A GOLDEN DECADE OF GAMMA-RAY PULSAR ASTRONOMY

Abstract

To celebrate the tenth anniversary since the launch of Fermi Gamma-ray Space Telescope, we take a retrospect to a series of breakthroughs Fermi has contributed to pulsar astronomy in the last decade. Apart from significantly enlarging the population of ${\gamma}$-ray pulsars, observations with the Large Area Telescope onboard Fermi also show the population is not homogeneous. Instead, many classes and sub-classes have been revealed. In this paper, we will review the properties of different types of ${\gamma}$-ray pulsars, including radio-quiet ${\gamma}$-ray pulsars, millisecond pulsars, ${\gamma}$-ray binaries. Also, we will discuss the prospects of pulsar astronomy in the high energy regime.

Figure 1. Seven γ−ray pulsars detected in the EGRET era. (Figure courtesy: NASA HEASARC Education and Public Information database, https://heasarc.gsfc.nasa.gov/docs/objects/pulsars/pulsars_lc.html)

Figure 2. Fermi on the ground just before its launch. LAT is the box-shape detector on the top. The GBM detectors and the telemetry antennas can be seen on the left side. On the right side, there is the folded solar panel. (Photo courtesy: NASA FSSC)

Figure 3. The distribution of 167 γ−ray pulsars in our Galaxy as detected by Fermi LAT with 4 years data. (cf. Acero et al. 2015)

Figure 4. γ-ray light curve of PSR B1957+20 at energies > 2.7 GeV which are folded at the orbital period. Two orbits are shown for clarity. The shaded regions correspond to the phase of radio eclipse. (Wu et al. 2012)

Figure 5. The main panel shows the multi-wavelength (i.e., from UV to γ-ray) lightcurves of PSR J1023+0038 from June 1, 2013 to November 13, 2013 with different flux scales for each energy band (see upper left corner for details) while the inset box indicates the detailed evolution of the γ-ray emissions between June 6 to 24 July. UV/X-ray: Each datum represents an individual observation taken by Swift. γ-ray: Each datum in the main panel (inset) corresponds to two weeks (3 days), and 95% c.l. upper limits are given for the time intervals during which the detection significances is ≲ 3σ. (Takata et al. 2014)

Figure 7. γ-ray and radio pulse profiles of PSR J1823−3021A in the globular cluster NGC 6624. (Freire et al. 2011)

Figure 8. Gamma-ray pulse profile (upper panel) and the phaseogram (i.e., the phases of both pulses as a function of time lower panel) of PSR B1821-24 in the globular cluster M28. Despite the detection at a significance > 4σ, the wig-gling pulse phases in the phaseogram suggest the presence of inaccuracies in the adopted timing ephermeris. (Wu et al. 2013)

Figure 9. Edge-on views of the fundamental-plane relations of γ−ray GCs based on the updated sample. (Oh & Hui 2017)

Figure 10. Left panel: Comparison of the magnetic field strength at the light cylinders of radio-quiet γ−ray pulsars and their radio-loud counterparts Right panel: Comparison of the γ−ray spectral curvatures between these two populations. (Hui et al. 2017)

Figure 11. Evolution of γ−ray flux (top panel) and spin-down rate (bottom panel) of PSR J2021+4026. A sudden flux jump, which is accompanied by an increase in the spin-down rate, can be seen around the epoch of MJD 55850. The pulsar remained in a lower flux and higher spin-down rate until the epoch around MJD 57000 and then gradually recovered to the pre-glitch stage. (Zhao et al. 2017)

Figure 12. Illustration of the periastron passages of PSR B1259-63/LS2883 as seen in Decemeber 2010. (Illustration: NASA, https://www.nasa.gov/mission_pages/GLAST/news/odd-couple.html)

Figure 13. Simulated γ−ray sky as expected to be observed by CTA during its Galactic plane survey. (Image: CTA Consortium)

Figure 6. (Left panel:) Comparison of the effective photon indices of black-widows (BWs) and redbacks (RBs) in X-ray. (Right panel:) Comparison of the X-ray luminosities of BWs and RBs. The p−values results from the two-sample Kolmogorov-Smirnov (KS) test and Anderson-Darling (AD) test are given in each figure, which strongly indicate the differences between these two classes of MSPs. (Lee et al. 2018)