Abbas Askar University of Belgrade 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

2-year Erasmus Mundus Masters Course in Astronomy and Astrophysics that started in Fall year Erasmus Mundus Masters Course in Astronomy and Astrophysics that started in Fall 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

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

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 G High magnetic fields B ≈ 10 7 G to 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

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

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

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

Rise time ≈ seconds Rise time ≈ seconds Decay time ≈ seconds Decay time ≈ seconds Recurrence time ≈ hours to day Recurrence time ≈ hours to day Energy release in 10 seconds ≈ ergs Energy release in 10 seconds ≈ ergs 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

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 s time resolution and no spectral resolution 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

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

Observational Data Observational Data – Downloaded Standard-1 RXTE data for 1187 bursts cataloged by Galloway et al 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

4U /Feb/19994U /Sep/ th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

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

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 /Oct/ th November th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

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

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

SourceTypeNo. of Bursts with slow onsets Total Bursts from the Source KS TOS127 4U AO2106 EXO TG122 4U AOS15172 SAX J TG216 4U TAOS331 4U A247 Aql X-1TAO157 EXO TD194 Type T = transient O=burst oscillations D= dipper A=atoll source S= superburst G=global Cluster Association

Normalized gradients for data with slow rises Normalized gradients for data with slow rises 4U /Nov/ th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

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

Comparing normalized persistent flux level Comparing normalized persistent flux level For 4U For 4U Average NPF level Average NPF level th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

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

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

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

Review of X-ray Bursts: Review of X-ray Bursts: – Strohmayer & Bildsten, “New Views of Thermonuclear Bursts” (2003) – Theoretical Review: Page & Reddy, “Dense Matter in Compact Stars: Theoretical Developments and Observational Constraints” (2006) – Lattimer & Prakash, “Neutron Star Observations: Prognosis for Equation of State Constraints” (2006) 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): ph/ ph/ http://arxiv.org/abs/astro- ph/ 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