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: 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 “offstates for the 20-40 keV range. 5. Present our findings regarding flares and offstates for the 1-10 keV range. 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. Where is Vela X-1? 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. 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. 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. Kreykenbohm’s Flares (20-40 keV) • Characteristics – Long Flares • TRise/TTotal > 0.5 • Hardness Plot does not change. – Short Flares • TRise/TTotal < 0.3 • Hardness Plot does change: the soft x-rays increase Kreykenbohm’s Flare Models Flip-Flop Instability The Lucy Situation 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. 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. 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? 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 Pre-Rise Time: 40 cts/sec +/- .447cts/sec Fall Time This indicates spectral softening. 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 This does not indicate Spectral Softening Off-States Hardness plot fluctuates for an off-state which is consistent with Kreykenbohm’s results. 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 • 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. Future Research • Write a paper presenting our findings • Look at other MXRB to compare Vela X-1 flaring behaviors with those sources.