1. Abbas Askar abbas.askar@gmail.com University of Belgrade 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

2. 2-year Erasmus Mundus Masters Course in Astronomy and Astrophysics that started in Fall 2010. 2-year Erasmus Mundus Masters Course in Astronomy and Astrophysics that started in Fall 2010. 3 semesters of courses+1 semester for thesis 3 semesters of courses+1 semester for thesis Offered by a consortium of 5 Universities across 4 countries Offered by a consortium of 5 Universities across 4 countries Standard Grad School Requirements: Bachelor Degree, Application Form: Motivation Letter, 2 References, English Proficiency, CV Standard Grad School Requirements: Bachelor Degree, Application Form: Motivation Letter, 2 References, English Proficiency, CV Many Scholarships are Available Many Scholarships are Available 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

3. Introduction to Neutron Stars and the X-ray Burst Phenomena Introduction to Neutron Stars and the X-ray Burst Phenomena Introduction to my Bachelor Research Project Introduction to my Bachelor Research Project – Observation and Analysis – Results – Conclusions – Further Research General Conclusions General Conclusions 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

4. One of the Final States of a Star One of the Final States of a Star Very compact – about 10 km radius Very compact – about 10 km radius Typical Mass > 1.4 M ⊙ Typical Mass > 1.4 M ⊙ Very dense – one teaspoon of neutron star material weighs as much as all the buildings in Manhattan Very dense – one teaspoon of neutron star material weighs as much as all the buildings in Manhattan Spin rapidly – as fast as 600 times per second Spin rapidly – as fast as 600 times per second High magnetic fields B ≈ 10 7 G to 10 15 G High magnetic fields B ≈ 10 7 G to 10 15 G Some of the most extreme conditions of the universe exist in neutron stars. Some of the most extreme conditions of the universe exist in neutron stars. 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

5. 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia Isolated Neutron Stars and Neutron Stars in Binary Systems Isolated Neutron Stars and Neutron Stars in Binary Systems Neutron Stars have been observed in Binaries along with other stars and compact objects Neutron Stars have been observed in Binaries along with other stars and compact objects LMXB and HMXB: Determined by the mass of the companion star LMXB and HMXB: Determined by the mass of the companion star

6. Neutron Star or black hole with a secondary companion with a mass less than 1 solar mass (this could be a main sequence star, a red giant or even a white dwarf) Neutron Star or black hole with a secondary companion with a mass less than 1 solar mass (this could be a main sequence star, a red giant or even a white dwarf) When the Roche Lobe of the secondary companion fills up a accretion disk forms and matter is accreted onto the compact object When the Roche Lobe of the secondary companion fills up a accretion disk forms and matter is accreted onto the compact object These binaries are luminous in X-rays which originate from the surface of the neutron star and the inner accretion disk These binaries are luminous in X-rays which originate from the surface of the neutron star and the inner accretion disk Magnetic Field of Neutron stars: B ≈ 10 7 G to 10 9 G Magnetic Field of Neutron stars: B ≈ 10 7 G to 10 9 G 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

7. Matter from a Companion Star accretes onto a Neutron Star Matter from a Companion Star accretes onto a Neutron Star When enough accreted material builds up (a few months)► thermonuclear reactions occur on the neutron star surface (for a few seconds) ► Results in X- ray Bursts When enough accreted material builds up (a few months)► thermonuclear reactions occur on the neutron star surface (for a few seconds) ► Results in X- ray Bursts 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

8. Rise time ≈ 0.5 - 5 seconds Rise time ≈ 0.5 - 5 seconds Decay time ≈ 10 - 100 seconds Decay time ≈ 10 - 100 seconds Recurrence time ≈ hours to day Recurrence time ≈ hours to day Energy release in 10 seconds ≈ 10 39 ergs Energy release in 10 seconds ≈ 10 39 ergs 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

9. Analysis of the onset of thermonuclear bursts Analysis of the onset of thermonuclear bursts – Expected to occur within a fraction of second – However, there are examples where the onset takes hundreds of seconds RXTE RXTE – Proportional Counter Array – High Time Resolution – Standard-1 Mode with 0.125 s time resolution and no spectral resolution 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

10. Research Aims: Research Aims: – Systematically search through all RXTE-detected flashes for slow onsets – Find correlations with other parameters of the relevant neutron star 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

11. Observational Data Observational Data – Downloaded Standard-1 RXTE data for 1187 bursts cataloged by Galloway et al. 2008 from NASA archives – Observations detected from 48 sources up to 3 rd June 2007 – Light Curves 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

12. 4U 1702-429 21/Feb/19994U 1636-536 17/Sep/2001 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

13. Task: Task: Find bursts with slow onsets from data for 1187 X-ray bursts Find bursts with slow onsets from data for 1187 X-ray bursts Devise an algorithm that can determine whether a burst observation has a slow onset Devise an algorithm that can determine whether a burst observation has a slow onset 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

14. Fit data 150, 100 and 50 seconds before the burst to a straight line Fit data 150, 100 and 50 seconds before the burst to a straight line Obtain values for gradient of the three intervals Obtain values for gradient of the three intervals KS 1731-260 3/Oct/1998 12 th November 2011 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

15. Chi square merit function Chi square merit function Filtering conditions and Light Curve Plots Filtering conditions and Light Curve Plots – Gradient of the 3 intervals should be more than 0.5 c/s -2 – Reduced chi square values for the straight line fit should be less than 2 – Gradient/Error should be greater than 3 – Gradient between the interval -50 and 0 should be greater than the gradient between -100 and 0 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

16. 28 bursts from the Galloway et al. 2008 catalogue have slow onsets 28 bursts from the Galloway et al. 2008 catalogue have slow onsets Bursts with slow onsets found in 8 out of the 48 X-ray burst sources catalogued by Galloway et al 2008. Bursts with slow onsets found in 8 out of the 48 X-ray burst sources catalogued by Galloway et al 2008. 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

17. SourceTypeNo. of Bursts with slow onsets Total Bursts from the Source KS 1731-260TOS127 4U 1728-34AO2106 EXO 1745-248TG122 4U 1636-536AOS15172 SAX J1748.9- 2021TG216 4U 1608-52TAOS331 4U 1705-44A247 Aql X-1TAO157 EXO 0748-676TD194 Type T = transient O=burst oscillations D= dipper A=atoll source S= superburst G=global Cluster Association

18. Normalized gradients for data with slow rises Normalized gradients for data with slow rises 4U 1608-52 21/Nov/2001 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

19. For 4U 1636-536 For 4U 1636-536 – Values of normalized gradient (between -100 and 0) vary between 0.6 and 2.6

20. Comparing normalized persistent flux level Comparing normalized persistent flux level For 4U 1636-536 For 4U 1636-536 Average NPF level 0.038 Average NPF level 0.038 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

21. Slow onsets found for 28 bursts from 8 sources Slow onsets found for 28 bursts from 8 sources No more than approximately 10% of bursts have slow onsets No more than approximately 10% of bursts have slow onsets 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

22. Correlate data of slow onset burts with other properties of the source Correlate data of slow onset burts with other properties of the source Study power spectra of the slow onsets Study power spectra of the slow onsets Possible relationship between mHz Quasi- Periodic Oscillations (QPO) and slow onsets Possible relationship between mHz Quasi- Periodic Oscillations (QPO) and slow onsets 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

23. Studies of thermonuclear X-ray bursts can be very useful in order to constrain properties of neutron stars (mass, spin rate, radius etc) Studies of thermonuclear X-ray bursts can be very useful in order to constrain properties of neutron stars (mass, spin rate, radius etc) Extensive observational data is available in archives that can be easily obtained and studied! Extensive observational data is available in archives that can be easily obtained and studied! 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

24. Review of X-ray Bursts: Review of X-ray Bursts: – Strohmayer & Bildsten, “New Views of Thermonuclear Bursts” (2003) http://arxiv.org/abs/astro-ph/0301544 http://arxiv.org/abs/astro-ph/0301544 – Theoretical Review: Page & Reddy, “Dense Matter in Compact Stars: Theoretical Developments and Observational Constraints” (2006) http://arxiv.org/abs/astro-ph/0608360 http://arxiv.org/abs/astro-ph/0608360 – Lattimer & Prakash, “Neutron Star Observations: Prognosis for Equation of State Constraints” (2006) http://arxiv.org/abs/astro-ph/0612440 http://arxiv.org/abs/astro-ph/0612440 Catalogue: Catalogue: – Galloway D. et al, "Thermonuclear (Type I) X-Ray Bursts Observed by the Rossi X-Ray Timing Explorer." The Astrophysical Journal Supplement Series Volume 179, Issue 2(2008): 360-422 http://arxiv.org/abs/astro- ph/0608259 http://arxiv.org/abs/astro- ph/0608259http://arxiv.org/abs/astro- ph/0608259 mHz Oscillations: Altamirano D. et al, "Millihertz Oscillation Frequency Drift Predicts the Occurrence of Type I X-Ray Bursts." The Astrophysical Journal Volume 673, Issue 1(2008): L35-L38 mHz Oscillations: Altamirano D. et al, "Millihertz Oscillation Frequency Drift Predicts the Occurrence of Type I X-Ray Bursts." The Astrophysical Journal Volume 673, Issue 1(2008): L35-L38 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia