1. A Pulsar’s Life Continues Melissa Anholm University of Wisconsin, Milwaukee 6 October, 2008

2. Outline  Initial Slowing Energy lost as radio waves. Energy lost as radio waves. Pulsar slows and dims. Pulsar slows and dims.  “Recycling” of Pulsars Pulsar steals matter from another star Pulsar steals matter from another star Rotation speed is changed Rotation speed is changed X-rays are emitted. X-rays are emitted.  Recycled Pulsars After accretion stops, so do X-rays. After accretion stops, so do X-rays. Original emission mechanism has become active again. Original emission mechanism has become active again. Predictable timing - useful for experiments. Predictable timing - useful for experiments.

3. Speed of Rotation Strength of Magnetic Field http://www.shatters.net/forum/viewtopic.php?t=11372 The amount of electromagnetic radiation produced by a pulsar depends on: Note: Mechanism is still not well-understood.

4. Pulsar Population Young Pulsars

5. The pulsar’s rotation slows. The pulsar stops emitting electromagnetic radiation. Electromagnetic Radiation Carries Energy Away http://www.shatters.net/forum/viewtopic.php?t=11372

6. Pulsar Population Young Pulsars

7. Pulsars in Binary Systems May Be Able to Shine Again Accretion Disk Companion Star Neutron Star http://www.noao.edu/outreach/press/pr08/pr0802.html

8. Spinning Things Spread Out into a Disk

9. So what happens to the neutron star? The stolen matter gives the neutron star a “kick”. The neutron star’s rotation speeds up or slows down. Rapidly rotating neutron stars can again emit beams of radio waves. http://www.noao.edu/outreach/press/pr08/pr0802.html “Recycling”

10. Infalling Matter Reaches Very High Speeds before Impact Stolen matter hits hard and produces heat.

11. Hot Spots Form on Magnetic Poles Accretion Disk Hot Spot at Magnetic Pole Magnetic Field Lines Axis of Rotation Flow of Hot Gas

12. Hot Things Glow “Red Hot” “X-Ray Hot”

13. Rotating Hot Spots Emit X-Rays When the hot spots come into view, we detect a “pulse” of When the hot spots come into view, we detect a “pulse” of X-ray radiation. X-ray radiation. It’s an X-ray pulsar, now!

14. http://spacibm.rice.edu/~baring/astr350/astr350_cosmos.html Two Emission Mechanisms X-Rays Radio Waves Emission mechanism depends on infalling matter producing hot spots. Emission mechanism depends on infalling matter producing hot spots. Hot spots glow--radiation is sent in all directions. Hot spots glow--radiation is sent in all directions. We observe pulses when the hot spots are on the side of the neutron star facing us. We observe pulses when the hot spots are on the side of the neutron star facing us. Emission mechanism depends on rotational speed and magnetic field strength. Emission mechanism depends on rotational speed and magnetic field strength. Radio waves are directed in beams from the magnetic poles. Radio waves are directed in beams from the magnetic poles. We observe pulses when the beams are directed at us We observe pulses when the beams are directed at us

15. http://spacibm.rice.edu/~baring/astr350/astr350_cosmos.html X-Ray Pulsars and Radio Pulsars X-Ray-emitting hot spots glow in all X-Ray-emitting hot spots glow in all directions. directions. Radio waves are emitted in beams from Radio waves are emitted in beams from the magnetic poles. the magnetic poles. For many pulsars, we observe X-rays, but not radio waves, even though we think they emit both.

16. Accretion Must Eventually End Supernova Companion shrinks when it exhausts fuel Companion is completely evaporated Passing star disrupts orbits http://upload.wikimedia.org/wikipedia/commons/1/10/Supernova_Companion_Star.jpg

17. “Recycled” Pulsars When the accretion process ceases, the hot spots on the neutron star cool. No more X-rays. The neutron star may now be rotating quickly again. Initial mechanism for producing radio waves has been re-activated. http://commons.wikimedia.org/wiki/Image:Pulsar_schematic.svg

18. Spinning Faster More Massive http://www.shatters.net/forum/viewtopic.php?t=11372 It takes a bigger push to change the rotation speed by a measurable amount. Pulses are very predictable. Good for GW detection! What’s so Great about a Recycled Pulsar?