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. 6 Apr. 12

Spectroscopy

Phase Average Analysis Phase 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)

April Sep.

coun

t sec

-1

Pulse Phase0 0.5 1 1.5 2

Energy keV

coun

ts s

-1 k

eV-1

ParameterValue

(1σ error)

NH (1022 cm-2) 3.0 ±0.3

α 1.12 +0.04 -0.03

Ecut (keV) 24.8 +0.9-1.0

APL 2.00 ± 0.05

kTBB (keV) 2.13 +0.05-0.04

RBB (km) 0.63 +0.22-0.21

EFe (keV) 6.41 +0.07-0.06

σFe (keV) 0.1 (fixed)

AFe (10-3 cm-2 s-1) 1.5 ± 0.2

χ2red (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

PCAHEXTE

- 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.

Pul

se P

rofil

eco

unt s

-1χ2 re

d

2-10 keV

10-20 keV

NH (1022 cm-2)

Ecut (keV)

APL (10-12 ergs s-1 cm-2)

ABB (Rkm/D10kpc)2

AFe (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

2010/3/15 4/4 4/24 5/15

3/31MAXI ATel

RXTE4/6, 12, 15

Swift4/1, 3, 21

cou

nt

s-1 c

m-2

cou

nt

s-1 c

m-2

Contact to me to take more discussions ! usui@hp.phys.titech.ac.jp

Tokyo Institute of Technology

KAWAI LABRyuichi USUI, Mikio MORII, Nobuyuki KAWAI, and MAXI team

0 0.5 1 1.5 2

Unit of APL : 10-9 ergs cm-2 s-1 in energy range 3-10 keVBlackbody radius RBB assuming a distance of 3.3 kpc ([4])

Δχ

Dip