New optical/uv counterparts and SEDs of Isolated NS ATISH KAMBLE, D. KAPLAN (UW-MILWAUKEE), M. VAN KERKWIJK (TORONTO) AND W. HO (SOUTHAMPTON)
RX J1856...a puzzle! Featureless BB spectrum instead of harder than Wien tail or any spectral features (Burwitz et al 2001, 2003) Optical excess = 8 (Walter & Matthews 1997; van Kerkwijk & Kulkarni 2001) but Rayleigh-Jeans Fλ (erg/s/cm 2 /Å) 10 12 10 13 10 14 10 15 10 16 10 17 10 18 10 19 XMM CXO WFPC2/F170W WFPC2/F300W WFPC2/F450W WFPC2/F606W X-ray => Too small Radii 10 20 10 1 10 2 10 3 Wavelength (Å) Optical => too large Radii (Braje & Romani 2002)
Is RX J1856 special or do all INSs show similar behavior (Optical Excess, Rayleigh- Jeans spectrum)? Could this behavior be explained?
Identifying counterparts easy HST photometry => very reliable 4
easy Identifying counterparts some-what easy
Identifying counterparts easy some-what easy difficult Mignani et al. 2009
Identifying counterparts optical
Identifying counterparts optical UV Estimated proper motions => consistent with Motch et al. (2005, 2009)
10 12 CXO 10 13 XMM Fλ (erg/s/cm 2 /Å) 10 14 10 15 10 16 10 17 10 18 WFPC2/F170W WFPC2/F300W WFPC2/F450W WFPC2/F606W 10 19 10 20 10 1 10 2 10 3 Wavelength (Å)
5 FUVMAMA F25SRF2 F140LP 0420.0 5022 F170W F25QTZ F300W F450W F475W 50CCD F606W F28X50LP Cooler WFPC2/F170W 6 1856.5 3754 CXO WFPC2/F450W WFPC2/F606W WFPC2/F300W 4 10 12 10 13 10 14 XMM Fλ (erg/s/cm 2 /Å) 10 15 10 16 10 17 10 18 10 19 10 20 10 1 10 2 10 3 Wavelength (Å) power law with index : 4.2-2.5 opt excess : 5-50 power law might be too simplistic => lines/ wings (Pavlov s talk PSR0656) log10 [λ 4 Fλ (Å 4 erg/s/cm 2 /Å)] 5 5 6 5 6 5 6 5 6 5 0806.4 4123 0720.0 3125 1605.3+3249 1308.6+2127 2143.0+0654 6 1000 2000 3000 4000 5000 6000 7000 Wavelength (Å) Hotter
Different emission regions : Pulsed fraction v/s Optical Excess 25 Braje & Romani 2002, Kaplan et al. 2011 25 20 20 Pulsed Fraction (%) 15 10 Pulsed Fraction (%) 15 10 5 5 0 0 5 10 15 20 25 30 35 40 45 50 55 Optical Excess 0 2 4 6 8 10 12 14 Optical Excess small hotspot => large pulsed fraction and optical excess : No strong correlation
Different emission regions : Opt/UV as separate BBs Braje & Romani 2002, Kaplan et al. 2011 100 RX J2143 RX J1605 ROUV/RX 10 RX J1308 RX J0720 RX J0806 RX J1856 RX J0420 Dotted lines : unabsorbed BB 1 0.02 0.1 1 T OUV /T X
Different emission regions : Pulsed fraction v/s Optical Excess Braje & Romani 2002, Kaplan et al. 2011 small Hotspot => large pulsed fraction and optical excess : No strong correlation Separate BB : Unreasonably high radii for NS Spectral Index 4.6 4.4 4.2 4 3.8 3.6 3.4 3.2 Rayleigh-Jeans 3 spectral-index v/s kt : 2.8 Hotter objects have 2.6 smaller spectral index 2.4 40 50 60 70 80 90 100 110 kt (ev)
Magnetospheric emission : non-thermal Lum-X v/s Edot 38 37 Isolated Neutron Stars Rotation Powered Pulsars NT Lum-X of INSs are close to 100% of Edot. Comparatively, radio pulsars have NT Lum-X = 10^-3 x Edot (Becker & Trumper 1997) Log(Luminosity : 0.1-2.4 kev) (erg/s) 36 35 34 33 32 31 30 29 28 27 29 30 31 32 33 34 35 36 37 38 39 Log(Edot) (erg/s)
Magnetospheric emission : Lum-opt v/s Edot NT Lum-X of INSs are close to 100% of Edot. Comparatively, radio pulsars have NT Lum-X = 10^-3 x Edot (Becker & Trumper 1997) Lum-Opt of INSs are >10^-3 x Edot. Radio pulsars have Lum-Opt <10^-6 x Edot (Zalin & Pavlov 2004) Log(Optical Luminosity) (erg/s) 36 34 32 30 28 26 24 Isolated Neutron Stars Rotation Powered Pulsars 22 30 32 34 36 38 40 42 Log(Edot) (erg/s)
Magnetospheric emission : Optical Excess v/s Edot NT Lum-X of INSs are close to 100% of Edot. Comparatively, radio pulsars have NT Lum-X = 10^-3 x Edot (Becker & Trumper 1997) Lum-Opt of INSs are >10^-3 x Edot. Radio pulsars have Lum-Opt <10^-6 x Edot (Zalin & Pavlov 2004) Optical Excess 100 10 If part of the optical emission is due to spin down => Optical Excess - Edot correlation : No such definitive correlation is seen 1 29 29.5 30 30.5 31 31.5 32 Log(Edot) (erg/s)
Magnetized Atmosphere models Magnetized atmosphere models (Ho et al. 2008) => Optical/UV excess may depend on B models : B = 1-30 x 10^12 G, kt = 20-400 ev, partially ionised hydrogen Brightness differs from BB but Rayleigh-Jeans behavior stays Wings of Proton-Cyclotron line can reproduce the spectral behavior of INSs partly => B_model << B_timing
Conclusions Counterparts of all seven INSs have been identified unambiguously All INSs show optical excess The Excess in some cases deviate significantly from the Rayleigh-Jeans regime Explanations ranging from different emission regions to mechanisms considered. None seems sufficient. More observations required to clearly characterize the optical/uv excess
Details & Back up slides
RCS models Resonant Cyclotron Scattering (Lyutikov & Gavriil 2006) => thermal photons matching cyclotron freq. of the NS magnetosphere undergo efficient repeated scatterings Photons are up-scattered => Thermal spectrum gets modified => produces BB+PL hard tail (see Rea et al. 2008) The model would retain Rayleigh-Jeans spectrum Would it produce optical/uv excess? (Also see Tong et al 2010, 2011)