The FAST Discovery of Two Radio Pulsars Coincident with Fermi-LAT Gamma-ray Sources

ATel #17382; T. Liu (NAOC), Z. Pan (NAOC), D. A. Smith (CNRS and U. Bordeaux), X. Hou (YNAO), L. Qian (NAOC), R. B. Ding (BNU), S. Cao (BNU), and P. Jiang (NAOC)
on 10 Sep 2025; 05:49 UT
Credential Certification: Shuo Cao (caoshuo@bnu.edu.cn)

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We report the FAST (Five-hundred-meter Aperture Spherical radio Telescope, [1]) discovery of two radio pulsars from the searches of unassociated Fermi-LAT gamma-ray sources from the Fourth Fermi-LAT catalog (4FGL, [2][3]). The pulsars were discovered in the directions of 4FGL J0237.8+5238 and 4FGL J0533.6+5945. Both of them have GeV spectral energy distributions that resemble those of most known gamma-ray pulsars.

The pulsar PSR J0237+5238, which is associated with 4FGL J0237.8+5238, was first detected in the observation taken on 24 February, 2025. The signal has been confirmed in subsequent observations. Preliminary timing analysis shows that it is a binary millisecond pulsar (MSP) with a spin period of 4.35 ms and a dispersion measure (DM) of 10.30 pc cm-3. The orbital period and the projected semi-major axis are 15.9 days and 18.0 light seconds, respectively. Assuming a pulsar mass of 1.4 solar masses, the minimum companion mass is approximately 0.24 solar mass. The long, circular orbit and the companion mass suggest that it is a pulsar-white dwarf system, as the pulsar finished its mass accretion phase, and turned into a stable binary state [4].

The pulsar PSR J0534+5945, associated with 4FGL J0533.6+5945, was detected in the observation taken on 04 March, 2025 and subsequently confirmed. This is a pulsar with a spin period of 191 ms and a DM of 18.75 pc cm^-3. Possibly being a young pulsar, its spin period derivative can be obtained in one single observation and presents a positive value (2.08 x 10^-15 s/s). The characteristic age is estimated to be 1.45 Myr accordingly [5]. Single pulses should be detected via FAST while this is quite a bright pulsar in FAST data.

With limited archival FAST data, further timing observations are ongoing, aiming to obtain the position and spin period derivative of these two pulsars, and catch the possible glitches of PSR J0534+5945.

References:

[1]The Five-Hundred Aperture Spherical Radio Telescope (fast) Project
Nan et al. 2011, IJMPD, 20, 989
doi: 10.1142/S0218271811019335
arXiv: 1105.3794

[2]Fermi Large Area Telescope Fourth Source Catalog Data Release 4 (4FGL-DR4)
Ballet, J. et al. 2023
arXiv: 2307.12546

[3]The Third Fermi Large Area Telescope Catalog of Gamma-ray Pulsars
Smith, D.A. et al. 2023, ApJ, 958, 191
doi: 10.3847/1538-4357/acee67
arXiv: 2307.11132

[4]Formation and evolution of binary and millisecond radio pulsars
Bhattacharya & van den Heuvel, 1991, Phys. Rep., 203, 1
doi: 10.1016/0370-1573(91)90064-S

[5]Handbook of Pulsar Astronomy
Lorimer, D. R., & Kramer, M., 2004, Cambridge University Press.
ISBN: 978-0521828239