Single Thermal Model Research Articles

X-ray study of high Galactic latitude supernova remnant DA 530 with Suzaku

DA 530 is a high Galactic latitude supernova remnant (SNR) located in low density medium and extremely faint in X-ray. The previous Chandra observation of DA 530 revealed optically thin thermal plasma with overabundance of Si. The XMM-Newton observation detected a large extended source (XMM J205314.4+551528) in the radio bright southeast (SE) rim of DA 530. In this work, we analyze archival Suzaku data to examine the emission nature of the SE region of the SNR. We found that the spectrum is well described by a single thermal model with an electron temperature of kT e ∼ 3.2 keV, or a combination of thermal model with kT e ∼ 2.2 keV and non-thermal model with a photon index Γ ∼ 1.96. Our analysis shows that the pulsar wind nebula scenario cannot be ruled out. This result is consistent with the previous XMM-Newton study. Assuming the distance of 2.2 kpc to the SNR, we confirm that DA 530 is a young ( ∼ 3.2 kyr) SNR, expanding in low-density medium ( ∼ 0.23 cm - 3 ) and has a low X-ray-emitting mass ( ∼ 1.29 M ⊙ ). We also perform the XRISM and Athena simulations to investigate their capabilities of detecting thermal emission lines in the faint SNRs like DA 530.

NuSTAR Observation of Energy Release in 11 Solar Microflares.

Solar flares are explosive releases of magnetic energy. Hard X-ray (HXR) flare emission originates from both hot (millions of Kelvin) plasma and nonthermal accelerated particles, giving insight into flare energy release. The Nuclear Spectroscopic Telescope ARray (NuSTAR) utilizes direct-focusing optics to attain much higher sensitivity in the HXR range than that of previous indirect imagers. This paper presents 11 NuSTAR microflares from two active regions (AR 12671 on 2017 August 21 and AR 12712 on 2018 May 29). The temporal, spatial, and energetic properties of each are discussed in context with previously published HXR brightenings. They are seen to display several "large flare" properties, such as impulsive time profiles and earlier peak times in higher-energy HXRs. For two events where the active region background could be removed, microflare emission did not display spatial complexity; differing NuSTAR energy ranges had equivalent emission centroids. Finally, spectral fitting showed a high-energy excess over a single thermal model in all events. This excess was consistent with additional higher-temperature plasma volumes in 10/11 microflares and only with an accelerated particle distribution in the last. Previous NuSTAR studies focused on one or a few microflares at a time, making this the first to collectively examine a sizable number of events. Additionally, this paper introduces an observed variation in the NuSTAR gain unique to the extremely low livetime (<1%) regime and establishes a correction method to be used in future NuSTAR solar spectral analysis.

Microflare Heating of a Solar Active Region Observed with NuSTAR, Hinode/XRT, and SDO/AIA

Abstract NuSTAR is a highly sensitive focusing hard X-ray (HXR) telescope and has observed several small microflares in its initial solar pointings. In this paper, we present the first joint observation of a microflare with NuSTAR and Hinode/XRT on 2015 April 29 at ∼11:29 UT. This microflare shows the heating of material to several million Kelvin, observed in soft X-rays with Hinode/XRT, and was faintly visible in the extreme ultraviolet with SDO/AIA. For three of the four NuSTAR observations of this region (pre-flare, decay, and post-flare phases), the spectrum is well fitted by a single thermal model of 3.2–3.5 MK, but the spectrum during the impulsive phase shows additional emission up to 10 MK, emission equivalent to the A0.1 GOES class. We recover the differential emission measure (DEM) using SDO/AIA, Hinode/XRT, and NuSTAR, giving unprecedented coverage in temperature. We find that the pre-flare DEM peaks at ∼3 MK and falls off sharply by 5 MK; but during the microflare’s impulsive phase, the emission above 3 MK is brighter and extends to 10 MK, giving a heating rate of about erg s−1. As the NuSTAR spectrum is purely thermal, we determined upper limits on the possible non-thermal bremsstrahlung emission. We find that for the accelerated electrons to be the source of heating, a power-law spectrum of with a low-energy cutoff keV is required. In summary, this first NuSTAR microflare strongly resembles much more powerful flares.

MIXED-MORPHOLOGY SUPERNOVA REMNANTS IN X-RAYS: ISOTHERMAL PLASMA IN HB21 AND PROBABLE OXYGEN-RICH EJECTA IN CTB 1

(Abridged) We present an analysis of X-ray observations made of the Galactic supernova remnants (SNRs) HB21 (G89.0+4.7) and CTB 1 (G116.9+0.2), two well-known mixed-morphology (MM) SNRs. We find a marked contrast between the X-ray properties of these SNRs: for HB21, the extracted ASCA spectra of the northwest and southeast regions of the X-ray emitting plasma can be fit with a single thermal model with marginally enhanced silicon and sulfur abundances. For both of these regions, the derived column density and temperature are N_H~0.3x10^22 cm^-2 and kT~0.7 keV, respectively. No significant spatial differences in temperature or elemental abundances between the two regions are detected and the X-ray-emitting plasma in both regions is close to ionization equilibrium. Our Chandra spectral analysis of CTB 1 reveals that this source is likely an oxygen-rich SNR with enhanced abundances of oxygen and neon. The extracted ASCA spectra for the southwestern and northeastern regions of CTB 1 cannot be fit with a single thermal component. Based on our fits to these spectra, we derive a column density N_H~0.6x10^22 cm^-2 and a temperature for the soft thermal component of kT_soft~0.28 keV. The hard emission from the southwest may be modeled with either a thermal component (kT_hard~3 keV) or by a power law component (Gamma~2-3) while the hard emission from the northeast may be modeled with a power law component (Gamma~1.4). We have also extracted ASCA GIS spectra of the discrete X-ray source 1WGA J0001.4+6229 which is seen in projection toward CTB 1. These spectra are best fit using a power-law model with a photon index Gamma=2.2^{+0.5}_{-1.2} which is typical for featureless power-law continua produced by rotation-powered pulsars. This source may be a neutron star associated with CTB 1.

A preliminary Chandra X-ray spectroscopy of the supernova remnant N132D

We present the preliminary results of a Chandra X-ray study of N132D, a young shell-like supernova remnant (SNR) in the Large Magellanic Cloud. The equivalent width maps of emissions from O, Ne, Mg, Si, and S are provided. Spatially resolved spectral analysis for the small-scale regions were tentatively performed. X-ray spectra of the interior can be described with a single-thermal model. The faint interior regions have lower density, higher temperature above 1 keV than that of bright interior regions. The X-ray spectra along the shell can be phenomenally fitted with either a double- vpshock model or a vpshock + powerlaw model. If the non-thermal component is true, N132D would be listed as another X-ray synchrotron SNR.

Rhessi Images and Spectra of Two Small Flares

We studied the evolution of two small flares (GOES class C2 and C1) that developed in the same active region with different morphological characteristics: one is extended and the other is compact. We analyzed the accuracy and the consistency of different algorithms implemented in Reuven Ramaty High-Energy Spectroscopic Imager (RHESSI) software to reconstruct the image of the emitting sources, for energies between 3 and 12 keV. We found that all tested algorithms give consistent results for the peak position, while the other parameters can differ at most by a factor 2. Pixon and Forward-fit generally converge to similar results but Pixon is more reliable for reconstructing a complex source. We investigated the spectral characteristics of the two flares during their evolution in the 3–25 keV energy band. We found that a single thermal model of the photon spectrum is inadequate to fit the observations and we needed to add either a non-thermal model or a hot thermal one. The non-thermal and the double thermal fits are comparable. If we assume a non-thermal model, the non-thermal energy is always higher than the thermal one. Only during the very final decay phase a single thermal model fits the observed spectrum fairly well.