability in astronomically significant parameters such as temperature and precipitable water vapour. We do, however, find that maximum wind speeds have increased over the past decades, with the frequency of wind speeds above 15~m~s$^{-1}$ increasing in frequency by 1--2%, which may have a significant impact on ground-layer turbulence. Importantly, we find that the Fried parameter has not changed in the last 40 years, suggesting there has not been an increase in optical turbulence strength above the summit. Ultimately, more data and data sources-including profiling instruments-are needed at the site to ensure continued monitoring into the future and to detect changes in the summit climate.
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