Abstract
We report the detection of gamma-ray emission from pulsar wind nebula (PWN) Kes 75 and PSR J1846−0258. Through modeling the spectral energy distribution incorporating the new Fermi-LAT data, ...we find that the observed gamma-ray emission is likely a combination of both the PWN and pulsar magnetosphere. The spectral shape of this magnetospheric emission is similar to the
γ
-ray spectrum of rotation-powered pulsars detected by Fermi-LAT, and the results from our best-fit model suggest that the pulsar’s magnetospheric emission accounts for 1% of the current spin-down luminosity. Prior works attempted to characterize the properties of this system and found a low supernova (SN) explosion energy and low SN ejecta mass. We reanalyze the broadband emission incorporating the new Fermi emission and compare the implications of our results to prior reports. The best-fit gamma-ray emission model suggests a second very hot photon field possibly generated by the stellar wind of a Wolf–Rayet star embedded within the nebula, which supports the low ejecta mass found for the progenitor in prior reports and here in the scenario of binary mass transfer.
Abstract We obtained a 108 ks Chandra X-ray Observatory (CXO) observation of PSR J1849-0001 and its pulsar wind nebula (PWN) coincident with the TeV source HESS J1849-000. By analyzing the new and ...old (archival) CXO data, we resolved the pulsar from the PWN, explored the PWN morphology on arcsecond and arcminute scales, and measured the spectra of different regions of the PWN. Both the pulsar and the compact inner PWN spectra are hard with power-law photon indices of 1.20 ± 0.07 and 1.49 ± 0.20, respectively. The jet-dominated PWN has a relatively low luminosity, lack of γ -ray pulsations, relatively hard and nonthermal spectrum of the pulsar, and sine-like pulse profile, which indicates a relatively small angle between the pulsar’s spin and magnetic dipole axis. In this respect, it shares similar properties with a few other so-called MeV pulsars. Although the joint X-ray and TeV spectral energy distribution can be roughly described by a single-zone model, the obtained magnetic field value is unrealistically low. A more realistic scenario is the presence of a relic PWN, no longer emitting synchrotron X-rays but still radiating in TeV via inverse-Compton upscattering. We also serendipitously detected surprisingly bright X-ray emission from a very wide binary whose components should not be interacting.
Abstract
We report the second extragalactic pulsar wind nebula (PWN) to be detected in the megaelectronvolt–gigaelectronvolt band by the Fermi-LAT, located within the Large Magellanic Cloud. The only ...other known PWN to emit in the Fermi band outside of the Milky Way is N157B, which lies to the west of the newly detected gamma-ray emission at an angular distance of 4°. Faint, pointlike gamma-ray emission is discovered at the location of the composite supernova remnant (SNR) B0453-685 with a ∼4
σ
significance with energies ranging from 300 MeV–2 TeV. We present the Fermi-LAT data analysis of the new gamma-ray source, coupled with a detailed multiwavelength investigation to understand the nature of the observed emission. Combining the observed characteristics of the SNR and the physical implications from broadband modeling, we argue it is unlikely that the SNR is responsible for the gamma-ray emission. While the gamma-ray emission is too faint for a pulsation search, we try to distinguish between any pulsar and PWN component of SNR B0453-685 that could be responsible for the observed gamma-ray emission using semi-analytic models. We determine the most likely scenario is that the old PWN (
τ
∼ 14,000 yr) within B0453-685 has been impacted by the return of the SNR reverse shock with a possible substantial pulsar component below 5 GeV.
HEX-P is a probe-class mission concept that will combine high spatial resolution X-ray imaging (
<
1
0
″
full width at half maximum) and broad spectral coverage (0.2–80 keV) with an effective area ...far superior to current facilities (including
XMM
-Newton and
NuSTAR
) to enable revolutionary new insights into a variety of important astrophysical problems. HEX-P is ideally suited to address important problems in the physics and astrophysics of supernova remnants (SNRs) and pulsar wind nebulae (PWNe). For shell SNRs, HEX-P can greatly improve our understanding via more accurate spectral characterization and localization of non-thermal X-ray emission from both non-thermal-dominated SNRs and those containing both thermal and non-thermal components, and can discover previously unknown non-thermal components in SNRs. Multi-epoch HEX-P observations of several young SNRs (e.g., Cas A and Tycho) are expected to detect year-scale variabilities of X-ray filaments and knots, thus enabling us to determine fundamental parameters related to diffusive shock acceleration, such as local magnetic field strengths and maximum electron energies. For PWNe, HEX-P will provide spatially-resolved, broadband X-ray spectral data separately from their pulsar emission, allowing us to study how particle acceleration, cooling, and propagation operate in different evolution stages of PWNe. HEX-P is also poised to make unique and significant contributions to nuclear astrophysics of Galactic radioactive sources by improving detections of, or limits on,
44
Ti in the youngest SNRs and by potentially discovering rare nuclear lines as evidence of double neutron star mergers. Throughout the paper, we present simulations of each class of objects, demonstrating the power of both the imaging and spectral capabilities of HEX-P to advance our knowledge of SNRs, PWNe, and nuclear astrophysics.
HEX-P is a probe-class mission concept that will combine high spatial resolution X-ray imaging (<10"FWHM) and broad spectral coverage (0.2--80 keV) with an effective area far superior to current ...facilities (including XMM-Newton and NuSTAR) to enable revolutionary new insights into a variety of important astrophysical problems. With the recent discoveries of over 40 ultra-high-energy gamma-ray sources (detected above 100 TeV) and neutrino emission in the Galactic Plane, we have entered a new era of multi-messenger astrophysics facing the exciting reality of Galactic PeVatrons. In the next decade, as more Galactic PeVatrons and TeV gamma-ray sources are expected to be discovered, the identification of their acceleration and emission mechanisms will be the most pressing issue in both particle and high-energy astrophysics. In this paper, along with its companion papers (Reynolds et al. 2023, Mori et al. 2023), we will present that HEX-P is uniquely suited to address important problems in various cosmic-ray accelerators, including Galactic PeVatrons, through investigating synchrotron X-ray emission of TeV--PeV electrons produced by both leptonic and hadronic processes. For Galactic PeVatron candidates and other TeV gamma-ray sources, HEX-P can fill in a large gap in the spectral-energy distributions (SEDs) of many objects observed in radio, soft X-rays, and gamma rays, constraining the maximum energies to which electrons can be accelerated, with implications for the nature of the Galactic PeVatrons and their contributions to the spectrum of Galactic cosmic rays beyond the knee at $\sim3$ PeV. In particular, X-ray observation with HEX-P and TeV observation with CTA will provide the most powerful multi-messenger diagnostics to identify Galactic PeVatrons and explore a variety of astrophysical shock mechanisms. We present simulations of each class of Galactic TeV--PeV sources, demonstrating the power of both the imaging and spectral capabilities of HEX-P to advance our knowledge of Galactic cosmic-ray accelerators. In addition, we discuss HEX-P’s unique and complementary roles to upcoming gamma-ray and neutrino observatories in the 2030s.
Abstract
We report the discovery of MeV–GeV
γ
-ray emission by the Fermi-LAT positionally coincident with the TeV pulsar wind nebula (PWN) HESS J1554–550 within the host supernova remnant (SNR) ...G327.1–1.1. The
γ
-ray emission is point-like and faint but significant (>4
σ
) in the 300 MeV–2 TeV energy range. We report here the Fermi-LAT analysis of the observed
γ
-ray emission followed by a detailed multiwavelength investigation to understand the nature of the emission. The central pulsar powering the PWN within G327.1–1.1 has not been detected in any wave band; however, it is likely embedded within the X-ray nebula, which is displaced from the center of the radio nebula. The
γ
-ray emission is faint and therefore a pulsation search to determine if the pulsar may be contributing is not feasible. Prior detailed multiwavelength reports revealed an SNR system that is old,
τ
∼ 18,000 yr, where the interaction of the reverse shock with the PWN is underway or has recently occurred. We find that the
γ
-ray emission agrees remarkably well with a detailed broadband model constructed in a prior report based on independent hydrodynamical and semianalytic simulations of an evolved PWN. We further investigate the physical implications of the model for the PWN evolutionary stage incorporating the new Fermi-LAT data and attempt to model the distinct particle components based on a spatial separation analysis of the displaced PWN counterparts.
We report on the investigation of a very high-energy, Galactic γ-ray source recently discovered at >50 GeV using the Large Area Telescope on board Fermi. This object, 2FHL J0826.1−4500, displays one ...of the hardest >50 GeV spectra (photon index Γγ ∼ 1.6) in the 2FHL catalog, and a follow-up observation with XMM-Newton has uncovered diffuse, soft thermal emission at the position of the γ-ray source. A detailed analysis of the available multi-wavelength data shows that this source is located on the western edge of the Vela supernova remnant (SNR): the observations and the modeling of the spectral energy distribution support a scenario where this γ-ray source is the byproduct of the interaction between the SNR shock and a neutral hydrogen cloud. If confirmed, this shock-cloud interaction would make 2FHL J0826.1−4500 a promising candidate for efficient particle acceleration.
Studies of the non-thermal Galactic source population are essential to understand how and where the bulk of cosmic rays are being accelerated and to understand the mechanisms underlying very high ...energy (VHE, E > 50 GeV) emitters (Karg, 2013; Renaud, 2009). The plane of the Milky Way is rich with supernova remnants (SNRs) and pulsar wind nebulae (PWNe) which are efficient accelerators of cosmic rays (CRs)—whose interaction with the surrounding photon fields produces energetic γ-rays and neutrinos. SNRs and PWNe are some of the most powerful objects in our Galaxy and because they emit at very high energies (VHE, E > 50 GeV), γ-rays represent an excellent probe of the non-thermal astrophysical processes in these objects.Relativistic electrons (i.e. leptons) can produce γ-rays by non-thermal bremsstrahlung or by inverse Compton scattering (IC) on ambient photon fields, whereas protons and heavier nuclei (i.e. hadrons) can generate γ-rays by the process of pion decay, produced in collisions between relativistic hadrons and ambient material. Understanding the particle population responsible for the observed γ-ray emission can provide clues to the potential of CR acceleration as most cosmic rays are made of protons or heavier nuclei (~ 10% of all cosmic rays are leptons) so, if it can be established that the γ-ray emission is hadronic in origin, then we can better understand the likelihood for hadron CR acceleration in VHE objects.%Electron populations are most likely contributing to the re-acceleration of pre-existing CRs infiltrating the region whereas proton populations, especially in high density regions, are most likely contributing to the production of fresh CRs in the region.In this thesis, we report on the investigation of a very high energy (VHE), Galactic γ-ray source recently discovered at > 50 GeV using the Large Area Telescope (LAT) on board Fermi. This object, 2FHL~J0826.1–4500, displays one of the hardest > 50 GeV spectra (Γγ ~ 1.6) in the 2FHL sample, and a follow-up observation with XMM-Newton has uncovered diffuse, soft thermal emission at the position of the γ-ray source.A detailed analysis of the available multi-wavelength data shows that this source is located on the Western edge of the Vela supernova remnant: the observations and the spectral energy distribution modeling support a scenario where this γ-ray source is the byproduct of the interaction between the SNR shock and a neutral Hydrogen cloud. If confirmed, this shock-cloud interaction would make 2FHL~J0826.1–4500 a promising candidate for efficient particle acceleration. This work has been recently published in the Astrophysical Journal (Eagle, 2019).In chapter 1, the objective of this thesis is introduced. In chapter 2, SNRs and PWNe are explained in detail with a focus on the Vela SNR - the closest composite SNR to Earth. In chapter 3, we discuss the main instruments used to obtain the γ-ray and X-ray data, namely XMM-Newton, and the Fermi-LAT. Chapter 4 describes the data reduction process and spectral analysis and a multi-wavelength description of 2FHL~J0826.1–4500 is presented in chapter 5. Chapter 6 tests the spectral energy distribution (SED) of the source, attempting to determine the dominant parent particle population to better understand its emission mechanisms. In chapter 7 we report our conclusions on 2FHL~J0826.1–4500 and emphasize important properties that still need to be probed in order to best answer the underlying question: if 2FHL~J0826.1–4500 is an efficient particle accelerator, can we safely establish if this is a site generating fresh CRs or does the energetic environment favor a scenario where pre-existing CRs are being re-accelerated here?
There are at least 125 Galactic pulsar wind nebulae (PWNe) that have been discovered from radio wavelengths to TeV gamma-rays, the majority of which were first identified in radio or X-ray surveys. ...An increasing number of PWNe are being identified in the TeV band by ground-based air Cherenkov Telescopes such as HESS, MAGIC, and VERITAS such that they constitute the dominant source class of Galactic TeV emitters. Combining available MeV-GeV data with observations in the TeV band is critical for precise characterization of high-energy emission from the relativistic particle population in PWNe, thus revealing the capability to produce a significant fraction of the detected Galactic CR flux. However, MeV-GeV PWN counterparts are still largely lacking even after 12 years of continuous observation of the entire sky. Less than a dozen PWNe are currently identified by the Fermi-LAT in the MeV-GeV band. Most PWNe are located along the Galactic plane embedded within the prominent, diffuse Galactic gamma-ray emission, which makes these sources difficult to disentangle from the bright diffuse background. We present a systematic search for gamma-ray counterparts to known PWNe in the 300MeV - 2TeV energy band using 11.5 years of Fermi-LAT data. For the first part of this search, we target the locations of PWNe previously identified across the electromagnetic spectrum that are not powered by pulsars previously detected by the Fermi-LAT as pulsating gamma-ray signals, which includes 6 Fermi PWNe and 7 Fermi PWN associations. We report the analysis of 58 total regions of interest and provide all firm and tentative detections along with their morphological and spectral characteristics. There are 11 unidentified gamma-ray sources that we classify as firm PWN counterparts, which doubles the PWN population detected by the Fermi-LAT, and 22 gamma-ray sources that are PWN candidates.
We report the detection of gamma-ray emission from PWN Kes 75 and PSR J1846-0258. Through modeling the spectral energy distribution incorporating the new Fermi-LAT data, we find the the observed ...gamma-ray emission is likely a combination of both the PWN and pulsar magnetosphere. The spectral shape of this magnetospheric emission is similar to the gamma-ray spectrum of rotation powered pulsars detected by Fermi-LAT and the results from our best-fit model suggest the pulsar's magnetospheric emission accounts for 1% of the current spin-down luminosity. Prior works attempted to characterize the properties of this system and found a low supernova explosion energy and low SN ejecta mass. We re-analyze the broadband emission incorporating the new Fermi emission and compare the implications of our results to prior reports. The best-fit gamma-ray emission model suggests a second very hot photon field possibly generated by the stellar wind of a Wolf-Rayet star embedded within the nebula, which supports the low ejecta mass found for the progenitor in prior reports and here in the scenario of binary mass transfer.
PDF
