Session Q09: Pulsars, Supernova Remnants and Galactic Sources

Live

Recent NICER results suggest substantial deviations from the commonly assumed purely dipolar magnetic field geometry in the millisecond pulsar J0030+0451. We will present vacuum and force-free models corresponding to the sum of off-center dipole and quadrupole magnetic moments that reproduce the hot-spots indicated by the NICER results. We will discuss the broader implications of this study that are related to the physical processes that produce the magnetic fields and the pair cascades near the stellar surface. Finally, we will show that a global model using the NICER-implied field structure can self-consistently reproduce the Fermi gamma-ray light curve of this pulsar.   

Live

Black widow (BW) and redback (RB) systems are compact binaries in which a millisecond pulsar heats its low-mass companion by its intense wind of relativistic particles and emission. Radio and optical follow-up of unidentified Fermi Large Area Telescope (LAT) sources has expanded the number of these systems from four to nearly 30. Orbital modulation in X-rays observed in many systems suggests an intrabinary shock exists as a site for particle acceleration, which in many instances wraps around the pulsar. We model the broadband spectral components from nearby `spider binaries', including diffusion, convection and radiative energy losses of shock-accelerated particles in an axially-symmetric, steady-state approach. The resulting spectra comprise two main components: synchrotron radiation from X-rays to soft gamma rays and inverse-Compton emission at TeV energies from scattering thermal photons from the companion star. Two sources, J1723-2837 (RB) and J1311-3430 (BW), have been observed by Fermi-LAT, leading to constraints on the maximum particle energy and particle acceleration in these mini pulsar wind nebulae. We find that nearby binaries in a `flaring state' are promising targets for H.E.S.S. and the future Cherenkov Telescope Array and that GeV photons may be detectable by Fermi-LAT. Moreover, some of these systems will be excellent targets for future MeV missions such as AMEGO.   

Live

We present evidence for a pair of 3:2 ratio high frequency quasi-periodic oscillations (HFQPO) at 500 and 750 Hz in the X-ray flux from the black hole candidate EXO 1846$-$031 in observations made with the {\it Neutron Star Interior Composition Explorer} ({\it NICER}). The source went into outburst in late July, 2019 after 34 years in quiescence, with {\it NICER} monitoring beginning on 31 July. An average power spectrum accumulated in the 1 - 6 keV band over the initial 9 day intensity rise shows evidence at the $4\sigma$ significance level for a HFQPO at 500 Hz, with a fractional amplitude (rms) of $3.3 \%$, and coherence $Q = \nu / \Delta\nu \approx 20$. A second, weaker feature is also evident at 750 Hz, consistent with a 3:2 relationship with the 500 Hz QPO. Assessing the significance of both features together yields an overall significance at the $4.4\sigma$ level. The source spectral state evolves from a hard intermediate (or steep power-law) state to a soft-intermediate state during the outburst rise, states known to be associated with HFQPO in other black hole systems. Based on the observed inverse mass scaling of 3:2 ratio black hole HFQPOs the detection of 500 and 750 Hz signals in EXO 1846$-$031 would suggest a mass of $3.24 \pm 0.14$ $M_{\odot}$.   

Live

The High Altitude Water Cherenkov (HAWC) Observatory is the world’s most sensitive observatory for exploring the universe at extreme γ-ray energies. The wide field-of-view and high uptime capabilities of HAWC are well suited do perform deep, unbiased surveys of the TeV sky. This has enabled unprecedented discoveries of large extended sources, as well as the discovery of the highest energy particle acceleration sites in our galaxy. Using this expansive data set, studies on molecular clouds, SuperNova Remnants, TeV Halos, Star-Forming Regions, and microquasars can all be performed. This talk will be a review of the latest findings from the HAWC galactic science group.   

Live

We present observations of several gamma-ray objects emitting above 100 TeV. These are the highest-energy Galactic sources ever detected with any astrophysical messenger. The data were collected using the High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory, a TeV instrument located in Puebla, Mexico. HAWC’s wide field-of-view ($\sim$2 sr) makes it an excellent instrument to perform unbiased all-sky surveys. All of the sources are extended in apparent size and located within half a degree of a high spin-down power pulsar, raising questions about whether ultra-high-energy emission (above 50 TeV) is a generic feature of gamma-ray emission associated with such pulsars. This also raises questions about diffusion near pulsars, as the electrons associated with the highest-energy gamma rays are expected to cool quickly.   

Live

The supernova remnant IC 443 is one of the most thoroughly studied, and one of the clearest examples of interaction with molecular clouds. We combined the observations of IC 433 in the multi-TeV energy range using data from the High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory with the previously published results from Fermi-LAT and VERITAS covering an extended energy range. The energy spectrum is fitted in the context of existing models for gamma-ray production in IC 443.   

Live

Gamma-ray binaries, rare binary systems consisting of a massive star orbiting with a compact object, have in recent years been shown to be capable of efficient particle acceleration up to multi-TeV energies. These systems are characterized by non-thermal emission from radio up to very high energy gamma rays (VHE; E > 100 GeV) which can be variable on timescales ranging from days to years. While little is known for sure about the underlying mechanisms driving emissions from these systems, much progress has been made in recent years by coordinated multi-wavelength observations led by Imaging Atmospheric Cherenkov Telescopes (IACTs), which are well-suited to observe these systems at very high energies where their emission is often the most powerful. Here we present results of recent VERITAS observations of gamma-ray binaries, including the detection of the 50-year period, pulsar-driven binary PSR J2032+4127, a ten-year X-ray and TeV light curve of HESS J0632+057, and potential super-orbital variability from LS I +61 303. We discuss the implications of these results together with contemporaneous multi-wavelength observations.   

On Demand

We present two years of Neutron star Interior Composition Explorer (NICER) X-ray observations of three young and energetic rotation-powered millisecond pulsars: PSRs B1937+21, B1821−24, and J0218+4232. We fit Gaussians and Lorentzians to the pulse profiles for different energy sub-bands of the soft X-ray regime to measure the energy dependence of pulse separation and width. We find that the separation between pulse components of PSR J0218+4232 decreases with increasing energy at 3$\sigma$ confidence. Our phase-resolved spectral results provide updated constraints on the non-thermal X-ray emission of these three pulsars. The photon indices of the modeled X-ray emission spectra for each pulse component of PSR B1937+21 are inconsistent with each other at the 90\% confidence level.   

Not Participating

The Dynamic Ultraviolet Explorer Telescope (DUET) is wide-field UV Small Explorer mission that repeatedly images large fields in the sky nearly continuously for long durations. DUET is agile, accessing a large fraction of the sky and rapidly responding to targets of opportunity. DUET explores the gravitational wave frontier by observing the afterglows of neutron star mergers triggered by ground-based gravitational wave observatories. DUET pinpoints the early UV emission and follows its temporal and spectral evolution from an hour to days after the coalescence. DUET probes the nature of supernova progenitors and explores the origin and evolution of stars and galaxies by observing the earliest UV light from the demise of massive stars, minutes to days after the explosion. DUET measures the UV characteristics of a large sample of Galactic stars to reveal how stellar activity depends on mass, age, and rotation rate. These data provide critical inputs to models examining the evolutionary history of exoplanet atmospheres, informing us about their potential to host life. Over its two-year mission, DUET provides the first wide-field, UV time-domain survey of the sky, generating rapid alerts for diverse transient phenomena from tidal disruption events to fast blue optical transients