Multiwavelength Investigation of Pulsar Wind Nebula DA 495 with HAWC, VERITAS, and NuSTAR

Abstract

Pulsar Wind Nebula (PWN) DA 495 (G65.7+1.2) was detected in TeV gamma-rays by the High Altitude Water Cherenkov Observatory (HAWC) in 2017 (2HWC J1953+294). Follow-up observations by the Very Energetic Radiation Imaging Telescope Array System (VERITAS) confirmed the association between 2HWC J1953+294 and DA 495 and found the TeV emission to be spatially coincident with the radio emission first reported in 1968. The detection of TeV gamma-rays from DA 495, along with past X-ray detection up to 10 keV, prompted high energy X-ray observations as part of the NuSTAR Galactic Legacy Survey. We present the results of these NuSTAR observations, combined with archival Chandra and XMM-Newton observations, and confirm the previous X-ray photon index of Γ 2−20 keV = 2.0 ± 0.1. We find no spectral cutoff up to 20 keV. With the spectral information for DA 495 extended to TeV gamma-rays, we were able to perform analytical modeling to test leptonic and hadronic emission scenarios. The leptonic models can explain the broadband emission, but also imply a diffuse X-ray nebula of similar extent to the radio and TeV nebulae, which cannot be confirmed by our observations. The hadronic models can simultaneously explain the spectrum and the spatial extent in all wavelengths; however, we need a very high magnetic field strength pervading the radio and TeV nebulae and a surprisingly high particle kinetic energy. These requirements deepen the mystery of the physical nature of DA 495. Future observations in radio to infrared bands and spatially resolved γ-rays can further constrain the physical conditions and radiation mechanisms in DA 495.

NuSTAR broad-band X-ray observational campaign of energetic pulsar wind nebulae in synergy with VERITAS, HAWC and Fermi gamma-ray telescopes

“…There are also several middle-aged PWNe whose high-energy emission is not explained by a leptonic model alone. For example, NuSTAR observation of the evolved PWN DA 495 found that a hybrid SED model composed of both leptonic and hadronic components is required to account for the multi-wavelength SED [12].…”

“…We will jointly analyze available X-ray data from Chandra and XMM observations in order to maximize our capacity to characterize the broad-band X-ray morphology/spectra of PWNe. We largely follow the NuSTAR data analysis of other PWNe such as DA 495 [12]. Upon detecting a pulsation signal, we can remove photon events from the pulsed components using a folded lightcurve or extrapolate the pulsar's Chandra spectrum and estimate its contribution in the NuSTAR band -these are the standard methods for mitigating the contamination of the pulsar [5].…”

Multiwavelength Observations of 2HWC J1928+177: Dark Accelerator or New TeV Gamma-Ray Binary?

“…We used a 90-ks NuSTAR observation (ObsID 30362002002) taken in 2017 June as a part of the NuSTAR-VERITAS-HAWC Legacy program which includes observations of PWN DA 495 (Coerver et al 2019) and the TeV gamma-ray binary HESS J0632+057 (Archer et al 2020), and two archival Chandra observations (ObsIDs 9081 and 22145) which were taken with 10 ks exposures in 2008 and 2019, respectively. We also considered a handful of Swift/XRT observations of the field, but their short exposures yielded only a few counts in each observation, and so the Swift data are not very useful even after combining all the data.…”

“…However, the small ratio of W e /W p ∼ 0.01-0.03 is still difficult to reconcile with the p-p collision case since the total kinetic energy of secondary electrons (i.e. byproducts of charged pion decays) should be ∼ 1/3 of the total radiation energy of π 0 gamma-rays (Coerver et al 2019). In order to yield the ratio W e /W p comparable to ∼ 1/3, it requires a lower ambient B-field, which seems implausible within a molecular cloud where the B-field should be amplified.…”

Observations of supernova remnants at very high energies with VERITAS

“…The results of this analysis were originally reported on in Abeysekara et al (2018b) as part of a follow-up study on new TeV gamma-ray sources detected by HAWC, and the strong magnetic fields measured by study of the radio spectrum made the TeV detection unexpected (Kothes et al, 2008). Second, starting with Section 5.2, the entire text of a paper accepted for publication in the Astrophysical Journal, titled: "Multiwavelength Study of Pulsar Wind Nebula DA 495 with NuSTAR, VERITAS and HAWC," is included (Coerver et al, 2019).…”