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Register a new user{it NuSTAR} hard X-ray studies of the pulsar wind nebula 3C~58
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Hongjun An
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We report on new NuSTAR and archival Chandra observations of the pulsar wind nebula (PWN) 3C 58. Using the X-ray data, we measure energy-dependent morphologies and spatially-resolved spectra of the PWN. We find that the PWN size becomes smaller with increasing energy and that the spectrum is softer in outer regions. In the spatially integrated spectrum of the PWN, we find a hint of a spectral break at $sim$25 keV. We interpret these findings using synchrotron-radiation scenarios. We attribute the size change to the synchrotron burn-off effect. The radial profile of the spectral index has a break at $Rsim80$, implying a maximum electron energy of $sim$200 TeV which is larger than a previous estimate, and the 25-keV spectral break corresponds to a maximum electron energy of $sim$140 TeV for an assumed magnetic field strength of 80 $mu$G. Combining the X-ray data and a previous radio-to-IR SED, we measure a cooling break frequency to be $sim 10^{15}$ Hz, which constrains the magnetic-field strength in 3C 58 to be 30-200$mu$G for an assumed age range of 800-5000 years.
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We investigate broadband emission properties of the pulsar wind nebula (PWN) 3C 58 using a spectral energy distribution (SED) model. We attempt to match simultaneously the broadband SED and spatial variations of X-ray emission in the PWN. We further the model to explain a possible far-IR feature of which a hint is recently suggested in 3C 58: a small bump at $sim$$10^{11}$ GHz in the PLANCK and Herschel band. While external dust emission may easily explain the observed bump, it may be internal emission of the source implying an additional population of particles. Although significance for the bump is not high, here we explore possible origins of the IR bump using the emission model and find that a population of electrons with GeV energies can explain the bump. If it is produced in the PWN, it may provide new insights into particle acceleration and flows in PWNe.
The pulsar wind nebula (PWN) 3C 58 is one of the historical very-high-energy (VHE; E>100 GeV) gamma-ray source candidates. It is energized by one of the highest spin-down power pulsars known (5% of Crab pulsar) and it has been compared to the Crab Nebula due to their morphological similarities. This object was previously observed by imaging atmospheric Cherenkov telescopes (Whipple, VERITAS and MAGIC), although not detected, with an upper limit of 2.4% Crab Unit (C.U.) at VHE. It was detected by Fermi-LAT with a spectrum extending beyond 100 GeV. We analyzed 81 hours of 3C 58 data taken with the MAGIC telescopes and we detected VHE gamma-ray emission with a significance of 5.7 sigma and an integral flux of 0.65% C.U. above 1 TeV. The differential energy spectrum between 400 GeV and 10 TeV is well described by a power-law function dphi/dE=f_0(E/1TeV)^{-Gamma} with f_0=(2.0pm0.4_{stat}pm0.6_{sys})times10^{-13}cm^{-2}s^{-1}TeV^{-1} and Gamma=2.4pm0.2_{stat}pm0.2_{sys}. The skymap is compatible with an unresolved source. We report the first significant detection of PWN 3C 58 at TeV energies. According to our results 3C 58 is the least luminous VHE gamma-ray PWN ever detected at VHE and the one with the lowest flux at VHE to date. We compare our results with the expectations of time-dependent models in which electrons up-scatter photon fields. The best representation favors a distance to the PWN of 2 kpc and Far Infrared (FIR) comparable to CMB photon fields. If we consider an unexpectedly high FIR density, the data can also be reproduced by models assuming a 3.2 kpc distance. A low magnetic field, far from equipartition, is required to explain the VHE data. Hadronic contribution from the hosting supernova remnant (SNR) requires unrealistic energy budget given the density of the medium, disfavoring cosmic ray acceleration in the SNR as origin of the VHE gamma-ray emission.
The pulsar wind nebula (PWN) 3C 58 has been proposed as a good candidate for detection at VHE (VHE; E>100 GeV) for many years. It is powered by one of the highest spin-down power pulsars known (5% of Crab pulsar) and it has been compared to the Crab Nebula due to its morphology. This object was previously observed by imaging atmospheric Cherenkov telescopes (Whipple, VERITAS and MAGIC), and upper limit of 2.4% Crab Unit (C.U.) at VHE. It was detected by Fermi-LAT with a spectrum extending beyond 100 GeV. We analyzed 81 hours of 3C 58 data taken with the MAGIC telescopes and we detected VHE gamma-ray emission with a significance of 5.7 sigma and an integral flux of 0.65% C.U. above 1 TeV. We report the first significant detection of PWN 3C 58 at TeV energies. According to our results 3C 58 is the least luminous VHE gamma-ray PWN ever detected at VHE and the one with the lowest flux at VHE to date. We compare our results with the expectations of time-dependent models in which electrons up-scatter photon fields. The best representation favors a distance to the PWN of 2 kpc and Far Infrared (FIR) comparable to CMB photon fields. If we consider an unexpectedly high FIR density according to GALPROP, the data can also be reproduced by models assuming a 3.2 kpc distance. A low magnetic field, far from equipartition, is required to explain the VHE data. Hadronic contribution from the hosting supernova remnant (SNR) requires an unrealistic energy budget given the density of the medium, disfavoring cosmic ray acceleration in the SNR as origin of the VHE gamma-ray emission.
Since the day of its explosion, SN 1987A (SN87A) was closely monitored with the aim to study its evolution and to detect its central compact relic. The detection of neutrinos from the supernova strongly supports the formation of a neutron star (NS). However, the constant and fruitless search for this object has led to different hypotheses on its nature. Up to date, the detection in the ALMA data of a feature somehow compatible with the emission arising from a proto Pulsar Wind Nebula (PWN) is the only hint of the existence of such elusive compact object. Here we tackle this 33-years old issue by analyzing archived observations of SN87A performed Chandra and NuSTAR in different years. We firmly detect nonthermal emission in the $10-20$ kev energy band, due to synchrotron radiation. The possible physical mechanism powering such emission is twofold: diffusive shock acceleration (DSA) or emission arising from an absorbed PWN. By relating a state-of-the-art magneto-hydrodynamic simulation of SN87A to the actual data, we reconstruct the absorption pattern of the PWN embedded in the remnant and surrounded by cold ejecta. We found that, even though the DSA scenario cannot be firmly excluded, the most likely scenario that well explains the data is the PWN emission.
We present an investigation of the spectral and spatial structure of the X-ray emission from 3C 58 based on a 350 ks observation with the Chandra X-ray Observatory. This deep image, obtained as part of the Chandra Large Project program, reveals new information on nearly all spatial scales in the pulsar wind nebula (PWN). On the smallest scales we derive an improved limit of T < 1.02 X 10^6 K for blackbody emission from the entire surface of the central neutron star (NS), confirming the need for rapid, nonstandard cooling in the stellar interior. Furthermore, we show that the data are consistent with emission from a light element atmosphere with a similar temperature. Surrounding the NS, a toroidal structure with a jet is resolved, consistent with earlier measurements and indicative of an east-west orientation for the projected rotation axis of the pulsar. A complex of loop-like X-ray filaments fills the nebula interior, and corresponds well with structures seen in the radio band. Several of the structures coincide with optical filaments as well. The emission from the interior of the PWN, including the pulsar, jet, and filaments, is primarily nonthermal in nature. The power law index steepens with radius, but appears to also show small azimuthal variations. The outermost regions of the nebula require a thermal emission component, confirming the presence of an ejecta-rich swept up shell.
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