1. Long Term Variability Of Vela X-1 with RXTE/ASm
Jamie Keating (University College Dublin)
Tutor: Peter Kretschmar
ESAC Trainee Project 2009

2. Outline Vela X-1 Instruments Data Analysis Problems Results
Conclusions
Future

3. The Project
The aim of the project is to take the existing data of Vela X-1 from the RXTE ASM and to study the variation of the source, from orbit to orbit and with respect to the average 'orbit profile'.
Motivation
Little is known about the long term variability of pulsars.
No long term study has been done previously.
Similarities between sgHMXB and SFXT (IGR J Jain et al. 2009)

4. Vela X-1: A quick overview
Super giant High Mass X-ray Binary (HMXB)
Neutron star with a OB supergiant companion HD 77581
Orbital period of 8.96 days
Contained in a dense stellar wind
X-ray emission powered through wind accretion

5. Vela X-1: Wind Accretion
Interaction of the wind with the NS leads to X-ray emission.
Material is accelerated outwards.
Luminous OB stars produce powerful winds.
Inhomogeneous wind.
Clumpy wind model
Blondin et al.

6. RXTE and the ASM: In a nutshell
Launched on 30th December 1995
2-10 keV
80% of the sky every 90 minutes
3 shadow cameras covering 6 x 90 degree FOV
heasarc.gsfc.nasa.gov

7. Data Analysis Programs created in the IDL environment. Light curves
- Long Term
- Comparison between day variations in orbital profiles
Judging by eye at first to get an idea of data trends
Average profile with shifting average

8. Data Analysis
Profile comparison for multiple orbits over the full light curve
Secondary peak in a lot of average orbital profiles over a few hundred days.
Long term flux per orbit
Study of the deviation of this flux value from the average profile per orbit.
Statistical analysis: Chi squared test, average flux distribution.
Periodic variation? Xronos software (efsearch)

9. Problems
ASM channel drifting post 2001

10. More Problems Distinguishing between an off-state and missing data
Some data also deemed as unreliable (1996 gap)

11. Results Movement of middle peak
Drowned out over the long term due to this movement.

12. Results
Histogram showing the phase bin where max and min values for each orbit fall.

13. Results Long term binned profile
Evolution of Chi squared value per orbit over a long time scale.

14. Results
Gaussian on average flux
Chi squared distribution

15. Swift-BAT Burst Alert Telescope
Primarily designed for rapid response to GRB events
Highly sensitive over a 15-50keV range
heasarc.gsfc.nasa.gov

16. Why use Swift-BAT?
Flux is dramatically effected by absorption in the soft X-ray range.
Swift-BAT gives an insight to the higher energies.
Results similar to the ASM results will give an indication of a general tendency of Vela X-1

17. Swift Light Curve
Raw data. No filtering has been done.

18. Conclusions so far... Very variable x-ray source
No apparent super-orbital periodicity in the data studied so far
Interesting orbital features at the 2-10keV energy range
Possibly different for the higher energies
Lots still to do!

19. What Next?.... Create colour plots for the RXTE/ASM data.
Use the Swift-BAT data to compare.
Look for any trends in the data with more statistical methods.
Try and come to a conclusion on the tendencies of the long term variability of Vela X-1.

20. Thanks!!!
Any (easy) Questions?