HESS J1825−137 is a pulsar wind nebula (PWN) whose TeV emission extends across ∼1
$\deg$
. Its large asymmetric shape indicates that its progenitor supernova interacted with a molecular cloud located ...in the north of the PWN as detected by previous CO Galactic survey (e.g. Lemiere, Terrier & Djannati-Ataï). Here, we provide a detailed picture of the interstellar medium (ISM) towards the region north of HESS J1825−137, with the analysis of the dense molecular gas from our 7 and 12 mm Mopra survey and the more diffuse molecular gas from the Nanten CO(1–0) and GRS 13CO(1–0) surveys. Our focus is the possible association between HESS J1825−137 and the unidentified TeV source to the north, HESS J1826−130. We report several dense molecular regions whose kinematic distance matched the dispersion measured distance of the pulsar. Among them, the dense molecular gas located at (RA, Dec.) = (18h421h,−13
$_{.}^{\circ}$
282) shows enhanced turbulence and we suggest that the velocity structure in this region may be explained by a cloud–cloud collision scenario. Furthermore, the presence of a H α rim may be the first evidence of the progenitor supernova remnant (SNR) of the pulsar PSR J1826−1334 as the distance between the H α rim and the TeV source matched with the predicted SNR radius R
SNR ∼ 120 pc. From our ISM study, we identify a few plausible origins of the HESS J1826−130 emission, including the progenitor SNR of PSR J1826−1334 and the PWN G018.5−0.4 powered by PSR J1826−1256. A deeper TeV study however, is required to fully identify the origin of this mysterious TeV source.
ABSTRACT
HESS J1825 − 137 is one of the most powerful and luminous TeV gamma-ray pulsar wind nebulae, making it an excellent laboratory to study particle transportation around pulsars. We present a ...model of the (diffusive and advective) transport and radiative losses of electrons from the pulsar PSR J1826 − 1334 powering HESS J1825 − 137 using interstellar medium gas (ISM) data, soft photon fields, and a spatially varying magnetic field. We find that for the characteristic age of $21\, \mathrm{k}\mathrm{yr}$, PSR J1826 − 1334 is unable to meet the energy requirements to match the observed X-ray and gamma-ray emission. An older age of $40\, \mathrm{k}\mathrm{yr}$, together with an electron conversion efficiency of 0.14 and advective flow of v = 0.002c, can reproduce the observed multiwavelength emission towards HESS J1825 − 137. A turbulent ISM with magnetic field of $B=20 \,{\rm to}\, 60 \,\mathrm{\mu }{\rm G}$ to the north of HESS J1825 − 137 (as suggested by ISM observations) is required to prevent significant gamma-ray contamination towards the northern $\mathrm{T}\mathrm{e\mathrm{V}}$ source HESS J1826 − 130.
N132D is the brightest gamma-ray supernova remnant (SNR) in the Large Magellanic Cloud (LMC). We carried out 12CO(J = 1-0, 3-2) observations toward the SNR using the Atacama Large ...Millimeter/submillimeter Array (ALMA) and Atacama Submillimeter Telescope Experiment. We find diffuse CO emission not only at the southern edge of the SNR as previously known, but also inside the X-ray shell. We spatially resolved nine molecular clouds using ALMA with an angular resolution of 5″, corresponding to a spatial resolution of ∼1 pc at the distance of the LMC. Typical cloud sizes and masses are ∼2.0 pc and ∼100 M , respectively. High intensity ratios of CO J = 3-2/1-0 > 1.5 are seen toward the molecular clouds, indicating that shock heating has occurred. Spatially resolved X-ray spectroscopy reveals that thermal X-rays in the center of N132D are produced not only behind a molecular cloud but also in front of it. Considering the absence of a thermal component associated with the forward shock toward one molecular cloud located along the line of sight to the center of the remnant, this suggests that this particular cloud is engulfed by shock waves and is positioned on the near side of the remnant. If the hadronic process is the dominant contributor to the gamma-ray emission, the shock-engulfed clouds play a role as targets for cosmic rays. We estimate the total energy of cosmic-ray protons accelerated in N132D to be ∼0.5-3.8 × 1049 erg as a conservative lower limit, which is similar to that observed in Galactic gamma-ray SNRs.
ABSTRACT
HESS J1825-137 is one of the most powerful and luminous TeV gamma-ray pulsar wind nebulae (PWN). To the south of HESS J1825-137, Fermi-LAT observation revealed a new region of GeV gamma-ray ...emission with three apparent peaks (termed here, GeV-ABC). This study presents interstellar medium (ISM) data and spectral energy distribution (SED) modelling towards the GeV emission to understand the underlying particle acceleration. We considered several particle accelerator scenarios – the PWN associated with HESS J1825-137, the progenitor SNR also associated with HESS J1825-137, plus the gamma-ray binary system LS 5039. It was found that the progenitor SNR of HESS J1825-137 has insufficient energetics to account for all GeV emission. GeV-ABC may be a reflection of an earlier epoch in the history of the PWN associated with HESS 1825-137, assuming fast diffusion perhaps including advection. LS 5039 cannot meet the required energetics to be the source of particle acceleration. A combination of HESS J1825-137 and LS 5039 could be plausible sources.
Abstract
The shell-type supernova remnant HESS J1731 − 347 emits TeV gamma-rays, and is a key object for the study of the cosmic ray acceleration potential of supernova remnants. We use 0.5–1 arcmin ...Mopra CO/CS(1–0) data in conjunction with H i data to calculate column densities towards the HESS J1731 − 347 region. We trace gas within at least four Galactic arms, typically tracing total (atomic+molecular) line-of-sight H column densities of 2–3× 1022 cm−2. Assuming standard X-factor values and that most of the H i/CO emission seen towards HESS J1731 − 347 is on the near-side of the Galaxy, X-ray absorption column densities are consistent with H i+CO-derived column densities foreground to, but not beyond, the Scutum–Crux Galactic arm, suggesting a kinematic distance of ∼3.2 kpc for HESS J1731 − 347. At this kinematic distance, we also find dense, infrared-dark gas traced by CS(1–0) emission coincident with the north of HESS J1731 − 347, the nearby H ii region G353.43−0.37 and the nearby unidentified gamma-ray source HESS J1729 − 345. This dense gas lends weight to the idea that HESS J1729 − 345 and HESS J1731 − 347 are connected, perhaps via escaping cosmic-rays.
We analyzed the 2.6 mm CO and 21 cm H i lines toward the Magellanic superbubble 30 Doradus C, in order to reveal the associated molecular and atomic gas. We uncovered five molecular clouds in a ...velocity range from 251 to 276 km s−1 toward the western shell. The non-thermal X-rays are clearly enhanced around the molecular clouds on a parsec scale, suggesting possible evidence for magnetic field amplification via shock-cloud interaction. The thermal X-rays are brighter in the eastern shell, where there are no dense molecular or atomic clouds, opposite to the western shell. The TeV γ-ray distribution may spatially match the total interstellar proton column density as well as the non-thermal X-rays. If the hadronic γ-ray is dominant, the total energy of the cosmic-ray protons is at least erg with the estimated mean interstellar proton density ∼60 cm−3. In addition, the γ-ray flux associated with the molecular cloud (e.g., MC3) could be detected and resolved by the Cherenkov Telescope Array (CTA). This should permit CTA to probe the diffusion of cosmic-rays into the associated dense ISM.
Abstract
30 Doradus C is a superbubble that emits the brightest non-thermal X- and TeV gamma-rays in the Local Group. To explore the detailed connection between the high-energy radiation and the ...interstellar medium, we have carried out new CO and H
i
observations using the Atacama Large Millimeter/Submillimeter Array (ALMA), Atacama Submillimeter Telescope Experiment, and the Australia Telescope Compact Array with resolutions of up to 3 pc. The ALMA data of
12
CO(
J
= 1–0) emission revealed 23 molecular clouds, with typical diameters of ∼6–12 pc and masses of ∼600–10,000
M
⊙
. A comparison with the X-rays of XMM–Newton at ∼3 pc resolution shows that X-rays are enhanced toward these clouds. The CO data were combined with the H
i
to estimate the total interstellar protons. A comparison of the interstellar proton column density and the X-rays revealed that the X-rays are enhanced with the total proton column density. These are most likely to be caused by the shock-cloud interaction, which is modeled by magnetohydrodynamical simulations (Inoue et al. 2012). We also note a trend for the X-ray photon index to vary with distance from the center of the high-mass star cluster. This suggests that the cosmic-ray electrons are accelerated by one or multiple supernovae in the cluster. Based on these results, we discuss the role of the interstellar medium in cosmic-ray particle acceleration.
RX J0046.5−7308 is a shell-type supernova remnant (SNR) in the Small Magellanic Cloud (SMC). We carried out new 12CO(J = 1-0, 3-2) observations toward the SNR using Mopra and the Atacama ...Submillimeter Telescope Experiment. We found eight molecular clouds (A-H) along the X-ray shell of the SNR. The typical cloud size and mass are ∼10-15 pc and ∼1000-3000 M☉, respectively. The X-ray shell is slightly deformed and has the brightest peak in the southwestern shell where two molecular clouds A and B are located. The four molecular clouds A, B, F, and G have high intensity ratios of 12CO(J = 3-2)/12CO(J = 1-0) > 1.2, which are not attributable to any identified internal infrared sources or high-mass stars. The H i cavity and its expanding motion are found toward the SNR, which are likely created by strong stellar winds from a massive progenitor. We suggest that the molecular clouds A-D, F, and G and H i clouds within the wind-blown cavity at VLSR = 117.1-122.5 km s−1 are associated with the SNR. The X-ray spectroscopy reveals the dynamical age of yr and the progenitor mass of 30 M☉, which is also consistent with the proposed scenario. We determine physical conditions of the giant molecular cloud LIRS 36A using the large velocity gradient analysis with archival data sets of the Atacama Large Millimeter/submillimeter Array; the kinematic temperature is K and the number density of molecular hydrogen is cm−3. The next generation of γ-ray observations will allow us to study the pion-decay γ-rays from the molecular clouds in the SMC SNR.
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