arXiv subjects

Manuel Meyer

Publications and source records attributed to Manuel Meyer.

At least 37 records · Page 2Linked to original sources

arXiv2023

A first application of machine and deep learning for background rejection in the ALPS II TES detector

Axions and axion-like particles are hypothetical particles predicted in extensions of the standard model and are promising cold dark matter candidates. The Any Light Particle Search (ALPS II) experiment is a light-shining-through-the-wall experiment that aims to produce these particles from a strong light source and magnetic field and subsequently detect them through a reconversion into photons. With an expected rate $\sim$ 1 photon per day, a sensitive detection scheme needs to be employed and characterized. One foreseen detector is based on a transition edge sensor (TES). Here, we investigate machine and deep learning algorithms for the rejection of background events recorded with the TES. We also present a first application of convolutional neural networks to classify time series data measured with the TES.

hep-ex↗

arXiv2023

Interpretation of multi-TeV photons from GRB221009A

The nearby GRB221009A at redshift $z=0.1505$ has been observed up to a maximum energy of 18 TeV with the LHAASO air shower array. The expected optical depth for a photon with energy $E_γ=18$ TeV varies between 9.4 and 27.1 according to existing models of the extra-galactic background light (EBL) in the relevant mid infra-red range. The resulting suppression of the flux in several (but not all) EBL models makes it for these EBL models unlikely that this photon could have been observed at the claimed energy. If the photon event and its energy are confirmed and possibly even more photons above 10 TeV have been observed, the photon-pair production process would have to be suppressed by mechanisms predicted in extensions of the Standard Model of particle physics. We consider the possibilities of photon mixing with a light pseudo-scalar (e.g., axion-like particles; ALPs) in the magnetic field of the host galaxy and the Milky Way and Lorentz invariance violation (LIV). In the case of photon-ALP mixing, the boost factor would reach values $\sim10^6$ for photon couplings not ruled out by the CAST experiment, but limited by other astrophysical constraints. Viable scenarios would require either very efficient mixing in or near to the GRB or that the largest part of the total luminosity is radiated at TeV energies, different from previous GRB afterglows. In the case of LIV, required boost factors are achievable for a LIV breaking energy scale $\lesssim 2\times 10^{29}$~eV ($\lesssim 4\times 10^{21}$~eV) for the linear (quadratic) modification of the dispersion relation. A more simple explanation would be a misidentification of a charged cosmic-ray air shower.

astro-ph.HE↗

arXiv2022

Incremental Fermi Large Area Telescope Fourth Source Catalog

We present an incremental version (4FGL-DR3, for Data Release 3) of the fourth Fermi-LAT catalog of gamma-ray sources. Based on the first twelve years of science data in the energy range from 50 MeV to 1 TeV, it contains 6658 sources. The analysis improves on that used for the 4FGL catalog over eight years of data: more sources are fit with curved spectra, we introduce a more robust spectral parameterization for pulsars, and we extend the spectral points to 1 TeV. The spectral parameters, spectral energy distributions, and associations are updated for all sources. Light curves are rebuilt for all sources with 1 yr intervals (not 2 month intervals). Among the 5064 original 4FGL sources, 16 were deleted, 112 are formally below the detection threshold over 12 yr (but are kept in the list), while 74 are newly associated, 10 have an improved association, and seven associations were withdrawn. Pulsars are split explicitly between young and millisecond pulsars. Pulsars and binaries newly detected in LAT sources, as well as more than 100 newly classified blazars, are reported. We add three extended sources and 1607 new point sources, mostly just above the detection threshold, among which eight are considered identified, and 699 have a plausible counterpart at other wavelengths. We discuss degree-scale residuals to the global sky model and clusters of soft unassociated point sources close to the Galactic plane, which are possibly related to limitations of the interstellar emission model and missing extended sources.

astro-ph.HE↗

arXiv2022

The Future of Gamma-Ray Experiments in the MeV-EeV Range

Gamma-rays, the most energetic photons, carry information from the far reaches of extragalactic space with minimal interaction or loss of information. They bring messages about particle acceleration in environments so extreme they cannot be reproduced on earth for a closer look. Gamma-ray astrophysics is so complementary with collider work that particle physicists and astroparticle physicists are often one in the same. Gamma-ray instruments, especially the Fermi Gamma-ray Space Telescope, have been pivotal in major multi-messenger discoveries over the past decade. There is presently a great deal of interest and scientific expertise available to push forward new technologies, to plan and build space- and ground-based gamma-ray facilities, and to build multi-messenger networks with gamma rays at their core. It is therefore concerning that before the community comes together for planning exercises again, much of that infrastructure could be lost to a lack of long-term planning for support of gamma-ray astrophysics. Gamma-rays with energies from the MeV to the EeV band are therefore central to multiwavelength and multi-messenger studies to everything from astroparticle physics with compact objects, to dark matter studies with diffuse large scale structure. These goals and new discoveries have generated a wave of new gamma-ray facility proposals and programs. This paper highlights new and proposed gamma-ray technologies and facilities that have each been designed to address specific needs in the measurement of extreme astrophysical sources that probe some of the most pressing questions in fundamental physics for the next decade. The proposed instrumentation would also address the priorities laid out in the recent Astro2020 Decadal Survey, a complementary study by the astrophysics community that provides opportunities also relevant to Snowmass.

astro-ph.HE↗

arXiv2021

Relevance of photon-photon dispersion within the jet for blazar axionlike particle searches

Axionlike particles (ALPs) could mix with photons in the presence of astrophysical magnetic fields. Searching for this effect in gamma-ray observations of blazars has provided some of the strongest constraints on ALP parameter space so far. Previously, photon-photon dispersion of gamma-rays off of the CMB has been shown to be important for these calculations, and is universally included in ALP-photon mixing models. Here, we assess the effects of dispersion off of other photon fields within the blazar (produced by the accretion disk, the broad line region, the dust torus, starlight, and the synchrotron field) by modelling the jet and fields of the flat spectrum radio quasar 3C454.3 and propagating ALPs through the model both with and without the full dispersion calculation. We find that the full dispersion calculation can strongly affect the mixing, particularly at energies above 100 GeV -- often reducing the ALP-photon conversion probability. This could have implications for future searches planned with, e.g., the Cherenkov Telescope Array, particularly those looking for a reduced opacity of the universe at the highest energies.

astro-ph.HE↗

arXiv2021

CTA sensitivity for probing cosmology and fundamental physics with gamma rays

The Cherenkov Telescopic Array (CTA), the next-generation ground-based gamma-ray observatory, will have unprecedented sensitivity, providing answers to open questions in gamma-ray cosmology and fundamental physics. Using simulations of active galactic nuclei observations foreseen in the CTA Key Science Program, we find that CTA will measure gamma-ray absorption on the extragalactic background light with a statistical error below 15% up to the redshift of 2 and detect or establish limits on gamma halos induced by the intergalactic magnetic field of at least 0.3 pG. Extragalactic observations using CTA also demonstrate the potential for testing physics beyond the Standard Model. The best state-of-the-art constraints on the Lorentz invariance violation from astronomical gamma-ray observations will be improved at least two- to threefold. CTA will also probe the parameter space where axion-like particles can represent a significant proportion - if not all - of dark matter. Joint multiwavelength and multimessenger observations, carried out together with other future observatories, will further foster the growth of gamma-ray cosmology.

astro-ph.IM↗

arXiv2021

Searching for Axion-Like Particles from Core-Collapse Supernovae with Fermi LAT's Low Energy Technique

Light axion-like particles (ALPs) are expected to be abundantly produced in core-collapse supernovae (CCSNe), resulting in a $\sim$10-second long burst of ALPs. These particles subsequently undergo conversion into gamma-rays in external magnetic fields to produce a long gamma-ray burst (GRB) with a characteristic spectrum peaking in the 30--100-MeV energy range. At the same time, CCSNe are invoked as progenitors of {\it ordinary} long GRBs, rendering it relevant to conduct a comprehensive search for ALP spectral signatures using the observations of long GRB with the \textit{Fermi} Large Area Telescope (LAT). We perform a data-driven sensitivity analysis to determine CCSN distances for which a detection of an ALP signal is possible with the LAT's low-energy (LLE) technique which, in contrast to the standard LAT analysis, allows for a a larger effective area for energies down to 30~MeV. Assuming an ALP mass $m_a \lesssim 10^{-10}$~eV and ALP-photon coupling $g_{aγ} = 5.3\times 10^{-12}$ GeV$^{-1}$, values considered and deduced in ALP searches from SN1987A, we find that the distance limit ranges from $\sim\!0.5$ to $\sim\!10$~Mpc, depending on the sky location and the CCSN progenitor mass. Furthermore, we select a candidate sample of twenty-four GRBs and carry out a model comparison analysis in which we consider different GRB spectral models with and without an ALP signal component. We find that the inclusion of an ALP contribution does not result in any statistically significant improvement of the fits to the data. We discuss the statistical method used in our analysis and the underlying physical assumptions, the feasibility of setting upper limits on the ALP-photon coupling, and give an outlook on future telescopes in the context of ALP searches.

astro-ph.HE↗

arXiv2021

Extending the sample of core-collapse supernovae for searches of axion-like-particle induced gamma-ray bursts with the Fermi LAT

During a core-collapse supernova (SN), axion-like particles (ALPs) could be produced through the Primakoff process and subsequently convert into gamma rays in the magnetic field of the Milky Way. Using a sample of well studied extragalactic SNe at optical wavelengths, we estimate the time of the core collapse and search for a coincident gamma-ray burst with the Fermi Large Area Telescope (LAT). Under the assumption that at least one SN was contained within the LAT field of view, we exclude photon-ALP couplings within a factor of $\sim$5 of previous limits from SN1987A. With the increasing number of SNe observed with optical surveys, our results demonstrate the potential to probe ALP dark matter with combined optical and gamma-ray observations. We also provide preliminary results for the estimation of explosion times of 15 close-by SNe observed recently with ZTF. Our findings show that the explosion time can be estimated within one day (statistical uncertainty only) making them promising targets for a follow-up LAT analysis.

astro-ph.HE↗

arXiv2021

gammaALPs: An open-source python package for computing photon-axion-like-particle oscillations in astrophysical environments

Axions and axion-like particles (ALPs) are hypothetical particles that occur in extensions of the Standard Model and are candidates for cold dark matter. They could be detected through their oscillations into photons in the presence of external electromagnetic fields. gammaALPs is an open-source python framework that computes the oscillation probability between photons and axions/ALPs. In addition to solving the photon-ALP equations of motion, gammaALPs includes models for magnetic fields in different astrophysical environments such as jets of active galactic nuclei, intra-cluster and intergalactic media, and the Milky Way. Users are also able to easily incorporate their own custom magnetic-field models. We review the basic functionality and features of gammaALPs, which is heavily based on other open-source scientific packages such as numpy and scipy. Although focused on gamma-ray energies, gammaALPs can be easily extended to arbitrary photon energies.

astro-ph.HE↗

arXiv2021

Detection of new Extreme BL Lac objects with H.E.S.S. and Swift XRT

Extreme high synchrotron peaked blazars (EHBLs) are amongst the most powerful accelerators found in nature. Usually the synchrotron peak frequency of an EHBL is above $10^{17}\,$Hz, i.e., lies in the range of medium to hard X-rays making them ideal sources to study particle acceleration and radiative processes. EHBL objects are commonly observed at energies beyond several TeV, making them also powerful probes of gamma-ray absorption in the intergalactic medium. During the last decade, several attempts have been made to increase the number of EHBL detected at TeV energies and probe their spectral characteristics. Here we report new detections of EHBLs in the TeV energy regime, each at a redshift of less than 0.2, by the High Energy Stereoscopic System (H.E.S.S.). Also, we report on X-ray observations of these EHBLs candidates with Swift XRT. In conjunction with the very high energy observations, this allows us to probe the radiation mechanisms and the underlying particle acceleration processes.

astro-ph.HE↗

arXiv2021

The observability of plasmoid-powered $γ$-ray flares with the Fermi Large Area Telescope

The exact mechanism for the production of fast $γ$-ray variability in blazars remains debated. Magnetic reconnection, in which plasmoids filled with relativistic particles and magnetic fields are formed, is a viable candidate to explain the broadband electromagnetic spectrum and variability of these objects. Using state-of-the-art magnetic reconnection simulations, we generate realistic $γ$-ray light curves that would be observed with the Fermi Large Area Telescope. A comparison with observed $γ$-ray flares from flat spectrum radio quasars (FSRQs) reveals that magnetic reconnection events lead to comparable flux levels and variability patterns, in particular when the reconnection layer is slightly misaligned with the line of sight. Emission from fast plasmoids moving close to the line of sight could explain fast variability on the time scales of minutes for which evidence has been found in observations of FSRQs. Our results motivate improvements in existing radiative transfer simulations as well as dedicated searches for fast variability as evidence for magnetic reconnection events.

astro-ph.HE↗

arXiv2021

The first GeV flare of the radio-loud narrow-line Seyfert 1 galaxy PKS 2004-447

On 2019 October 25, the Fermi-Large Area Telescope observed the first gamma-ray flare from the radio-loud narrow-line Seyfert 1 (NLSy 1) galaxy PKS 2004$-$447 ($z=0.24$). We report on follow-up observations in the radio, optical-UV, and X-ray bands that were performed by ATCA, the Neil Gehrels Swift observatory, XMM-Newton, and NuSTAR, respectively, and our multi-wavelength analysis. We study the variability across all energy bands and additionally produce $γ$-ray light curves with different time binnings to study the variability on short timescales during the flare. We examine the X-ray spectrum from 0.5$-$50 keV by describing the spectral shape with an absorbed power law. We analyse multi-wavelength datasets before, during, and after the flare and compare these with a low activity state of the source by modelling the respective SEDs with a one-zone synchrotron inverse Compton radiative model. Finally, we compare our results to gamma-ray flares previously observed from other $γ$-loud NLSy 1 galaxies. At gamma-ray energies (0.1$-$300 GeV) the flare reached a total maximum flux of $(2.7\pm0.6)\times10^{-6}$~ph~cm$^{-2}$~s$^{-1}$ in 3-hour binning. With a photon index of $Γ_{0.1-300\mathrm{GeV}}=2.42\pm0.09$ during the flare, this corresponds to an isotropic gamma-ray luminosity of $(2.9\pm0.8)\times10^{47}\,\mathrm{erg}\,\mathrm{s}^{-1}$. The $γ$-ray, X-ray, and optical-UV light curves covering the end of September to the middle of November show significant variability, and we find indications for flux-doubling times of $\sim 2.2$~hours at $γ$-ray energies. During the flare, the SED exhibits large Compton dominance. While the increase in the optical-UV range can be explained by enhanced synchrotron emission, the elevated $γ$-ray flux can be accounted for by an increase in the bulk Lorentz factor of the jet, similarly observed for flaring gamma-ray blazars.

astro-ph.HE↗

arXiv2021

Relevance of jet magnetic field structure for blazar axionlike particle searches

Many theories beyond the Standard Model of particle physics predict the existence of axionlike particles (ALPs) that mix with photons in the presence of a magnetic field. One prominent indirect method of searching for ALPs is to look for irregularities in blazar gamma-ray spectra caused by ALP-photon mixing in astrophysical magnetic fields. This requires the modelling of magnetic fields between Earth and the blazar. So far, only very simple models for the magnetic field in the blazar jet have been used. Here we investigate the effects of more complicated jet magnetic field configurations on these spectral irregularities, by imposing a magnetic field structure model onto the jet model proposed by Potter & Cotter. We simulate gamma-ray spectra of Mrk 501 with ALPs and fit them to no-ALP spectra, scanning the ALP and B-field configuration parameter space and show that the jet can be an important mixing region, able to probe new ALP parameter space around $m_a\sim$ 1-1000 neV and $g_{aγ}\gtrsim$ $5\times10^{-12}$ GeV$^{-1}$. However, reasonable (i.e. consistent with observation) changes of the magnetic field structure can have a large effect on the mixing. For jets in highly magnetized clusters, mixing in the cluster can overpower mixing in the jet. This means that the current constraints using mixing in the Perseus cluster are still valid.

astro-ph.HE↗

arXiv2020

Search for Axionlike-Particle-Induced Prompt Gamma-Ray Emission from Extragalactic Core-Collapse Supernovae with the Fermi Large Area Telescope

During a core-collapse supernova (SN), axionlike particles (ALPs) could be produced through the Primakoff process and subsequently convert into $γ$ rays in the magnetic field of the Milky Way. We do not find evidence for such a $γ$-ray burst in observations of extragalactic SNe with the Fermi Large Area Telescope (LAT). The SN explosion times are estimated from optical light curves and we find a probability of about $\sim$90% that the LAT observed at least one SN at the time of the core collapse. Under the assumption that at least one SN was contained within the LAT field of view, we exclude photon-ALP couplings $\gtrsim 2.6\times10^{-11}$GeV$^{-1}$ for ALP masses $m_a \lesssim 3\times 10^{-10}$ eV, within a factor of $\sim 5$ of previous limits from SN1987A.

astro-ph.HE↗

arXiv2020

Search for the imprint of axion-like particles in the highest-energy photons of hard $γ$-ray blazars

Axion-like particles (ALPs), predicted in theories beyond the Standard Model, can have observational effects on the transparency of the Universe to $γ$ rays in the presence of magnetic fields. In this work, we search for effects compatible with the existence of ALPs with 80 months of data from the ${\it Fermi}$ Large Area Telescope, by comparing the distributions of observed highest energy photons from sources beyond redshifts of z $\geq$ 0.1 with theoretical predictions in the presence of ALPs. We find no evidence for an increased $γ$-ray transparency due to ALPs and therefore we set limits on the ALPs parameters assuming a value of the intergalactic magnetic field strength of 1 nG. Photon-ALP couplings above $10^{-11}$ GeV$^{-1}$ are excluded for ALP masses $m_{a}$ $\lesssim3.0$ neV. These limits exclude a region of the parameter space not covered by other $γ$-ray telescopes and are compatible with constraints imposed by other experiments.

astro-ph.HE↗

arXiv2020

Characterizing the Gamma-Ray Variability of the Brightest Flat Spectrum Radio Quasars Observed with the Fermi LAT

Almost 10 yr of $γ$-ray observations with the Fermi Large Area Telescope (LAT) have revealed extreme $γ$-ray outbursts from flat spectrum radio quasars (FSRQs), temporarily making these objects the brightest $γ$-ray emitters in the sky. Yet, the location and mechanisms of the $γ$-ray emission remain elusive. We characterize long-term $γ$-ray variability and the brightest $γ$-ray flares of six FSRQs. Consecutively zooming in on the brightest flares, which we identify in an objective way through Bayesian blocks and a hill-climbing algorithm, we find variability on subhour time scales and as short as minutes for two sources in our sample (3C279, CTA102) and weak evidence for variability at time scales less than the Fermi satellite's orbit of 95 minutes for PKS1510-089 and 3C454.3. This suggests extremely compact emission regions in the jet. We do not find any signs for $γ$-ray absorption in the broad-line region (BLR), which indicates that $γ$-rays are produced at distances greater than hundreds of gravitational radii from the central black hole. This is further supported by a cross-correlation analysis between $γ$-ray and radio/millimeter light curves, which is consistent with $γ$-ray production at the same location as the millimeter core for 3C273, CTA102, and 3C454.3. The inferred locations of the $γ$-ray production zones are still consistent with the observed decay times of the brightest flares if the decay is caused by external Compton scattering with BLR photons. However, the minute-scale variability is challenging to explain in such scenarios.

astro-ph.HE↗

arXiv2019

Observations of blazar PKS 2023-07 in flaring state with HESS and Fermi-LAT in 2016-2017 and constraints on an intrinsic cut-off

PKS 2023-07 is a flat spectrum radio quasar located at a redshift $z=1.388$, farther than any source currently detected at very high energies ($E>100$ GeV). At such energies, absorption by the extragalactic background light (EBL) renders the detection of distant sources particularly challenging. The High Energy Stereoscopic System (H.E.S.S.) observed the source following reports from AGILE (April 2016) and Fermi-LAT (April 2016, September and October 2017) on high-flux states in gamma rays. During each of the three flaring periods, near-simultaneous observations were obtained with H.E.S.S., Fermi-LAT and multiple telescopes at other wavelengths. Though the source was not significantly detected by H.E.S.S., upper limits were derived for each observation period. Through constraints given by Fermi-LAT in the MeV--GeV domain and differential upper limits by H.E.S.S., we searched for an intrinsic cutoff in the EBL-corrected gamma ray spectrum of PKS 2023-07.

astro-ph.HE↗

arXiv2019

Probing the Fundamental Nature of Dark Matter with the Large Synoptic Survey Telescope

Astrophysical and cosmological observations currently provide the only robust, empirical measurements of dark matter. Future observations with Large Synoptic Survey Telescope (LSST) will provide necessary guidance for the experimental dark matter program. This white paper represents a community effort to summarize the science case for studying the fundamental physics of dark matter with LSST. We discuss how LSST will inform our understanding of the fundamental properties of dark matter, such as particle mass, self-interaction strength, non-gravitational couplings to the Standard Model, and compact object abundances. Additionally, we discuss the ways that LSST will complement other experiments to strengthen our understanding of the fundamental characteristics of dark matter. More information on the LSST dark matter effort can be found at https://lsstdarkmatter.github.io/ .

astro-ph.CO↗