Outburst of LS V +44 17 detected by MAXI, RXTE, Swift

1. Outburst of LS V +44 17 detected by MAXI, RXTE, Swift RXTE 4/6, 12, 15 Tokyo Institute of Technology KAWAI LAB 3/31 MAXI ATel Swift 4/1, 3, 21 Ryuichi USUI, Mikio MORII, Nobuyuki KAWAI, and MAXI team 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. 2010/3/15 4/4 4/24 5/15 INTRODUCTION Outbursts of LS V +44 17 Be X-ray Binary • 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). • - 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. MAXI GSC (2-20 keV) LS V +44 17 count s-1 cm-2 count s-1 cm-2 • 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 Swift BAT (15-50 keV) April Sep. ANALYSIS Pulse Profile (RXTE/PCA) Dip Apr. 6 Apr. 12 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. count sec-1 0 0.5 1 1.5 2 0 0.5 1 1.5 2 Pulse Phase Spectroscopy 2-10 keV Phase Average Analysis Phase Resolved Analysis Pulse Profile count s-1 • 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. • 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. 10-20 keV χ2red NH(1022 cm-2) Spectrum obtained on Apr. 6 Ecut (keV) PCA HEXTE APL (10-12 ergs s-1 cm-2) counts s-1 keV-1 ABB (Rkm/D10kpc)2 Δχ AFe (cm-2 s-1) Energy keV ⇧ The accretion geometry of X-ray pulsars ([2]). When the accretion column covers the neutron star surface, a partial ‘eclipse’ occurs. Unit of APL : 10-9 ergs cm-2 s-1 in energy range 3-10 keV Blackbody radius RBB assuming a distance of 3.3 kpc ([4]) 0 0.5 1 Pulse Phase [1] Reig and Roche 1999 [2] Galloway et al. 2001 [3] Palombara and Mereghetti 2006 [4] Reig et al. 2005 Contact to me to take more discussions ! REFERENCES usui@hp.phys.titech.ac.jp