Casey BrinkmanandJoanna Rankin
Physics Department, University of Vermont, Burlington, Vermont 05401, USA
E-mail: clbrinkm@uvm.edu
(Accepted XXX. Received YYY; in original form ZZZ)
Abstract
In this paper we study a set of twelve pulsars that previously had not beencharacterized. Our timing shows that eleven of them are“normal” isolated pulsars, with rotation periods between 0.22 and 2.65 s,characteristic ages between 0.25 Myr and 0.63 Gyr, and estimated magnetic fieldsranging from 0.05 to 3.8G. The youngest pulsar in our sample,PSRJ0627+0706, is located near the Monoceros supernova remnant (SNR G205.5+0.5), but itis not yet clear whether it is associated with it.We also confirmed the existence of a candidate from an early Arecibosurvey, PSRJ2053+1718, its subsequent timing and polarimetry are also presented here.It is an isolated pulsar with a spin period of119 ms, a relatively low magnetic field of anda characteristic age of 6.7 Gyr;this suggests the pulsar was mildly recycled by accretion from a companion starwhich became unbound when that companion became a supernova.We report the results of single-pulse and average Arecibo polarimetry atboth 327 and 1400 MHz aimed at understanding the basic emission properties andbeaming geometry of these pulsars. Three of them (PSRsJ0943+2253, J1935+1159 and J2050+1259)have strong nulls and sporadic radio emission, several others exhibit interpulses(PSRs J0627+0706 and J0927+2345) and one shows regular drifting sub-pulses (J1404+1159).
keywords:
pulsars: general, pulsars: individual:PSR J0627+0706, pulsars: individual:PSR J2053+1718, astrometry: polarization
1 Introduction and motivation
Table1. Pulsar characteristics and timing parameters. *See also 2013MNRAS.429..579B ** Previous unconfirmed candidate. | ||||||||
Previous name | Reference | New Name | Start | Finish | Ref. | NTOA | rms | Reduced |
(MJD) | (MJD) | (MJD) | (ms) | |||||
J0435+27 | 1996ApJ...470.1103R | J0435+2749 | 52854 | 53785 | 53400 | 96 | 0.12 | 5.83 |
J0517+22 | 2003PhDT.........2C | J0517+2212 | 53418 | 53774 | 53400 | 98 | 0.11 | 2.07 |
J0627+07* | 2003PhDT.........2C | J0627+0706 | 53418 | 53675 | 53400 | 91 | 0.26 | 13.71 |
J0927+23 | 1996ApJ...470.1103R | J0927+2345 | 53318 | 53858 | 50000 | 23 | 0.47 | 1.59 |
J0943+22 | 1993ApJ...416..182T | J0943+2253 | 53318 | 53910 | 50000 | 83 | 0.20 | 1.80 |
J0947+27 | 1996ApJ...470.1103R | J0947+2740 | 53318 | 53910 | 50000 | 35 | 0.28 | 1.88 |
J1246+22 | 1993ApJ...416..182T | J1246+2253 | 53294 | 53672 | 53294 | 88 | 0.24 | 1.61 |
J1404+12 | 2003PhDT.........2C | J1404+1159 | 53309 | 53672 | 50000 | 66 | 0.37 | 1.98 |
J1756+18 | 2003ApJ...594..943N | J1756+1822 | 52645 | 53307 | 52751 | 89 | 1.23 | 2.90 |
J1935+12 | 2003PhDT.........2C | J1935+1159 | 53306 | 53580 | 53295 | 40 | 2.43 | 0.70 |
J2050+13 | 2003ApJ...594..943N | J2050+1259 | 52636 | 53306 | 52773 | 27 | 8.81 | 6.31 |
J2052+17** | 1996ApJ...470.1103R | J2053+1718 | 53295 | 56837 | 55000 | 728 | 0.028 | 1.34 |
Since the discovery of the first radio pulsar in 1967 (1968Natur.217..709H), morethan 2500 rotation-powered pulsars havebeen discovered (2005AJ....129.1993M).Of these, more than 400 have no published phase-coherent timing solutions, so that we lacka rudimentary knowledge of their proper motions, spin-down parameters (includingcharacteristic age, magnetic field, spin-down luminosity) and possible orbital elements. Similarly, many newly discovered pulsars lack average polarimetry andfluctuation-spectral analysis, and for many pulsars even basic quantities likeflux densities and spectral indices are still lacking. Because of this, the scientificpotential for many of these objects is simply not known and is not being exploited.
In this and subsequent papers, we attempt a partial remedy to this situation bycharacterizing some of these pulsars: we present theirtiming solutions (with derivations of characteristic ages, surface magnetic fieldand rotational spin-down) and study some of their radio emission properties.As for all previously well characterized pulsars, the measurements presented here andin subsequent papers will aidfuture studies of the pulsar population and contribute to the understanding of theiremission physics.
In this first paper, we focus primarily on a group of a dozen pulsars discovered with the430-MHz line feed of the Arecibo 305-m radio telescope in Puerto Rico beforethe Arecibo upgrade, i.e., pulsars that have been known (and not followed up) formore than 20 years.Most pulsars in this group were discovered in drift-scan surveys: two, J0943+22 and J1246+22,were reported by 1993ApJ...416..182T and three others (J0435+27, J0927+23, J0947+27)were discovered in the completion of that survey by 1996ApJ...470.1103R.Five further pulsars (J0517+22, J0627+07, J1404+12, J1935+12 and J1938+22) werediscovered in the Arecibo-Caltech drift-scan survey (2003PhDT.........2C),but again no timing solutionswere presented for any of them. Two of these pulsars were later timedby other authors: J0627+0706, which we timed from 2005 Feb. 17 to Nov. 1,was detected by the Perseus Arm pulsar survey and subsequently timedfrom 2006 Jan 1 to 2011 May 9 (2013MNRAS.429..579B).Their timing results are similar to ours, but more precise given the largertiming baseline.J1938+22, which we did not follow up, was later timed by2013MNRAS.434..347L, so that it is now known as J1938+2213.
Two other pulsars (J1756+18 and J2050+13) were discovered in the Arecibo 430-MHzintermediate latitude (pointed) survey (2003ApJ...594..943N). They were reportedin the above paper describing that survey, but without timing solutions because althoughthey were originally detected on the 19th and 13th of July 1990respectively, they were confirmed only in January 2003.
Finally, in 1996ApJ...470.1103R an additional pulsar candidate (J2052+17) was listed, but theauthors were unable to confirm it because of the start of the Arecibo upgrade. Thecandidate had a spin period of 119.26 ms and a DM of pc. In 2004 October we confirmed the existence of this pulsar using the 327 MHzGregorian receiver of the 305-m Arecibo radio telescope and the Wideband AreciboPulsar Processors (WAPPs, 2000ASPC..202..275D) as back-ends. Both the topocentric spinperiod (119.27 ms) and DM of pc were compatible with theparameters in 1996ApJ...470.1103R. The pulsar has an exceptionally narrow profile,which represents less than 1% of a rotation cycle as presented inFig.1 and in more detail in Fig.A12.
In what follows, we present detailed studies for these objects, both oftheir timing and emission properties. In §2 we discussbriefly the timing observations and analytical results,§3 describes the pulse-sequence, profile and polarization analyses,§4 discusses the origin of PSRJ2053+1718and §5 summarizes the various results.
Table2. Timing Parameters | |||||
---|---|---|---|---|---|
Pulsar Name | RA | Dec | DM | ||
(Hz) | ( Hz s-1) | (pc cm-3) | |||
J0435+2749 | 04 35 51.8178(16) | 27 49 1.68(16) | 3.06457408039(5) | 0.767(4) | 53.192(9) |
J0517+2212 | 05 17 17.159(7)(72) | 22 12 48.8(1.6) | 4.9707996302(9) | 2.20(6) | 18.691(9) |
J0627+0706 | 06 27 44.2168(15) | 07 06 12.67(29) | 2.10139608235(13) | 1314.82(11) | 138.29 |
J0927+2345 | 09 27 45.26(4) | 23 45 11.(1) | 1.3125269006(16) | 5.26(5) | 17.24(10) |
J0943+2253 | 09 43 32.403(5) | 22 53 5.98(11) | 1.87626174158(26) | 3.168(8) | 27.209(17) |
J0947+2740 | 09 47 21.287(13) | 27 40 43.48(18) | 1.1750682463(7) | 5.937(21) | 29.09(5) |
J1246+2253 | 12 46 49.3610(28) | 22 53 43.12(10) | 2.11028093179(6) | 3.89(4) | 17.793(22) |
J1404+1159 | 14 04 36.961(8) | 11 59 14.4(3) | 0.3772960811(6) | 1.893(18) | 18.530(27) |
J1756+1822 | 17 56 17.582(5) | 18 22 55.26(13) | 1.34408437573(3) | 9.266(17) | 70.80 |
J1935+1159 | 19 35 15.87(23) | 11 59 6.(54) | 0.5155281800(14) | 2.7(11) | 191.6(26) |
J2050+1259 | 20 50 57.21(5) | 12 59 9.69(14) | 0.81898743453(12) | 3.38(6) | 52.40 |
J2053+1718 | 20 53 49.4806(4) | 17 18 44.692(7) | 8.384495640456(4) | 0.002014(7) | 26.979 |
Table3. Derived Parameters | ||||||||
Pulsar Name | Galactic Coordinates | |||||||
(s) | (s s-1 ) | (yr) | (G) | (kpc) | (erg s-1) | |||
J0435+2749 | 171 50 32.0 | 13 04 17.3 | 0.326279534509(6) | 0.00816(5) | 0.63 | 0.052 | 1.8 | 0.93 |
J0517+2212 | 182 10 37.1 | 09 00 46.0 | 0.222366515211(5) | 0.01087(28) | 0.32 | 0.050 | 0.66 | 3.90 |
J0627+0706 | 203 54 25.4 | 01 59 35.5 | 0.47587411455(3) | 29.7748(24) | 0.00025 | 3.81 | 4.7 | |
J0927+2345 | 205 17 09.1 | +44 12 05.6 | 0.7618891464(9) | 0.3051(28) | 0.040 | 0.49 | 0.66 | 2.72 |
J0943+2253 | 207 53 11.5 | +47 27 29.9 | 0.53297467930(7) | 0.09000(23) | 0.094 | 0.22 | 1.2 | 2.35 |
J0947+2740 | 201 08 31.0 | +49 23 04.2 | 0.8510136770(5) | 0.4300(15) | 0.031 | 0.61 | 1.28 | 2.75 |
J1246+2253 | 288 48 32.7 | +85 38 23.7 | 0.473870556729(13) | 0.0874(8) | 0.086 | 0.21 | 1.5 | 3.24 |
J1404+1159 | 355 04 37.3 | +67 06 51.9 | 2.650438343(4) | 1.330(13) | 0.032 | 1.90 | 1.4 | 0.28 |
J1756+1822 | 43 50 08.5 | +20 11 07.1 | 0.744000910999(17) | 0.5129(9) | 0.023 | 0.63 | 4.2 | 4.92 |
J1935+1159 | 48 36 43.9 | 04 03 31.7 | 1.939758172(5) | 1.0(4) | 0.03 | 1.4 | 6.8 | 0.5 |
J2050+1259 | 59 26 11.6 | 19 14 21.3 | 1.22101995445(17) | 0.504(9) | 0.038 | 0.79 | 3.1 | 1.09 |
J2053+1718 | 63 33 13.9 | 17 15 51.8 | 0.11926775835804(5) | 0.0002864(10) | 6.7 | 0.0058 | 1.9 | 0.65 |
2 Timing observations and results
The aforementioned pulsars are relatively bright, and for that reason were used astest pulsars during the very early demonstration stages of the Arecibo 327-MHz drift scan survey(2013ApJ...775...51D). These observations were carried out with the 327-MHzGregorian feed and one of the four WAPPs as backends.They all were acquired in search mode, with 256 spectral channels, a sampling time of 64s and abandwidth of 50 MHz. They were later dedispersed and folded using the PRESTOroutine “prepfold” (2002AJ....124.1788R), and then topocentric pulse times of arrival (TOAs)were derived from the resulting profiles using the FFT technique described by1992RSPTA.341..117T and implemented in the PRESTO routine get_TOAs.py.
The characteristics of the timing observations are given in Table1, togetherwith the number of TOAs derived for each, the root mean square (rms) of the residuals(measured TOA - model prediction for the respective pulse, depicted graphicallyin Fig. 2 for PSRJ2053+1718 as an example)and the reduced of each fit.For some pulsars this is much larger than 1, implying the presence ofeffects that have not been modeled, such as timing noise. This is more prominent for theyounger pulsars in this work, in particular for J0627+0706; in agreement with the resultsof 2013MNRAS.429..579B. The table also gives the new names for thesepulsars, now possible given the precise measurements of Right Ascension () anddeclination (); these names are used throughout the remainder of this paper.The best fit values for and are presented in Table2, togetherwith the other numerical parameters of the timing solution such the rotation frequency (),its derivative (), and dispersion measure (DM).
Finally, the derived parameters are given in Table3: Galactic coordinates ()and distance (), derived from the DM using the NE2001 model of theelectron distribution of the Galaxy (2002astro.ph..7156C), spin frequency () and itsperiod derivative (), characteristic age (), magnetic field (), andspin-down energy (). The expressions for these quantities were adopted from2004hpa..book.....L: , and , where is the moment of inertia of theneutron star, which is generally assumed to be . All pulsars inthe list are isolated, and most of them belong to the “normal” group, with fairly typicalrotation periods (between 0.22 and 2.65 s), characteristic ages (between 0.25 Myr and0.63 Gyr) and B-fields (from 0.05 to 3.8G).We now discuss the characteristic of the two extreme objects in our sample.
2.1 PSR J2053+1718
PSRJ2053+1718 has a much smaller spin periodderivative and is clearly much older than the other pulsars in this sample.A first simple fit for , , , and propermotion along these two directions ( and )yields a reduced of 1.80, and visible trends inthe residuals. Given the low frequency used in the timing and the relatively highprecision of the measurements, these are likely due to variations in DM caused bythe Earth’s and the pulsar’s movement through space. We used the DMX model(2013ApJ...762...94D) to measure the DM variations (displayedin Fig.2) and subtract them; once this is done thereduced decreases to 1.34. In this model we obtain and .The NE 2001 model places this pulsar at a distance of 1.9 kpc,which implies a transverse velocity of ,which is typical among recycled pulsars (e.g., 2011ApJ...743..102G).This proper motion allows for a correction of the observed , where wesubtract the Shklovskii effect (1970SvA....13..562S) and the Galacticacceleration of this pulsar relative to that of Solar System, projected along theline of sight (1991ApJ...366..501D) (this was calculated using the latestmodel for the rotation of the Galaxy from2014ApJ...783..130R). These terms mostly cancel each other, so thatthe intrinsic spin-down, , is very similar to the observed . This implies a low B-field ofG and a characteristic age of Gyr. The origin of this pulsar is discussed in §4.
2.2 PSRJ0627+0706
With a characteristic age of only 250 kyr PSRJ0627+0706 is two orders of magnitudeyounger than any other pulsar in this group; its spin-down power is more than 220 timeslarger than any other pulsar in this sample. This object displays a prominent interpulse,suggesting an orthogonal rotator. It also has significant timing noise, which isagain typical of young pulsars. This is the reason for the very high reduced of its solution.
2003PhDT.........2C remarked that this pulsar lies, in projection,within of the centre of the old, large Monoceros supernova remnant (SNR G205.5+0.5);which is located at .For this reason they proposed that, if PSRJ0627+0706 has an age similar to thatof SNR G205.5+0.5 (30 to 100 kyr, 1986MNRAS.220..501L), it could be acandidate in association with that SNR (they point out that the positional offsetis possible given the age of the SNR and the proper motions of other pulsarsobserved in the Galaxy).
The age we and 2013MNRAS.429..579Bmeasure for PSRJ0627+0706 is larger by a factor of 2.5 to 8. However, this is notvery constraining: pulsars can be substantially younger than their characteristic ageif they are born with a spin period similar to their current spin period.
Another way of verifying the association is through distance measurements.The estimated distance to the Monoceros SNR, 1.6 kpc (1986ApJ...301..813O),is much smaller than the estimated distance to this pulsar, 4.5 kpc, whichis based on its unusually large DM relative to other pulsars in the Galactic anticentre.This, again, is not necessarily an indication that the pulsar is much more distant thanthe SNR: the large amount of ionized gas in the vicinity of this SNR could be itselfan explanation for the large DM of the pulsar.
We note that this area of the Galaxy has an abundance ofrelatively young pulsars that could potentially be associated withSNR G205.5+0.5. In particular, the “radio quiet” gamma-ray pulsar PSRJ0633+0632, discoveredin data from the Fermi satellite (2009Sci...325..840A), was listed inthe latter paper as a “plausible” association with SNR G205.5+0.5based on its location within of the SNR centre.Later 2011ApJS..194...17R measured the characteristic age of PSRJ0633+0632 (59 kyr)which is also more compatible with the estimated age of the SNR.
We conclude therefore that PSRJ0633+0632 is more likely to be associatedto SNR G205.5+0.5 than PSRJ0627+0706.
3 Pulse-sequence and Profile Analyses
Recently, we conducted single-pulse polarimetric observations on most of the abovepulsars as well as a few others of related interest. The Arecibo observations werecarried out at both P band (327 MHz) and L band (1400 MHz) using total bandwidthsof 50 MHz and typically 250 MHz, respectively. Four Mock spectrometers were usedto sample adjacent sub-bands after MJD 56300 (see 2016MNRAS.460.3063M) and fourWideband Arecibo Pulsar Processors (WAPPs) earlier (2013MNRAS.433..445R) to achievemilliperiod resolution. The observations were then processedto provide pulse sequences that were used both to compute average polarizationprofiles and fluctuation spectra. Rotation measures (RMs) were determined for eachof the pulsars in the course of the polarimetric analyses, and these will be publishedseparately with many others.
A summary of these polarimetric observations are given in Table4, as describedabove. Nominal values of the rotation measure are also given in the table, and acomplete description of the methods and errors will be given in Rankin, Venkataraman& Weisberg (2017). Belowwe treat the various pulsars object by object referring to the polarized profiles andfluctuation spectra in the Appendix figures. The analyses proceed from polarimetryto fluctuation spectra and finally to quantitative geometry following the proceduresof 1993ApJS...85..145R; 1993ApJ...405..285R. The longitude-resolved fluctuation(LRF) spectra of the pulsesequences (e.g., see 2001MNRAS.322..438D) were computed in an effort toidentify subpulse “drift” or stationary modulation associated with a rotating (conal)subbeam system.
3.1 Polarimetry and Fluctuation-spectral Analysis
J0435+2749 has a clear triple profile at both frequencies as shownin FigureA1, though the L-band one is of better quality.The leading and trailing components have very different spectralindices: the trailing component is much stronger at 327 MHz, but the leadingis much stronger at L-band.The fractional linearpolarization is low in both profiles such that the polarization-angle traverse is welldefined only at the higher frequency. The power under the leading component mayrepresent a different orthogonal polarization mode (OPM) than the others, suggestinglittle position angle (PPA) rotation across the profile. Both fluctuation spectra showbroad peaks at about 0.05 cycles/period, primarily in the two outer components, whichsuggest a 20-period conal modulation.
J0517+2212 has a double component profile at L-band, whereas itsP-band profile shows some structure in the second component. The polarizationtraverse show little rotation at P band apart from the two 90°“jumps” and thebehaviour seems similar at L band but less well resolved perhaps because of thediminished fractional linear polarization. The fluctuation spectra show a peaks around 0.12cycles/period, suggesting an 8 rotation-period modulation.
J0627+0706 has a bright interpulse, a component-peak separationof 177°(main pulse minus interpulse peak longitudes) as can be seen inFig.A3. Because both features have structure, more detailed interpretationis needed to assess how close to 180°they fall; however, given the narrownessof both features, it seems likely that they represent emission from the stars two poles,implying an orthogonal geometry where is close to 90°. PPA tracksgive hints about the geometry only at L band, and here little to go on apart from aprobable 90°“jump” under the main pulse. The main pulse might have threecomponents and the interpulse two. The fluctuation spectra are not displayed becausethey showed only flat “white” fluctuations.
J0927+2345 shows an interesting feature at P-band approximately180°away from the main pulse (Fig.A4). This apparent interpulse isdiscernible only in the P-band profile, and disappears in the L-band profile. Again, bothprofiles show so little linear polarization that a reliable PPA rate can be estimated foronly a narrow longitude interval at P band. The main pulse appears to have threeclosely spaced features. The fluctuation spectra are not given for this pulsar either because theyshowed no discernible features.
J0943+2253 nulls as seen in Fig.1 above, but the fluctuationspectra show no quasiperiodic behavior. The polarization is slight and the PPA trackshows what appears to be a 90°“jump” within the narrow interval where it isclearly defined.
J0947+2740 shows three components at both frequencies, though theleading region may be more complex at the lower frequency, probably representinga core and closely spaced inner cone. At L-band the conal components are weaker, andthe PPA traverse is more complex, perhaps showing a 90°“jump” in the region ofrapid PPA rotation. RVM behaviour, and the slope of it’s polarization traverse could notbe determined. This pulsar is also known to exhibit sporadic emission between intervalsof weakness or nulls as in Fig.1. The fluctuation spectra seem to hint at fluctuationpower at periods longer than about 3 or 4 pulses.
J1246+2253 has a single component at P band, which develops into aresolved triple form at L band in what may be the characteristic core-single manner.The fractional linear polarization at both frequencies is low, so little can be discernedreliably from the PPA tracks. Also no clear features are seen in the fluctuation spectraas is often the case for core-single profiles.
J1404+1159 exhibits a narrow peak in its fluctuation spectra around 0.2cycles/period, suggesting a modulation period of some 5 rotation periods. Adisplay of its individual pulses bears this out, and a display of the its emission foldedat shows that the modulation is highly regular. The PPA rate at the profilecenter suggests an outside sightline traverse as is usual for conal single “drifters”.See FigureA8.
J1756+1822 appears to have two profile components, and its profilebroadens perceptibly with wavelength, suggesting a conal double configuration. TheP-band polarization is negligible, whereas a hint of a moderately steep negative PPAtraverse is seen at L-band. The fluctuation spectra showed no features and were thusomitted.
J1935+1159’s long nulls (see Fig.1) make this pulsar difficult toobserve sensitively, and neither clear profile structure nor polarization signature is seenat either frequency. Similarly, fluctuation spectra showed nothing useful.
J2050+1259 also exhibits frequent nulls as seen above in Fig.1.However, its single profile at L band broadens and bifurcates at P band in the usualconal double manner, and a steep PPA traverse is seen at the lower frequency. Finally,here we do see strong low frequency features in the fluctuation spectra indicative ofmodulation on a scale of 50 rotation periods or longer.
J2053+1718 Our P and L band observations donot provide much polarization information or fluctuation-spectral information apartits having a single profile at both frequencies.
Table4. Polarimetric Observations | |||||||
Name | MJD | Pulses | Flux Estimates (mJy) | RM | |||
P-band | L-Band | P-band | L-Band | P-Band | L-Band | (rad-m2) | |
J0435+2749 | 53490 | 54541 | 1840 | 3065 | — | 0.24(3) | +2 |
J0517+2212 | 57123 | 54540 | 2696 | 2698 | 119.(8) | 0.52(2) | –16 |
J0627+0706 | 57123 | 57113 | 518 | 2520 | 8(5)0 | 0.25(4) | +212 |
J0927+2345 | 57525 | 57347 | 4724 | 2502 | 1.9(8) | 0.02(2) | –8 |
J0943+2253 | 57379 | 7775 | 5.3(1) | +8? | |||
J0947+2740 | 57379 | 57524 | 3172 | 4699 | 8.8(1) | 0.027(9) | +32 |
J1246+2253 | 52840 | 57307 | 1266 | 1885 | — | 0.21(9) | +4? |
J1404+1159 | 55905 | 57307 | 509 | 1591 | 68.(8) | 0.01 | +4 |
J1756+1822 | 57567 | 57567 | 2156 | 3571 | 0.008 | 0.05 | +70 |
J1935+1159 | 57288 | 57533 | 1004 | 1090 | 10 | 0.47(5) | –83 |
J2050+1259 | 57524 | 57525 | 2046 | 1966 | 10.(4) | 0.025(8) | –80 |
J2053+1718 | 57524 | 57533 | 5023 | 21624 | 19 | 0.0006 | –5 |
Table5. Conal Geometry Models | ||||||
---|---|---|---|---|---|---|
Pulsar | Class | |||||
(°) | (°) | (°) | (°) | (km) | ||
J0435+2749 | T | 18 | 3.4 | 59.0 | 10.3 | 230 |
J0517+2212 | D | 31 | 0 | 45.2 | 11.7 | 205 |
J0627+0706m | St | 90 | -7.2 | 4.54 | 7.5 | 131 |
J0627+0706i | D | 90 | -6.4 | 6 | 6.9 | 129 |
J0927+2345m | D/T? | 69 | 3.4 | 8 | 5.1 | 130 |
J0943+2253 | D/T? | 42 | -5.5 | 7 | 5.9 | 123 |
J0947+2740 | T/M | 42 | -1.2 | 18 | 6.0 | 205 |
J1246+2253 | St | 81 | -4.7 | 6.5 | 5.7 | 103 |
J1404+1159 | Sd | 25 | 2.2 | 5.3 | 0.88 | 114 |
J1756+1822 | D | 50 | 2.5 | 16 | 6.7 | 224 |
J1935+1159 | D | 10.13 | -1.0 | 50.4 | 4.3 | 239 |
J2050+1259 | Sd | 27 | -2.6 | 21 | 5.2 | 223 |
J2053+1718 | St? | 63 | -17.2 | 2.5 | 17.2 | 235 |
Notes: outer half-power widths interpolated to 1 GHz above:
J0435+2749: 63°at P-band and 59°at L-band; 5°/°.
J0517+2212: The profile narrows from at P-band to at L-band. There was a similar angle of polarization angle traverse at both frequencies. I suggest central traverse, beta about 0
J0627+0706: The main pulse measures approximately at both L-band and P-band at half maximum, while the interpulse is wider at half maximum measuring . The main pulse and the interpulse are appart.
J0927+2345: 5°at P-band and 6.4°at L-band.
J0943+2253: This pulsar has width at P-band half max. The core widths are measured as at L-band and at P-band. The PPA slope was measured at P-band.
J0947+2740: Outside 3-db widths of 19.4°at P-band and 17°at L-band; central component widths of roughly 8°at P-band and 10°atL-band; 32°/°.
J1246+2253 5.7°at P-band and 7.4°at L-bandinterpolated to 6.5°at 1 GHz above; +12°/°.
J1404+1159: 11.This pulsar has width at P-band and at L-band.
J1756+1822 This pulsar has estimated core widths at P-band and at L-band, with total profile widths of at P-band and at L-band. The PPA traverse was measured using L-band data.16°at P-band and 15°at L-band; –18°/°.
J1935+1159:This pulsar has width at P-band and at L-band.
J2050+1259 widths 25°at P-band and 18°at L-band.Despite very weak polarization across the pulse, we’ve estimated the polarization angle traverse as at P band where there is a clear signature.
J2053+1718: This pulsar has width at P-band and at L-band.
3.2 Quantitative Geometry
We have also attempted to classify the profiles where possible and conduct aquantitative geometrical analysis following the procedures of the core/double-conemodel in Rankin (1993a,b; hereafter ETVI). Outside half-power (3-db) widths aremeasured for both conal components or pairs—and where possible estimated forcores. Core widths can be used to estimate , PPA-traverse central rates can be used to compute , and the conal widths can be used to computeconal beam radii using eqs. (1) through (6) of the above paper.
The notes to Table5 summarize our measurements, and the table values show theresults of the geometrical model for the pulsar’s emission beams. The profiles classis given in the first column, and in next two per the value whenpossible. The conal component profile widths , conal beam radii , andcharacteristic emission heights are tabulated in the rightmost three columns.
J0435+2749’s average profile has a triple component configurationat both frequencies, and the observed conal spreading suggests a core/outer conegeometry. The core width can only be estimated at the higher frequency at perhaps9°maximum, implying that is less that some 1.4°per ETVI, eq.(1).
The PPA traverse shows a much more complex behavior than the Rotation VectorModel (RVM) describes; however, the roughly 90°rotation near the center ofthe pulse may be so interpreted. The spherical geometric beam model in Table5seems compatible with a core-cone triple T classification.
J0517+2212’s profile shows two primary components. There is morestructure at L-band, as well as overall pulse narrowing. These factors, along with thelack of PPA traverse suggest that and imply the outer conal beamgeometry shown in Table5.
J0627+0706’s main-pulse profile may have two or three closely spacedcomponents. The pulse width at half maximum interestingly widens from P-bandto L-band suggesting a core-single configuration where the conal emission is seenmainly at high frequency. The polarization traverse is clearer at L-band, marked byprominent 90°modal “jumps”. It thus seems likely that is small for themain pulse and perhaps larger for the inter pulse, but that is close to 90°,yielding the classifications and model values in Table5. The emission heights given forboth the main pulse and interpulse suggest that it is inner conal emission.
J0927+2345’s average profile has two clear components and possiblyan unresolved trailing one as well. Its half width interestingly broadens from P-bandto L-band suggesting a core single evolution where conal “outriders” appear or becomemore prominent at high frequency. The polarization traverse is well defined only fora short interval at L band, which provides a useful value that leads to thegeometric beam model in Table5. If this profile were triple, the central component wouldbe wide.
J0943+2253’s average profile also has two closely spaced componentsand perhaps and unresolved weak feature on its leading edge, suggesting a doubleor triple configuration. We only have a P-band observation so cannot see how theprofile evolves, and the linear polarization is slight and difficult to interpret. However,we can guess a central PPA rate of 7°/°in order to compute the geometricmodel parameters in Table5, which suggest an inner-conal configuration.
J0947+2740’s profile is comprised by three main components, and the fact that itswidth increases with wavelength indicates an outer-conal configuration. Its PPA traverseseems interpretable per the RVM model at P band, but its L-band traverse seems to bedistorted by what may be a 90°“jump” just prior to the profile center. Its profilethen seems to be a core/outer cone triple, and the quantitative beam geometry modelis shown in Table5. The core width is estimated around , which is muchmore narrow than the central component of the profile ( at P-band and at L-band), which indicates that thecentral component contains both core and conal emission.
J1246+2253’s single profile at P band becoming triple at L band stronglysuggests a core single configuration. Despite the low fractional linear polarization, thetrailing positive traverse through roughly 90°was used to computer the geometricalmodel in Table5. The core width is estimated at .
J1404+1159 has a single component profile at both frequencies, and its narrowfluctuation feature identifies it as having regular drifting subpulses as shown in Fig.A8.The pulsar then appears to have a classic conal single profile. Both PPA tracks show anegative-going traverse with a central slope of about –12°/°. Here we also giveshort pulse-sequences folded at the modulation period of some 0.2 rotation-periods/cycle.
J1756+1822 has an interestingly shaped profile that appears to have twoseparate components. The P and L-band profiles have similar forms with the longerwavelength one somewhat broader in the usual pattern of the conal double class.The fractional linear profiles is low at both frequencies, but at L-band there seems to bea hint of a traverse through more than 90°across the profile. The fluctuation spectraare not shown as no features could be discerned.
J1935+1159 Appears to be a five component pulsar; even though only twoindividual components can be resolved, it appears to be filled which could hide additional components.According to the emission heights, and the profile narrowing from P-band to L-band, indicate that thisis an outer cone which is filled with inner conal and/or core emission. For the geometric computations,we have estimated a central traverse of .
J2050+1259’s profile has a single component at Lband and two closelyspaced components at P band as seen in Figs.1 and A11. Its profile isbroader at the lower frequency, and strong hints of a roughly 180°PPA traverse areseen in both profiles, suggesting that this is a conal single profile with a small impactangle with the beaming parameters as given in Table5.
J2053+1718 show a single component at both frequencies, though in thehigher frequency observation the time resolution was poor with only 232 samples acrossthe rotation cycle. The polarization information and fluctuation spectra do not give muchto go on either. Curiously, this pulsar has a wider profile in L-band than in P-band, howevermuch of this can probably be attributed to the quality of the observation. Its short 119-ms rotation periodand single profile do suggest acore-single classification.
4 On the origin of PSR J2053+1718
In double neutron star systems, the first-born neutron star was recycled by accretion of massfrom the progenitor of the second-formed neutron star. This accretion spun up thefirst formed NS to spin periods between 22 and 186 ms (for the known DNSs, likelyfaster right after they formed) and, by mechanisms that are not clearly understood,it induced a decrease in its magnetic field to values between G. Such pulsars spin down very slowly and therefore will stay in theactive part of the - diagram for much longer than non-recycledpulsars; this is the reason why we mostly see the recycled pulsars in these systems(the second-formed non-recycled pulsars are observed in two DNSs only).
Some isolated pulsars like PSRJ2053+1718are in the same area of the - diagram as the recycled pulsars in DNSs, but have no companion to explain therecycling. The conventional explanation for their formation is that, like therecycled pulsars in DNSs, they were spun up by a massive stellar companion; thedifference is that when the latter star goes supernova and forms a neutron star, the systems unbinds,owing to the kick and mass loss associated with the supernova (e.g.,2010MNRAS.407.1245B). For this reason they have been labelled “DisruptedRadio Pulsars”, or DRPs.
We should keep in mind the possibility of alternative origins for these pulsars:some NSs observed in the center of supernova remnants, despite being obviouslyyoung, have small B-fields and large characteristic ages similar to those of DRPs— these objects are known as Central Compact Objects, or CCOs(see e.g., 2010ApJ...709..436H). Therefore,one could expect that some DRPs formed as CCOs. However, 2013ApJ...773..141Gfind after extensive study of DRPs in X-rays that none appears to have thermalX-ray emission, implying that there is likely no relation between CCOs and DRPs.This results in a mystery: a substantial fraction of neutron stars appear to form asCCOs, which one might reasonably expect to form DRP-like radio pulsars, some of themwith strong thermal X-ray emission, but these large numbers of DRPs (and “hot”DRPs) are not observed. Either, for some unknown reason, they never develop radioemission, or their B-field increases significantly after birth, making them lookmore like normal pulsars. In any case, the results of 2013ApJ...773..141Gseem to exclude the possibility that DRPs such as PSRJ2053+1718formed from central Compact Objects.
Any model that explains quantitatively the observed distribution oforbital eccentricitiesand spatial velocities of DNSs should also be able to explain the relative fractionof DRPs to DNSs and, furthermore, the velocity distribution of the two classesof objects. As already discussed by 2010MNRAS.407.1245B, the relative number ofDNSs and DRPs implies that the second SN kick must be, on average,significantly smaller than that observed for single pulsars. The evidence for thisamong DNSs has been growing in recent years and is now very strong (see summary inTauris et al. 2017). It is therefore clear that more measurements of proper motions,spin periods, ages and B-fields of DRPs such as those presented here give us importantclues for understanding the formation of DNS systems.
5 Discussion
In the foregoing sections we have characterized agroup of pulsars that had not been the target of any previous detailed studies.We determined timing solutions for them; most are normal, isolated pulsars.One of them, PSRJ0627+0706, is relatively young ( kyr)and is located near the Monoceros SNR, however it is not clear whether thepulsar and that SNR originated in the same supernova event.We confirmed a candidate from a previous survey, PSR J2053+1718;subsequent timing shows that, despite being solitary, this object was recycled;it appears to be a member of a growing class of objects that appear to result fromthe disruption of double neutron stars at formation. We highlight that measurementsof the characteristics of these objects (spin period, age, B-field, velocity)are important for understanding the formation of double neutron star systems.
As part of our characterization, we have also observed these pulsars polarimetrically withthe Arecibo telescope at both L and P band in an effort to explore their pulse-sequenceproperties and quantitative geometry.Three of them (PSRsJ0943+2253, J1935+1159 and J2050+1259)have strong nulls and sporadic radio emission, several others exhibit interpulses (PSRsJ0627+0706 and J0927+2345) and one shows regular drifting subpulses (J1404+1159).All these measurements will contribute to future, more global assessments of theemission properties of radio pulsars and studies of the NS population in the Galaxy.
Acknowledgments
The authors sincerely thank Dr. Paulo Freire of the Max Planck Institute for Radioastronomy in Bonn for his generous assistance with the timing analyses. Much of the work was made possible by support from the US National Science Foundation grant 09-68296 as well as NASA SpaceGrants. One of us (JMR) also thanks the Anton Pannekoek Astronomical Instituteof the University of Amsterdam for their support. Arecibo Observatory is operatedby SRI International under a cooperative agreement with the US National ScienceFoundation, and in alliance with SRI, the Ana G. Méndez-Universidad Metropolitana,and the Universities Space Research Association. This work made use of the NASAADS astronomical data system.