Article

Pulsar searches in nearby dwarf spheroidal galaxies

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Abstract

We have been undertaking a comprehensive survey for pulsars and fast radio transients in the dwarf spheroidal satellite galaxies of the Milky Way using the Green Bank Radio Telescope operating at a central frequency of 350 MHz. Our search pipeline allows the detection of periodical signals and single dispersed pulses and it is optimized to search for millisecond radio pulsars. Here we present preliminary results of the searches we have conducted in the Ursa Minoris, Draco and Leo I dwarf spheroidal satellite galaxies. Our searches have revealed no periodic signals but a few unconfirmed millisecond single pulses at various dispersion measures, possibly related to neutron stars. Detecting neutron stars in these systems can potentially help to test the existence of haloes of dark matter surrounding these systems as predicted by Dehnen & King (2006).

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... Another place where favourable conditions could exist are dwarf spheroidal galaxies that are considered to be DM dominated [13,14] and have very low velocity dispersions [13]. However, at present compact objects such as NS or WD have not been observed in dwarf spheroidal galaxiesn although, surveys for pulsars and X-ray binaries have already revealed some hints on NSs existence in dSph galaxies [15,16]. ...
Preprint
The radio pulsar and rotating radio transient populations are only known in and near the Milky Way. Investigating such populations in other galaxies requires deep pulsar and transient searches. We performed 4-h radio observations of nearby galaxies M33, M81 and M82 with LOFAR. Our main purpose was to characterise the bright end of the pulsar population in other galaxies, and compare it to that of the Milky Way. We searched for extragalactic radio pulsars through a periodic-pulse search, and for sporadic fast radio transients through a single-pulse search. We coherently combined at most 23 LOFAR Core High-Band Antenna (HBA) stations and covered M33, M81, and M82 in their entirety using multiple tied-array beams. No pulsating sources or single pulses were found. We have, therefore established stricter limits on the extragalactic pulsar flux density at lower frequencies than those obtained in previous Arecibo, GBT, and WSRT searches. We conclude that in nearby galaxies M33, M81, and M82 there are no pulsars shining toward Earth with pseudo luminosities greater than a few times that of the brightest pulsars in our Milky Way.
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Full-text available
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Article
The radio pulsar and rotating radio transient populations are only known in and near the Milky Way. Investigating such populations in other galaxies requires deep pulsar and transient searches. We have performed 4-h radio observations of nearby galaxies M33, M81 and M82 with LOFAR. Our main purpose was to characterise the bright end of the pulsar population in other galaxies, and compare it to that of the Milky Way. We searched for extragalactic radio pulsars through a periodic-pulse search, and for sporadic fast radio transients through a single-pulse search. We coherently combined 24 LOFAR Core High-Band Antenna (HBA) stations and covered M33, M81, and M82 in their entirety using multiple tied-array beams. No pulsating sources or single pulses were found. We therefore have established stricter limits on the extragalactic pulsar flux density at lower frequencies than those obtained in previous Arecibo and WSRT searches. We conclude that in nearby galaxies M33, M81, and M82 there are no pulsars shining toward Earth with pseudo luminosities greater than 10 times that of the brightest pulsars in our Milky Way.
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We report the results of a deep Chandra survey of the Sculptor dwarf spheroidal galaxy. We find five X-ray sources with LX of at least 6 × 1033 ergs−1 with optical counterparts establishing them as members of Sculptor. These X-ray luminosities indicate that these sources are X-ray binaries, as no other known class of Galactic point sources can reach 0.5–8 keV luminosities this high. Finding these systems proves definitively that such objects can exist in an old stellar population without stellar collisions. Three of these objects have highly evolved optical counterparts (giants or horizontal branch stars), as do three other sources whose X-ray luminosities are in the range which includes both quiescent low-mass X-ray binaries and the brightest magnetic cataclysmic variables. We predict that large area surveys of the Milky Way should also turn up large numbers of quiescent X-ray binaries.
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