Extreme optical outbursts from a magnetar-like transient source: SWIFT J1955+26 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-85758 Garching, Germany 2 now: Kayser-Threde, Munich 3 University of Zielona Góra, 65-417 Zielona Góra Poland 4 School of Physics, University College Dublin, Belfield, Dublin 4, Ireland. 5 Institut d'estudis Espacials de Catalunya (IEEC) CSIC, 08034 Barcelona, Spain Reference Oct 22, 2012 PSR WS, MPIfR, Bonn 1
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 GRB070610 XRT could only observe 50 min later due to viewing constraint: R.A. = 19h55m09.6s, Dec = +26d14'06.7" (J2000) Peak flux (15-150 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
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 -2 4 2 X-ray peak: 7.5x10 37 d 2 5kpc erg/s 1 st week level : 1.3x10 34 d 2 5kpc erg/s 40 60 80 100 T-T Oct 22, 2012 PSR WS, MPIfR, Bonn 0 [78500+s] 3 0
Searching for GRB optical afterglows: OPTIMA-Burst High time resolution optical (450-950 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
GRB070611 at (l,b) = (63.3,-1.0) is most likely a galactic source at d~5kpc à Swift J195509.6+261406 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
1 first 10 sec exposure 2 2 nd exposure Oct 22, 2012 PSR WS, MPIfR, Bonn 6
Oct 22, 2012 PSR WS, MPIfR, Bonn 7 1
Oct 22, 2012 PSR WS, MPIfR, Bonn 8 2
2 Optical lightcurve during first hour of observations Oct 22, 2012 PSR WS, MPIfR, Bonn 9
6 4 2 0 Swift XRT 40 60 80 100 Oct 22, 2012 PSR T-TWS, 0 [78500+s] MPIfR, Bonn 10
Oct 22, 2012 PSR WS, MPIfR, Bonn 11
Oct 22, 2012 PSR WS, MPIfR, Bonn 12
OPTIMA Keck: 15 Jun 2007 12:30 à t-t0=4x10 5 s Much later >24.5 in R, i Oct 22, 2012 PSR WS, MPIfR, Bonn 13
Late time optical counterpart of Swift J1955+26 (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
Details of optical outbursts: Oct 22, 2012 PSR WS, MPIfR, Bonn 15
t~95400 t~96260 0.1446 Hz (X-ray burst) Kasliwal et al.,2008 Oct 22, 2012 PSR WS, MPIfR, Bonn 16
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
Summary of observational facts: Swift BAT (15-150 kev): single outburst T 90 = 4.6 s peak luminosity: 1.5 x 10 38 (d/5kpc) 2 erg s -1 Swift XRT (0.3-10 kev): one large & several small flares peak luminosity: 7.5 x 10 37 (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 10 35 (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
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 10 14 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
Magnetar with twisted fields Solar Flare outburst @ 1.5 10 15 Hz Type II burst @ 20 MHz Oct 22, 2012 PSR WS, MPIfR, Bonn 20
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
Overview of 5 nights of observations of Swift J1955+26 X-ray flare P60 opt. at 78560 sec data Oct 22, 2012 PSR WS, MPIfR, Bonn 22
Fitting the 69 individual bursts with FRED functions <τ rise > ~ 6 sec min,max: 0.42 62 s <τ decay > ~ 13 sec : 0.33 69 s Oct 22, 2012 PSR WS, MPIfR, Bonn 23
OPTIMA-Burst at 1.3m Skinakas Observatory, University of Heraklion, Crete, Greece Oct 22, 2012 PSR WS, MPIfR, Bonn 24
X-ray spectral index vs. spin down: (Marsden, D. & White, N.E. 2001, ApJ, 551, L155) Swift J1955+26 burst spectrum May 25 Oct 22, 26, 2012 2010 Vulcano PSR WS, Workshop MPIfR, Bonn 2010 Spin-down: (2-7)x10-11 rad s -2
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 10 15 G 10 (1.7-3) x 10 15 G PSR WS, MPIfR, Bonn Oct 22, 2012 26
Summary of observational facts: Very bright optical flares with Δm>6mag, I~14 à 1.8 x 10 35 (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