1. Vela X-1: Flares & Off States West Orange High School Manthan Kothari, Lucy Zipf, Neil Savalia, Brian Meise, Krish Pillai

2. IN TODAY’S PRESENTATION, WE WILL: 1.Discuss how we chose our project. 2.Describe the Vela X-1 system. 3.Present the Characteristics & Models for flaring behavior for the 20-40 keV range. 4.Present the Characteristics & Models for “off- states for the 20-40 keV range. 5.Present our findings regarding flares and off- states for the 1-10 keV range.

3. 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.

4. Where is Vela X-1?

5. 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 ~10 36 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.

6. 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.

7. 3. System --Using values for the orbital speed and the orbital period (from literature), we found the orbital radius of HD77581 to be 2.6x10 9 m and the orbital radius of the neutron star to be 3.45x10 10 m. –Therefore the radius of the neutron star’s orbit is ~50 solar radii (~1.7R HD77581 ). –M HD77581 ~24M sun (using Kepler’s 3 rd 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.

10. Kreykenbohm’s Flares (20-40 keV) Characteristics –Long Flares T Rise /T Total > 0.5 Hardness Plot does not change.

11. –Short Flares T Rise /T Total < 0.3 Hardness Plot does change: the soft x-rays increase

12. Kreykenbohm’s Flare Models Flip-Flop Instability The Lucy Situation

13. 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.

14. 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 infalling ram pressure and the magnetic pressure.

16. Our Research Questions 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?

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

18. This indicates spectral softening.

19. 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

20. This does not indicate Spectral Softening

21. Off-States

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

23. Summary of Our Findings Flares –Flare behavior for 1-10 keV range is consistent 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 by the Kreykenbohm study

24. 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.

25. Future Research Write a paper presenting our findings Look at other MXRB to compare Vela X-1 flaring behaviors with those sources.