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Vela X-1: Flares & Off States. West Orange High School Manthan Kothari, Lucy Zipf, Neil Savalia, Brian Meise, Krish Pillai. IN TODAY’S PRESENTATION, WE WILL:. Discuss how we chose our project. Describe the Vela X-1 system.

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Vela X-1: Flares & Off States

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Vela x 1 flares off states l.jpg

Vela X-1: Flares & Off States

West Orange High School

Manthan Kothari, Lucy Zipf, Neil Savalia, Brian Meise, Krish Pillai

In today s presentation we will l.jpg


  • Discuss how we chose our project.

  • Describe the Vela X-1 system.

  • Present the Characteristics & Models for flaring behavior for the 20-40 keV range.

  • Present the Characteristics & Models for “off-states for the 20-40 keV range.

  • Present our findings regarding flares and off-states for the 1-10 keV range.

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Why Flares & Off States?

  • Literature Review

    • Kreykenbohm et al., 2008

      Discusses flaring behavior of Vela X-1 for 20-40 keV X-Ray energy range based on data from the INTEGRAL (International Gamma-Ray Astrophysics Laboratory, Launched in 2002) satellite.

  • RAI:

    We look at X-Rays in the 1-10 keV range from the Exosat (European Space Agency X-Ray Observatory, finished its mission in 1986). So, we decided to compare Vela X-1’s flaring behavior in this energy range versus Kreykenbohm’s findings.

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Where is Vela X-1?

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Parameters of Vela X-1

1. Compact Object

  • Period (from the Power Spectrum) of the compact object is ~283 seconds and it is not changing.

  • The compact object is a neutron star based on its luminosity (from the energy spectrum flux) of ~1036 ergs sec-1

  • It is a pulsar because it is in a MXRB and has a Power law Model fit.

Literature support: Kretschmar, 2004, Charles and Seward, 1995, Kreykenbohm, 2008.

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2. Companion OB Star

  • The luminosity (from the distance modulus) of the OB star companion HD77581 is

    63,000 times that of the sun.

  • The radius is (using Stephan-Boltzmann)

    21 times that of the sun.

Literature support: Kaper, 1997, Kretschmar, 2004.

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3. System

--Using values for the orbital speed and the orbital period (from literature), we found the orbital radius of HD77581 to be 2.6x109 m and the orbital radius of the neutron star to be 3.45x1010 m.

  • Therefore the radius of the neutron star’s orbit is

    ~50 solar radii (~1.7RHD77581).

  • MHD77581~24Msun(using Kepler’s 3rd Law and Center of Mass independently)

  • This tells us this is a close MXRB meaning solar winds account for accretion of matter onto the NS.

Literature support: Quaintrall et al., 2003, Van Paradijs et al., 1976. Kretschmar et al.,2004, Willems et al., 2005.

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Kreykenbohm’s Flares (20-40 keV)

  • Characteristics

    • Long Flares

      • TRise/TTotal > 0.5

      • Hardness Plotdoes not change.

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  • Short Flares

    • TRise/TTotal < 0.3

    • Hardness Plot does change:

      the soft x-rays increase

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Kreykenbohm’s Flare Models

Flip-Flop Instability

The Lucy Situation

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Kreykenbohm’s Off-States

  • Characteristics

    • Occurs suddenly without a transition phase (almost like a switch)

    • Not an eclipse but count rate drops to below detection limits, almost 0.

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Kreykenbohm’s Off-State Models

  • The “Biggest Loser” Model

    • Dense blobs of stellar winds (thanks to the close binary)

  • Propeller Effect

    • Inhibition of Accretion via balancing of infallingram pressure and the magnetic pressure.

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Do light curves in the 1-10 keV range exhibit flaring and off-state behaviors?

If these behaviors are present, do they have the same characteristics as in the 20-40 keV range?

If they’re present but with different characteristics, what model(s) might account for the difference?

Our Research Questions

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Flaring Behaviors

Average cts/sec ~ 40 cts/sec +/- 0.03 cts/sec

Rise Time = ~2500 secs.

Flare Time = ~5000 secs.

Therefore, this is a LONG FLARE.

Fall Time

Rise time

Pre-Rise Time: 40 cts/sec +/- .447cts/sec

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This indicates spectral softening.

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Average cts/sec ~ 38 cts/sec +/- 0.031 cts/sec

Rise Time = ~1000 secs.

Flare Time = ~3000 secs.

Therefore, this is a SHORT FLARE.

Pre-Rise Time:

25 cts/sec +/- .35 cts/sec

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This does not indicate Spectral Softening

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Hardness plot fluctuates for an off-state which is consistent with Kreykenbohm’s results.

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Summary of Our Findings

  • Flares

    • Flare behavior for 1-10 keV range isconsistent with Kreykenbohm’s 20-40 keV data.

    • Hardness plots for flaring behavior were just the opposite of the Kreykenbohm results!!!!

    • Result: we have evidence that

      (1) supports the flare models but

      (2) is inconsistent with hardness plot

      results found bytheKreykenbohm study

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  • Off-States

    • One of the off-states was consistent with Kreykenbohm time wise while the other one was not (for a longer period of time).

    • The hardness plots for both off-states are consistent with Kreykenbohm’s 20-40 keV range results.

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Future Research

  • Write a paper presenting our findings

  • Look at other MXRB to compare Vela X-1 flaring behaviors with those sources.

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