Probing the Faraday screen in the nuclear region of 3C 84 Minchul - PowerPoint PPT Presentation

Probing the Faraday screen in the nuclear region of 3C 84 Minchul Kam, Sascha Trippe, Jongho Park Seoul National University East Asian VLBI Workshop 2018 | Sep. 04 - 08. 2018

HST 1.73’ view of NGC 1275 VLBA 22GHz z ~ 0.018 http://pc.astro.brandeis.edu/ images/3c84.html d ~ 75 Mpc

3C 84 – central region of NGC 1275 ● VLBA 43 GHz VLBA 22 GHz c e s r a p 1 = s a m 3 http://pc.astro.brandeis.edu/ images/3c84.html https://www.bu.edu/blazars/VLBA_GLAST/0316.html

3C 84 is an interesting target ! ● 1) very close (z~0.018, d~75 Mpc) → 1 pc scale structure of the central region is resolved! core : bright, upstream region 1 pc where the jet begins hotspot : the local-brightest region in the bowshock-like structure 2) very low polarization → - synchrotron radiation polarization ! contours : total intensity colors : polarized intensity

3C 84 is an interesting target ! ● 1) very close (z~0.018, d~75 Mpc) → 1 pc scale structure of the central region is resolved! core : bright, upstream region 1 pc where the jet begins hotspot : the local-brightest region in the bowshock-like structure 2) very low polarization → - synchrotron radiation polarization ! What people think for the reason is… → Originally, it is polarized but something depolarizes it. → the prime suspect : Faraday rotation !

Polarization angle (EVPA) is rotated by B-field. ● B-field polarized emission φ 1 = φ 0 + ∆ φ 1 φ 2 = φ 0 + ∆ φ 2 φ 1, φ 2 : different observed EVPAs φ 0 : thesameintrinsic EVPA φ 1 = φ 0 + ∆ φ 1 Depolarization ! φ 2 = φ 0 + ∆ φ 2

Polarization angle (EVPA) is rotated by B-field. ● B-field polarized emission φ 0 : intrinsic EVPA RM ∝ ∫ n B los dl 2 RM ∆ φ = λ λ ↓ ( ν ↑ ) → ∆ φ ↓ → m ↑ The effect of Faraday rotation is smaller at higher frequency. → Polarization would be stronger at higher frequency.

Polarization angle (EVPA) is rotated by B-field. ● B-field polarized emission φ 0 : intrinsic EVPA 2 RM φ 1 = φ 0 + λ 1 φ 1 = φ 0 + ∆ φ 1 RM ∝ ∫ n B los dl 2 RM φ 2 = φ 0 + λ 2 2 RM φ 2 = φ 0 + ∆ φ 2 ∆ φ = λ 2 − λ 2 2 ) RM φ 1 − φ 2 =( λ 1 λ ↓ ( ν ↑ ) → ∆ φ ↓ → m ↑ RM is obtained from multi-frequency polarimetry 1. Does m% increase at higher frequency? 2. How large is the RM?

Data information ● 1. Very Long Baseline Array (VLBA) – 10 antennas, ~8000 km Period : Jun. 2014 ~ Sep. 2017 (BU data) Freq : 43.008 / 43.087 / 43.151 / 43.215 GHz 2. Korea VLBI Network (KVN) – 3 antennas, ~480 km Period : Dec. 2016 ~ (The KVN Large Program - PAGaN) Freq : 22 / 43 / 86 / 129 GHz

VLBA 43 GHz (Dec. 2016 ~ Sep. 2017)

The hotspot VLBA 43 GHz (Dec. 2016 ~ Sep. 2017) The hotspot

The core VLBA 43 GHz (Dec. 2016 ~ Sep. 2017) The core

KVN 86 GHz (Dec. 2016 ~ Dec. 2017)

VLBA 43 GHz Does m% really increase at higher frequency? (Dec. 2016 ~ Apr. 2017) KVN 86 GHz

Fractional polarization (m%) do increase at higher frequency ! ● BU 43 GHz KVN 86 GHz observation date 2016 DEC 0.9 % (23) 1.6 % (9) 2017 JAN 0.3 % (14) 2.2 % (16) 2017 FEB 0.4 % (4) 6.1 % (25) 2017 MAR 0.9 % (19) 2.2 % (22) 2017 APR 0.5 % (16) 1.5 % (21) BU 43 GHz images were convolved 2017 JUN 0.3 % (8) 1.2 % (1) with the KVN 86 GHz beamsize. Yes, m% increases at higher frequency !

The hotspot (43.008 / 43.088 / 43.151 / 43.215 GHz, Jan. 2017) ●

The hotspot (43.008 / 43.088 / 43.151 / 43.215 GHz, Jan. 2017) ●

The RM at the hotspot - summary ● 2015 | RM | ∼ 4.4 × 10 5 rad / m 2

The core (43.008 / 43.088 / 43.151 / 43.215 GHz, Jun. 2017) ●

The core (43.008 / 43.088 / 43.151 / 43.215 GHz, Jun. 2017) ●

The RM at the core - summary ● | RM | ∼ 6.6 × 10 5 rad / m 2

Point I - The core RM is lower than the expectation ! ● RM hsp = 4.4 × 10 5 rad / m 2 RM core = 6.6 × 10 5 rad / m 2 RM ∝ ∫ n e B φ dl

Point II - Detection of the negative core RM ● - SMA & CARMA cannot resolve the core. - Assumption! Most of the emission at 220 & 340 GHz originates from the core region. Only positive core RM at 220 & 340 GHz Plambeck+ 2014

Scenario I : Internal Faraday rotation (Emitting region itself) ● Faraday screen : sphere Faraday screen : slab → → lower frequency lower frequency Burn 1966 2 ∝ λ 2 , µ : random component of B-field u Except the case that emitting region is slab with zero random component of B-field, EVPA rotation will be saturated at low frequencies.

Scenario I : Internal Faraday rotation (Emitting region itself) ● Faraday screen : sphere Faraday screen : slab ← higher frequency ← higher frequency Burn 1966 2 , µ : random component of B-field 2 ∝ λ u Except the case that emitting region is slab with zero random component of B-field, EVPA rotation will be saturated at low frequencies. If 43 GHz, where we obtained the RM, is located in this saturated range, (1) positive & negative core RM, and (2) the low core RM would be explained.

Scenario I : Internal Faraday rotation (Emitting region itself) ● Faraday screen : sphere Faraday screen : slab ← higher frequency ← higher frequency Burn 1966 2 ∝ λ 2 , µ : random component of B-field u Except the case that emitting region is slab with zero random component of B-field, EVPA rotation will be saturated at low frequencies. If 43 GHz, where we obtained the RM, is located in this saturated range, (1) positive & negative core RM, and (2) the low core RM would be explained. → RM will increase at higher frequency where the EVPA rotation is less saturated.

Scenario II : External Faraday rotation (Hot accretion flow) ● Li+ 2016 hot accretion flow - geometrically thick & optically thin turbulent If polarized emission from the core passes through this accretion flow, (1) positive & negative core RM, (2) the low core RM can be explained. → RM will not increase at higher frequency.

To probe the Faraday screen.. ● Case I : internal to the jet – RM will increase at higher frequency. Case II : external to the jet – RM will not increase at higher frequency. → RM at higher frequency is necessary ! KVN observation at frequencies higher than 86 GHz ● We proposed multi-frequency KVN observation at 86 - 90 - 94 & 129 - 138 - 142 GHz. → The first attempt to obtain the core RM at this high frequency range.

To probe the Faraday screen.. ● Case I : internal to the jet – RM will increase at higher frequency. Case II : external to the jet – RM will not increase at higher frequency. → RM at higher frequency is necessary ! KVN observation at frequencies higher than 86 GHz ● approved ! We proposed multi-frequency KVN observation at 86 - 90 - 94 & 129 - 138 - 142 GHz. → The first attempt to obtain the core RM at this high frequency range.