Probing Pulsar Winds with Gamma Rays

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1 Probing Pulsar Winds with Gamma Rays Dmitry Khangulyan Institute of Space and Astronautical Science (ISAS/JAXA) in coll. with Felix Aharonian&Sergey Bogovalov International School on Neutron Star Matter March 4-7, 2014, Kyoto, Japan

2 Conventional view on the Crab Pulsar Related Emitting Zones Pulsar(Massaro+) PWN(Aharonian&Atoyan) There are a few plausible emissions sites with very different conditions: magnetosphere for the pulsed emission, and nebula for the steady component.

3 Pulsar Nebula is a colorimeter of the wind Pulsar Related Emitting Zones Pulsar(Massaro+) PWN(Aharonian&Atoyan) Wind is not expected to emit any obvious radiation component, however it is possible to infer its properties through the non-thermal emission of the nebula

4 Kennel&Coroniti1984 Sketch of the model Pulsar wind Total Luminosity L w erg/s Bulk Lorentz Factor Γ w Wind Magnetization σ D MHD model by Kennel&Coroniti favored an ultrarelativistic weakly magnetized wind. This requirement remain valid also in 2D modeling.

5 VHE observations of the Crab pulsar Veritas Collaboration(2011) MAGIC Collaboration(2011) MAGIC Collaboration(2014) Currently there is a general agreement between different experiments regarding the detection of the pulsed VHE emission from the Crab pulsar

6 Where is the pulsed VHE emission produced? Calculations by K.Hirotani Pulsar Magnetosphere (e.g. Aleksić+2012) PWN Pulsar Wind (Bogovalov&Aharonian2001) The magnetospheric origin of the pulsed VHE signal is strongly favored, however the modeled lightcurve is not yet in acceptable agreement

7 Where is the pulsed VHE emission produced? Pulsar Magnetosphere (e.g. Aleksić+2012) PWN Pulsar Wind (Bogovalov&Aharonian2001) Crab Flare (Buehler+2012) Production of pulsed emission in the nebula is impossible, but till recently the Crab flares were also impossible...

8 Where is the pulsed VHE emission produced? However, it was predicted that the pulsar wind can also emit potentially detectable emission, which under certain conditions can be pulsed Signal produced by cold pulsar wind Pulsar Magnetosphere (e.g. Aleksić+2012) PWN Pulsar Wind (Bogovalov&Aharonian2001)

9 Bulk Comptonization of the wind Sketch of the scenario (Aharonian+2012) If the pulsar wind is accelerated enough close to the magnetosphere, a quite strong IC emission can be generated

10 Inverse Compton interaction angle is determined from the first principles Energy Angular Momentum losses of pulsar: Ė sd = ΩṀsd Energy carried by an electron: Γ w mc 2 Angular Momentum carried by an electron: Γ w mr v Pulsar wind trajectory (if σ 1 ): r = c Ω = R L It is plausible that during the acceleration stage the wind trajectories are bended leading to a non-zero IC interaction angle

11 Is the wind IC emission pulsed? Sketch of the scenario (Aharonian+2012) The X- and gamma-ray signals are perfectly synchronized if the wind is formed NOT very close to the pulsar

12 Spectrum can be explained SED accounting for the wind signal (Aharonian+2012) The flux level appears to depend strongly on the both model parameters: wind formation distance and wind Lorentz factor

13 Wind signal lightcurve Light Curve (Aharonian+2012) Although the VHE lightcurve is consistent with the data points if the wind is formed not very close to the pulsar, there are certain disagreements. The most striking difference is the strong excess in the inter-pulse region...

14 Wind signal lightcurve (UPDATED) Light Curve (MAGIC 2014) However this seems to agree better with the most recent lightcurve

15 Summary The pulsed VHE signal is the best interpreted as IC emission from the wind Current measurements of the pulsed VHE signal allows to constraint the key properties of the pulsar wind Bulk Lorentz factor Γ w Wind formation distance R w 30R L The high level of the emission predicted for the bridge region seems to be consistent with the most recent data reported by MAGIC Coll. To match precisely to the VHE lightcurve, some wind anisotropy is required If the future data confirm the wind origin of the signal, this provides important information about the physics of the pulsar winds