Abbas Askar [email protected] University of Belgrade 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia

Abbas AskarAbbas Askar

[email protected]@gmail.com

University of BelgradeUniversity of Belgrade

1212thth November 2011 November 2011 Astronomy Workshop PresentationAstronomy Workshop Presentation Belgrade, SerbiaBelgrade, Serbia

• 2-year Erasmus Mundus Masters Course in 2-year Erasmus Mundus Masters Course in Astronomy and Astrophysics that started in Fall Astronomy and Astrophysics that started in Fall 2010. 2010.

• 3 semesters of courses+1 semester for thesis3 semesters of courses+1 semester for thesis• Offered by a consortium of 5 Universities across 4 Offered by a consortium of 5 Universities across 4

countriescountries

• Standard Grad School Requirements: Bachelor Standard Grad School Requirements: Bachelor Degree, Application Form: Motivation Letter, 2 Degree, Application Form: Motivation Letter, 2 References , English Proficiency, CV References , English Proficiency, CV

• Many Scholarships are AvailableMany Scholarships are Available


• Introduction to Neutron Stars and the Introduction to Neutron Stars and the X-ray Burst PhenomenaX-ray Burst Phenomena

• Introduction to my Bachelor Research Introduction to my Bachelor Research ProjectProject– Observation and AnalysisObservation and Analysis– ResultsResults– ConclusionsConclusions– Further ResearchFurther Research

• General ConclusionsGeneral Conclusions1212thth November 2011 November 2011 Astronomy Workshop PresentationAstronomy Workshop Presentation Belgrade, SerbiaBelgrade, Serbia

• One of the Final States of a Star One of the Final States of a Star • Very compact – about 10 km radiusVery compact – about 10 km radius• Typical Mass > 1.4 MTypical Mass > 1.4 M⊙⊙

• Very dense – one teaspoon of neutron Very dense – one teaspoon of neutron star material weighs as much as all the star material weighs as much as all the buildings in Manhattanbuildings in Manhattan

• Spin rapidly – as fast as 600 times per Spin rapidly – as fast as 600 times per secondsecond

• High magnetic fields High magnetic fields B ≈ 10B ≈ 107 7 G to 10G to 1015 15 GG• Some of the most extreme conditions of Some of the most extreme conditions of

the universe exist in neutron stars.the universe exist in neutron stars.1212thth November 2011 November 2011 Astronomy Workshop PresentationAstronomy Workshop Presentation Belgrade, SerbiaBelgrade, Serbia


• Isolated Neutron Stars and Neutron Isolated Neutron Stars and Neutron Stars in Binary SystemsStars in Binary Systems• Neutron Stars have been observed in Neutron Stars have been observed in Binaries along with other starsBinaries along with other stars and and compact objectscompact objects•LMXB and HMXB: Determined by the LMXB and HMXB: Determined by the mass of the companion starmass of the companion star

• Neutron Star Neutron Star or black hole with a secondary or black hole with a secondary companion with a mass less than 1 solar mass companion with a mass less than 1 solar mass (this could be a main sequence star, a red (this could be a main sequence star, a red giant or even a white dwarf)giant or even a white dwarf)

• When the Roche Lobe of the secondary When the Roche Lobe of the secondary companion fills up a accretion disk forms companion fills up a accretion disk forms and and matter is accreted onto the compact objectmatter is accreted onto the compact object

• These binaries are luminous in X-rays which These binaries are luminous in X-rays which originate from the surface of the neutron star originate from the surface of the neutron star and the inner accretion diskand the inner accretion disk

• Magnetic Field of Neutron stars: Magnetic Field of Neutron stars: B ≈ 10B ≈ 107 7 G to G to 10109 9 GG


• Matter from a Companion Star accretes onto Matter from a Companion Star accretes onto a Neutron Star a Neutron Star • When enough accreted material builds up (a When enough accreted material builds up (a few months)► thermonuclear reactions occur few months)► thermonuclear reactions occur on the neutron star surface (for a few on the neutron star surface (for a few seconds) ► Results in X-ray Burstsseconds) ► Results in X-ray Bursts


• Rise time ≈ 0.5 - 5 secondsRise time ≈ 0.5 - 5 seconds•Decay time ≈ 10 - 100 secondsDecay time ≈ 10 - 100 seconds•Recurrence time ≈ hours to dayRecurrence time ≈ hours to day

•Energy release in 10 seconds ≈Energy release in 10 seconds ≈ 10103939 ergsergs


• Analysis of the onset of thermonuclear Analysis of the onset of thermonuclear burstsbursts– Expected to occur within a fraction of second Expected to occur within a fraction of second – However, there are examples where the onset However, there are examples where the onset

takes hundreds of secondstakes hundreds of seconds

• RXTERXTE– Proportional Counter ArrayProportional Counter Array– High Time ResolutionHigh Time Resolution– Standard-1 Mode with 0.125 s time resolution Standard-1 Mode with 0.125 s time resolution

and no spectral resolutionand no spectral resolution


• Research Aims: Research Aims: – Systematically search through all RXTE-Systematically search through all RXTE-

detected flashes for slow onsetsdetected flashes for slow onsets– Find correlations with other parameters Find correlations with other parameters

of the relevant neutron star of the relevant neutron star


• Observational DataObservational Data– Downloaded Downloaded Standard-1 Standard-1 RXTE data for RXTE data for

1187 bursts cataloged by Galloway et al. 1187 bursts cataloged by Galloway et al. 2008 from NASA archives2008 from NASA archives

– Observations detected from 48 sources Observations detected from 48 sources up to 3up to 3rdrd June 2007 June 2007

– Light CurvesLight Curves


4U 1702-429 21/Feb/1999 4U 1636-536 17/Sep/2001


• Task:Task:• Find bursts with slow onsets from data Find bursts with slow onsets from data

for 1187 X-ray burstsfor 1187 X-ray bursts

• Devise an algorithm that can Devise an algorithm that can determine whether a burst determine whether a burst observation has a slow onsetobservation has a slow onset


• Fit data 150, 100 Fit data 150, 100 and 50 seconds and 50 seconds before the burst to before the burst to a straight linea straight line

• Obtain values for Obtain values for gradient of the gradient of the three intervalsthree intervals

KS 1731-260 3/Oct/1998

• 1212thth November November 20112011 Astronomy Workshop PresentationAstronomy Workshop Presentation Belgrade, SerbiaBelgrade, Serbia

• Chi square merit functionChi square merit function

• Filtering conditions and Light Curve PlotsFiltering conditions and Light Curve Plots– Gradient of the 3 intervals should be more than Gradient of the 3 intervals should be more than

0.5 c/s0.5 c/s-2-2

– Reduced chi square values for the straight line fit Reduced chi square values for the straight line fit should be less than 2should be less than 2

– Gradient/Error should be greater than 3Gradient/Error should be greater than 3– Gradient between the interval -50 and 0 should Gradient between the interval -50 and 0 should

be greater than the gradient between -100 and 0be greater than the gradient between -100 and 0

2

1

2 ),(

N

i i

ii bxayba


• 28 bursts from the Galloway et al. 28 bursts from the Galloway et al. 2008 catalogue have slow onsets2008 catalogue have slow onsets

• Bursts with slow onsets found in 8 Bursts with slow onsets found in 8 out of the 48 X-ray burst sources out of the 48 X-ray burst sources catalogued by Galloway et al 2008.catalogued by Galloway et al 2008.


Source Type No. of Bursts with slow onsets

Total Bursts from the Source

KS 1731-260 TOS 1 274U 1728-34 AO 2 106EXO 1745-248

TG 1 224U 1636-536 AOS 15 172SAX J1748.9-2021

TG 2 164U 1608-52 TAOS 3 314U 1705-44 A 2 47Aql X-1 TAO 1 57EXO 0748-676 TD 1 94

TypeT = transient O=burst oscillations D= dipperA=atoll source S= superburst G=global Cluster Association

http://vizier.cfa.harvard.edu/viz-bin/VizieR-5?-out.add=.&-source=21790360&-corr=PK=Name&-out.max=9999&Name==KS%201731-260

http://vizier.cfa.harvard.edu/viz-bin/VizieR-5?-out.add=.&-source=21790360&-corr=PK=Name&-out.max=9999&Name==4U%201728-34

http://vizier.cfa.harvard.edu/viz-bin/VizieR-5?-out.add=.&-source=21790360&-corr=PK=Name&-out.max=9999&Name==EXO%201745-248

http://vizier.cfa.harvard.edu/viz-bin/VizieR-5?-out.add=.&-source=21790360&-corr=PK=Name&-out.max=9999&Name==EXO%201745-248


http://vizier.cfa.harvard.edu/viz-bin/VizieR-5?-out.add=.&-source=21790360&-corr=PK=Name&-out.max=9999&Name==SAX%20J1748.9-2021

http://vizier.cfa.harvard.edu/viz-bin/VizieR-5?-out.add=.&-source=21790360&-corr=PK=Name&-out.max=9999&Name==SAX%20J1748.9-2021



• Normalized gradients for data with Normalized gradients for data with slow risesslow rises

4U 1608-52 21/Nov/2001


• For 4U 1636-536For 4U 1636-536– Values of normalized gradient (between Values of normalized gradient (between

-100 and 0) vary between 0.6 and 2.6-100 and 0) vary between 0.6 and 2.6

• Comparing normalized persistent flux Comparing normalized persistent flux levellevel

• For 4U 1636-536For 4U 1636-536

• Average NPF level 0.038Average NPF level 0.0381212thth November 2011 November 2011 Astronomy Workshop PresentationAstronomy Workshop Presentation Belgrade, SerbiaBelgrade, Serbia

• Slow onsets found for 28 bursts from Slow onsets found for 28 bursts from 8 sources8 sources

• No more than approximately 10% of No more than approximately 10% of bursts have slow onsetsbursts have slow onsets


• Correlate data of slow onset burts Correlate data of slow onset burts with other properties of the sourcewith other properties of the source

• Study power spectra of the slow Study power spectra of the slow onsetsonsets

• Possible relationship between mHz Possible relationship between mHz Quasi-Periodic Oscillations (QPO) and Quasi-Periodic Oscillations (QPO) and slow onsetsslow onsets


• Studies of thermonuclear X-ray Studies of thermonuclear X-ray bursts can be very useful in order to bursts can be very useful in order to constrain properties of neutron stars constrain properties of neutron stars (mass, spin rate, radius etc)(mass, spin rate, radius etc)

• Extensive observational data is Extensive observational data is available in archives that can be available in archives that can be easily obtained and studied! easily obtained and studied!


• Review of X-ray Bursts:Review of X-ray Bursts:– Strohmayer & Bildsten, “New Views of Thermonuclear Bursts” Strohmayer & Bildsten, “New Views of Thermonuclear Bursts”

(2003) http://arxiv.org/abs/astro-ph/0301544(2003) http://arxiv.org/abs/astro-ph/0301544– Theoretical Review: Page & Reddy, “Dense Matter in Compact Theoretical Review: Page & Reddy, “Dense Matter in Compact

Stars: Theoretical Developments and Observational Constraints” Stars: Theoretical Developments and Observational Constraints” (2006) http://arxiv.org/abs/astro-ph/0608360(2006) http://arxiv.org/abs/astro-ph/0608360

– Lattimer & Prakash , “Neutron Star Observations: Prognosis for Lattimer & Prakash , “Neutron Star Observations: Prognosis for Equation of State Constraints” (2006) http://arxiv.org/abs/astro-Equation of State Constraints” (2006) http://arxiv.org/abs/astro-ph/0612440ph/0612440

• Catalogue: Catalogue: – Galloway D. et al, "Thermonuclear (Type I) X-Ray Bursts Galloway D. et al, "Thermonuclear (Type I) X-Ray Bursts

Observed by the Rossi X-Ray Timing Explorer." Observed by the Rossi X-Ray Timing Explorer." The Astrophysical The Astrophysical Journal Supplement Series Volume 179, Issue Journal Supplement Series Volume 179, Issue 2(2008): 360-422 2(2008): 360-422 http://arxiv.org/abs/astro-ph/0608259http://arxiv.org/abs/astro-ph/0608259

• mHz Oscillations: Altamirano D. et al, "Millihertz Oscillation mHz Oscillations: Altamirano D. et al, "Millihertz Oscillation Frequency Drift Predicts the Occurrence of Type I X-Ray Frequency Drift Predicts the Occurrence of Type I X-Ray Bursts." Bursts." The Astrophysical Journal Volume 673, Issue 1(2008): The Astrophysical Journal Volume 673, Issue 1(2008): L35-L38L35-L38


Documents

Abbas Askar [email protected] University of Belgrade 12 th November 2011 Astronomy Workshop Presentation Belgrade, Serbia