Phase-resolved analysis of LS 5039 with Fermi LAT Gene Leung HKU - - PowerPoint PPT Presentation

Phase-resolved analysis of LS 5039 with Fermi LAT

Gene Leung HKU FAN4 Workshop

Co-workers:Jumpei Takata, KS Cheng

LS 5039

• High-mass X-ray binary
• One of the few HMXBs detected at both GeV and TeV

energies

• Consists of an O6.5V star (~28 MSun) and a compact object

(>~1.8MSun)

• Nature of compact object undetermined
• Black hole? Neutron star?

Orbital configuration

Casares et al. Aragona et al. Sarty et al. (2005) (2009) (2011)

Superior conjunction ~0.05 ~0.65 Inferior conjunction

e ~ 0.24-0.35 w ~ 225°-237° f(SUPC) ~ 0.05 f(INFC) ~ 0.65-0.72

Aragona et al. (2009)

Past Fermi studies

• Abdo et al. (2009), Hadasch et al. (2012)
• Spectral analysis in two broad phase intervals
• Best fitted with power-law with exponential cutoff
• Hadasch et al. (2012) found high energy (>10 GeV) emission

feature

Comparison with previous studies

• Background sources: 1FGL vs 2FGL
• Data, IRFs, diffuse BG: Pass 6 vs Pass 7
• Length of observation: 2.5 years vs 4 years
• Finer binning of orbital phase

Data set

• Time span: 2008 Aug 14 to 2012 May 19
• Energy: 0.1-300 GeV
• ROI: 20°x20° region centered at LS 5039
• Event class: Pass 7 source
• Pass 7 source v6 instrumental response functions
• Excluded events with zenith angle < 100 degrees to avoid

Earth's albedo

• Excluded events from pulse phase (0.05,0.2) and (0.6,0.75) of

nearby pulsar PSR J1826-1256

Phase-averaged spectrum

G = -2.07 +/- 0.07 EC = 2.76 +/- 0.46 GeV

Light curves

0.1-300 GeV S U P C I N F C A p a s t r

• n

P e r i a s t r

• n

S U P C I N F C A p a s t r

• n

Light curves

1-100 GeV 0.1-1 GeV S U P C I N F C A p a s t r

• n

P e r i a s t r

• n

S U P C I N F C A p a s t r

• n

Modulation more prominent in low energies

Hardness ratio

S U P C I N F C A p a s t r

• n

P e r i a s t r

• n

S U P C I N F C A p a s t r

• n

Phase-resolved spectral analysis

• Define 3 equally spaced phase intervals:

– [0.83,1.17] (periastron and INFC) – [0.17,0.5] – [0.5,0.83] (SUPC)

• Perform likelihood fits in each phase intervals, fixing spectral

parameters of sources more than 5 degrees from the target

Division of orbital phase

S U P C I N F C A p a s t r

• n

P e r i a s t r

• n

S U P C I N F C A p a s t r

• n

G = 2.18 +/- 0.07 EC = 2.06 +/- 0.42 GeV G = 1.71 +/- 0.14 EC = 2.12 +/- 0.56 GeV G = 2.09 +/- 0.13 EC = 3.87 +/- 1.50 GeV

• Reduced flux in ~0.1-0.3GeV

compared with previous studies (improved IRFs, diffuse background, etc)

• Enhancement in ~0.1-1GeV for

0.83<f<1.17, i.e. SUPC and periastron

• High energy component most

significant in 0.17<f<0.5

SUPC INFC

Theoretical model (Takata et al. 2013)

• Pulsar scenario
• Magnetospheric emissions
• IC of stellar photons and cold-relativistic pulsar wind
• Termination shocks at two emission regions

Theoretical model fitting

0.5<f<0.83

• Modulation of IC

emissions from cold- relativistic pulsar wind in ~0.1-1 GeV

• IC of shocked pulsar

wind at ~>10 GeV

SUPC INFC

Theoretical model fitting

S U P C I N F C A p a s t r

• n

Summary

• Spectral analysis for 3 phase intervals
• Orbital modulation in 0.1-1 GeV due to cold pulsar wind
• High energy emissions of shocked pulsar wind
• Orbital modulation of spectral hardness