Chandra and Multiwavelength Study of Pevatron Candiate HESS J1702-420A

summary

The gist

The gist HESS J1702–420A is a promising Galactic PeVatron candidate whose physical nature remains unknown.

In short

The study investigated HESS J1702–420A, a candidate for accelerating PeV cosmic rays, using Chandra X-ray observations. While initial searches found no strong counterparts, new high-resolution data resolved the emission into distinct lobes. The analysis concluded that Src11 is the most plausible pulsar candidate associated with the diffuse X-ray emission, strengthening the case for a compact object/PWN system.

Key concepts

PeVatrons: These are Galactic sources hypothesized to accelerate cosmic rays up to 10^15 eV. They are a key target for understanding how the highest energy particles in the universe are produced within our galaxy.
Pulsar Wind Nebula (PWN): A PWN is an extended structure created by the wind of a rapidly rotating neutron star, known as a pulsar. These nebulae emit high-energy radiation and are often associated with TeV sources observed by telescopes like HESS.
Hard Spectrum ($\Gamma$): The spectral index, or $\Gamma$, describes the shape of the energy spectrum of particles emitted by a source. A hard spectrum, like the one found in HESS J1702–420A ($\Gamma = 1.53$), indicates that a significant fraction of the emitted energy is concentrated at higher energies.
X-ray Morphology: This refers to the physical shape and structure of X-ray emission observed by Chandra. Resolving this into distinct eastern and western lobes helps scientists determine if the structure resembles a typical PWN, such as a bow shock or jet.

Terminology used across episodes

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This episode discusses

The paper

Chandra and Multiwavelength Study of Pevatron Candiate HESS J1702-420A · Read on arXiv

IRAP · Department of Physics, The George Washington University · Astrophysics Science Division, NASA Goddard Space Flight Center · Center for Research and Exploration in Space Science and Technology, NASA/GSFC · The Catholic University of America

Aims: HESS J1702-420A is a promising Galactic PeVatron candidate whose physical nature remains unknown. Previous XMM-Newton observations revealed hard, apparently extended X-ray emission from XMMU J170147.3-421407, offset from the center of the TeV source, suggesting a possible pulsar wind nebula (PWN) association. We aim to resolve its X-ray morphology, investigate compact-object candidates in the field, and assess their possible association with HESS J1702-420A. Methods: We obtained three new ACIS-I observations from the Chandra X-ray observatory (CXO) with a total exposure of 50.4 ks. We performed imaging, source detection, spectral and variability analyses, and multiwavelength (MW) machine-learning (ML) source classification. Neutron star (NS) candidates were further investigated using deep near-infrared and radio imaging. Results: The Chandra observations resolve XMMU J170147.3-421407 into a faint point-like source, Src11 (CXO J170144.5-421415), and asymmetric diffuse emission comprising eastern and western lobes. The X-ray spectral, variability, and MW properties of Src11 and the diffuse emission are consistent with those commonly observed in pulsar/PWN systems, further supported by the ML classifications. However, the asymmetric diffuse morphology is unlike a typical bow-shock/tail or jet/torus PWN, and the about7' offset from HESS J1702-420A makes a firm physical association difficult to establish. A possible shell-like radio structure north-west of Src11 may indicate a more complex PWN/SNR environment. Other NS candidates are less consistent with a pulsar/PWN interpretation, making Src11 the most compelling candidate in the field.

Transcript

Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: I'm Vera.

Jocelyn: And I'm Jocelyn, here with Subrahmanyan.

Vera: We're looking at the paper: "Chandra and Multiwavelength Study of Pevatron Candiate HESS J1702-420A".

Jocelyn: Here's the gist of the paper. The gist HESS J1702–420A is a promising Galactic PeVatron candidate whose physical nature remains unknown.

Vera: PeVatrons are Galactic sources responsible for accelerating cosmic rays up to 1015 eV However, despite several plausible associations (i.e., Cao et al.

Jocelyn: 2021; Tibet ASγ Collaboration et al.

Vera: 2021), no observation to date has established an unambiguous multi-wavelength (MW) counterpart directly identifying the accelerator responsible for PeV particle acceleration TeV observations have revealed an entirely new population of extended Galactic sources (Aharonian et al.

Title and authors: Vera: So, to recap where we are, this paper is taking that hard X-ray emission from HESS J1702–420A and trying to use Chandra’s better resolution to map out the structure and see if it links up with a pulsar or a supernova remnant <ref:2610.30378#pg1>. Jocelyn It’s about moving past just saying it’s a candidate and actually looking at the details of its environment, which is crucial for identifying the accelerator.

Subrahmanyan: From my side, I'm wondering how they use these X-ray measurements to constrain the particle acceleration spectrum. If we can nail down the shape of that emission, we can better test models for PeV cosmic ray production.

Vera: Well, they’re looking at spectral parameters too; one part of their work is fitting the spectra from the western and eastern lobes separately to see if they behave differently.

Jocelyn: That makes sense because different regions could be affected by different things, like whether you're seeing a pulsar wind nebula right next to something else or just diffuse shock emission.

The paper's summary: Vera: The summary of this paper boils down to the fact that they found an extended source XMMU J170147 point 3–four hundred twenty-one thousand four hundred seven offset from the TeV source, and they are trying to resolve its X-ray morphology with Chandra observations <ref:2610.30378#pg1,XMMU J170147.3–421407 offset from the>. Jocelyn They’re essentially testing if this offset structure is a possible pulsar wind nebula, which would mean linking it directly to a neutron star system.

Subrahmanyan: The paper suggests that the observed asymmetry in the X-ray PWN might be due to the pulsar's motion or interaction with an internal shock in a supernova remnant, which is important for understanding how these things evolve over time.

Vera: And they are also looking at other compact object candidates because those are often mixed into these observations, and they want to see if any of them fit the pulsar/PWN model better than others.

Jocelyn: It’s interesting how they are using the X-ray properties to narrow down the possibilities for what’s actually causing that hard TeV emission we see from HESS J1702–420A <ref:2610.30378#pg1>.

The paper's improvements: Vera: The authors of this paper suggest a few ways they could improve their study. One thing is using a Multiwavelength Machine Learning pipeline to classify eighteen X-ray sources based on spectral properties and hardness ratios to better distinguish pulsar candidates from things like cataclysmic variables or young stellar objects.

Jocelyn: That’s smart because it means we can use machine learning to sift through all the data and pick the most plausible candidate, which is what they think Src B is.

Subrahmanyan: I’m thinking about the morphological analysis; they suggest using high angular resolution Chandra observations to really resolve those eastern and western lobes, allowing them to test interpretations like a relic PWN or a subsonic PWN distorted by an SNR environment.

Vera: That high resolution is key because lower resolution data can't tell you if it’s a jet structure or just some general cloud interaction. It lets them test those specific scenarios more rigorously.

Conclusion: Jocelyn: So, to wrap up the main points of the "Chandra and Multiwavelength Study of Pevatron Candiate HESS J1702-420A," they’ve shown that while the structure isn't a textbook PWN shape, they still point strongly toward Src B being a pulsar/PWN candidate <ref:2610.30378#pg1,Chandra and Multiwavelength Study of Pevatron Candiate HESS J1702-420A>. Vera They've strengthened the case for a compact-object system because of the X-ray properties and by finding constraints on other objects.

Subrahmanyan: The paper confirms that these results make Src B the most compelling candidate among the sources seen in those Chandra observations, which is a significant step toward understanding where PeV cosmic rays might be coming from.

Jocelyn: It’s a solid piece of work because it uses multiple wavelengths to build a case for one specific physical scenario, even when the morphology isn't perfectly conventional.

Vera: Indeed, the study of HESS J1702-420A through this Chandra and Multiwavelength Study of Pevatron Candiate HESS J1702-420A gives us a much clearer picture of what’s going on in that region of the sky <ref:2610.30378#pg1,Chandra and Multiwavelength Study of Pevatron Candiate HESS J1702-420A>.

Subrahmanyan: It really shows how integrating observations from different energy regimes helps us connect the particle acceleration process to the structure we see in space.

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