a pulsar census of the local group
TRANSCRIPT
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.
A Pulsar Census of the Local GroupVlad Kondratiev (ASTRON), Duncan Lorimer, Maura McLaughlin (WVU),
Scott Ransom (NRAO)
Extragalactic pulsars — why? Manchester et al. 2006 ● Are guides of pulsar
population in host galaxies
● 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
B0540-69, with Giant Pulses(Johnston & Romani, 2004)
ObservationsGBT, Spigot820 MHzBW=50MHz1024/2048 channels8 bitΔt = 81.92 μs
Arecibo, 4 WAPPs327 MHzBW=50 MHz1024 lags 16-bit Δt = 128 μs
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
● DM gridding of 0.2 pc cm-3 for DM range 0-408 pc cm-3 for 1024-chan data, and for DM range 0-816 pc cm-3 for 2048-chan data
● Both periodicity and single-pulse searches
Crab-like B1937+21-like
Galaxy l (°)
b(°)
d (kpc)
DM (cm-3 pc)
Smin (kJy)
NGP/h Smin
(kJy)NGP/h
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
Selection criteria
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.
● Nearby galaxies within 1 Mpc● High galactic latitudes |b| > 26°● Visible at either Arecibo or GBT
Interesting candidates
● The DM of the candidate is much larger than DM of 42 pc cm-3 from NE2001 model (Cordes & Lazio 2002) for the line-of-sight to Sex dw ― the strongest argument against it.
● Significance of the profile of 2.1σ is also very low.
Sextans dSph
Credit: S.D. Van Dyk (IPAC/Caltech) et al.
Though interesting, this single-pulse 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
Detectability
Image credit: http://www.iac.es/galeria/noelia/LG.html
From McLaughlin & Cordes (2003) for Crab-like pulsars:
For MSPs, such as B1937+21: