J/A+A/635/A76 LOFAR census of pulsars at low frequencies (Bondonneau+, 2020)
A census of the pulsar population observed with the international LOFAR station
FR606 at low frequencies (25-80 MHz).
Bondonneau L., Griessmeier J.-M., Theureau G., Bilous A.V.,
Kondratiev V.I., Serylak M., Keith M.J., Lyne A.G.
<Astron. Astrophys. 635, A76 (2020)>
=2020A&A...635A..76B 2020A&A...635A..76B (SIMBAD/NED BibCode)
ADC_Keywords: Pulsars ; Radio sources
Keywords: pulsar: general - telescopes - ISM: general
Abstract:
To date, only 69 pulsars have been identified with a detected pulsed
radio emission below 100MHz.
A LOFAR-core LBA census and a dedicated campaign with the Nancay LOFAR
station in stand-alone mode were carried out in the years 2014-2017
in order to extend the known population in this frequency range.
In this paper, we aim to extend the sample of known radio pulsars at
low frequencies and to produce a catalogue in the frequency range of
25-80 MHz. This will allow future studies to probe the local Galactic
pulsar population, in addition to helping explain their emission
mechanism, better characterising the low-frequency turnover in their
spectra, and obtaining new information about the interstellar medium
through the study of dispersion, scattering, and scintillation.
We observed 102 pulsars that are known to emit radio pulses below
200MHz and with declination above -30°. We used the the Low Band
Antennas (LBA) of the LOw Frequency ARray (LOFAR) international
station FR606 at the Nancay Radio Observatory in stand-alone mode,
recording data between 25-80MHz.
Out of our sample of 102 pulsars, we detected 64. We confirmed the
existence of ten pulsars detected below 100 MHz by the LOFAR LBA
census for the first time (Bilous et al., 2019, submitted) and we
added two more pulsars that had never before been detected in this
frequency range. We provided average pulse profiles, DM values, and
mean flux densities (or upper limits in the case of non-detections).
The comparison with previously published results allows us to identify
a hitherto unknown spectral turnover for five pulsars, confirming the
expectation that spectral turnovers are a widespread phenomenon.
Description:
Our observations were carried out with the International
LOFAR Station in Nancay, FR606, used in standalone mode, between 2016
and 2017.
The sources of pulsating radio emission observed during our study were
selected considering the pulsars previously detected at low
frequencies by Zakharenko et al. (2013MNRAS.431.3624Z 2013MNRAS.431.3624Z) and Stovall et
al. (2015ApJ...808..156S 2015ApJ...808..156S). We added some of the pulsars detected in
the LOFAR HBA census (110-188MHz, Bilous et al., 2016A&A...591A.134B 2016A&A...591A.134B,
Cat. J/A+A/591/A134), along with some additional pulsars we deemed
interesting. We only kept radio sources with declination ≥20°.
With this limit, the minimum elevation at meridian observed at Nancay
Radio Observatory is 20°, and the effective area of the telescope
is 11.5% of the value for an observation at zenith. As an exception to
this limit, we observed the bright sources B0628-28 and B1749-28 down
to an elevation of 14. We discarded all pulsars with a dispersion
measure higher than 140pc/cm3. Based on these criteria, we were left
with 102 radio sources, as detailed in Table 1 (detections) and
Table A.1 (non-detections).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 120 64 Pulsars detected in this census
tablea1.dat 60 38 Pulsars that were not detected in this census.
profiles/* . 64 Reduced pulse profiles for detected pulsars
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See also:
J/A+A/591/A134 : LOFAR census of non-recycled pulsars (Bilous+, 2016)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- JName J2000 Name (JHHMM+DDMM or JHHMM+DD)
12- 21 A10 --- DName Discovery Name (JHHMM+DDMM, JHHMM+DD
or BHHMM+DD)
23- 27 F5.3 s P0 Pulsar period
29- 36 F8.5 pc/cm+3 DM Best-fit dispersion measure calculated
using pdmp
38- 43 F6.5 pc/cm+3 e_DM rms uncertainty on DM
44 A1 --- n_DM [te] Note on DM (1)
46- 50 F5.1 % tau/P0 Scattering time as estimated using YMW16
(Yao et al., 2017ApJ...835...29Y 2017ApJ...835...29Y), at 60MHz
divided by the pulsar period,
τclacscat/P0
52- 55 F4.1 % DutyCycle Effective width in pulses profiles
(based on w50)
57- 59 I3 --- SNR Signal-to-noise-ratio of the detected
pulsar profile
61- 63 I3 min Dur Total observation length
65- 66 I2 MHz Freqc Centre frequency of the observation
68- 69 I2 deg Elevavg Average elevation during the observation
71- 74 I4 mJy Fluxmean Mean flux density determined for the
corresponding centre frequency
76- 79 I4 mJy e_Fluxmean Error bar of 50% on Fluxmean
80 A1 --- n_Fluxmean Note on Fluxmean (1)
82-120 A39 --- FileName Name of the file with reduced pulse profile
in subdirectory profiles
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Note (1): Notes as follows:
t = the dispersion measure is not corrected for the effect of intrinsic
profile evolution with frequency (see Section 5.1).
e = the file is folded using an ephemeris file from either Jodrell
BankObservatory or Nancay Radio Observatory (see Section 3).
s = pulsed flux density only (due to scatter broadening, part of the pulsar's
energy reaches the telescope as continuum, see Section 5.2)
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Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- JName J2000 Name (JHHMM+DDMM or JHHMM+DD)
12- 21 A10 --- DName Discovery Name (JHHMM+DDMM, JHHMM+DD or
BHHMM+DD)
23- 28 F6.4 s P0 Pulsar period
29 A1 --- n_P0 [*] Note on PO (1)
31- 38 F8.4 pc/cm3 DM Dispersion measure (2)
40- 45 F6.1 % tau/P0 Scattering time divided by the pulsar period,
τcalcscat/P0 (3)
47- 49 I3 min Dur Total duration of the observation
51- 52 I2 deg Elev Average elevation of the observation
54- 57 I4 mJy Slim upper limit for the mean flux density
59- 60 A2 --- n_Slim [te] Note on SLim (4)
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Note (1): Note as follows:
* = the file is folded using an ephemeris file from either Jodrell Bank
Observatory or Nancay Radio Observatory (see Section 3.3).
Note (2): DM used to coherently disperse the observations from Zakharenko et al.
(2013MNRAS.431.3624Z 2013MNRAS.431.3624Z), Stovall et al. (2015ApJ...808..156S 2015ApJ...808..156S) and Bilous et al.
(2016A&A...591A.134B 2016A&A...591A.134B, Cat. J/A+A/591/A134), and ATNF to complete.
Note (3): estimated using YMW16 (Yao et al., 2017ApJ...835...29Y 2017ApJ...835...29Y) at 60MHz.
Note (4): Note as follows:
e = excluding the contribution of the nebula to Tsky
t = upper limit for the mean flux density is not valid (tau/P0>100%)
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Acknowledgements:
Louis Bondonneau, louis.bondonneau(at)cnrs-orleans.fr
(End) Patricia Vannier [CDS] 09-Dec-2019