Wide-Band Spectral Studies of Magnetar Burst and Persistent Emissions

Transcription

1 Wide-Band Spectral Studies of Magnetar Burst and Persistent Emissions Yujin E. Nakagawa Waseda University, Japan Collaborators Kazuo Makishima 1, Teruaki Enoto 2, Takanori Sakamoto 3, Tatehiro Mihara 4, Mutsumi Sugizaki 4, Kazutaka Yamaoka 5, Kevin Hurley 6 Atsumasa Yoshida 5, Poshak Gandhi 7, Makoto S. Tashiro 8, Mikio Morii 9 and HETE-2 Team 1. University of Tokyo, 2. Sanford University, 3. GSFC/NASA, 4. RIKEN, 6. Aoyama Gakuin University, 7. U. C. Berkeley, 8.ISAS/JAXA, 8. Saitama Universisty, 9. Tokyo Institute of Technology Current Understanding and Future Study of Magnetars: Research Strategy in the ASTRO-H era 1 September 2012

2 Highly Magnetized Neutron Star Magnetar Characteristics Typical Light Curves of The Short Burst Magnetic Field : B ~ 14 G Dissipation of Magnetic Energy Thompson & Duncan 1995 SGR (HETE-2) 2-30 kev ~0 ms Nakagawa et al X-ray Counterparts 1. Soft Gamma Repeater (SGR) 6(+3) Objects 2. Anomalous X-ray Pulsar (AXP) (+1) Objects Pulse Periods : P ~ 2-12 s X-ray Persistent Emission Sporadic Burst Activities Location : Galactic Plane 30-0 kev A Distribution of SGRs and AXPs MAXI/GSC SGR U E RXS J SGR 6(+3) AXP (+1) CXOU J CXOU J E E E SGR SGR SGR SGR XTE J AX J SGR CXOU J

3 Typical Energy Spectrum of Magnetar Phenomenological Studies Soft Comp. Hard Comp. Persistent Emission ~ 11 erg cm 2 e.g., 2BB or BB+PL e.g., Marsden & White 2001; Tiengo et al. 2008; Nakagawa et al. 2009; Enoto 20 PL (Hard X-ray Component) e.g., Kuiper et al. 2006; Enoto et al. 20 s 1 2BB : Two-Blackbody Model, BB+PL : Blackbody+Powerlaw, PL : Powerlaw Small SGR/AXP Bursts ~ 8 erg cm 2BB 2 PL (Hard X-ray Component) Nakagawa, Makishima & Enoto 2011; Enoto et al Submitted s 1 Bright SGR Bursts 7 ~ 6 erg cm 2BB e.g., Olive et al. 2004, Nakagawa et al. 2007??? 2 s 1 Persistent Emission Small SGR Bursts Enoto et al. 20 (SGR ) Nakagawa, Makishima & Enoto 2011 (SGR ) Low Temperature BB High Temperature BB Hard X-ray Component Low Temperature BB High Temperature BB Hard X-ray Component

4 Spectral Correlations kt LT -kt HT Correlation L 2BB -L PL Correlation kt kt ( ) kt HT LT / ktht r 0.99 (Sys. Err. : 15%) LT ( / d.o.f. 86 / 92) Nakagawa, Makishima & Enoto 2011 L2BB L PL Persistent Emission Bursts SGR Small bursts SGR Strong burst (See also Enoto et al. 2009) SGR Persistent emission (See also Enoto et al. 20) Nakagawa et al A common radiation mechanism between the bursts and persistent emission. A possibility that the persistent X-ray emission may consist of numerous micro bursts. Nakagawa et al. 2009; Nakagawa, Makishima & Enoto 2011

5 Topics of My Talk 1. HETE-2 X-ray Observations of Bright bursts from SGR Contributions of hard X-ray components in bright SGR bursts. 2. Suzaku X-ray Observations of AXP 4U Comparisons of persistent emission in active phase and quiescent phase.

6 HETE-2 Observations of Bursts from SGR HETE-2 Satellite High Energy Transient Explorer 2 (HETE-2) Launched on 9 October 2000 Gamma-Ray Bursts, SGR Bursts, X-ray Bursts 89 cm Observations of SGR Bursts Mass : 124 kg Height : 89 cm Width : 66 cm Altitude : 625 km Inclination : 0-2 degree (Equatorial Orbit) Attitude : Anti-Solar Pointing 181 Events (18 June August 2005) SGR : 62 Events --> 50 Bursts SGR : 6 Events --> 5 Bursts Out of Filed of View : 113 Events Same Data Sets with Nakagawa et al

7 SGR Bursts Analyses of Individual Spectra We re-analyzed SGR bursts with the following spectral model individually. XSPEC Spectral Model Flux of Hard X-ray Component N H (Blackbody Blackbody Powerlaw) 2 : Estimated with Errors N H [cm 2 ] fixed (Nakagawa et al. 2009) 22 Bursts : Upper Limits 1.5 (SGR ) fixed (Enoto et al. 2011) BID 3326 BID : Burst ID 08 FPL (2-40keV) erg cm 2 s 1 BID 3369 BID : Burst ID FPL (2-40keV) erg cm 2 s 1

8 SGR Bursts Summed Light Curves The BB temperatures of the SGR bright bursts are almost constant. We divided 50 SGR bursts into the following 6 groups and re-analyzed them individually. GROUP1 ( [-6 erg cm-2 s-1]) kev 2- kev 2- kev -25 kev -25 kev kev kev kev 40-0 kev 40-0 kev 40-0 kev kev kev kev kev 0 GROUP3 ( [-6 erg cm-2 s-1]) -25 kev GROUP4 ( [-6 erg cm-2 s-1]) -0.2 GROUP2 ( [-6 erg cm-2 s-1]) GROUP5 ( [-6 erg cm-2 s-1]) 2- kev GROUP6 ( [-6 erg cm-2 s-1]) Bursts 2- kev -25 kev -25 kev -25 kev kev kev kev 40-0 kev 40-0 kev 40-0 kev kev kev kev

9 SGR Bursts 2BB Temperatures XSPEC Spectral Model ~11 kev ~4 kev (Nakagawa et al. 2007) N H (Blackbody Blackbody Powerlaw) N H [cm 2 ] fixed (Nakagawa et al. 2009) free parameter

10 SGR Bursts Summed Spectra (1) GROUP1 ( [-6 erg cm-2 s-1]) Prob (stat.)=1*^-6 (18) GROUP2 ( [-6 erg cm-2 s-1]) Prob (stat.)=2*^-5 (13) 2BB 0 (Enoto et al. 2011) 0 2 (d.o.f.) 1.2(56) 2 (d.o.f.) 1.2(57) 2BB+PL Quiescent Emission Spectra : G = (d.o.f.) 1.3 (58) 2BB 2 (d.o.f.) 0.8 (53) 2BB+PL Prob (stat.)=0.04 (3) 2 (d.o.f.) 1.7 (59) 2 (d.o.f.) 1.3 (55) 2BB GROUP3 ( [-6 erg cm-2 s-1]) 0 2BB+PL Quiescent Emission Spectra : G = 1.5 Quiescent Emission Spectra : G = 1.5 (Enoto et al. 2011) (Enoto et al. 2011) 0 0

11 SGR Bursts Summed Spectra (2) GROUP4 ( [-6 erg cm-2 s-1]) Prob (stat.)=3*^-5 (12) GROUP5 ( [-6 erg cm-2 s-1]) Prob (stat.)=1*^-5 (14) Prob (stat.)=2*^-8 (24) Bursts 2BB 2BB 0 2BB+PL Quiescent Emission Spectra : G = 1.5 (Enoto et al. 2011) 0 2 (d.o.f.) 1.4(68) 2 (d.o.f.) 1.3(64) 2 (d.o.f.) 1.5 (65) 2BB+PL 2 (d.o.f.) 2.3 (70) 2 (d.o.f.) 1.8 (66) 2 (d.o.f.) 2.0 (67) 2BB GROUP6 ( [-6 erg cm-2 s-1]) 0 2BB+PL Quiescent Emission Spectra : G = 1.5 Quiescent Emission Spectra : G = 1.5 (Enoto et al. 2011) (Enoto et al. 2011) 0 0

12 Suzaku ToO Observation of AXP 4U Observation during Active Interval ObsID : (AO-6) Date : :44: :46:21 Nominal Position : XIS XIS Mode : XIS0&XIS1-->Normal, XIS3-->1/4Window Net Exposure : XIS-->41ks, HXD/PIN-->42ks No obvious bursts. XIS0+XIS1+XIS3 (0.2-12keV, Background Subtracted) HXD/PIN (-70keV)

13 AXP 4U Source and Background Regions Source and Background Regions XIS0 XIS1 Background (2 arcmin) Background (2 arcmin) Source (2 arcmin) Source (2 arcmin) kev Background (4x3.5 arcmin) XIS kev Source (4x3.5 arcmin) kev

14 AXP 4U Hardness Ratios Ratio of active and quiescent phase spectra. Hardness Ratios XIS0+XIS1+XIS3 1 HXD/PIN

15 AXP 4U Spectra Spectrum Quoted errors are 90% confidence levels. Tuned background data was used for HXD/PIN analyses. CXB was also subtracted from HXD/PIN spectrum. Black : XIS0 Red : XIS1 Green: XIS3 Blue : HXD/PIN NH = 0.63+/-0.01 (cm-2) ktl = / (kev) kth = 0.63+/-0.01 (kev) G = 1.27+/-0.06 c2 (d.o.f.) = 2932 (1820) F(2-keV) = 7.73+/-0.05 * -11 (erg cm-2 s-1) (Absorbed Flux)

16 AXP 4U nfn Spectra nfn Spectrum High Temperature BB Low Temperature BB Hard X-ray Emission

17 AXP 4U Spectral Parameters Spectral Parameters in Active Phase and Quiescent Phase Quoted errors are 90% confidence levels. Active Phase Quiescent Phase (*) NH (cm-2) 0.63+/ / ktl (kev) / / kth (kev) 0.63+/ /-0.01 G 1.27+/ /-0.11 L2BB (36 erg s-1) (-0., +0.12) / LPL (36 erg s-1) 0.2 (-0.006, ) (-0.009, +0.0) c2 (d.o.f.) 2932 (1820) (*) See Enoto et al for detailed analyses (2508) ~5% ~19%

18 Summary Bright Bursts of SGR We re-analyzed 50 bright bursts from SGR detected by HETE-2, in order to examine effects of the hard Xray component on them. Some bright bursts are well fitted by the two-blackbody model plus the power-law model. Persistent Emission of AXP 4U The Suzaku ToO (AO-6) observation of AXP 4U was performed on 7 September 2011 in active phase. The spectra during the active phase might be harder than that during the quiescent phase. The PL luminosity for the persistent emission of AXP 4U was calculated in the 2-0 kev band.. SGR Bright Bursts -- This Work L2BB LPL SGR Small bursts -- Nakagawa et al SGR (Suzaku AO-1 ToO) Persistent Emission in Active Phase -- Nakagawa et al SGR Strong burst -- Enoto et al Nakagawa et al AXP 4U (Suzaku AO-6 ToO) Persistent Emission in Active Phase -- This Work AXP 4U (Suzaku AO-2) Persistent Emission in Quiescent Phase -- Enoto et al SGR Persistent emission -- Enoto et al. 20