J1158+5820 1400 MHz CGCG292-057 DSS Chandra view on the … · 2017. 7. 10. · Figure 6: model D=...
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Chandra view on the active nucleus of the restarted radio galaxy CGCG 292-057 K. Balasubramanian 1 , A. Goyal 1 , R. Thimmappa 1 , L. Stawarz 1 , M.Sobolewska 2 , A. Siemiginowska 2 , C. C. Cheung 3 , D. Koziel-Wierzbowska 1 , & M. Jamrozy 1 1 Astronomical observatory, Jagiellonianuniversity, Orla 171, 30-244 Krakow, Poland(email : [email protected]) 2 Harvard Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138, USA; 3 Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352, USA). Abstract We present an analysis of the 90 ksec Chandra ACIS-I data for the galaxy CGCG 292-057 (z =0.054), which is a remarkable system showing at optical wavelengths, strong evidence for a relatively recent merger event. Radio images reveal a similarly complex picture, with a pair of compact young/inner radio lobes confined to the host galaxy, and embedded within larger-scale old/outer radio lobes characterized by the X-shaped morphology. The active nucleus in the system is clearly detected in the newly obtained Chandra data. We model the X-ray spectrum of the core assuming various emission models, including an absorbed power-law, a power-law plus thermal emission component, and a two-temperature thermal plasma. The best fit was however obtained assuming a model consisting of a power-law emission scattered by a hot ionized gas (giving rise to the 6.7 keV iron line). Introduction In Active Galactic Nuclei (AGN), relativistic jets and high-energy emission of accretion disks can interact with the interstellar medium (ISM) of host galaxies by ionizing, heating, mixing, and pushing out the surrounding gas, affecting in this way the properties and structure of the hosts (e.g. Fabian 2012; Morganti et al. 2013). CGCG 292-057 is a well known post-merger starforming galaxy (Singh et al. 2015), with two pair of lobes (hereafter, outer and inner), clearly indicative of an intermittent jet activity (Fig. 1; Koziel-Wierzbowska et al. 2012). The outer lobes are believed to have formed during the previous, long-terminated cycle of the jet activity, while the inner coaxial lobes are considered as a manifestation of a new episode of the enhanced jet production in the system, triggered by a sudden increase in the SMBH accretion rate. The inner structure of CGCG 292-057 is still confined within the host galaxy, making the source an excellent target for a de- tailed study of the interaction between newly-born radio jets and a post-merger ISM. The spatially resolved (∼ 0.5 00 at the pointing center) Chandra observations can, in principle, help to disentan- gle the different contributors to the X-ray emission (e.g., reprocessed emission from corona versus shock heating of the ISM due to expanding radio lobes) in CGCG 292-057. J1158+5820 1400 MHz DECLINATION (J2000) RIGHT ASCENSION (J2000) 12 00 00 11 59 45 30 15 00 58 45 30 58 26 24 22 20 18 16 14 outer lobes background source CGCG292-057 DSS inner lobes RIGHT ASCENSION (J2000) 11 59 12 10 08 06 04 02 00 58 21 30 15 00 20 45 30 15 00 19 45 Figure 1: DSS optical image overlayed with 1.4 GHz radio contours from NVSS (black; beam size ∼ 45 00 ) and FIRST (white; beam size ∼ 5 00 ). The NVSS map of the target reveals extended radio lobes of the “X-shape morphology”. Chandra X-ray observations, data, and spectral analysis CGCG 292-057 was imaged with the ACIS instrument onboard Chandra X-ray observa- tory for a total of 93 ks in cycle 16. The data analysis was carried out with CIAO version 4.8 software, CALDB version 4.7.2, using standard procedure. A circular region of 1 00 .5 radius centered on a source position was used for spectral extraction while an an- nular region with inner and outer radii of 1 00 .8 and 4 00 .4, respectively, was used for local background extraction (Fig. 2). Spectral fit- ting was carried out with Sherpa using Cstat. The results of our preliminary analysis are presented in Table 1 and Figs 3-8. Figure 2: ACIS-S image of CGCG 292-057 Table 1: Spectral models and the model parameters for CGCG 292-057 Model N (1) H N (2) H kT (a) kT (b) Γ E line EW line Cstat/DOF [×10 22 cm -2 ][×10 22 cm -2 ] [keV] [keV] [keV] [eV] (1) (2) (3) (4) (5) (6) (7) (8) (9) A 2.67 +0.30 -0.27 — — — 0.88 +0.04 -0.04 —- —- 669.08/886 B 2.00 +0.8 -0.45 — — — 0.61 +0.40 -0.25 6.7 +0.9 -0.7 209 +142.2 -0.06 663.10/884 C 3.56 +0.32 -0.28 — > 10 —- —- — — 674.60/886 D 1.01 +0.20 -0.16 5.37 +0.46 -0.43 0.32 +0.07 -0.24 —- 1.56 +0.23 -0.05 — — 636.41/883 E 1.96 +0.57 -0.52 2.26 +1.14 -1.99 > 10 0.09 +0.12 -0.02 — — — 636.07/883 F 0.48 +0.32 -0.07 7.60 +5.168 -2.42 — — 1.39 +0.99 -0.28 6.9 +1.2 -0.8 22.5 +15.3 -7.2 665.11/884 Data within the range 0.5–7.0 keV; modeled using the C-stat. Fitting optimized with levmar and neldermead methods. Background not subtracted, but modeled (as unabsorbed power-law) simultaneously with the source. Galactic absorption modeled with phabs assuming N (Gal ) H =0.0143 × 10 22 cm -2 . Power-law Figure 3: model A = zphabs*PL. Power-law + Gauss Figure 4: model B= zphabs*(PL + xszgauss) with σ =0.1 keV. APEC Figure 5: model C = zphabs*bvapec with Z i = Z . APEC+Power-law Figure 6: model D= zphabs(1)*bvapec+zphabs(2)*PL with Z i = Z . APEC+APEC Figure 7: model E= zphabs(1)*bvapec(a)+zphabs(2)*bvapec(b) with Z i = Z except for the iron in bvapec(a) (best fit value: Z Fe ∼ 1.65 × Z ). Scattered Power-law + Gauss Figure 8: model F= zphabs*(1 - fsc)*PL+zphabs2*(fsc * PL + xszgauss) with the scattered PL fraction fsc = 0.03 and σ =0.1 keV. Conclusions The main conclusions from our preliminary analysis of the X-ray core emission in CGCG 292-057: (1) Simple power-law fits imply rather flat photon indices (Γ ≤ 1), which would rule out coronal emission, and instead suggest inner jets/compact lobes as a dominant source of the observed X-ray emission. (2) Simple thermal models are not favoured, because of poorly constrained very high gas temperatures implied by the fitting (kT > 10 keV); however, hints for a colder gas at soft X-rays (kT < 1keV). (3) Evidence for the presence of ionized iron line around ∼ 6.7 keV. (4) Absorption at the source, at the level of N H ∼ a few × 10 22 cm -2 , consistent with the ISM of a gas-rich, starforming host galaxy. (5) Our fits favour the model consisting of a power-law emission scattered by a hot ionized gas giving rise to the 6.7 keV iron line; for such, the implied power-law photon index Γ > 1 and the 0.5–7.0 keV luminosity of 5 × 10 41 erg/s, consistent with the LINER classification of the active nucleus in CGCG 292-057. Acknowledgments This work was supported by the Polish National Science Centre (DEC- 2012/04/A/ST9/00083) and the Chandra guest investigator program GO5-16109X. This research was supported in part by NASA through con- tract NAS8-03060 (A.S., M.S.) to the Chandra X-ray Center. References Fabian, A. C. 2012, ARAA, 50, 455 Koziel-Wierzbowska, D., Jamrozy, M., et al. 2012, MNRAS, 422, 1546 Morganti R., Fogasy J., Paragi Z., et al., 2013, Sci, 341, 1082 Singh, V., Ishwara-Chandra, C. H., Sievers, J., et al. 2015, MNRAS, 454, 1556
Transcript of J1158+5820 1400 MHz CGCG292-057 DSS Chandra view on the … · 2017. 7. 10. · Figure 6: model D=...
Chandra view on the active nucleus of the restarted radio galaxy CGCG 292-057K. Balasubramanian1, A. Goyal1, R. Thimmappa1, Ł. Stawarz1, M.Sobolewska2, A. Siemiginowska2, C. C. Cheung3, D. Kozieł-Wierzbowska1, & M. Jamrozy1
1Astronomical observatory, Jagiellonian university, Orla 171, 30-244 Krakow, Poland(email : [email protected])2Harvard Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138, USA; 3Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352, USA).
Abstract
We present an analysis of the 90 ksec Chandra ACIS-I data for the galaxy CGCG 292-057 (z = 0.054), which is a remarkable system showing at optical wavelengths, strong evidence for a relatively recentmerger event. Radio images reveal a similarly complex picture, with a pair of compact young/inner radio lobes confined to the host galaxy, and embedded within larger-scale old/outer radio lobescharacterized by the X-shaped morphology. The active nucleus in the system is clearly detected in the newly obtained Chandra data. We model the X-ray spectrum of the core assuming various emissionmodels, including an absorbed power-law, a power-law plus thermal emission component, and a two-temperature thermal plasma. The best fit was however obtained assuming a model consisting of apower-law emission scattered by a hot ionized gas (giving rise to the 6.7 keV iron line).
Introduction
In Active Galactic Nuclei (AGN), relativistic jets and high-energy emission of accretion diskscan interact with the interstellar medium (ISM) of host galaxies by ionizing, heating, mixing, andpushing out the surrounding gas, affecting in this way the properties and structure of the hosts(e.g. Fabian 2012; Morganti et al. 2013). CGCG 292−057 is a well known post-merger starforminggalaxy (Singh et al. 2015), with two pair of lobes (hereafter, outer and inner), clearly indicative ofan intermittent jet activity (Fig. 1; Kozieł-Wierzbowska et al. 2012). The outer lobes are believed tohave formed during the previous, long-terminated cycle of the jet activity, while the inner coaxiallobes are considered as a manifestation of a new episode of the enhanced jet production in thesystem, triggered by a sudden increase in the SMBH accretion rate. The inner structure of CGCG292−057 is still confined within the host galaxy, making the source an excellent target for a de-tailed study of the interaction between newly-born radio jets and a post-merger ISM. The spatiallyresolved (∼ 0.5′′ at the pointing center) Chandra observations can, in principle, help to disentan-gle the different contributors to the X-ray emission (e.g., reprocessed emission from corona versusshock heating of the ISM due to expanding radio lobes) in CGCG 292−057.
J1158+5820 1400 MHz
DE
CL
INA
TIO
N (
J200
0)
RIGHT ASCENSION (J2000)12 00 00 11 59 45 30 15 00 58 45 30
58 26
24
22
20
18
16
14
outer lobes
backgroundsource
CGCG292-057 DSS
inner lobes
RIGHT ASCENSION (J2000)11 59 12 10 08 06 04 02 00
58 21 30
15
00
20 45
30
15
00
19 45
Figure 1: DSS optical image overlayed with 1.4 GHz radio contours from NVSS (black; beam size ∼ 45′′) and FIRST(white; beam size ∼ 5′′). The NVSS map of the target reveals extended radio lobes of the “X-shape morphology”.
Chandra X-ray observations, data, and spectral analysis
CGCG 292−057 was imaged with the ACISinstrument onboard Chandra X-ray observa-tory for a total of 93 ks in cycle 16. Thedata analysis was carried out with CIAOversion 4.8 software, CALDB version 4.7.2,using standard procedure. A circular regionof 1′′.5 radius centered on a source positionwas used for spectral extraction while an an-nular region with inner and outer radii of1′′.8 and 4′′.4, respectively, was used for localbackground extraction (Fig. 2). Spectral fit-ting was carried out with Sherpa using Cstat.The results of our preliminary analysis arepresented in Table 1 and Figs 3-8.
Figure 2: ACIS-S image of CGCG 292−057
Table 1: Spectral models and the model parameters for CGCG 292−057
Model N(1)H N
(2)H kT (a) kT (b) Γ Eline EWline Cstat/DOF
[×1022 cm−2] [×1022 cm−2 ] [keV] [keV] [keV] [eV](1) (2) (3) (4) (5) (6) (7) (8) (9)
A 2.67+0.30−0.27 — — — 0.88+0.04
−0.04 —- —- 669.08/886B 2.00+0.8
−0.45 — — — 0.61+0.40−0.25 6.7+0.9
−0.7 209+142.2−0.06 663.10/884
C 3.56+0.32−0.28 — > 10 —- —- — — 674.60/886
D 1.01+0.20−0.16 5.37+0.46
−0.43 0.32+0.07−0.24 —- 1.56+0.23
−0.05 — — 636.41/883E 1.96+0.57
−0.52 2.26+1.14−1.99 > 10 0.09+0.12
−0.02 — — — 636.07/883F 0.48+0.32
−0.07 7.60+5.168−2.42 — — 1.39+0.99
−0.28 6.9+1.2−0.8 22.5+15.3
−7.2 665.11/884
Data within the range 0.5–7.0 keV; modeled using the C-stat.Fitting optimized with levmar and neldermead methods.Background not subtracted, but modeled (as unabsorbed power-law) simultaneously with the source.Galactic absorption modeled with phabs assuming N (Gal)
H = 0.0143× 1022 cm−2.
Power-law
Figure 3: model A = zphabs*PL.
Power-law + Gauss
Figure 4: model B= zphabs*(PL + xszgauss) with σ=0.1 keV.
APEC
Figure 5: model C = zphabs*bvapec with Zi = Z�.
APEC+Power-law
Figure 6: model D= zphabs(1)*bvapec+zphabs(2)*PL with Zi = Z�.
APEC+APEC
Figure 7: model E= zphabs(1)*bvapec(a)+zphabs(2)*bvapec(b) with Zi =Z� except for the iron in bvapec(a) (best fit value: ZFe ∼ 1.65× Z�).
Scattered Power-law + Gauss
Figure 8: model F= zphabs*(1 - fsc)*PL+zphabs2*(fsc * PL + xszgauss) withthe scattered PL fraction fsc = 0.03 and σ = 0.1 keV.
ConclusionsThe main conclusions from our preliminary analysis of the X-ray core emission in CGCG 292-057: (1) Simple power-law fits imply rather flat photon indices (Γ ≤ 1), which would rule out coronal emission, and instead suggest inner jets/compactlobes as a dominant source of the observed X-ray emission. (2) Simple thermal models are not favoured, because of poorly constrained very high gas temperatures implied by the fitting (kT > 10 keV); however, hints for a colder gas at softX-rays (kT < 1keV). (3) Evidence for the presence of ionized iron line around ∼ 6.7 keV. (4) Absorption at the source, at the level of NH ∼ a few × 1022 cm−2, consistent with the ISM of a gas-rich, starforming host galaxy. (5) Our fits favourthe model consisting of a power-law emission scattered by a hot ionized gas giving rise to the 6.7 keV iron line; for such, the implied power-law photon index Γ > 1 and the 0.5–7.0 keV luminosity of 5 × 1041 erg/s, consistent with the LINERclassification of the active nucleus in CGCG 292-057.
AcknowledgmentsThis work was supported by the Polish National Science Centre (DEC-
2012/04/A/ST9/00083) and the Chandra guest investigator programGO5-16109X. This research was supported in part by NASA through con-
tract NAS8-03060 (A.S., M.S.) to the Chandra X-ray Center.
ReferencesFabian, A. C. 2012, ARAA, 50, 455
Kozieł-Wierzbowska, D., Jamrozy, M., et al. 2012, MNRAS, 422, 1546Morganti R., Fogasy J., Paragi Z., et al., 2013, Sci, 341, 1082Singh, V., Ishwara-Chandra, C. H., Sievers, J., et al. 2015, MNRAS, 454,
1556
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