EIGHT γ-RAY PULSARS DISCOVERED IN BLIND FREQUENCY SEARCHES OF<i>FERMI</i>LAT DATA

Abstract

We report the discovery of eight gamma-ray pulsars in blind frequency\nsearches using the LAT, onboard the Fermi Gamma-ray Space Telescope. Five of\nthe eight pulsars are young (tau_c&lt;100 kyr), energetic (Edot&gt;10^36 erg/s), and\nlocated within the Galactic plane (|b|&lt;3 deg). The remaining three are older,\nless energetic, and located off the plane. Five pulsars are associated with\nsources included in the LAT bright gamma-ray source list, but only one, PSR\nJ1413-6205, is clearly associated with an EGRET source. PSR J1023-5746 has the\nsmallest characteristic age (tau_c=4.6 kyr) and is the most energetic\n(Edot=1.1E37 erg/s) of all gamma-ray pulsars discovered so far in blind\nsearches. PSRs J1957+5033 and J2055+25 have the largest characteristic ages\n(tau_c~1 Myr) and are the least energetic (Edot~5E33 erg/s) of the\nnewly-discovered pulsars. We present the timing models, light curves, and\ndetailed spectral parameters of the new pulsars. We used recent XMM\nobservations to identify the counterpart of PSR J2055+25 as XMMU\nJ205549.4+253959. In addition, publicly available archival Chandra X-ray data\nallowed us to identify the likely counterpart of PSR J1023-5746 as a faint,\nhighly absorbed source, CXOU J102302.8-574606. The large X-ray absorption\nindicates that this could be among the most distant gamma-ray pulsars detected\nso far. PSR J1023-5746 is positionally coincident with the TeV source HESS\nJ1023-575, located near the young stellar cluster Westerlund 2, while PSR\nJ1954+2836 is coincident with a 4.3 sigma excess reported by Milagro at a\nmedian energy of 35 TeV. Deep radio follow-up observations of the eight pulsars\nresulted in no detections of pulsations and upper limits comparable to the\nfaintest known radio pulsars, indicating that these can be included among the\ngrowing population of radio-quiet pulsars in our Galaxy being uncovered by the\nLAT, and currently numbering more than 20.\n