Goals, Strategies and First Discoveries of AO327, the Arecibo All-Sky 327 MHz Drift Pulsar Survey

We report initial results from AO327, a drift survey for pulsars with the Arecibo telescope at 327 MHz. The first phase of AO327 will cover the sky at declinations of -1 to 28 degrees, excluding the region within 5 degrees of the Galactic plane, where high scattering and dispersion make low-frequency surveys sub-optimal. We record data from a 57 MHz bandwidth with 1024 channels and 125 us sampling time. The 60 s transit time through the AO327 beam means that the survey is sensitive to very tight relativistic binaries even with no acceleration searches. To date we have detected 44 known pulsars with periods ranging from 3 ms to 2.21 s and discovered 24 new pulsars. The new discoveries include three millisecond pulsars, three objects with periods of a few tens of milliseconds typical of young as well as mildly recycled pulsars, a nuller, and a rotating radio transient. Five of the new discoveries are in binary systems. The second phase of AO327 will cover the sky at declinations of 28 to 38 degrees. We compare the sensitivity and search volume of AO327 to the Green Bank North Celestial Cap survey and the GBT350 drift survey, both of which operate at 350 MHz.Comment: Accepted for publication in Ap

New Discoveries from the Arecibo 327 MHz Drift Pulsar Survey Radio Transient Search

We present Clusterrank, a new algorithm for identifying dispersed astrophysical pulses. Such pulses are commonly detected from Galactic pulsars and rotating radio transients (RRATs), which are neutron stars with sporadic radio emission. More recently, isolated, highly dispersed pulses dubbed fast radio bursts (FRBs) have been identified as the potential signature of an extragalactic cataclysmic radio source distinct from pulsars and RRATs. Clusterrank helped us discover 14 pulsars and 8 RRATs in data from the Arecibo 327 MHz Drift Pulsar Survey (AO327). The new RRATs have DMs in the range $23.5 - 86.6$ pc cm$^{-3}$ and periods in the range $0.172 - 3.901$ s. The new pulsars have DMs in the range $23.6 - 133.3$ pc cm$^{-3}$ and periods in the range $1.249 - 5.012$ s, and include two nullers and a mode-switching object. We estimate an upper limit on the all-sky FRB rate of $10^5$ day$^{-1}$ for bursts with a width of 10 ms and flux density $\gtrsim 83$ mJy. The DMs of all new discoveries are consistent with a Galactic origin. In comparing statistics of the new RRATs with sources from the RRATalog, we find that both sets are drawn from the same period distribution. In contrast, we find that the period distribution of the new pulsars is different from the period distributions of canonical pulsars in the ATNF catalog or pulsars found in AO327 data by a periodicity search. This indicates that Clusterrank is a powerful complement to periodicity searches and uncovers a subset of the pulsar population that has so far been underrepresented in survey results and therefore in Galactic pulsar population models.Comment: 41 pages, 16 figures, 4 tables, accepted by ApJ; added minor corrections to final ApJ proo

Pulsar J0453+1559: A Double Neutron Star System with a Large Mass Asymmetry

To understand the nature of supernovae and neutron star (NS) formation, as well as binary stellar evolution and their interactions, it is important to probe the distribution of NS masses. Until now, all double NS (DNS) systems have been measured to have a mass ratio close to unity (q $\geq$ 0.91). Here we report the measurement of the individual masses of the 4.07-day binary pulsar J0453+1559 from measurements of the rate of advance of periastron and Shapiro delay: The mass of the pulsar is 1.559(5) $M_{\odot}$ and that of its companion is 1.174(4) $M_{\odot}$; q = 0.75. If this companion is also a neutron star (NS), as indicated by the orbital eccentricity of the system (e=0.11), then its mass is the smallest precisely measured for any such object. The pulsar has a spin period of 45.7 ms and a spin derivative of 1.8616(7) x$10^-19$; from these we derive a characteristic age of ~ 4.1 x $10^9$ years and a magnetic field of ~ 2.9 x $10^9$ G,i.e, this pulsar was mildly recycled by accretion of matter from the progenitor of the companion star. This suggests that it was formed with (very approximately) its current mass. Thus NSs form with a wide range of masses, which is important for understanding their formation in supernovae. It is also important for the search for gravitational waves released during a NS-NS merger: it is now evident that we should not assume all DNS systems are symmetric

Discovery of Gamma-ray Pulsations from the Transitional Redback PSR J1227-4853

The 1.69 ms spin period of PSR J1227-4853 was recently discovered in radio observations of the low-mass X-ray binary XSS J12270-4859 following the announcement of a possible transition to a rotation-powered millisecond pulsar state, inferred from decreases in optical, X-ray, and gamma-ray flux from the source. We report the detection of significant (5$\sigma$) gamma-ray pulsations after the transition, at the known spin period, using ~1 year of data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. The gamma-ray light curve of PSR J1227-4853 can be fit by one broad peak, which occurs at nearly the same phase as the main peak in the 1.4 GHz radio profile. The partial alignment of light-curve peaks in different wavebands suggests that at least some of the radio emission may originate at high altitude in the pulsar magnetosphere, in extended regions co-located with the gamma-ray emission site. We folded the LAT data at the orbital period, both pre- and post-transition, but find no evidence for significant modulation of the gamma-ray flux. Analysis of the gamma-ray flux over the mission suggests an approximate transition time of 2012 November 30. Continued study of the pulsed emission and monitoring of PSR J1227-4853, and other known redback systems, for subsequent flux changes will increase our knowledge of the pulsar emission mechanism and transitioning systems.Comment: 5 figures, 1 table, accepted for publication in ApJ, updated to reflect accepted version and add additional coautho

Pulsar J1411+2551: A Low Mass New Double Neutron Star System

In this work, we report the discovery and characterization of PSR J1411+2551, a new binary pulsar discovered in the Arecibo 327 MHz Drift Pulsar Survey. Our timing observations of the radio pulsar in the system span a period of about 2.5 years. This timing campaign allowed a precise measurement of its spin period (62.4 ms) and its derivative (9.6 $\pm$ 0.7) $\times 10^{-20}\, \rm s\, s^{-1}$; from these, we derive a characteristic age of $\sim 10\,$Gyr and a surface magnetic field strength of 2.5 $\times 10^{9}$ G. These numbers indicate that this pulsar was mildly recycled by accretion of matter from the progenitor of the companion star. The system has an eccentric ($e\, = \, 0.17$) 2.61 day orbit. This eccentricity allows a highly significant measurement of the rate of advance of periastron, $\dot{\omega} = 0.07686 \pm 0.00046 ^{\circ}~{\rm yr}^{-1}$. Assuming general relativity accurately models the orbital motion, this implies a total system mass M = $2.538 \pm 0.022 M_{\odot}$. The minimum companion mass is $0.92\, M_{\odot}$ and the maximum pulsar mass is $1.62\, M_{\odot}$. The large companion mass and the orbital eccentricity suggest that PSR J1411+2551 is a double neutron star system; the lightest known to date including the DNS merger GW 170817. Furthermore, the relatively low orbital eccentricity and small proper motion limits suggest that the second supernova had a relatively small associated kick; this and the low system mass suggest that it was an ultra-stripped supernova.Comment: Accepted for publication in APJ letter