ALMA polarization observations of the particle accelerators in the hotspot of the radio galaxy 3C 445

Orienti, M.; Brunetti, G.; Nagai, Hiroshi; Paladino, R.; Mack, K.‐H.; Prieto, M. A.

doi:10.1093/mnrasl/slx067

Cited by 12 publications

(5 citation statements)

References 22 publications

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“…The double synchrotron interpretation was invoked for the infrared knots of the jet in the quasar 3C 273 (Uchiyama et al 2006). The multi-component interpretation was applied to the polarimetric properties observed with the Atacama Large Millimeter Array (ALMA) from kpc-scale structures associated with the hot spot of 3C 445 (Orienti et al 2017). Thus, the mid-infrared observations have gradually revealed that the acceleration phenomena in the hot spots are actually complicated and heterogeneous rather than the simple one-zone Fermi acceleration.…”

Section: Introductionmentioning

confidence: 99%

Mid-infrared Excess from the West Hot Spot of the Radio Galaxy Pictor A Unveiled by WISE

Isobe

Koyama

Kino

et al. 2017

ApJ

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Mid-infrared properties are reported of the west hot spot of the radio galaxy Pictor A with the Wide-field Infrared Survey Explorer (WISE). The mid-infrared counterpart to the hot spot, WISE J051926.26−454554.1, is listed in the AllWISE source catalog. The source was detected in all the four WISE photometric bands. A comparison between the WISE and radio images reinforces the physical association of the WISE source to the hot spot. The WISE flux density of the source was carefully evaluated. A close investigation of the multi-wavelength synchrotron spectral energy distribution from the object reveals a mid-infrared excess at the wavelength of λ = 22 µm with a statistical significance of 4.8σ over the simple power-law extrapolation from the synchrotron radio spectrum. The excess is reinforced by single and double cutoff power-law modeling of the radio-to-optical spectral energy distribution. The synchrotron cutoff frequency of the main and excess components was evaluated as 7.1 × 10 14 Hz and 5.5 × 10 13 Hz, respectively. From the cutoff frequency, the magnetic field of the emission region was constrained as a function of the region size. In order to interpret the excess component, an electron population different from the main one dominating the observed radio spectrum is necessary. The excess emission is proposed to originate in a sub structure within the hot spot, in which the magnetic field is by a factor of a few stronger than that in the minimum energy condition. The relation of the mid-infrared excess to the X-ray emission is briefly discussed.

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Section: Introductionmentioning

confidence: 99%

Mid-infrared Excess from the West Hot Spot of the Radio Galaxy Pictor A Unveiled by WISE

Isobe

Koyama

Kino

et al. 2017

ApJ

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“…In addition, a denser short-baseline coverage enabled by ALMA is useful to search for 100pc scale substructures which were possibly missed in the VLBA observation by Tingay et al (2008). Finally, polarimetric information obtained with ALMA is expected to be very useful to constrain the magnetic field configu-ration and to infer the particle acceleration process (e.g., Orienti et al 2017). ACKNOWLEDGMENTS…”

Section: Future Perspectivementioning

confidence: 99%

Herschel SPIRE discovery of far-infrared excess synchrotron emission from the west hot spot of the radio galaxy Pictor A

Isobe,

Sunada,

Kino

et al. 2020

Preprint

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A far-infrared counterpart to the west hot spot of the radio galaxy Pictor A is discovered with the Spectral and Photometric Imaging REceiver (SPIRE) onboard Herschel. The color-corrected flux density of the source is measured as 70.0 ± 9.9 mJy at the wavelength of 350 µm. A close investigation into its radio-to-optical spectrum indicates that the mid-infrared excess over the radio synchrotron component, detected with WISE and Spitzer, significantly contributes to the far-infrared band. Thanks to the SPIRE data, it is revealed that the spectrum of the excess is described by a broken power-law model subjected to a high-energy cutoff. By applying the radiative cooling break under continuous energy injection (∆α = 0.5), the broken power-law model supports an idea that the excess originates in 10-pc scale substructures within the hot spot. From the break frequency, ν b = 1.6 +3.0 −1.0 × 10 12 Hz, the magnetic field was estimated as B ≃ 1-4 mG. This is higher than the minimum-energy magnetic field of the substructures by a factor of 3-10. Even if the origin of the excess is larger than ∼ 100 pc, the magnetic field stronger than the minimum-energy field is confirmed. It is proposed that regions with a magnetic field locally boosted via plasma turbulence are observed as the substructures. The derived energy index below the break, α ∼ 0.22 (conservatively < 0.42), is difficult to be attributed to the strong-shock acceleration (α = 0.5). Stochastic acceleration and magnetic reconnection are considered as a plausible alternative mechanism.

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“…The turbulence (e.g., Asano et al 2014) and associated magnetic reconnection (e.g., Sironi & Spitkovsky 2014) are theoretically proposed to behave as an efficient accelerator. However, concrete signatures of these acceleration processes in the hot spots have not yet been confirmed, except for an observational suggestion by Orienti et al (2017).…”

Section: Introductionmentioning

confidence: 99%

ALMA ACA Detection of Submillimeter Emission Associated with the Western Hot Spot of the Radio Galaxy Pictor A

Isobe¹,

Nagai²,

Kino³

et al. 2023

ApJ

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In order to investigate the far-infrared excess detected from the western hot spot of the radio galaxy Pictor A with the Herschel observatory, submillimeter photometry is performed with the Atacama Compact Array (ACA) of the Atacama Large Millimeter/submillimeter Array at Band 8 with the reference frequency of 405 GHz. A submillimeter source is discovered at the radio peak of the hot spot. Because the 405 GHz flux density of the source, 80.7 ± 3.1 mJy, agrees with the extrapolation of the synchrotron radio spectrum, the far-infrared excess is suggested to exhibit no major contribution at the ACA band. In contrast, by subtracting the power-law spectrum tightly constrained by the radio and ACA data, the significance of the excess in the Herschel band is well confirmed. No diffuse submillimeter emission is detected within the ACA field of view, and thus, the excess is ascribed to the western hot spot itself. In comparison to the previous estimate based on the Herschel data, the relative contribution of the far-infrared excess is reduced by a factor of ∼1.5. The spectrum of the excess below the far-infrared band is determined to be harder than that of the diffusive shock acceleration. This strengthens the previous interpretation that the excess originates via the magnetic turbulence in the substructures within the hot spot. The ACA data are utilized to evaluate the magnetic field strength of the excess and of diffuse radio structure associated with the hot spot.

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ALMA polarization observations of the particle accelerators in the hotspot of the radio galaxy 3C 445

Cited by 12 publications

References 22 publications

Mid-infrared Excess from the West Hot Spot of the Radio Galaxy Pictor A Unveiled by WISE

Mid-infrared Excess from the West Hot Spot of the Radio Galaxy Pictor A Unveiled by WISE

Herschel SPIRE discovery of far-infrared excess synchrotron emission from the west hot spot of the radio galaxy Pictor A

ALMA ACA Detection of Submillimeter Emission Associated with the Western Hot Spot of the Radio Galaxy Pictor A

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