Abstracts of Interest
Selected by:
Violet Harvey
Abstract: arxiv:2211.01737
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Title:Selected results from IceCube
Download PDFAbstract: Neutrino astronomy saw its birth with the discovery by IceCube of a diffuse flux at energies above 60 TeV with intensity comparable to a predicted upper limit to the flux from extra-galactic sources of ultra-high energy cosmic rays (UHECRs). While such an upper limit corresponds to the case of calorimetric sources, in which cosmic rays lose all their energy into photo-pion production, the first statistically significant coincident observation between neutrinos and gamma rays was observed from a blazar of intriguing nature. A very-high-energy muon event, of most probable neutrino energy of 290 TeV for an $E^{-2.13}$ spectrum, alerted other observatories triggering a large number of investigations in many bands of the electromagnetic (EM) spectrum. A high gamma-ray state from the blazar was revealed soon after the event and in a follow-up to about 40 days. A posteriori observations also in the optical and radio bands indicated a rise of the flux from the TXS 0506+056 blazar. A previous excess of events of the duration of more than 100~d was observed by IceCube with higher significance than the alert itself. These observations triggered more complex modeling than simple one-zone proton synchrotron models for proton acceleration in jets of active galactic nuclei (AGNs) and more observations across the EM spectrum. A second piece of evidence was a steady excess of about 50 neutrino events with reconstructed soft spectrum in a sample of lower energy well-reconstructed muon events than the alert event. A hot spot was identified in a catalog of 110 gamma-ray intense emitters and starburst galaxies in a direction compatible with NGC 1068 with a significance of $2.9\sigma$. NGC 1068 hosts a mildly relativistic jet in a starburst galaxy, seen not from the jet direction but rather through the torus. This Seyfert II galaxy is at only 14.4~Mpc from the Earth. We discuss these observations.
Abstract: arxiv:2211.04460
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Title:Hidden Hearts of Neutrino Active Galaxies
Download PDFAbstract: Recent multimessenger studies have provided evidence for high-energy neutrino sources that are opaque to GeV-TeV gamma-rays. We investigate the connection between high-energy neutrinos and gamma-rays in the active galaxy NGC 1068, and find that the neutrinos most likely come from regions within about 100 Schwarzschild radii. This is especially the case if neutrinos are produced via the photomeson production process, although the constraints could be alleviated if hadronuclear interactions are dominant. We consider the most favorable neutrino production regions, and discuss coronae, jets, winds, and their interactions with dense material. The results strengthen the importance of understanding dissipation mechanisms near the coronal region and the base of outflows. There could be a connection between active galactic nuclei with near-Eddington accretion and tidal disruptions events, in that neutrinos are produced in the obscured vicinity of supermassive black holes.
Abstract: arxiv:2211.02493
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Title:Proton Synchrotron, an explanation for possible extended VHE gamma-ray activity of TXS 0506+056 in 2017
Download PDFAbstract: TXS 0506+056, a source of the extreme energy neutrino event, IceCube-170922A, was observed on 22 September 2017. The Fermi-LAT detector reported high energy (HE) $\gamma$-ray flare between 100 MeV and 100 GeV starting from 15 September 2017 from this source. Several attempts to trace the very high energy (VHE) gamma-ray counterparts around the IceCube-170922A resulted in no success. Only after 28 September, the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes observed the first VHE gamma-rays from the blazar above 100 GeV. The $\sim$ 41 hr survey resulted in VHE-$\gamma$ ray activity till 31 October 2017. Here we propose the extended GeV $\gamma-$rays can be explained by taking two production channels, electron synchrotron self Compton and proton synchrotron for HE and VHE emissions, respectively. The 45 days of VHE emission from the peak of the HE-flare can be explained with $ {L_p'}{\simeq}10^{47}$ erg/sec in the jet frame and magnetic field of 2.4 G, consistent with the ${L}_{Edd}$ for a blackhole mass $5\times 10^{9} {M}_\odot$
Abstract: arxiv:2211.00661
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Title:Combined X-ray and optical analysis to probe the origin of the plateau emission in $γ$-ray bursts afterglows
Download PDFAbstract: A large fraction of gamma-ray bursts (GRBs) shows a plateau phase during the X-ray afterglow emission, whose physical origin is still debated. In this work we define a sample of 30 GRBs with simultaneous X-ray and optical data during and after the plateau phase. Through a time-resolved spectral analysis of the X-ray plateaus, we test the consistency of the unabsorbed optical fluxes with those obtained via X-ray-to-optical spectral extrapolation by assuming a synchrotron spectrum. Combining X-ray with optical data, we find that 63% (19/30) GRBs are compatible with a single synchrotron spectrum thus suggesting that both the optical and X-ray radiations are produced from a single emitting region. For these GRBs we derive the temporal evolution of the break frequency and we compare it with the expectations predicted by several models. For 11/30 GRBs the optical emission is above the predicted range of values extrapolated from the X-rays in at least one temporal bin of the light curve. These GRBs may not be explained with a single zone emission, indicating the necessity of invoking two cooperating processes in order to explain the broad band spectral behaviour during X-ray plateaus. We discuss our findings in the framework of different scenarios invoked to explain the plateau feature, including the energy injection from a spinning-down magnetar and the high latitude emission from a structured jet.
Abstract: arxiv:2211.00686
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Title:Constraints on Electron Acceleration in Gamma-Ray Bursts Afterglows from Radio Peaks
Download PDFAbstract: Studies of gamma-ray bursts (GRBs) and their multi-wavelength afterglows have led to insights in electron acceleration and emission properties from relativistic, high-energy astrophysical sources. Broadband modeling across the electromagnetic spectrum has been the primary means of investigating the physics behind these sources, although independent diagnostic tools have been developed to inform and corroborate assumptions made in particle acceleration simulations and broadband studies. We present a methodology to constrain three physical parameters related to electron acceleration in GRB blast waves: the fraction of shock energy in electrons, $\epsilon_e$; the fraction of electrons that gets accelerated into a power-law distribution of energies, $\xi_e$; and the minimum Lorentz factor of the accelerated electrons, $\gamma_m$. These parameters are constrained by observations of the peaks in radio afterglow light curves and spectral energy distributions. From a sample of 49 radio afterglows, we are able to find narrow distributions for these parameters, hinting at possible universality of the blast wave microphysics, although observational bias could play a role in this. Using radio peaks and considerations related to the prompt gamma-ray emission efficiency, we constrain the allowed parameter ranges for both $\epsilon_e$ and $\xi_e$ to within about one order of magnitude, $0.01\lesssim\epsilon_e\lesssim0.2$ and $0.1\lesssim\xi_e\lesssim1$. Such stringent constraints are inaccessible for $\xi_e$ from broadband studies due to model degeneracies.
Abstract: arxiv:2211.01516
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Title:Afterglow Polarization from Off-Axis GRB Jets
Download PDFAbstract: As we further our studies on Gamma-ray bursts (GRBs), both on theoretical models and observational tools, more and more options begin to open for exploration of its physical properties. As transient events primarily dominated by synchrotron radiation, it is expected that the synchrotron photons emitted by GRBs should present some degree of polarization throughout the evolution of the burst. Whereas observing this polarization can still be challenging due to the constraints on observational tools, especially for short GRBs, it is paramount that the groundwork is laid for the day we have abundant data. In this work, we present a polarization model linked with an off-axis spreading top-hat jet synchrotron scenario in a stratified environment with a density profile $n(r)\propto r^ {-k}$. We present this model's expected temporal polarization evolution for a realistic set of afterglow parameters constrained within the values observed in the GRB literature for four degrees of stratification $k=0,1,1.5 {\rm \, and\,} 2$ and two magnetic field configurations with high extreme anisotropy. We apply this model and predict polarization from a set of GRBs exhibiting off-axis afterglow emission. In particular, for GRB 170817A, we use the available polarimetric upper limits to rule out the possibility of a extremely anisotropic configuration for the magnetic field.
Abstract: arxiv:2211.00940
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Title:Continuous gravitational wave detection to understand the generation mechanism of fast radio bursts
Download PDFAbstract: Since the unexpected discovery of fast radio bursts (FRBs), researchers have proposed varied theories and models to explain their phenomena. One such model that has recently been developed incorporates the so-called Gertsenshtein-Zel'dovich (GZ) effect, which states that when gravitational waves traverse the pulsar magnetosphere, a portion of their gravitational radiation is transformed into electromagnetic (EM) radiation. The observed properties of FRBs are consistent with the properties of this EM radiation, implying, remarkably, that the GZ effect can account for both repeating and non-repeating FRBs. If this model is correct, the pulsar's properties should not change over time, and it would continue to emit both EM dipole and gravitational quadrupole radiation for a long period of time. This article targets the gravitational radiation produced by the pulsar mechanism and shows that several proposed gravitational wave detectors can detect these gravitational waves. If such detections are performed in the future from the positions of FRBs, it will validate the GZ process for FRB production and can rule out several other FRB theories.
Abstract: arxiv:2211.01172
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Title:Calculation of rescaling factors and nuclear multiplication of muons in extensive air showers
Download PDFAbstract: Recent results obtained from leading cosmic ray experiments indicate that simulations using LHC-tuned hadronic interaction models underestimate the number of muons in extensive air showers compared to experimental data. This is the so-called muon deficit problem. Determination of the muon component in the air shower is crucial for inferring the mass of the primary particle, which is a key ingredient in the efforts to pinpoint the sources of ultra-high energy cosmic this http URL this paper, we present a new method to derive the muon signal in detectors, which uses the difference between the total reconstructed (data) and simulated signals is roughly independent of the zenith angle, but depends on the mass of the primary cosmic ray. Such a method offers an opportunity not only to test/calibrate the hadronic interaction models, but also to derive the $\beta$ exponent, which describes an increase of the number of muons in a shower as a function of the energy and mass of the primary cosmic ray. Detailed simulations show a dependence of the $\beta$ exponent on hadronic interaction properties, thus the determination of this parameter is important for understanding the muon deficit problem. We validate the method by using Monte Carlo simulations for the EPOS-LHC and QGSJetII-04 hadronic interaction models, and showing that this method allows us to recover the ratio of the muon signal between EPOS-LHC and QGSJetII-04 and the average $\beta$ exponent for the studied system, within less than a few percent. This is a consequence of the good recovery of the muon signal for each primary included in the analysis.
Abstract: arxiv:2211.01445
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Title:The apparent eta Carinae's long-term evolution and the critical role played by the strengthening of P Cygni absorption lines
Download PDFAbstract: Over the entire 20th century, Eta Carinae (\ec) has displayed a unique spectrum, which recently has been evolving towards that of a typical LBV. The two competing scenarios to explain such evolution are: (1) a dissipating occulter in front of a stable star or (2) a decreasing mass loss rate of the star. The first mechanism simultaneously explains why the central star appears to be secularly increasing its apparent brightness while its luminosity does not change; why the Homunculus' apparent brightness remains almost constant; and why the spectrum seen in direct light is becoming more similar to that reflected from the Homunculus (and which resembles a typical LBV). The second scenario does not account for these facts and predicts an increase in the terminal speed of the wind, contrary to observations. In this work, we present new data showing that the P Cygni absorption lines are secularly strengthening, which is not the expected behaviour for a decreasing wind-density scenario. CMFGEN modelling of the primary's wind with a small occulter in front agrees with observations. One could argue that invoking a dissipating coronagraphic occulter makes this object even more peculiar than it already appears to be. However, on the contrary, it solves the apparent contradictions between many observations. Moreover, by assigning the long-term behaviour to circumstellar causes and the periodic variations due to binarity, a star more stable after the 1900s than previously thought is revealed, contrary to the earlier paradigm of an unpredictable object.
Abstract: arxiv:2211.01619
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Title:The Steady-State Multi-TeV Diffuse Gamma-Ray Emission Predicted with GALPROP and Prospects for the Cherenkov Telescope Array
Download PDFAbstract: Cosmic Rays (CRs) interact with the diffuse gas, radiation, and magnetic fields in the interstellar medium (ISM) to produce electromagnetic emissions that are a significant component of the all-sky flux across a broad wavelength range. The Fermi Large Area Telescope (LAT) has measured these emissions at GeV $\gamma$-ray energies with high statistics. Meanwhile, the High-Energy Stereoscopic System (H.E.S.S.) telescope array has observed large-scale Galactic diffuse emission in the TeV $\gamma$-ray energy range. The emissions observed at GeV and TeV energies are connected by the common origin of the CR particles injected by the sources, but the energy dependence of the mixture from the general ISM (true `diffuse'), those emanating from the relatively nearby interstellar space about the sources, and the sources themselves, is not well understood. In this paper, we investigate predictions of the broadband emissions using the GALPROP code over a grid of steady-state 3D models that include variations over CR sources, and other ISM target distributions. We compare, in particular, the model predictions in the VHE ($\geq$100 GeV) $\gamma$-ray range with the H.E.S.S. Galactic plane survey (HGPS) after carefully subtracting emission from catalogued $\gamma$-ray sources. Accounting for the unresolved source contribution, and the systematic uncertainty of the HGPS, we find that the GALPROP model predictions agree with lower estimates for the HGPS source-subtracted diffuse flux. We discuss the implications of the modelling results for interpretation of data from the next generation Cherenkov Telescope Array (CTA).
Abstract: arxiv:2211.02028
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Title:Neutrino Origin of LHAASO's 18 TeV GRB221009A Photon
Download PDFAbstract: LHAASO collaboration detected photons with energy above 10 TeV from the most recent gamma-ray burst (GRB), GRB221009A. Given the redshift of this event, $z\sim 0.15$, photons of such energy are expected to interact with the diffuse extragalactic background light (EBL) well before reaching Earth. In this paper we provide the first neutrino-related explanation of the most energetic 18 TeV event reported by LHAASO. We find that the minimal viable scenario involves both mixing and transition magnetic moment portal between light and sterile neutrinos. The production of sterile neutrinos occurs efficiently via mixing while the transition magnetic moment portal governs the decay rate in the parameter space where tree-level decays via mixing to non-photon final states are suppressed. Our explanation of this event, while being consistent with the terrestrial constraints, points to the non-standard cosmology.
Abstract: arxiv:2211.04057
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Title:Deciphering the ~18 TeV photons from GRB 221009A
Download PDFAbstract: On 9 October, 2022, an extremely powerful gamma-ray burst, GRB 221009A, was detected by several instruments. Despite being obstructed by the Milky Way galaxy, its afterglow outburst outshone all other GRBs seen before. LHAASO detected several thousands very-high energy photons extending up to 18 TeV. Detection of such energetic photons are unexpected due to the large opacity of the Universe. It is possible that in the afterglow epoch the intrinsic very high-energy photon flux from the source might have increased manifolds, which could compensate the attenuation by pair-production with the extragalactic background light. We propose such a scenario and show that very high-energy photons can be observed on the Earth from the interaction of very-high energy protons with the seed synchrotron photons in the external forward shock region of the GRB jet.
Abstract: arxiv:2211.02059
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Title:Evidence for multiple shocks from the $γ$-ray emission of RS Ophiuchi
Download PDFAbstract: In August of 2021, Fermi-LAT, H.E.S.S., and MAGIC detected GeV and TeV $\gamma$-ray emission from an outburst of recurrent nova RS Ophiuchi. This detection represents the first very high energy $\gamma$-rays observed from a nova, and opens a new window to study particle acceleration. Both H.E.S.S. and MAGIC described the observed $\gamma$-rays as arising from a single, external shock. In this paper, we perform detailed, multi-zone modeling of RS Ophiuchi's 2021 outburst including a self-consistent prescription for particle acceleration and magnetic field amplification. We demonstrate that, contrary to previous work, a single shock cannot simultaneously explain RS Ophiuchi's GeV and TeV emission, particularly the spectral shape and distinct light curve peaks. Instead, we put forward a model involving multiple shocks that reproduces the observed $\gamma$-ray spectrum and temporal evolution. The simultaneous appearance of multiple distinct velocity components in the nova optical spectrum over the first several days of the outburst supports the presence of distinct shocks, which may arise either from the strong latitudinal dependence of the density of the external circumbinary medium (e.g., in the binary equatorial plane versus the poles) or due to internal collisions within the white dwarf ejecta (as powers the $\gamma$-ray emission in classical novae).
Abstract: arxiv:2211.02857
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Title:Constraining the sources of ultra-high-energy cosmic rays across and above the ankle with the spectrum and composition data measured at the Pierre Auger Observatory
Download PDFAbstract: In this work we present the interpretation of the energy spectrum and mass composition data as measured by the Pierre Auger Collaboration above $6 \times 10^{17}$ eV. We use an astrophysical model with two extragalactic source populations to model the hardening of the cosmic-ray flux at around $5\times 10^{18}$ eV (the so-called "ankle" feature) as a transition between these two components. We find our data to be well reproduced if sources above the ankle emit a mixed composition with a hard spectrum and a low rigidity cutoff. The component below the ankle is required to have a very soft spectrum and a mix of protons and intermediate-mass nuclei. The origin of this intermediate-mass component is not well constrained and it could originate from either Galactic or extragalactic sources. To the aim of evaluating our capability to constrain astrophysical models, we discuss the impact on the fit results of the main experimental systematic uncertainties and of the assumptions about quantities affecting the air shower development as well as the propagation and redshift distribution of injected ultra-high-energy cosmic rays (UHECRs).
Abstract: arxiv:2211.03086
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Title:Uncertainties of the 30-408 MHz Galactic emission as a calibration source for radio detectors in astroparticle physics
Download PDFAbstract: Context. Arrays of radio antennas have proven to be successful in astroparticle physics with the observation of extensive air showers initiated by high-energy cosmic rays in the Earth's atmosphere. Accurate determination of the energy scale of the primary particles' energies requires an absolute calibration of the radio antennas for which, in recent years, the utilization of the Galactic emission as a reference source has emerged as a potential standard. Aims. To apply the "Galactic Calibration", a proper estimation of the systematic uncertainties on the prediction of the Galactic emission from sky models is necessary, which we aim to determine on a global level as well as for the specific cases of selected radio arrays. We further aim to quantify the influence of the quiet Sun on the Galactic Calibration. Methods. We look at four different sky models that predict the full-sky Galactic emission in the frequency range from 30 to 408 MHz and compare them. We make an inventory of the reference maps on which they rely and use the output of the models to determine their global level of agreement. Next, we take the sky exposures and frequency bands of selected radio arrays into account and repeat the comparison for each of them. Finally, we study the relative influence of the Sun in its quiet state by projecting it onto the sky with brightness data from recent measurements. Results. We find systematic uncertainty of 12% on the predicted power from the Galactic emission, which scales to approximately half of that value as the uncertainty on the determination of the energy of cosmic particles. When looking at the selected radio arrays, the uncertainty on the predicted power varies between 10% and 19%. The influence of the quiet Sun turns out to be insignificant at the lowest frequencies but increases to a relative contribution of ~ 20% around 400 MHz.
Abstract: arxiv:2211.03400
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Title:A New Sample of Gamma-Ray Emitting Jetted Active Galactic Nuclei
Download PDFAbstract: We considered the fourth catalog of gamma-ray point sources produced by the Fermi Large Area Telescope (LAT) and selected only jetted active galactic nuclei (AGN) or sources with no specific classification, but with a low-frequency counterpart. Our final list is composed of 2980 gamma-ray point sources. We then searched for optical spectra in all the available literature and publicly available databases, to measure redshifts and to confirm or change the original LAT classification. Our final list of gamma-ray emitting jetted AGN is composed of BL Lac Objects (40%), flat-spectrum radio quasars (23%), misaligned AGN (2.8%), narrow-line Seyfert 1, Seyfert, and low-ionization nuclear emission-line region galaxies (1.9%). We also found a significant number of objects changing from one type to another, and vice versa (changing-look AGN, 1.1%). About 30% of gamma-ray sources still have an ambiguous classification or lack one altogether.
Abstract: arxiv:2211.03488
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Title:The cosmic ray ionisation and $γ$-ray budgets of star-forming galaxies
Download PDFAbstract: Cosmic rays in star-forming galaxies are a dominant source of both diffuse $\gamma$-ray emission and ionisation in gas too deeply shielded for photons to penetrate. Though the cosmic rays responsible for $\gamma$-rays and ionisation are of different energies, they are produced by the same star formation-driven sources, and thus galaxies' star formation rates, $\gamma$-ray luminosities, and ionisation rates should all be linked. In this paper we use up-to-date cross-section data to determine this relationship, finding that cosmic rays in a galaxy of star formation rate $\dot{M}_*$ and gas depletion time $t_\mathrm{dep}$ produce a maximum primary ionisation rate $\zeta \approx 1\times 10^{-16} (t_\mathrm{dep}/\mbox{Gyr})^{-1}$ s$^{-1}$ and a maximum $\gamma$-ray luminosity $L_\gamma\approx 4\times 10^{39} (\dot{M}_*/\mathrm{M}_\odot\mbox{ yr}^{-1})$ erg s$^{-1}$ in the 0.1 - 100 GeV band. These budgets imply either that the ionisation rates measured in Milky Way molecular clouds include a significant contribution from local sources that elevate them above the Galactic mean, or that CR-driven ionisation in the Milky Way is enhanced by sources not linked directly to star formation. Our results also imply that ionisation rates in starburst systems are only moderately enhanced compared to those in the Milky Way. Finally, we point out that measurements of $\gamma$-ray luminosities can be used to place constraints on galactic ionisation budgets in starburst galaxies that are nearly free of systematic uncertainties on the details of cosmic ray acceleration.
Abstract: arxiv:2211.03807
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Title:$γ$-ray and ultra-high energy neutrino background suppression due to solar radiation
Download PDFAbstract: The Sun emits copious amounts of photons and neutrinos in an approximately spatially isotropic distribution. Diffuse $\gamma$-rays and ultra-high energy (UHE) neutrinos from extragalactic sources may subsequently interact and annihilate with the emitted solar photons and neutrinos respectively. This will in turn induce an anisotropy in the cosmic ray background due to attenuation of the $\gamma$-ray and UHE neutrino flux by the solar radiation. Measuring this reduction, therefore, presents a simple and powerful astrophysical probe of electroweak interactions. In this letter we compute such anisotropies, which at the Earth (Sun) can be $\simeq 2\times 10^{-3}\,(0.5)\%$ and $\simeq 1\times 10^{-16}\,(2\times 10^{-14})\%$ for TeV scale $\gamma$-rays and PeV scale UHE neutrinos respectively. We briefly discuss exciting observational prospects for experiments such as the Fermi Gamma-Ray Space Telescope Large Area Telescope (Fermi LAT), High Energy Stereoscopic System (H.E.S.S), High-Altitude Water Cherenkov (HAWC) detector and IceCube. The potential for measuring $\gamma$-ray attenuation at orbital locations of other active satellites such as the Parker Solar Probe and James Webb Space Telescope is also explored.
Abstract: arxiv:2211.03747
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Title:Monte Carlo Techniques for Addressing Large Errors and Missing Data in Simulation-based Inference
Download PDFAbstract: Upcoming astronomical surveys will observe billions of galaxies across cosmic time, providing a unique opportunity to map the many pathways of galaxy assembly to an incredibly high resolution. However, the huge amount of data also poses an immediate computational challenge: current tools for inferring parameters from the light of galaxies take $\gtrsim 10$ hours per fit. This is prohibitively expensive. Simulation-based Inference (SBI) is a promising solution. However, it requires simulated data with identical characteristics to the observed data, whereas real astronomical surveys are often highly heterogeneous, with missing observations and variable uncertainties determined by sky and telescope conditions. Here we present a Monte Carlo technique for treating out-of-distribution measurement errors and missing data using standard SBI tools. We show that out-of-distribution measurement errors can be approximated by using standard SBI evaluations, and that missing data can be marginalized over using SBI evaluations over nearby data realizations in the training set. While these techniques slow the inference process from $\sim 1$ sec to $\sim 1.5$ min per object, this is still significantly faster than standard approaches while also dramatically expanding the applicability of SBI. This expanded regime has broad implications for future applications to astronomical surveys.
Abstract: arxiv:2211.03796
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Title:Astronomia ex machina: a history, primer, and outlook on neural networks in astronomy
Download PDFAbstract: In recent years, deep learning has infiltrated every field it has touched, reducing the need for specialist knowledge and automating the process of knowledge discovery from data. This review argues that astronomy is no different, and that we are currently in the midst of a deep learning revolution that is transforming the way we do astronomy. We trace the history of astronomical connectionism from the early days of multilayer perceptrons, through the second wave of convolutional and recurrent neural networks, to the current third wave of self-supervised and unsupervised deep learning. We then predict that we will soon enter a fourth wave of astronomical connectionism, in which finetuned versions of an all-encompassing 'foundation' model will replace expertly crafted deep learning models. We argue that such a model can only be brought about through a symbiotic relationship between astronomy and connectionism, whereby astronomy provides high quality multimodal data to train the foundation model, and in turn the foundation model is used to advance astronomical research.
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