arXiv subjects

Stephen DiKerby

Publications and source records attributed to Stephen DiKerby.

9 recordsLinked to original sources

arXiv2026

Lynx2030 Science Analysis Group: Final Report

The Lynx2030 Science Analysis Group (SAG) was convened to reassess the scientific goals and technical drivers of the Lynx mission concept amid a rapidly evolving astrophysics landscape. Building on the original Lynx Concept Study, the SAG examined how recent discoveries, emerging facilities, and advances in instrumentation influence the scientific opportunities for a next-generation flagship X-ray observatory. Through focused working groups, the SAG investigated the scientific impact of enhanced capabilities: (i) improved angular resolution, (ii) broader bandpass coverage, (iii) an enhanced microcalorimeter, (iv) new capabilities and observing modes, and (v) larger fields of view. Across a broad range of topics, from the formation of the first black holes and the evolution of galaxies to the baryon cycle, compact objects, stellar explosions, multi-messenger astrophysics, and the dynamic high-energy Universe, the SAG finds that the scientific motivation for a Lynx-class observatory remains compelling and, in many areas, has significantly strengthened over the past decade, prominently through JWST's discovery of the "Little Red Dots", likely massive accreting black holes in infant galaxies whose nature is fundamentally an X-ray question. This report shows that modest extensions beyond the original Lynx design reference mission can unlock transformative science while preserving the observatory's core architecture. Powerful current and future facilities such as Roman, Rubin, JWST, SKA, ngVLA, LISA, and NewAthena highlight the unique role a high-angular-resolution, high-throughput X-ray observatory would play in the multi-wavelength and multi-messenger ecosystem of the 2030s and beyond. The findings of the Lynx2030 SAG confirm Lynx's central vision: an unprecedented view of the hot and energetic Universe, enabling discoveries that will define high-energy astrophysics in the coming decades.

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arXiv2026

Resolving the Fe K$\alpha$ Doublet of the Galactic Center Molecular Cloud G0.11-0.11 with XRISM

Fe K$\alpha$ line emission from Galactic center molecular clouds can be produced either via fluorescence after illumination by an X-ray source or by cosmic ray ionization. Unparalleled high-resolution X-ray spectroscopy obtained by XRISM-Resolve for the galactic center molecular cloud G0.11-0.11 resolves its Fe K$\alpha$ line complex for the first time, and points to a new method for discrimination between the X-ray reflection and cosmic ray ionization models. The Fe K$\alpha$ line complex is resolved into Fe K$\alpha_1$ at $E_{1} = 6.4040 \: \rm{keV}$ and Fe K$\alpha_2$ at $E_{2}= 6.3910 \:\rm{keV}$. Both lines have non-instrumental FWHM of $\approx 3 \:\rm{eV}$, close to the predicted quantum mechanical width of the lines, suggesting scant other sources of line broadening other than instrumental and quantum effects. We measure a radial velocity of $v_{\rm{LSR}} = 50 \pm 12_{fit} \pm 14_{scale} \:\rm{km/s}$ for G0.11-0.11, achieving the same precision reached by radio observations of such clouds. The high-resolution spectrum tests for the presence of secondary Fe K$\alpha$ lines, expected as a signature of cosmic ray proton/ion ionization. The absence of the secondary lines argues against the cosmic ray ionization model for G0.11-0.11. In the preferred X-ray reflection model, if the illuminating source is Sgr A$^{\star}$, the required luminosity for an X-ray outburst about 200 years ago is $L_8 \approx 10^{38} \:\rm{erg/s}$ in an $8\:\rm{keV}$-wide band at $8\:\rm{keV}$.

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arXiv2025

Classification of a New X-ray Catalog of Likely Counterparts to 4FGL-DR4 Unassociated Gamma-ray Sources Using a Neural Network

Our survey of the fourth $\mathit{Fermi}$ Large Area Telescope catalog (4FGL) unassociated gamma-ray source regions using the X-Ray Telescope (XRT) and Ultraviolet/Optical Telescope (UVOT) aboard the Neil Gehrels $\mathit{Swift}$ Observatory ($\mathit{Swift}$) provides new XRT and UVOT source detections and localizations to help identify potential low-energy counterparts to unassociated $\mathit{Fermi}$ gamma-ray sources. We present a catalog of 218 singlet and 70 multiplet $\mathit{Swift}$ X-ray sources detected within the positional uncertainty ellipses of 244 unassociated $\mathit{Fermi}$ gamma-ray sources from the 4FGL-DR4 catalog, 144 of which are not previously cataloged by Kerby et al. (2021b). For each X-ray source, we derive its X-ray flux and photon index, then use simultaneous UVOT observations with optical survey data to estimate its $V$-band magnitude. We use these parameters as inputs for a multi-layer perceptron (MLP) neural network classifier (NNC) trained to classify sources as blazars, pulsars, or ambiguous gamma-ray sources. For the 213 singlet sources with X-ray and optical data, we classify 173 as likely blazars ($P_\mathrm{bzr} > 0.99$) and 6 as likely pulsars ($P_\mathrm{bzr} < 0.01$), with 34 sources yielding ambiguous results. Including 70 multiplet X-ray sources, we increase the number of $P_\mathrm{bzr} > 0.99$ to 227 and $P_\mathrm{bzr} < 0.01$ to 16. For the subset of these classifications that have been previously studied, a large majority agree with prior classifications, supporting the validity of using this NNC to classify the unknown and newly detected gamma-ray sources.

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arXiv2025

The Advanced X-ray Imaging Satellite (AXIS) Community Science Book

The AXIS Community Science Book represents the collective effort of 592 scientists worldwide to define the transformative science enabled by the Advanced X-ray Imaging Satellite (AXIS), a next-generation X-ray mission selected by NASA's Astrophysics Probe Program for Phase A study. AXIS will advance the legacy of high-angular-resolution X-ray astronomy with ~1.5'' imaging over a wide 24' field of view and an order of magnitude greater collecting area than Chandra in the 0.3-12 keV band. Combining sharp imaging, high throughput, and rapid response capabilities, AXIS will open new windows on virtually every aspect of modern astrophysics, exploring the birth and growth of supermassive black holes, the feedback processes that shape galaxies, the life cycles of stars and exoplanet environments, and the nature of compact stellar remnants, supernova remnants, and explosive transients. This book compiles 138 community-contributed science cases developed by five Science Working Groups focused on AGN and supermassive black holes, galaxy evolution and feedback, compact objects and supernova remnants, stellar physics and exoplanets, and time-domain and multi-messenger astrophysics. Together, these studies establish the scientific foundation for next-generation X-ray exploration in the 2030s and highlight strong synergies with facilities of the 2030s, such as JWST, Roman, Rubin/LSST, SKA, ALMA, ngVLA, and next-generation gravitational-wave and neutrino networks.

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arXiv2025

Technosignature Searches of Interstellar Objects

With the discovery of the third confirmed interstellar object (ISO), 3I/ATLAS, we have entered a new phase in the exploration of these long-predicted objects. Though confirmed discovery of ISOs is quite recent, their utility as targets in the search for technosignatures (historically known as the Search for Extraterrestrial Intelligence -- SETI) has been discussed for many decades. With the upcoming NSF-DOE Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), the discovery and tracking of such objects is expected to become routine, and thus so must our examination of these objects for possible technosignatures. Here we review the literature surrounding ISOs as targets for technosignatures, which provides a well-developed motivation for such exploration. We outline four broad classes of technosignatures that are well suited for ISO follow-up, including the type of data needed and the best timing for study. Given the limitations in the current understanding of ISOs, we show that care must be taken in identifying technosignatures based primarily on comparison to objects in the Solar System. We therefore provide a roadmap for careful and consistent study of the population of ISOs in the hope of identifying technosignatures.

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arXiv2025

Possibilities for SETI at High Energy

High-energy SETI pushes astrobiology to its limits, testing the most fundamental needs of life and the most extreme limits of technology. It has lagged behind the rest of the field, but the increased respectability of SETI could spark interest in the coming years. This white paper reviews the case for SETI in X-rays, gamma rays, and neutrinos, including rationales, challenges, and possible technosignatures, and suggests future strategies for observational work.

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arXiv2025

Discovery of a Pulsar Wind Nebula Candidate Associated with the Galactic PeVatron 1LHAASO J0343+5254u

The astronomical origin of the most energetic galactic cosmic rays and gamma rays is still uncertain. X-ray followup of candidate "PeVatrons", systems producing cosmic rays with energies exceeding 1 PeV, can constrain their spatial origin, identify likely counterparts, and test particle emission models. Using 120 ks of XMM-Newton observations, we report the discovery of a candidate pulsar wind nebula, a possible counterpart for the LHAASO PeVatron J0343+5254u. This extended source has a power law X-ray spectrum with spectral index of 1.9 - softer at greater distance from the center - and asymmetric spatial extension out to 2'. We conduct leptonic modeling of the X-ray and gamma ray radiation from this complex system, showing that a fully leptonic model with elevated IR photon fields can explain the multiwavelength emission from this source, similar to other VHE pulsar wind nebulae; excess gamma ray emissivity not explained by a leptonic model may be due to hadronic interactions in nearby molecular cloud regions, which might also produce detectable astroparticle flux.

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arXiv2025

Detection of molecular clouds in the PeVatron candidate source LHAASO J0341$+$5258 by the Nobeyama 45-m radio telescope

We report a new CO observation survey of LHAASO J0341$+$5258 using the Nobeyama Radio Observatory (NRO) 45-m telescope. LHAASO J0341$+$5258 is one of the unidentified ultra-high-energy (UHE; E $>$100 TeV) gamma-ray sources detected by LHAASO. Our CO observations were conducted in February and March 2024, with a total observation time of 36 hours, covering the LHAASO source ($\sim$0.3-0.5 degrees in radius) and its surrounding area (1$\times$1.5 degrees). Within the LHAASO source extent, we identified five compact ($<$ 2 pc) molecular clouds at nearby distances ($<$ 1-4 kpc). These clouds can serve as proton-proton collision targets, producing hadronic gamma rays via neutral pion decays. Based on the hydrogen densities (700-5000 cm$^{-3}$) estimated from our CO observations and archived HI data from the DRAO survey, we derived the total proton energy of $W_p$ (E $>$ 1 TeV) $\sim$ 10$^{45}$ erg to account for the gamma-ray flux. One of the molecular clouds appears to be likely associated with an asymptotic giant branch (AGB) star with an extended CO tail, which may indicate some particle acceleration activities. However, the estimated maximum particle energy below 100 TeV makes the AGB-like star unlikely to be a PeVatron site. We conclude that the UHE emission observed in LHAASO J0341$+$5258 could be due to hadronic interactions between the newly discovered molecular clouds and TeV-PeV protons originating from a distant SNR or due to leptonic emission from a pulsar wind nebula candidate, which is reported in our companion X-ray observation paper (DiKerby et al. 2025).

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arXiv2025

Fifteen Years of M31* X-ray Variability and Flares

We append an additional fifteen years (2009-2024) to the Chandra X-ray light curve of M31*, the supermassive black hole at the center of M31, the Andromeda galaxy. Extending and expanding on the work in Li et al. 2011, we show that M31* has remained in an elevated X-ray state from 2006 through at least 2016 (when regular Chandra monitoring ceased) and likely through 2024, with the most recent observations still showing an elevated X-ray flux. We identify one moderate flare in 2013 where the other nuclear X-ray sources are in low-flux states, making that flare a valuable target for followup with multiwavelength and multimessenger archival data. We extract a mostly uncontaminated spectrum for M31* from this observation, showing that its X-ray properties are similar to those observed at Sgr A* in its quiescent state by Baganoff et al. 2003. Furthermore, we find no substantial change in the source's hardness ratio in the 2006 and 2013 flares compared to the post-2006 elevated state, suggesting the these flares are increases in the regular X-ray emission mechanisms instead of entirely new emission modes. Our extended light curve for M31* provides valuable context for multimessenger or multiwavelength observations of nearby supermassive black holes.

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