1. Outburst of LS V +44 17 detected by MAXI, RXTE, Swift Be X-ray Binary LS V +44 17 INTRODUCTION - Be X-ray Binary consists of a neutron star and Be star (‘e’ stands for emission) - The orbit of the binary is wide and eccentric with orbital periods in a few – a few hundred days. - Mass transfer from the Be star to the neutron star take places through Be circumstellar disk. - Discovered by ROSAT All-sky survey X-ray source name : RX J0440.9+4431 - Known as persistent Be X-ray Binary - No recorded of outbursts - RXTE PCA observation ([1]) reported Pulse Period : 202.5 ± 0.5 sec Spectra fitted with cut-off power law model Outbursts of LS V +44 17 - MAXI detected an outburst from LS V +44 17 on 2010 March 31 (ATel # 2527). Also triggered Swift BAT ToO observations by RXTE - Another outburst reported on 2010 September 9 by INTEGRAL (ATel # 2828). ANALYSIS Pulse - Pulse period estimated by Epoch Folding Search for RXTE data is ~205 sec on Apr. 6. - Pulse profile on Apr. 6 has a narrow dip in soft band (2-10 keV). Similar dip structure reported for GX 1+4, A0535+262 and RX J0812.4-3114. The dip seen only at outburst peak. Not seen in other observations. Pulse Profile (RXTE/PCA) Apr. 6Apr. 12 Spectroscopy Phase Average AnalysisPhase Resolved Analysis On 2010 March 31, MAXI discovered an outburst from LS V +44 17 which is one of the Be/X-ray Binaries. LS V +44 17 had not showed any outbursts since 1997 when the source identified as the Be/X-ray Binary. After the MAXI discovery, RXTE and Swift observed the source both in three times. Pulse profiles of the outburst obtained by RXTE showed a dip structure at soft X-ray bands (2-10 keV) when the outburst was nearly most bright. These origin is interpreted as a partial ’eclipse’ of a shaded emission region by an accretion column of the neutron star. In my poster, I present results of phase resolved spectroscopy to explain the dip structure in the pulse profile of LS V +44 17. MAXI GSC (2-20 keV) Swift BAT (15-50 keV) AprilSep. count sec -1 Pulse Phase 0 0.5 1 1.5 2 Energy keV counts s -1 keV -1 Parameter Value (1σ error) N H (10 22 cm -2 )3.0 ±0.3 α1.12 +0.04 -0.03 E cut (keV)24.8 +0.9 -1.0 A PL 2.00 ± 0.05 kT BB (keV)2.13 +0.05 -0.04 R BB (km)0.63 +0.22 -0.21 E Fe (keV)6.41 +0.07 -0.06 σ Fe (keV)0.1 (fixed) A Fe (10 -3 cm -2 s -1 )1.5 ± 0.2 χ 2 red (d.o.f.)1.15 (116) - RXTE spectra (PCA : 3-30 keV, HEXTE : 20-100 keV) fit with the cut-off power law plus blackbody plus Fe emission line. - The blackbody temperature is ~2 keV, which is higher than other pulsars ([3]) and reaches near a temperature of local Eddinton Limit on the neutron star. Spectrum obtained on Apr. 6 PCA HEXTE - We carried out phase resolved spectroscopy with the same model of phase average analysis. - In the analysis we fixed the photon index, the black body temperature and the Fe line energy obtained in the phase average analysis. - At the dip phase, the absorption column density is much higher than other phases. We infer that the dip results from absorption by the accretion column. Pulse Profile count s -1 χ 2 red 2-10 keV 10-20 keV N H (10 22 cm -2 ) E cut (keV) A PL (10 -12 ergs s -1 cm -2 ) A BB (R km /D 10kpc ) 2 A Fe (cm -2 s -1 ) 0 0.5 1 ⇧ The accretion geometry of X-ray pulsars ([2]). When the accretion column covers the neutron star surface, a partial ‘eclipse’ occurs. REFERENCES [1] Reig and Roche 1999 [2] Galloway et al. 2001 [3] Palombara and Mereghetti 2006 [4] Reig et al. 2005 Pulse Phase 2010/3/154/44/24 5/15 3/31 MAXI ATel RXTE 4/6, 12, 15 Swift 4/1, 3, 21 count s -1 cm -2 Contact to me to take more discussions ! usui@hp.phys.titech.ac.jp Tokyo Institute of Technology KAWAI LAB Ryuichi USUI, Mikio MORII, Nobuyuki KAWAI, and MAXI team 0 0.5 1 1.5 2 Unit of A PL : 10 -9 ergs cm -2 s -1 in energy range 3-10 keV Blackbody radius R BB assuming a distance of 3.3 kpc ([4]) Δχ Dip