The TRAPUM L-band survey for pulsars in Fermi-LAT gamma-ray sources

Abstract

More than 100 millisecond pulsars (MSPs) have been discovered in radio observations of gamma-ray sources detected by the Fermi Large Area Telescope (LAT), but hundreds of pulsar-like sources remain unidentified. Here we present the first results from the targeted survey of Fermi-LAT sources being performed by the Transients and Pulsars with MeerKAT (TRAPUM) Large Survey Project. We observed 79 sources identified as possible gamma-ray pulsar candidates by a Random Forest classification of unassociated sources from the 4FGL catalogue. Each source was observed for 10 minutes on two separate epochs using MeerKAT’s L-band receiver (856–1712 MHz), with typical pulsed flux density sensitivities of $\sim 100\, \mu$Jy. Nine new MSPs were discovered, eight of which are in binary systems, including two eclipsing redbacks and one system, PSR J1526−2744, that appears to have a white dwarf companion in an unusually compact 5 hr orbit. We obtained phase-connected timing solutions for two of these MSPs, enabling the detection of gamma-ray pulsations in the Fermi-LAT data. A follow-up search for continuous gravitational waves from PSR J1526−2744 in Advanced LIGO data using the resulting Fermi-LAT timing ephemeris yielded no detection, but sets an upper limit on the neutron star ellipticity of 2.45 × 10−8. We also detected X-ray emission from the redback PSR J1803−6707 in data from the first eROSITA all-sky survey, likely due to emission from an intra-binary shock.

Swift Follow-up of Reported Radio Pulsars at Fermi 4FGL Unassociated Sources

“…In the error ellipse of 4FGL J1803.1−6708, we detect an S/N = 4.25 X-ray source at the same position as the TRAPUM radio pulsar. This X-ray source is spatially coincident with the eROSITA X-ray source noted in Clark et al (2023), confirming that detection. Using the procedure described in Section 3, we conduct a power-law fit to the X-ray data at this location.…”

“…We repeat this process for the smaller subsample of the eight known redback and black widow pulsars in our pulsar list using the median X-ray flux and photon index of that subsample (F X = 4.24 × 10 14 erg s −1 cm −2 and Γ X = 2.35). This subsample of redback and black widow pulsars is more similar to the millisecond pulsars detected in Clark et al (2023), but its small size and the biases of our larger pulsar sample once again preclude strong conclusions from this comparison alone. We plot the S/N for these median pulsars and redback/black widows, plus the 25th and 75th percentiles of each sample, in Figure 1.…”

“…Using the NNC from Kerby et al (2021b), we find that this source has P bzr = 0.145, suggesting a moderately pulsar-like source. Furthermore, Clark et al (2023) obtained a timing solution with gamma-ray pulsations from 4FGL J1803.1−6708, giving timing evidence that this source is indeed a radio and gammaray pulsar.…”

“…In Clark et al (2023), the TRAPUM consortium using the MeerKAT telescope (Jonas 2009) announced the discovery of several radio pulsars after an L-band radio survey of Fermi-LAT unassociated sources, including new redback/black widow pulsars. Clark et al (2023) also notes one target, 4FGL J1803.1−6708, where eROSITA X-ray data indicate significant X-ray flux at the radio position. To follow up at the TRAPUM radio positions, we submitted target of opportunity requests to Swift for six of the 4FGL unassociated sources in question to search for X-ray counterparts.…”

Green Bank Telescope Discovery of the Redback Binary Millisecond Pulsar PSR J0212+5321

“…PSR J0212+5321 is a P = 2.11 ms radio pulsar with a DM of 25.7 pc cm −3 . PSR J0212+5321 joins three other recently discovered redbacks, PSR J0838-2827, J0955-3949, and J2333-5526, found by the TRAPUM collaboration 7 (Clark et al 2023). PSR J0212 +5321ʼs detection makes it one of the longest binary period eclipsing MSPs known.…”