Systematic study of magnetar outbursts

Transcription

1 Systematic study of magnetar outbursts Francesco Coti Zelati Institute for Space Sciences, CSIC-IEEC, Barcelona In collaboration with N. Rea (CSIC-IEEC, U. Amsterdam), J. A. Pons (U. Alicante), S. Campana (INAF-OAB), P. Esposito (U. Amsterdam) Coti Zelati et al., submitted Physics of Neutron Stars 2017, Ioffe Institute, Saint Petersburg, July 10, 2017

2 Observational properties Swift-XRT INTEGRAL COMPTEL About 25 X-ray pulsars with Lx ~ erg s -1 Fermi-LAT X-ray luminosity generally larger than the rotational energy loss rate soft and hard X-ray emission ( kev); thermal + PL spectrum 4U Kuiper et al. 2004; Abdo et al rotating with P ~ 2-12 s magnetic fields of ~ Gauss flaring activity in soft gamma-rays ( s; Lx ~ erg s -1 ) faint infrared/optical emission (Israel et al. 2010) Kaspi et al transient pulsed radio emission (in 4 cases) see Rea & Esposito (2011); Turolla et al. (2015); Kaspi & Beloborodov (2017) for reviews Camilo et al. 2006

3 Magnetar flaring activity (timescale: seconds/minutes) Short bursts duration ~0.01-1s Lx ~ erg s -1 soft γ-rays thermal spectra (kt ~ kev) Intermediate bursts duration 1-40 s peak ~ erg s -1 abrupt on-set usually soft γ-rays thermal spectra Giant Flares very rare events (only 3 observed) Lx > 3x10 44 erg s -1 initial peak lasting <1 s with a hard spectrum ringing tail that can last > 500s, with softer spectrum and showing the NS spin pulsations Kaspi et al Israel et al Israel et al (Palmer et al. 2005) Palmer et al. 2005

4 Magnetar outburst activity (timescale: months/years) Bolometric luminosity (10 33 erg s 1 ) SGR (1998) 1E (2002) SGR CXOU (2006) SGR (2008) SGR E (2008) 1E (2009) SGR SGR Swift J Swift J CXOU (2011) 1E (2011) 1E (2012) SGR SGR E (2016) Time (days since outburst onset) Coti Zelati et al. submitted

5 Outburst mechanisms 1. Internal source of heat: Local magnetic stresses deform part of the stellar crust. Plastic flows convert the magnetic energy into heat. Partly is conducted up to the surface and radiated (thermal afterglow) 2. External source of heat: Crustal displacements twist up the external B-field. Returning currents hit and heat the NS surface. The bundle dissipates as the energy supply from the star interior decreases. Both processes are likely at work. Emission can be sustained up to a few years. Thompson et al. 2002; Beloborodov 2009; Pons & Rea 2012; Parfrey et al. 2013; Beloborodov & Levin 2014 Beloborodov & Li 2016; Li et al. 2016

6 Motivation for the study A systematic and homogeneous analysis of the spectral properties of magnetars in outbursts is needed to: (i) model all outbursts cooling curves in a consistent way; (ii) unveil possible correlations among different parameters Deeper insight into the emission processes via modelling with internal crustal cooling codes. Varying the injected energy Pons & Rea 2012 Pons & Rea 2012 Varying the quiescent luminosity

7 Systematic study magnetar outbursts: some numbers The magnetar outburst online catalog - 23 outbursts - 14 magnetars + 2 high-b RPPs + CCO in RCW about 1100 X-ray observations (12 Ms) between 1998 and mid May 2017

8 Systematic study magnetar outbursts: data analysis The magnetar outburst online catalog - reduction of raw data sets, extraction of spectra for all observations - spectral fitting with BB, 2BB, BB+PL and more physically-motivated models - extraction of fluxes and luminosities in each observation - extraction of the light curves - empirical modelling of the bolometric cooling curves - estimate of the outburst energetics and decay-timescale

9 High quality X-ray spectra 1E (2008) 1E (2009) Chandra Chandra SGR SGR XMM-Newton XMM-Newton Swift Swift XMM-Newton Chandra

10 Cooling curves: XTE J Absorbed X-ray flux BB1 X-ray luminosity Bolometric BB2 X-ray luminosity X-ray luminosity

11 The outburst sample, fitted models, energetics and timescales Bolometric luminosity (10 33 erg s -1 ) SGR (1998) 1E (2002) SGR CXOU (2006) SGR (2008) SGR E (2008) 1E (2009) SGR SGR Swift Swift J CXOU (2011) E (2011) E (2012) SGR E (2016) Time (days since outburst onset)

12 Correlations & Anticorrelations

13 Correlations & Anticorrelations SGR σ Swift J PSR J Swift SGR (2008) 1E (2009) 1E (2000) 1E (2008) 1E (2016) SGR SGR (1998) SGR CXOU (2006) PSR J CXOU (2011) SGR XTEJ E (2011) SGR E E (2016) 4U (2011, 2015) SGR (2001) 1E (2002) SGR (2006) 1E (2012) Pons & Rea 2012 The definition of transient magnetars as opposed to the persistent magnetars is deceptive: it only reflects their different quiescent luminosities 4.0 σ 1E (2009) SGR SGR E (2016) 1E (2011) Large flux enhancements can only be observed in faint quiescent magnetars 1E (2016) SGR (1998) 1E (2000) XTEJ CXOU (2006) SGR (2008) SGR PSR J Swift E (2012) PSR J Swift J SGR SGR E (2002) CXOU (2011) Pons & Rea 2012

14 Correlations & Anticorrelations Magnetars CCOs RPPs XDINSs CCOs depart significantly from the trend. 5.3 σ with CCOs Expected in the hidden magnetic field scenario: fallback accretion onto the NS ( MSun in hrs-days) can bury a B field of a few G into the inner crust (Viganò & Pons 2012; Torres-Forné et al. 2016). The external B field is lower than the internal hidden B field, hence does not trace the bolometric luminosity Magnetars CCOs RPPs XDINSs RPPs depart a bit from the trend. The larger luminosity wrt the prediction is likely due to slamming particles heating the NS surface, providing an additional source of heat 6.5 σ without CCOs

15 Correlations & Anticorrelations 3.7 σ 1E (2009) SGR E (2011) 1E (2016) XTEJ SGR (1998) CXOU (2006) SGR (2008) PSR J SGR SGR Broad agreement with the idea that magnetar outbursts are ultimately powered by the dissipation of the B-field PSR J Swift E (2012) Swift J E (2002) SGR SGR CXOU (2011) SGR SGR E (2009) 1E (2011) 3.3 σ 1E (2016) XTEJ SGR (1998) SGR (2008) CXOU (2006) SGR PSR J Young magnetars undergo more energetic outbursts PSR J Swift J E (2012) 1E (2002) Swift SGR SGR CXOU (2011)

16 Correlations & Anticorrelations 3.9 σ 1E (2009) SGR (1998) 1E (2000) Swift SGR (2008) 1E (2016) XTEJ E (2011) SGR SGR SGR E (2012) CXOU (2006) 1E (2016) SGR SGR PSR J CXOU (2011) PSR J E (2002) Swift J Similar decay pattern for all magnetar outbursts Expected in the interior crustal cooling model (the deeper the location of the energy release, the more energetic the outburst, the longer the time for heat diffusion) Expected in the untwisting bundle model (Τ E^0.5)

17 The magnetar outburst online catalog - online catalogues with all files and parameters soon publicly available magnetars.ice.csic.es

18 The magnetar outburst online catalog - online catalogues with all files and parameters soon publicly available Fit your favourite function to different parameters magnetars.ice.csic.es

19 The magnetar outburst online catalog - online catalogues with all files and parameters soon publicly available magnetars.ice.csic.es