Abstracts of Interest
Selected by:
Adila Abdul Halim
Abstract: 2401.10915
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Title:Machine Learning-Based Detection of Non-Axisymmetric Fast Neutrino Flavor Instabilities in Core-Collapse Supernovae
Download PDF HTML (experimental)Abstract:In dense neutrino environments like core-collapse supernovae (CCSNe) and neutron star mergers (NSMs), neutrinos can undergo fast flavor conversions (FFC) when their angular distribution of neutrino electron lepton number ($\nu$ELN) crosses zero along some directions. While previous studies have demonstrated the detection of axisymmetric $\nu$ELN crossings in these extreme environments, non-axisymmetric crossings have remained elusive, mostly due to the absence of models for their angular distributions. In this study, we present a pioneering analysis of the detection of non-axisymmetric $\nu$ELN crossings using machine learning (ML) techniques. Our ML models are trained on data from two CCSN simulations, one with rotation and one without, where non-axisymmetric features in neutrino angular distributions play a crucial role. We demonstrate that our ML models achieve detection accuracies exceeding 90\%. This is an important improvement, especially considering that a significant portion of $\nu$ELN crossings in these models eluded detection by earlier methods.
Abstract: 2401.11005
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Title:Deep Neural Networks for Estimation of Gamma-Ray Burst Redshifts
Download PDF HTML (experimental)Abstract:While the available set of Gamma-ray Burst (GRB) data with known redshift is currently limited, a much larger set of GRB data without redshift is available from different instruments. This data includes well-measured prompt gamma-ray flux and spectral information. We estimate the redshift of a selection of these GRBs detected by Fermi-GBM and Konus-Wind using Machine Learning techniques that are based on spectral parameters. We find that Deep Neural Networks with Random Forest models employing non-linear relations among input parameters can reasonably reproduce the pseudo-redshift distribution of GRBs, mimicking the distribution of GRBs with spectroscopic redshift. Furthermore, we find that the pseudo-redshift samples of GRBs satisfy (i) Amati relation between the peak photon energy of the time-averaged energy spectrum in the cosmological rest frame of the GRB ${E}_{\rm i, p}$ and the isotropic-equivalent radiated energy ${E}_{\rm iso}$ during the prompt phase; and (ii) Yonetoku relation between ${E}_{\rm i, p}$ and isotropic-equivalent luminosity ${L}_{\rm iso}$, both measured during the peak flux interval.
Abstract: 2401.11399
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Title:Prospects for Joint Detection of Gravitational Waves with Counterpart Gamma-Ray Bursts Detected by the HADAR Experiment
Download PDF HTML (experimental)Abstract:The detection of GW170817/GRB170817A implied the strong association between short gamma-ray bursts (SGRBs) and binary neutron star (BNS) mergers which produce gravitational waves (GWs). More evidence is needed to confirm the association and reveal the physical processes of BNS mergers. The upcoming High Altitude Detection of Astronomical Radiation (HADAR) experiment, excelling in a wide field of view (FOV) and a large effective area above tens of GeV, is a hope for the prompt detection of very-high-energy (VHE; > 10 GeV) SGRBs. The aim of this paper is to simulate and analyse GW/SGRB joint detections by future GW detector networks in synergy with HADAR, including the second generation LIGO, Virgo and KAGRA and the third generation ET and CE. We provide a brief introduction of the HADAR experiment for SGRB simulations and its expected SGRB detections. For GW simulations, we adopt a phenomenological model to describe GWs produced by BNS mergers and introduce the signal-noise ratios (SNRs) as detector responses. Following a theoretical analysis we compute the redshift-dependent efficiency functions of GW detector networks. We then construct the simulation of GW detection by Monte Carlo sampling. We compare the simulated results of LIGO-Virgo O2 and O3 runs with their actual detections as a check. The combination of GW and SGRB models is then discussed for joint detection, including parameter correlations, triggered SNRs and efficiency skymaps. The estimated joint detection rates are 0.09-2.52 per year for LHVK network with HADAR under different possible configurations, and approximately 0.27-7.89 per year for ET+CE network with HADAR.
Abstract: 2401.11566
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Title:A detectable ultra-high-energy cosmic ray outburst from GRB 221009A
Download PDF HTML (experimental)Abstract:Gamma-ray bursts (GRBs) have been proposed as one of promising sources of ultra-high-energy cosmic rays (UHECRs), but observational evidence is still lacking. The nearby B.O.A.T. (brightest of all time) GRB 221009A, an once-in-1000-year event, is able to accelerate protons to $\sim 10^{3}$ EeV. Protons arriving at the Milky Way are dominated by neutron-decay-induced protons. The inter-galactic magnetic fields would not yield a sizable delay of the $\geq 10{\rm~EeV}$ cosmic rays if its strength is $\lesssim 10^{-13}{\rm~G}$, while Galactic magnetic fields would cause a significant time delay. We predict that, an UHECR burst from GRB 221009A would be detectable by the Pierre Auger Observatory and the TA$\times$4, within $\sim$ 10 years. The detection of such an UHECR outburst will provide the direct evidence for UHECR acceleration in GRBs.
Abstract: 2401.11762
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Title:Very High-Energy ($>$50 GeV) Gamma-ray Flux Variability of Bright Fermi Blazars
Download PDFAbstract:Understanding the high-energy emission processes and variability patterns are two of the most challenging research problems associated with relativistic jets. In particular, the long-term (months-to-years) flux variability at very high energies (VHE, $>$50 GeV) has remained an unexplored domain so far. This is possibly due to the decreased sensitivity of the Fermi Large Area Telescope (LAT) above a few GeV, hence low photon statistics, and observing constraints associated with the ground-based Cherenkov telescopes. This paper reports the results obtained from the 0.05$-$2 TeV Fermi-LAT data analysis of a sample of 29 blazars with the primary objective to explore their months-to-year long VHE flux variability behavior. This systematic search has led to, for the first time, the detection of significant flux variations in 5 blazars at $>$99\% confidence level, whereas, 8 of them exhibit variability albeit at a lower confidence level ($\sim$95\%-99\%). A comparison of the 0.05$-$2 TeV flux variations with that observed at 0.1$-$50 GeV band has revealed similar variability behavior for most of the sources. However, complex variability patterns that are not reflected contemporaneously in both energy bands were also detected, thereby providing tantalizing clues about the underlying radiative mechanisms. These results open up a new dimension to unravel the VHE emission processes operating in relativistic jets, hence sowing the seeds for their future observations with the upcoming Cherenkov Telescope Array.
Abstract: 2401.10740
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Title:Testing Hadronic-Model Predictions of Depth of Maximum of Air-Shower Profiles and Ground-Particle Signals using Hybrid Data of the Pierre Auger Observatory
Download PDF HTML (experimental)Abstract:We test the predictions of hadronic interaction models regarding the depth of maximum of air-shower profiles, $X_{max}$, and ground-particle signals in water-Cherenkov detectors at 1000 m from the shower core, $S(1000)$, using the data from the fluorescence and surface detectors of the Pierre Auger Observatory. The test consists in fitting the measured two-dimensional ($S(1000)$, $X_{max}$) distributions using templates for simulated air showers produced with hadronic interaction models EPOS-LHC, QGSJet II-04, Sibyll 2.3d and leaving the scales of predicted $X_{max}$ and the signals from hadronic component at ground as free fit parameters. The method relies on the assumption that the mass composition remains the same at all zenith angles, while the longitudinal shower development and attenuation of ground signal depend on the mass composition in a correlated way.
The analysis was applied to 2239 events detected by both the fluorescence and surface detectors of the Pierre Auger Observatory with energies between $10^{18.5}$ to $10^{19.0}$ eV and zenith angles below $60^\circ$. We found, that within the assumptions of the method, the best description of the data is achieved if the predictions of the hadronic interaction models are shifted to deeper $X_{max}$ values and larger hadronic signals at all zenith angles. Given the magnitude of the shifts and the data sample size, the statistical significance of the improvement of data description using the modifications considered in the paper is larger than $5\sigma$ even for any linear combination of experimental systematic uncertainties.
Abstract: 2401.10609
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Title:First Digit Distributions of Gamma-Ray Bursts
Download PDF HTML (experimental)Abstract:The occurrence of the first significant digits from real world sources is usually not equally distributed, but is consistent with a logarithmic distribution instead, known as Benford's law. In this work, we perform a comprehensive investigation on the first digit distributions of the duration, fluence, and energy flux of gamma-ray bursts (GRBs) for the first time. For a complete GRB sample, we find that the first digits of the duration and fluence adhere to Benford's law. However, the energy flux shows a significant departure from this law, which may be due to the fact that a considerable part of the energy flux measurements are restricted by lack of spectral information. Based on the conventional duration classification scheme, we also check if the durations and fluences of long and short GRBs (with duration $T_{90}>2$ s and $T_{90}\leq2$ s, respectively) obey Benford's law. We find that the fluences of both long and short GRBs still agree with the Benford distribution, but their durations do not follow Benford's law. Our results hint that the long--short GRB classification scheme does not directly represent the intrinsic physical classification scheme.
Abstract: 2401.10548
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Title:The remarkable predictive power of infrared data in Blazars
Download PDF HTML (experimental)Abstract:Blazars are the brightest and most abundant persistent sources in the extragalactic gamma-ray sky. Due to their significance, they are often observed across various energy bands to explore potential correlations between emissions at different energies, yielding valuable insights into the emission processes of their powerful jets. In this study we utilised infrared (IR) data at 3.4 and 4.6 microns from the Near-Earth Object Wide-field Infrared Survey Explorer Reactivation Mission (NEOWISE), spanning eight years of observations, Swift X-ray data collected throughout the satellite lifetime, and twelve years of gamma-ray measurements from the Fermi Large Area Telescope's all-sky survey. Our analysis reveals that the IR spectral slope reliably predicts the peak frequency and maximum intensity of the synchrotron component of blazars spectral energy distributions, provided it is uncontaminated by radiation unrelated to the jet. A notable correlation between the IR and gamma-ray fluxes was observed, with the BL Lac subclass of blazars displaying a strong correlation coefficient of r = 0.80. Infrared band variability is more pronounced in flat spectrum radio quasars than in BL Lacs, with mean fractional variability values of 0.65 and 0.35, respectively. We also observed that the synchrotron peak intensity of intermediate-high-energy-peaked objects blazars can forecast their detectability at very high energy gamma-ray, energies. We used this predicting power to identify objects in current catalogues that could meet the detection threshold of the Cerenkov telescope array extragalactic survey, which should encompass approximately 180 blazars.
Abstract: 2401.11777
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Title:Modeling the late time merger ejecta emission in short Gamma Ray Bursts
Download PDFAbstract:The short Gamma Ray Bursts (GRBs) are the aftermath of the merger of binary compact objects (neutron star -- neutron star or neutron star -- black hole systems). With the simultaneous detection of Gravitational Wave (GW) signal from GW 170817 and GRB 170817A, the much-hypothesized connection between GWs and short GRBs has been proved beyond doubt. The resultant product of the merger could be a millisecond magnetar or a black hole depending upon the binary masses and their equation of state. In the case of a magnetar central engine, fraction of the rotational energy deposited to the emerging ejecta produces late time synchrotron radio emission from the interaction with the ambient medium. In this paper, we present an analysis of a sample of short GRBs located at a redshift of $z \leq 0.16$ which were observed at the late time to search for the emission from merger ejecta. Our sample consists of 7 short GRBs which have radio upper limits available from VLA and ATCA observations. We generate the model lightcurves using the standard magnetar model incorporating the relativistic correction. Using the model lightcurves and upper limits we constrain the number density of the ambient medium to be $10^{-5} - 10^{-3} cm^{-3}$ for rotational energy of the magnetar $E_{rot} \sim 5\times10^{51}$ erg. Variation of ejecta mass does not play a significant role in constraining the number density.
Abstract: 2401.11931
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Title:A catalogue of low-mass X-ray binaries in the Galaxy: from the INTEGRAL to the Gaia era
Download PDFAbstract:Low-mass X-ray binaries (LMXBs) are high-energy sources that require multi-wavelength follow up campaigns to be fully characterized. New transients associated to LMXBs are regularly discovered, and previously known systems are often revisited by astronomers to constrain their intrinsic parameters. All of this information compiled into a catalogue may build up to a useful tool for subsequent studies on LMXBs and their population. We provide an update on past LMXB catalogues dating back 16 years and propose to the community a database on Galactic LMXBs with the most complete manually curated set of parameters and their original references. On top of a fixed version accessible through Vizier, we propose to host the catalogue independently on our GitHub collaboration, side-by-side with our previous catalogue on high-mass X-ray binaries. The database will be regularly updated based on new publications and community inputs. We build a working base by cross-matching previous LMXB catalogues and supplementing them with lists of hard X-ray sources detected in the past 20 years. We compile information from Simbad on LMXBs as a starting point for a thorough, manual search in the literature to retrieve important parameters that characterize LMXBs. We retrieve newly detected LMXBs and candidates directly from literature searches. Counterparts to these LMXBs are compiled from hard X-rays to infrared and radio domains. Every piece of information presented on the LMXBs is curated and backed by accurate references. We present a catalogue of 339 Galactic LMXBs listing their coordinates, companion star spectral type, systemic radial velocity, component masses and compact object nature, the presence of type I X-ray bursts as well as orbital data. Coordinates and identifiers of counterparts at various wavelengths are given, including 140 LMXBs detected in {\it Gaia} DR3.
Abstract: 2401.11994
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Title:Citizen Science for IceCube: Name that Neutrino
Download PDFAbstract:Name that Neutrino is a citizen science project where volunteers aid in classification of events for the IceCube Neutrino Observatory, an immense particle detector at the geographic South Pole. From March 2023 to September 2023, volunteers did classifications of videos produced from simulated data of both neutrino signal and background interactions. Name that Neutrino obtained more than 128,000 classifications by over 1,800 registered volunteers that were compared to results obtained by a deep neural network machine-learning algorithm. Possible improvements for both Name that Neutrino and the deep neural network are discussed.
Abstract: 2401.12026
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Title:New IceTop Trigger in the context of the planned IceCube Surface Detector Enhancement at the South Pole
Download PDFAbstract:IceTop is the square kilometer surface array for cosmic-ray air showers of the IceCube Neutrino Observatory at the South Pole. IceTop consists of 81 stations, each comprised of a pair of ice-Cherenkov tanks, which over the years loses sensitivity due to snow coverage. This motivated the plan to enhance IceTop by the deployment of elevated scintillation panels and radio antennas. Coincident detection of an air shower with the IceTop tanks, the scintillators, and the antennas will increase the measurement accuracy of the cosmic-ray properties. While the radio antennas of the enhancement have a higher sensitivity to inclined showers, the current IceTop trigger, requiring coincident hits of both tanks of a station, loses efficiency for such showers. Therefore, we studied the feasibility of adding a trigger based on the multiplicity of single tank hits and studied its performance with simulations and data including a one-day test run at the South Pole. In this paper, we present the plans for the surface enhancement and the studies for the new IceTop trigger.
Abstract: 2401.12122
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Title:Awakening of A Blazar at Redshift 2.7 Temporally Coincident with Arrival of Cospatial Neutrino Event IceCube-201221A
Download PDFAbstract:We report on multiwavelength studies of the blazar NVSS J171822+423948, which is identified as the low-energy counterpart of 4FGL J1718.5+4237, the only gamma-ray source known to be cospatial with the IceCube neutrino event IC-201221A. After a 12-year long quiescent period undetected by Fermi-LAT, gamma-ray activities with a tenfold flux increase emerge soon (a few tens of days) after arrival of the neutrino. Associated optical flares in the ZTF $g$, $r$, and $i$ bands are observed together with elevated WISE infrared fluxes. Synchronized variations suggest that both the gamma-ray emission and the neutrino event are connected to the blazar. Furthermore, the optical spectrum reveals emission lines at a redshift $z$ = 2.68 $\pm$ 0.01. Thus, it is the first candidate for a neutrino-emitting blazar at the redshift above 2. Discussions of theoretical constraints of neutrino production and comparisons with other candidates are presented.
Abstract: 2401.12185
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Title:A Snapshot Survey of Nearby Supernovae with the Hubble Space Telescope
Download PDF HTML (experimental)Abstract:Over recent decades, robotic (or highly automated) searches for supernovae (SNe) have discovered several thousand events, many of them in quite nearby galaxies (distances < 30 Mpc). Most of these SNe, including some of the best-studied events to date, were found before maximum brightness and have associated with them extensive follow-up photometry and spectroscopy. Some of these discoveries are so-called SN impostors, thought to be superoutbursts of luminous blue variable stars, although possibly a new, weak class of massive-star explosions. We conducted a Snapshot program with the Hubble Space Telescope(HST) and obtained images of the sites of 31 SNe and four impostors, to acquire late-time photometry through two filters. The primary aim of this project was to reveal the origin of any lingering energy for each event, whether it is the result of radioactive decay or, in some cases, ongoing late-time interaction of the SN shock with pre-existing circumstellar matter, or the presence of a light echo. Alternatively, lingering faint light at the SN position may arise from an underlying stellar population (e.g., a host star cluster, companion star, or a chance alignment). The results from this study complement and extend those from Snapshot programs by various investigators in previous HST cycles.
Abstract: 2401.12376
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Title:Fostering innovation, inclusion, and diversity in astronomy education: The Czech Astronomy Olympiad experience
Download PDF HTML (experimental)Abstract:Astronomy education and outreach are very important when it comes to the future generation's interest in science. The Czech Astronomy Olympiad shows how an educational competition for secondary and high schools can help us drive innovation and promote inclusion and diversity. In this work, we introduce the scope of this competition and show statistics on participation. We also discuss some of the steps taken to make astronomy accessible to a wider audience, such as organising international workshops. In addition, we explore some of the approaches which were adopted to broaden the Olympiad's reach and impact. These include, e.g., developing a dedicated website environment or publishing Open Access booklets with solved problems.
Abstract: 2401.12403
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Title:Multi-energy diffuse neutrino fluxes originating from core-collapse supernovae
Download PDF HTML (experimental)Abstract:A comprehensive framework is proposed for the diffuse neutrino fluxes attributed to two different physical processes in core collapse of massive stars. In this scheme, models of thermal MeV-scale neutrinos produced at the core of collapsing stars and non-thermal high-energy neutrinos emitted from accelerated cosmic rays interacting with circumstellar material are bridged through features of core-collapse supernovae (progenitor mass and optical properties). The calculated diffuse fluxes are presented with discussion about their detection prospects at neutrino telescopes.
Abstract: 2401.12680
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Title:Multi-wavelength spectral modelling of the candidate neutrino blazar PKS 0735+178
Download PDF HTML (experimental)Abstract:The BL Lac object PKS 0735+178 was in its historic $\gamma$-ray brightness state during December 2021. This period also coincides with the detection of a neutrino event IC211208A, which was localized close to the vicinity of PKS 0735+178. We carried out detailed $\gamma$-ray timing and spectral analysis of the source in three epochs (a) quiescent state ($E_{1}$), (b) moderate activity state ($E_{2}$) and (c) high activity state ($E_{3}$) coincident with the epoch of neutrino detection. During the epoch of neutrino detection ($E_{3}$), we found the largest variability amplitude of 95%. The $\gamma$-ray spectra corresponding to these three epochs are well fit by the power law model and the source is found to show spectral variations with a softer when brighter trend. In the epoch $E_{3}$, we found the shortest flux doubling/halving time of 5.75 hrs. Even though the spectral energy distribution in the moderate activity state and in the high activity state could be modeled by the one-zone leptonic emission model, the spectral energy distribution in the quiescent state required an additional component of radiation over and above the leptonic component. Here we show that a photo-meson process was needed to explain the excess $\gamma$-ray emission in the hundreds of GeV which could not be accounted for by the synchrotron self-Compton process.
Abstract: 2401.12754
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Title:Research on the knee region of cosmic ray by using a novel type of electron-neutron detector array
Download PDF HTML (experimental)Abstract:By accurately measuring composition and energy spectrum of cosmic ray, the origin problem of so called "keen" region (energy > 1 PeV) can be solved. However, up to the present, the results of the spectrum in the knee region obtained by several previous experiments have shown obvious differences, so they cannot give effective evidence for judging the theoretical models on the origin of the knee. Recently, the Large High Altitude Air Shower Observatory (LHAASO) has reported several major breakthroughs and important results in astro-particle physics field. Relying on its advantages of wide-sky survey, high altitude location and large area detector arrays, the research content of LHAASO experiment mainly includes ultra high-energy gamma-ray astronomy, measurement of cosmic ray spectra in the knee region, searching for dark matter and new phenomena of particle physics at higher energy. The electron and Thermal Neutron detector (EN-Detector) is a new scintillator detector which applies thermal neutron detection technology to measure cosmic ray extensive air shower (EAS). This technology is an extension of LHAASO. The EN-Detector Array (ENDA) can highly efficiently measure thermal neutrons generated by secondary hadrons so called "skeleton" of EAS. In this paper, we perform the optimization of ENDA configuration, and obtain expectations on the ENDA results, including thermal neutron distribution, trigger efficiency and capability of cosmic ray composition separation. The obtained real data results are consistent with those by the Monte Carlo simulation.
Abstract: 2401.13120
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Title:On the source contribution to the Galactic diffuse gamma rays above 398 TeV detected by the Tibet ASγ experiment
Download PDF HTML (experimental)Abstract:Potential contribution from gamma-ray sources to the Galactic diffuse gamma rays observed above 100 TeV (sub-PeV energy range) by the Tibet AS{\gamma} experiment is an important key to interpreting recent multi-messenger observations. This paper reveals a surprising fact: none of the 23 Tibet AS{\gamma} diffuse gamma-ray events above 398TeV within the Galactic latitudinal range of |b| < 10 deg. come from the 43 sub-PeV gamma-ray sources reported in the 1LHAASO catalog, which proves that these sources are not the origins of the Tibet AS{\gamma} diffuse gamma-ray events. No positional overlap between the Tibet AS{\gamma} diffuse gamma-ray events and the sub-PeV LHAASO sources currently supports the diffusive nature of the Tibet AS{\gamma} diffuse gamma-ray events, although their potential origin in the gamma-ray sources yet unresolved in the sub-PeV energy range cannot be ruled out.
Abstract: 2401.13806
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Title:2FHLJ1745.1-3035: A Newly Discovered, Powerful Pulsar Wind Nebula Candidate
Download PDF HTML (experimental)Abstract:We present a multi-epoch, multi-observatory X-ray analysis for 2FHL J1745.1-3035, a newly discovered very high energy Galactic source detected by the Fermi Large Area Telescope (LAT) located in close proximity to the Galactic Center (l=358.5319°; b=-0.7760°). The source shows a very hard gamma-ray photon index above 50 GeV, Gamma_gamma=1.2+-0.4, and is found to be a TeV-emitter by the LAT. We conduct a joint XMM-Newton, Chandra and NuSTAR observing campaign, combining archival XMM-Newton observations, to study the X-ray spectral properties of 2FHL J1745.1-3035 over a time-span of over 20 years. The joint X-ray spectrum is best-fitted as a broken power law model with break energy E_b~7 keV: the source is very hard at energies below 10 keV, with photon index Gamma_1~0.6, and significantly softer in the higher energy range measured by NuSTAR with photon index Gamma_2~1.9. We also perform a spatially resolved X-ray analysis with Chandra, finding evidence for marginal extension (up to an angular size r~5 arcsec), a result that supports a compact pulsar wind nebula scenario. Based on the X-ray and gamma-ray properties, 2FHL J1745.1-3035 is a powerful pulsar wind nebula candidate. Given its nature as an extreme TeV emitter, further supported by the detection of a coincident TeV extended source HESS J1745-303, 2FHL J1745.1-3035 is an ideal candidate for a follow-up with the upcoming Cherenkov Telescope Array.
This page created: Mon Jan 29 12:23:21 ACDT 2024 by Adila Abdul Halim
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