DISCOVERY OF THREE RADIO PULSARS FROM AN X-RAY-SELECTED SAMPLE

摘要

We report the discovery of three radio pulsars (PSR J0631 + 10, J1843 + 20, and J1908+0457) in a search targeted at Einstein IPC X-ray sources. The fastest, J0631 + 10, has a period of 0.288 s and high period derivative (P = 104 x 10~(-15) s s~(-1)) corresponding to a spin-down age of only 43 kyr. From 1400 MHz to 2380 MHz the radio spectrum is nearly flat, and the pulse profile is very symmetrical with four narrow components and shows a high degree of linear polarization (>70%). In contrast, the 430 MHz pulse profile is significantly broader and depolarized, which we argue is because of propagation effects. Besides the Einstein detection, we also found a faint X-ray source at the pulsar's location in a ROSAT PSPC exposure. A search for X-ray pulsations was not possible since fewer than 50 net counts are available from either data set. Because both X-ray detections fall in the shadow of their respective detector supporting ribs, the uncertainties in the spectral analysis and X-ray position are rather large, making the separations between pulsar and X-ray source (～1′) still consistent with an association between the two. The dispersion measure (DM = 125.3 pc cm~(-3)) is the largest of any known pulsar in the Galactic anticenter and is likely to be due in part to an increase in the electron density associated with the star-forming region 3 Mon in the pulsar's foreground. Our analysis suggests that J0631 + 10 is interacting with (and possibly embedded inside) the dark cloud LDN 1605. In search for confirmation of its high-energy emission, we folded available Compton Gamma-Ray Observatory EGRET data at the pulsar's position and period, finding γ-ray modulations that have less than 1 % probability of being generated by noise. The two other pulsars, J1843 + 20 and J1908 + 0457, are also close to their respective X-ray sources (separation < 2′), but their small spin-down luminosities and large distances render them unlikely X-rav emitters.