Progressof Pulsar Astronomy inthe Last DecadeDavid C. Y. HuiOn behalf of Fermi Asian Network
Department of Astronomy & Space ScienceChungnam National University
Center of High Energy Astrophysics (CHEA)
ICRR, University of Tokyo
CTA-Japan Meeting 2017

Dec 18/19 2017• Our understandings of pulsars in the last ten
years have been advanced by Fermi and thecoordinated MWL follow-ups since 2008.

• Review a few major achievements in pulsar
science.

• Prospects of CTA in the light of theseachievements.

Magnificent 7 in EGRET Era

A New Era of Pulsar AstronomyBy now, there are
205 gamma-ray
selected pulsars.

Abdo et al. (2013)

What’s New?
• Radio-quiet gamma-ray pulsars• Variable pulsar wind nebula• Millisecond pulsars (MSPs)• Globular clusters• Variable gamma-ray pulsar (PSR J2021+4026)• Gamma-ray binaries

Importance of Synergy among
X-ray, Gamma-ray & Radio• Diﬀerent wavelengths reflects diﬀerent astrophysicalprocesses / emission regions.

• Theoretically, properties in one energy band can help toconstrain the properties in the others.

• Observationally, the limitations of observations in a particular
wavelength can be complemented by the other bands.

Geminga• The 1st RQ-PSR - Geminga• Its gamma-ray emission was detected by the experimentsin the early-days - SAS-2, COS-B.

Geminga
Detection of a possible X-ray counterpart in COS-B error box with
Einstein (Bignami et al. 1983)

Geminga• Discovery of 0.237s period in X-ray by ROSAT. (You have more photons in X-ray)• The X-ray ephemeris enabled the gamma-ray pulsation to be uncovered.

RQ as a Matter of Geometry

Animation courtesy: FSSCHigh Energy Pulsar
Magnetospheric Radiation

Wang et al. (2014)

Gamma-ray emission from Geminga

Abdo et al. (2010)

X-ray emission from Geminga

PL: Photon Index~1.7

BB2: kT~0.2 keVAnimation courtesy: ESA
BB1: kT~45 eVCaraveo et al. (2004)

Emission beyond theMagnetosphere• Most of the rotational energy are lost
through the relativistic pulsar windoutflow.

• Typical speed of pulsar ~ 250 km/s
• Producing bow-shock

Illustration courtesy: Dany Page

Extended X-rays from Geminga

Hui et al. (2017a)

Fast X-ray variabilities ofGeminga PWN

Hui et al. (2017a)

Fast X-ray variabilities ofGeminga PWN

Hui et al. (2017a)

Variability occurred at ~0.8c.
The fastest X-ray variation in PWN observed!

TeV Emission from Geminga PWN• Extended TeV emission isdetected by HAWC andMilagro.

• 13 sigma in 1-50 TeV byHAWC.

• Spatial extent of ~few tensof pc.

Questions for follow-up• Align with proper motion?
Abeysekara et al. (2017)• Counterpart in GeV?
• Variability?

Differences between RQ andRL gamma-ray Pulsars• In 2PC, there are 35 RQ
PSRs and 42 nonrecycled RL PSRs.

• Allow a meaningfulstatistical analysis.

Abdo et al. (2013)

Differences between RQ andRL gamma-ray Pulsars• Spectral shape of RQ and RL
gamma-ray PSRs areapparently diﬀerent.

Spectral Curvature

Hui et al. (2017b)

Differences between RQ andRL gamma-ray Pulsars• While the B-field at theB-field atstellar surface

stellar surfaces of RL
B-fieldandat RQ PSRs arelight cylinder
comparable,• B-field at the lightcylinder of these twopopulations are
significant diﬀerent.

Hui et al. (2017b)

Differences between RQ and
RL gamma-ray Pulsars
B-field atstellar surface

B-field at
Gamma-ray to X-ray fluxlight• cylinder
ratios of RQ gamma-ray
PSRs are apparently
higher.

Hui et al. (2017b)

Differences between RQ and
RL gamma-ray Pulsars
B-field atstellar surface

B-field atlight cylinder

Hui et al. (2017b)

Millisecond Pulsars (MSPs)

Animation courtesy: CXC

Source: ATNF Pulsar Catalog

Zoo of MSPs
• Black Widows (P<20 hrs, Mc < 0.05 Msun)• Redbacks(P<20 hrs, Mc ~ 0.2-0.4 Msun)• Isolated MSPs
• Wide-Orbit MSP/WD binaries• MSP-Planet binaryBlack Widows

Animation courtesy: FSSC

Black Widows

Ahnen et al. (2017)

Intrabinary Shock of Black Widow

Huang et al. (2012)

Wu et al. (2012)

Reynold et al. (2007)

Bow Shock of Black Widow
X-ray

H-alphaHuang et al. (2012)

VHE Emission from Black Widow Bowshock?
X-ray observations put strong constraints on the IC model

Bednarek & Sitarek (2013)

VHE Emission from Black Widow Bowshock?

Ahnen et al. (2017)

Redback

Animation courtesy: FSSC

Redback

Halpern et al. (2013)

Takata et al. (2014)

Intrabinary Shock from Redbacks
PSR J1723−2837

Hui et al. (2014)

PSR J2129-0429

Hui et al. (2015a)

VHE Emission from Redback PW?

Bednarek (2014)

X-ray Luminosities of MSPs
X-ray conversion eﬃciencies of MSP are comparable with non-recycled PSRs

Lee et al. submitted

Redbacks vs Black Widows
Rotational and orbital parameters of RBs and BWs are comparable.

Lee et al. submitted

Redback vs Black Widows
X-ray emission of RBs are stronger and harder than BWs.

Lee et al. submitted
With these updated X-ray results, we can refine the feasibility of observing
RB/BW with CTA.

Why the population ofMSPs expands
considerably?

Treasure Hunting in UFOs
There is plenty of discovery space in theunidentified Fermi Objects (UFOs)

Saz Parkinson et al. (2016)

Treasure Hunting in UFOs
Hui et al. (2015b)

Coupling Classification with
Automatic Feature Selection
1. Conventional classifications require some knowledge of the gamma-ray
properties of diﬀerent classes of objects which can be far from complete inview of the relatively short history of gamma-ray astronomy.
2. Instead of relying on a prior knowledge, automatic classification let the data
“speak for themselves” and generate the classification model.
3. In the previous attempts of classifying gamma-ray sources with machinelearning techniques (e.g. Saz Parkinson et al. 2016 ApJ 820 8), the power of
automatic feature selection has not be fully exploited.
4. By coupling the classifiers with automatic feature selection algorithms, weaim toi) Improving the prediction accuracyii) Provide a more cost-eﬀective prediction modeliii) Enhancing the discovery power in data mining

Coupling Classification with
Automatic Feature Selection

Leung et al. in prep

Coupling Classification with
Automatic Feature Selection

Leung et al. in prep

Coupling Classification with
Automatic Feature Selection

Leung et al. in prep

Unidentified TeV sources~30% of currently detected TeV sources are unidentified.

Source: TeVCat

source: CTA FB pageImpacts of Automatic Feature
Selection in CTA era• Improving the performance of classification.
• Instructing us in how to construct a costeﬀective catalog so as to minimize theredundancy.

• Identifying features that we don’t expect andadvancing our understanding of emission
nature od a specific class.

Hope we can do even betterin the next golden era of
gamma-ray astronomy!