<p>The spin behaviour of the two types of pulsar would usually be quite different. The $\dot{P}$ for a rotationally powered pulsar is always positive, and higher order time derivatives of $P$ are quite small. This is because the rotational kinetic energy is powering the pulsar emission and the neutron star continually spins down as it loses rotational energy.</p>

<p>Accretion powered pulsars can have very variable spin down or spin up characteristics, because they are powered by mass transfer and accretion in binary systems, and are influenced by a variety of factors affecting the accretion flow and how it couples to the pulsar magnetic field. The rates of spin down can be much higher than can be plausibly be accounted for by magnetic spin down as in a rotationally powered pulsar. Spin up cannot be accounted for in a rotationally powered model and neither can sign reversals or dramatic variability in $\dot{P}$.</p>

<p>Additionally, an accretion-powered pulsar would necessarily need to be in a short period binary system - therefore there would be a very obvious periodic modulation in the pulse period caused by the doppler shift as it travels in ts orbit.</p>

CC BY-SA 3.0
2015-12-18T15:08:19.657Z
if Lx is very low, the question is tricky.
questionhang
CC BY-SA 3.0
2015-12-18T15:37:26.787Z
@questionhang Explain? If you think it is a pulsar then it means you can measure the pulse period. My answer exclusively focuses on this. I am not clear what you think the X-ray luminosity has to do with it.
ProfRob
CC BY-SA 3.0
2015-12-18T16:25:16.780Z
pulsar magnetic field. 'The rates of spin down', you mean in X-ray band, right?
questionhang
CC BY-SA 3.0
2015-12-18T16:43:44.730Z
@questionhang You tell me - it's your pulsar. A pulsar pulses on the rotation period, it doesn't matter what waveband the pulses are measured in.
ProfRob
CC BY-SA 3.0
2015-12-19T03:15:00.820Z
If a pulsar pulses in X-ray band, and its Lx is very small, how to tell it is accretion-powered or rotation-powered?
questionhang
CC BY-SA 3.0
2015-12-19T03:24:07.393Z
Both rotation and accretion can lead to X-ray emission. How to tell how much X-ray emission is from rotation?
questionhang
CC BY-SA 3.0
2015-12-19T09:53:27.010Z
@questionhang That was not your original question.
ProfRob
CC BY-SA 3.0
2015-12-19T10:46:09.483Z
As I said, "if Lx is very low, the question is tricky“                                      If Lx is very small, smaller than the luminosity given by its rotation, how to tell it is rotation-powered or accretion-powered? There are not necessarily X-ray pulsations
questionhang
CC BY-SA 3.0
2015-12-19T11:39:44.223Z
@questionhang My answer stands. If it is a pulsar (your question) then you can measure the pulse period and $\dot{P}$.
ProfRob
CC BY-SA 3.0
2015-12-17T21:46:32.223Z
2015-12-19T11:38:36.267Z
2015-12-19T11:38:36.267Z
ProfRob
<p>We need to calculate P/Pdot?</p>

<p>A pulsar may switch between theses two states.</p>

<p>For a rotation powered pulsar, it can pulse and, the pulsed Lx can be much larger than the luminosity given by its rotation?  </p>

<p><strong>If Lx is very small, smaller than the luminosity given by its rotation, how to tell it is rotation-powered or accretion-powered? There are not necessarily X-ray pulsations</strong></p>

<p><strong>You can see I am asking a very tricky scenario.</strong></p>

CC BY-SA 3.0
2015-12-17T17:15:29.480Z
Are you accepting drawings from university papers?
Featherball
CC BY-SA 3.0
2015-12-18T15:10:00.453Z
@Daniel which kind of drawings?
questionhang
CC BY-SA 3.0
2015-12-18T20:00:13.680Z
Diagrams and maths
Featherball
<pulsar>
How to tell a pulsar is rotation-powered or accretion-powered?
questionhang
# How to tell a pulsar is rotation-powered or accretion-powered?

(Asked by: username_0 on 2015-12-05)

We need to calculate P/Pdot?

A pulsar may switch between theses two states.

For a rotation powered pulsar, it can pulse and, the pulsed Lx can be much larger than the luminosity given by its rotation?

**If Lx is very small, smaller than the luminosity given by its rotation, how to tell it is rotation-powered or accretion-powered? There are not necessarily X-ray pulsations**

**You can see I am asking a very tricky scenario.**

**Tags:** pulsar
> **Comments:**
> **username_1**: Are you accepting drawings from university papers?  
> **username_0**: @Daniel which kind of drawings?  
> **username_1**: Diagrams and maths  

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## 1 answers

### Answer by username_2 on 2015-12-17. Score: 1 | Accepted answer

The spin behaviour of the two types of pulsar would usually be quite different. The $\dot{P}$ for a rotationally powered pulsar is always positive, and higher order time derivatives of $P$ are quite small. This is because the rotational kinetic energy is powering the pulsar emission and the neutron star continually spins down as it loses rotational energy.

Accretion powered pulsars can have very variable spin down or spin up characteristics, because they are powered by mass transfer and accretion in binary systems, and are influenced by a variety of factors affecting the accretion flow and how it couples to the pulsar magnetic field. The rates of spin down can be much higher than can be plausibly be accounted for by magnetic spin down as in a rotationally powered pulsar. Spin up cannot be accounted for in a rotationally powered model and neither can sign reversals or dramatic variability in $\dot{P}$.

Additionally, an accretion-powered pulsar would necessarily need to be in a short period binary system - therefore there would be a very obvious periodic modulation in the pulse period caused by the doppler shift as it travels in ts orbit.

> **Comments:**
> **username_0**: if Lx is very low, the question is tricky.  
> **username_2**: @questionhang Explain? If you think it is a pulsar then it means you can measure the pulse period. My answer exclusively focuses on this. I am not clear what you think the X-ray luminosity has to do with it.  
> **username_0**: pulsar magnetic field. 'The rates of spin down', you mean in X-ray band, right?  
> **username_2**: @questionhang You tell me - it's your pulsar. A pulsar pulses on the rotation period, it doesn't matter what waveband the pulses are measured in.  
> **username_0**: If a pulsar pulses in X-ray band, and its Lx is very small, how to tell it is accretion-powered or rotation-powered?  
> **username_0**: Both rotation and accretion can lead to X-ray emission. How to tell how much X-ray emission is from rotation?  
> **username_2**: @questionhang That was not your original question.  
> **username_0**: As I said, "if Lx is very low, the question is tricky“                                      If Lx is very small, smaller than the luminosity given by its rotation, how to tell it is rotation-powered or accretion-powered? There are not necessarily X-ray pulsations  
> **username_2**: @questionhang My answer stands. If it is a pulsar (your question) then you can measure the pulse period and $\dot{P}$.  

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