Extreme optical outbursts from a magnetar-like transient source: SWIFT J

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1 Extreme optical outbursts from a magnetar-like transient source: SWIFT J Gottfried Kanbach 1 Alexander Stefanescu 1,2 Agnieszka Słowikowska 3 Jochen Greiner 1 Sheila McBreen 4 Glòria Sala 5 1 Max-Planck-Institut für extraterrestrische Physik, Giessenbachstr., D Garching, Germany 2 now: Kayser-Threde, Munich 3 University of Zielona Góra, Zielona Góra Poland 4 School of Physics, University College Dublin, Belfield, Dublin 4, Ireland. 5 Institut d'estudis Espacials de Catalunya (IEEC) CSIC, Barcelona, Spain Reference Oct 22, 2012 PSR WS, MPIfR, Bonn 1

2 Swift BAT reported a GRB on 10 June 2007, 20:52:52 UT: single peak t 90 ~4.6sec power law Γ~1.76 (15-150keV) named GRB XRT could only observe 50 min later due to viewing constraint: R.A. = 19h55m09.6s, Dec = +26d14'06.7" (J2000) Peak flux ( kev): 5x10-8 erg cm -2 s -1 Assume isotropic emission (distance 5 kpc): 1.5x10 38 d 2 5kpc erg/s Oct 22, 2012 PSR WS, MPIfR, Bonn 2

3 XRT observations of GRB070610: (Kasliwal et al, 2008) Spectra: absorbed power laws 6 Outside / Inside flare: Γ= 1.71±0.11 / 1.74±0.48 Out: N H = 7.2 (+1.4,-1.2)x10 21 cm -2 In: N H = 9.2 (+9.1,-5.7) x10 21 cm -2 N.B. galactic extinction uncertain (8 19) x10 21 cm X-ray peak: 7.5x10 37 d 2 5kpc erg/s 1 st week level : 1.3x10 34 d 2 5kpc erg/s T-T Oct 22, 2012 PSR WS, MPIfR, Bonn 0 [78500+s] 3 0

4 Searching for GRB optical afterglows: OPTIMA-Burst High time resolution optical ( nm) photometer with single photon time tagging; quick reaction to GRB notices TCS Skinakas Obs. 1.3m SWIFT GCN Oct 22, 2012 PSR WS, MPIfR, Bonn 4

5 GRB at (l,b) = (63.3,-1.0) is most likely a galactic source at d~5kpc à Swift J OPTIMA-Burst did what it was supposed to do: 57 sec after the GRB (28 sec after the GCN notice) the optical search for an afterglow started at the coarse BAT location Oct 22, 2012 PSR WS, MPIfR, Bonn 5

6 1 first 10 sec exposure 2 2 nd exposure Oct 22, 2012 PSR WS, MPIfR, Bonn 6

7 Oct 22, 2012 PSR WS, MPIfR, Bonn 7 1

8 Oct 22, 2012 PSR WS, MPIfR, Bonn 8 2

9 2 Optical lightcurve during first hour of observations Oct 22, 2012 PSR WS, MPIfR, Bonn 9

10 Swift XRT Oct 22, 2012 PSR T-TWS, 0 [78500+s] MPIfR, Bonn 10

11 Oct 22, 2012 PSR WS, MPIfR, Bonn 11

12 Oct 22, 2012 PSR WS, MPIfR, Bonn 12

13 OPTIMA Keck: 15 Jun :30 à t-t0=4x10 5 s Much later >24.5 in R, i Oct 22, 2012 PSR WS, MPIfR, Bonn 13

14 Late time optical counterpart of Swift J (Kasliwal et al., 2008): extinction corrected absolute magnitude NIR (K band) > 21.5 M K > 3.6 R > 26.0 M R > 4.8 à No giant or supergiant star in the system or star cooler than G8 (for d=10kpc cooler than M3) Most likely an isolated source of high-energy emission: à neutron star; black hole (with fossil accretion disk?) Oct 22, 2012 PSR WS, MPIfR, Bonn 14

15 Details of optical outbursts: Oct 22, 2012 PSR WS, MPIfR, Bonn 15

16 t~95400 t~ Hz (X-ray burst) Kasliwal et al.,2008 Oct 22, 2012 PSR WS, MPIfR, Bonn 16

17 log-normal fit to burst fluence (red) or binned rates: N(x,σ)=exp(-0.5(lnx/σ) 2 / (x σ sqrt(2π)) Oct 22, 2012 PSR WS, MPIfR, Bonn 17

18 Summary of observational facts: Swift BAT ( kev): single outburst T 90 = 4.6 s peak luminosity: 1.5 x (d/5kpc) 2 erg s -1 Swift XRT ( kev): one large & several small flares peak luminosity: 7.5 x (d/5kpc) 2 erg s -1 Optical: more than 70 major and minor flares brightest flares with Δm > 6mag, I max ~14 peak luminosity: 1.8 x (d/5kpc) 2 erg s -1 short timescales to ~0.3sec à emitting region <10 10 cm Consistent X-ray and optical QPOs; P = 6-8 sec Burst fluence distribution fitted by a log-normal fct. à similar to eartquakes or self-organized critical system no long term optical, NIR, or radio counterpart found Oct 22, 2012 PSR WS, MPIfR, Bonn 18

19 Proposed scenario: a magnetar with dominant optical flaring possible theoretical concepts: optical ion cyclotron emission: coherent microwave and radio emission emitted near the neutron star is absorbed higher in the magnetosphere by ions at their cyclotron resonance, and then re-emitted in the optical nearer to the poles, where the ion cyclotron-cooling and transit times become comparable. (Beloborodov and Thompson: Corona of magnetars, ApJ. 657, 967 (2007): Synchrotron emission in the outer magnetosphere: electrons with ~400 MeV in a field of 500 G produce characteristic synchrotron emission at 1.5x10 15 Hz and have a lifetime of ~ few seconds. That points to an altitude of ~ 6000 R NS for a surface field of G. For P Spin, NS ~7 sec the lightcylinder is at 1.5x10 7 R NS The electron accelerator could then be located in the outer magnetosphere Oct 22, 2012 PSR WS, MPIfR, Bonn 19

20 Magnetar with twisted fields Solar Flare Hz Type II 20 MHz Oct 22, 2012 PSR WS, MPIfR, Bonn 20

21 The End Publications: Markwardt et al., ATEL #1102, 17 Sep 2007 Kasliwal, M.M., et al., ApJ, 678, 1127 (2008) Stefanescu et al., Nature, 455, 503, 2008 Castro-Tirado et al., Nature, 455, 506, 2008 Oct 22, 2012 PSR WS, MPIfR, Bonn 21

22 Overview of 5 nights of observations of Swift J X-ray flare P60 opt. at sec data Oct 22, 2012 PSR WS, MPIfR, Bonn 22

23 Fitting the 69 individual bursts with FRED functions <τ rise > ~ 6 sec min,max: s <τ decay > ~ 13 sec : s Oct 22, 2012 PSR WS, MPIfR, Bonn 23

24 OPTIMA-Burst at 1.3m Skinakas Observatory, University of Heraklion, Crete, Greece Oct 22, 2012 PSR WS, MPIfR, Bonn 24

25 X-ray spectral index vs. spin down: (Marsden, D. & White, N.E. 2001, ApJ, 551, L155) Swift J burst spectrum May 25 Oct 22, 26, Vulcano PSR WS, Workshop MPIfR, Bonn 2010 Spin-down: (2-7)x10-11 rad s -2

26 The correlation of spectral index (1.7±0.3) and spin-down rate (Marsden & White, 2001, ApJ, 551, L155) converts the spectrum into a spin-down of (2-7)x10-11 rad s -2 The usual magnetic dipole radiation spin down ( ) gives a field P(s) B o (G) 5 (0.6-1) x G 10 (1.7-3) x G PSR WS, MPIfR, Bonn Oct 22,

27 Summary of observational facts: Very bright optical flares with Δm>6mag, I~14 à 1.8 x (d/5kpc) 2 erg s -1 short timescales to ~0.3sec à emitting region <10 10 cm Consistent X-ray and optical QPOs; P = 6-8 sec Burst optical fluence distribution fitted by a log-normal fct. à similar to eartquakes or self-organized critical system Lower optical fluences seem associated with larger time interval from preceding outburst Gamma (BAT), soft X-ray (XRT) and optical emissions don t seem to be tightly correlated 27