of the buried AGN in NGC 1068

Transcription

1 13 th AGN Meeting Milano, 9-12 October 2018 A deep NuSTAR view of the buried AGN in NGC 1068 Alessandra Zaino Roma Tre University In collaboration with: S. Bianchi, A. Marinucci and G. Matt

2 Outline What do we already know about NGC 1068? The NuSTAR monitoring Results Summary and conclusions

3 Unveiling the nucleus of NGC 1068 N H,2 = (1.4±0.1) 1023 cm -2 N H,1 ~ 1025 cm -2 The broadband cold reflected emission of NGC 1068 is due to multiple reflectors with three distinct column densities. Bauer et al Jaffe et al N H,3 ~ (4-10) 1024 cm -2 Torus consistent with a two-component dust distribution: o an inner (0.7±0.2 pc) hot (T > 800 K) component; o a more extended (~3-4 pc) colder component (T~320 K). 1 pc

4 Monitoring rationale NuSTAR observation Dec 2012 Aug 2014 Feb 2015 Bauer et al joint XMM-Newton flux excess above 20 kev F 20-80keV = erg cm -2 s -1 F 20-80keV = erg cm -2 s -1 F 20-80keV = erg cm -2 s -1 F 20-80keV = erg cm -2 s -1 Marinucci et al Marinucci et al Marinucci et al Compton-thick unveiling event (ΔN H cm 2 ) R 2 pc!!

5 Monitoring aim and method Aim: to give tighter constraints on the location of the absorbing circumnuclear material 31 July (50.0 ks) 27 Aug (52.5 ks) 6 Nov (49.7 ks) 5 Feb (54.6 ks) obscuring cloud R observer R= GM BH t2 n 2 2 N H M BH ~ 10 7 M n ~ cm -3 N H ~ cm -2 t ~ 1-6 months X-ray source D=N H / n R ~ pc

6 The monitoring spectra soft X band July 2017 Aug 2017 Nov 2017 Feb 2018 a. No evidence of Fe lines variation b. F 3-5.5keV increases by ~ 35% in Feb 2018 Countrate kev FPMA: ± cts/s FPMB: ± cts/s FPMA: ± cts/s FPMB: ± cts/s FPMA: ± cts/s FPMB: ± cts/s FPMA: ± cts/s FPMB: ± cts/s

7 A new object in NGC 1068? 30" Γ ~ 1.7±0.2 E cut-off ~ 20 kev 30" L 2-10keV ~ erg s -1 ² Simultaneous Swift data in the kev band Feb " Nov " L 2-10keV ~ erg s -1 L 2-10keV < 1039 erg s -1 February, June,

8 vs NGC 1068 during this monitoring shows a behaviour similar to that observed three years ago Aug 2017: high state Feb 2018: low state Jul&Nov 2017: to be explored! July 2017 Aug 2017 Nov 2017 Feb 2018 Aug 2014 Aug 2017 Feb 2015 Feb 2018 Countrate kev Aug 2014: 0.032±0.001 cts/s Aug 2017: 0.032±0.001 cts/s Countrate kev Feb 2015: 0.025±0.001 cts/s Feb 2018: 0.027±0.001 cts/s But now, we have one more observation between these two

9 Monitoring results We adopt the Bauer +15 model leaving only the obscuring N H and flux of the primary component free to vary. N H cm -2 norm = ph cm-2 s -1 kev -1 N H = ( ) cm -2 norm = ph cm-2 s -1 kev -1 July 2017 Aug 2017 N H = ( ) cm -2 norm = ph cm-2 s -1 kev -1 N H ~10 25 cm -2 norm = 1.29 ph cm-2 s -1 kev -1 Nov 2017 Feb 2018

10 Monitoring results To break the N H -norm degeneracy, we assume the same intrinsic X-ray luminosity during the whole monitoring July 2017 Aug 2017 Nov 2017 Feb 2018 χ 2 r ~1.1 We obtain an intrinsic X-ray luminosity consistent within the errors with those inferred using other proxies (e.g. mid-ir and [OIII]).

11 Monitoring results To break the N H -norm degeneracy, we assume the same intrinsic X-ray luminosity during the whole monitoring M cm -3 N H (10 24 cm -2 ) days July Aug Sep Oct Nov Dec Jan Feb Time (month) We observe N H variability on time-scales of ~1 month. R= GM BH t2 n 2 2 ~ t 2 2 NH 91 days cm N H OBS1 OBS2 ΔN H = (2.3±1.0) 1024 cm R=( )M 7 n 10 pc OBS3 OBS4 ΔN H (2.6±0.6) 1024 cm -2 R (0.40±0.26)M 7 n 2 10 pc

12 Summary and conclusions q Analysis of the latest NuSTAR monitoring of NGC 1068, composed of four observations of ~50 ks each and probing time-scales from 1 to 6 months. 1 A brand new flaring ULX reaching a luminosity of ~ erg/s in three months and disappearing in the following four months; 2 Two unveiling events due to Compton-thick material located in the innermost part of the torus or even more inside.

13 13 th AGN Meeting Milano, 9-12 October 2018 Any questions? Just ask!