An Analysis of the North Polar Spur Using HaloSat

Abstract

We present HaloSat X-ray observations of the entirety of the bright X-ray emitting feature known as the North Polar Spur (NPS). The large field of view of HaloSat enabled coverage of the entire bright NPS in only 14 fields, which were each observed for ≈30,000 s. We find that the NPS fields are distinct in both brightness and spectral shape from the surrounding halo fields. We fit the NPS as two thermal components in ionization equilibrium with temperatures » kT keV 0.087 cool and » kT keV 0.28 hot . We note a temperature gradient in the NPS hot component with an inner arc temperature warmer than the outer arc. The emission measures we find for the cool component of the NPS is a factor of 3-5 greater than that of the hot component, which suggests that the bulk of the NPS material is in the ≈0.1 keV component. We evaluate distance estimates of 0.4 and 8.0 kpc for the NPS. Our findings suggest a preference for a distant NPS with an energy of ≈ 6×10 54 erg, an age of ≈ 10 Myr, and pressures consistent with a 10μG magnetic field associated with the Fermi bubbles. The electron density ≈10×10 −3 cm −3 is consistent with estimates for the shock region surrounding a Galactic-scale event.Unified Astronomy Thesaurus concepts: X-ray astronomy (1810); Interstellar medium (847); Diffuse x-ray background (384); Superbubbles (1656)

Revisiting the Distance to Radio Loops I and IV Using Gaia and Radio/Optical Polarization Data

“…The finding that at high latitude the polarized radio Loop I is at ∼100 pc is in apparent contrast with the conclusions drawn from recent studies that analyzed X-ray data (Akita et al 2018;LaRocca et al 2020) and Faraday rotation (Sun et al 2015;Xu & Han 2019). There are three arguments put forward to argue that the NPS is farther than 200 pc.…”

The HaloSat and PolarLight CubeSat Missions for X-ray Astrophysics

“…HaloSat data have been used to study the North Polar Spur that was historically considered to be the result of a nearby supernova but has recently been interpreted as related to feedback from the nuclear supermassive black hole and to the bubbles seen by the Fermi satellite at GeV energies. The HaloSat results on pressure and electron density favor a Galactic-scale event with an energy of ∼ 6 × 10 54 erg and an age of ∼10 Myr [14]. HaloSat data on the Cygnus superbubble, a region of bright soft X-ray emission in the direction of local spiral arm, show that the temperature and absorption are consistent across different parts, suggesting a singular origin, potentially as a hypernova remnant [19].…”

“…The science instrument and its integration with the spacecraft, see Figure 2, is described in [13]. Design and construction of the instrument is described in [14] and ground calibration in [15]. Here, we summarize a few key features and design considerations.…”

“…The shield was electroplated with nickel and an outer layer of gold, chosen because it has no florescence lines in the energy band of interest. The charge pulses produced by X-rays detected in each SDD were processed using an analog electronics chain with a discriminator, preamplifier, shaping amplifier, and sample/hold [14]. Prototypes of each component of the instrument electronics were designed, built, and tested beginning early in the program with multiple iterations.…”

A Search for the 3.5 keV Line from the Milky Way’s Dark Matter Halo with HaloSat

“…Contributions from unresolved extragalactic X-ray sources to the CXB were modelled by a single absorbed power law with photon index Γ = 1.45 and a 1 keV normalization of 10.91 keV cm −2 s −1 sr −1 keV −1 (Cappelluti et al 2017) subject to a Galactic interstellar absorption column density calculated as the responseweighted equivalent N H across the HaloSat FoV from the SFD dust map (Schlegel et al 1998). The calculation of the response-weighted equivalent N H is described in LaRocca et al (2020). Absorptions were modelled with TBabs (Wilms et al 2000) and fixed in spectral analysis.…”