A Pulsar Census of the Local Group Vlad Kondratiev (ASTRON), Duncan Lorimer, Maura McLaughlin (WVU), Scott Ransom (NRAO) [email protected] We carried out observations of nearby galaxies with the GBT and Arecibo radio telescopes at 820 and 327 MHz, respectively, to search for extragalactic pulsars. Currently, the Magellanic Clouds are the only galaxies except for Milky Way known to harbor radio pulsars, with a total of 20 pulsars being discovered there to date. Discovery of pulsars in other galaxies can be used to trace the history of massive star formation and would allow to probe the intermediate intergalactic medium. We selected 22 galaxies of the Local Group at high galactic latitudes, |b| > 26 deg, with most of them being dwarf spheroidal with old star population. This makes them promising targets to search for giant pulses from recycled millisecond pulsars. Both single-pulse and periodicity searches were performed for trial dispersion measures up to about 1000. No extragalactic pulsars are found in one third of the selected targets processed so far. Extragalactic pulsars — why? Are guides of pulsar population in host galaxies Manchester et al. 2006 ● Are probes of ISM in host galaxies as well as intergalactic medium ● To date only 20 pulsars are extragalactic: 16 in LMC, 4 in SMC Detectability From McLaughlin & Cordes (2003) for Crab-like pulsars: For MSPs, such as B1937+21: Image credit: http://www.iac.es/galeria/noelia/LG.html B0540-69, with Giant Pulses (Johnston & Romani, 2004) Selection criteria Observations Nearby galaxies within 1 Mpc ● High galactic latitudes |b| > 26° ● Visible at either Arecibo or GBT ● GBT, Spigot 820 MHz BW=50MHz 1024/2048 channels 8 bit Δt = 81.92 μs Most of the selected galaxies (see the Table) are dwarf spheroidal galaxies that have very old star populations (several Gyrs, Bellazini et al. 2002) with a small population of younger stars (< 1 Gyr, Leo I, Lee et al., 1993), having many more RR Lyraes (Walker, 2003; Siegel & Majewski, 2000). This implies a presence of globular clusters that makes targeted dwarf galaxies very promising to search for giant pulses from old recycled millisecond pulsars. Crab-like d DM Smin (kpc) (cm-3 pc) (kJy) NGP/h Pipeline ● Standard PRESTO pipeline ● Using zero-DM technique (Eatough et al. 2009) ● DM range, from 0 to about 1000 pc cm-3 Number of DM trials per observation is 3528 for 1024-chan data, and 4704 for 2048-chan data ● Arecibo, 4 WAPPs 327 MHz BW=50 MHz 1024 lags 16-bit Δt = 128 μs DM gridding of 0.2 pc cm-3 for DM range 0-408 pc cm-3 for 1024-chan data, and for DM range 0816 pc cm-3 for 2048-chan data ● ● Both periodicity and single-pulse searches Interesting candidates Sextans dSph B1937+21-like Galaxy l (°) b (°) Smin NGP/h (kJy) And III 119 ‒26 899 57 64 2 198 0.003 And XI 122 ‒29 899 52 63 2.1 194 0.04 And XII 122 ‒28 899 54 63 2.1 194 0.04 And XIII 123 ‒30 899 51 64 2 198 0.04 And XIV 123 ‒33 899 47 63 2.1 194 0.04 Scl dw 288 ‒83 93 29 2.3 2120 7.1 1.1 LGS 3 127 ‒41 930 40 67 1.8 207 0.003 IC 1613 130 ‒61 899 32 63 2.1 195 0.003 And II 129 ‒29 899 53 63 2.1 1945 0.003 UMa II 152 +37 253 45 19 17 57 0.06 Leo T 215 +44 425 41 13 80 40 0.03 Leo A 197 +52 775 37 44 5 136 0.006 Leo I 226 +49 279 38 6 470 19 0.1 Sex dw 243 +42 99 42 2.3 2120 7.1 1.1 Willman 1 159 +57 46 34 0.5 61800 1.54 10 Leo II 220 +67 232 29 4 1200 12 0.2 CVn I 148 +84 226 20 4 1200 12 0.2 Boo dw 338 +70 62 24 0.3 460000 1 5.6 UMi dw 105 +45 75 36 1.6 4940 5 2 Dra dw 86 +35 78 43 2.3 2120 7 1.1 Peg dw 95 ‒44 930 37 67 1.8 207 0.02 And VI 106 ‒36 868 43 58 2.5 179 0.04 Credit: S.D. Van Dyk (IPAC/Caltech) et al. Though interesting, this singlepulse candidate occurs at DM of about 175 pc cm-3, also much higher than DM derived from NE2001 model. No dispersion sweep is seen in waterfall plot. Most likely to be RFI. Ursa Minor dSph Credit: S. Binnewies & J. Pöpsel ● The DM of the candidate is much larger than DM of 42 pc cm-3 from NE2001 model (Cordes & Lazio 2002) for the line-ofsight to Sex dw ― the strongest argument against it. ● Significance of the profile of 2.1σ is also very low.