J/A+A/591/A134 LOFAR census of non-recycled pulsars (Bilous+, 2016)
A LOFAR census of non-recycled pulsars: average profiles, dispersion measures,
flux densities, and spectra.
Bilous A.V., Kondratiev V., Kramer M., Keane E., Hessels J., Stappers B.,
Malofeev V., Sobey C., Breton R., Cooper S., Falcke H., Karastergiou A.,
Michilli D., Oslowski S., Sanidas S., ter Veen S., van Leeuwen J.,
Verbiest J., Weltevrede P., Zarka P., Griessmeier J.-M., Serylak M.,
Bell M., Broderick J., Eisloeffel J., Markoff S., Rowlinson A.
<Astron. Astrophys. 591, A134 (2016)>
=2016A&A...591A.134B 2016A&A...591A.134B (SIMBAD/NED BibCode)
ADC_Keywords: Pulsars ; Interstellar medium
Keywords: pulsars: general - telescopes - ISM: general
Abstract:
We present first results from a LOFAR census of non-recycled pulsars.
The census includes almost all such pulsars known (194 sources) at
declinations Dec>8° and Galactic latitudes |Gb|>3°, regardless
of their expected flux densities and scattering times. Each pulsar was
observed for ≥20minutes in the contiguous frequency range of
110-188MHz. Full-Stokes data were recorded. We present the dispersion
measures, flux densities, and calibrated total intensity profiles for
the 158 pulsars detected in the sample. The median uncertainty in
census dispersion measures (1.5x10-3pc/cm3) is ten times smaller,
on average, than in the ATNF pulsar catalogue. We combined census flux
densities with those in the literature and fitted the resulting
broadband spectra with single or broken power-law functions. For 48
census pulsars such fits are being published for the first time.
Typically, the choice between single and broken power-laws, as well as
the location of the spectral break, were highly influenced by the
spectral coverage of the available flux density measurements. In
particular, the inclusion of measurements below 100MHz appears
essential for investigating the low-frequency turnover in the spectra
for most of the census pulsars. For several pulsars, we compared the
spectral indices from different works and found the typical spread of
values to be within 0.5-1.5, suggesting a prevailing underestimation
of spectral index errors in the literature. The census observations
yielded some unexpected individual source results, as we describe in
the paper. Lastly, we will provide this unique sample of wide-band,
low-frequency pulse profiles via the European Pulsar Network Database.
Description:
Table obssum.dat contains an observing summary for all pulsars in the
LOFAR census sample. DM measurements and mean flux densities in
110-188MHz frequency range are listed for 158 detected sources. For
the non-detected pulsars the upper limits on mean flux density values
are given. Spectral fits for 165 pulsars with flux densities measured
at more than one frequency (census or literature) are presented in
table1pl.dat (a single power-law spectral model, 1PL), table2pl.dat
(a power-law with one break, 2PL) or in table3pl.dat (2 breaks, 3PL).
For 1PL models, the measured flux density values were modeled as
random variables, normally distributed in base 10 log space with
mean_lgS=lg(S0)+a*lg(f/f0) and dispersion sigma_lgS. For the
spectra consisting of small number of measurements, sigma_lgS was set
by the reported flux density errors. For the spectra consisting of
larger number of measurements, an additional scatter (sigmaunknlgS)
was added in quadrature to sigma_lgS and fitted for. This additional
parameter represents intrinsic flux variability or any kind of
unaccounted propagation or instrumental error. For 2PL models,
mean_logS was defined as lg(S0)+(alo)*lg(f/f0) for f<fbr and as
lg(S0)+(ahi)*lg(f/fbr)+(alo)*lg(fbr/f0) for f>fbr. For 3PL models
mean_lgS was modified accordingly. A 2PL or 3PL model was preferred
over a 1PL model in the cases where either of the former gave a
significantly smaller sigmaunknlgS.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
obssum.dat 216 194 Observation summary, DM and flux density
measurements (table B1)
table1pl.dat 54 124 Fitted parameters for the pulsars with spectra
modeled with a single power-law
table2pl.dat 80 40 Fitted parameters for the pulsars with spectra
modeled with a broken power-law
table3pl.dat 106 5 Fitted parameters for the pulsars with spectra
modeled with a power-law with two breaks
refs.dat 141 71 References
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See also:
http://www.atnf.csiro.au/people/pulsar/psrcat : ATNF pulsar catalogue
http://astron.nl/psrcensus : processed data and supplementary materials
for LOFAR pulsar census
Byte-by-byte Description of file: obssum.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- PSR Name of pulsar as in ATNF catalogue v.1.51
12- 16 F5.3 d Per Spin period as in ATNF catalogue v.1.51
18- 25 F8.2 d MJD Observing epoch
27- 28 I2 min Obs.time Length of observing session
30- 33 I4 --- S/N ?=- Peak S/N of the average profile
35- 43 F9.5 pc/cm3 DMcat Dispersion measure as in ATNF catalogue
v.1.51
44- 51 F8.5 pc/cm3 e_DMcat ? rms uncertainty on DMcat
53- 63 F11.7 pc/cm3 DMcen ?=- Dispersion measure at the epoch of
observation
72- 80 F9.7 pc/cm3 e_DMcen ? rms uncertainty on DMcen
84- 88 E5.1 --- tau/P Expected NE2001 scattering time at 150MHz
divided by pulsar period, τscat/P
89 A1 --- n_tau/P [*] Note on tau/P (1)
91- 94 F4.2 --- ModInd Expected flux modulation index due to
scintillation in the ISM (2)
96 A1 --- l_Flux Upper limit flag on Flux for non-detected
pulsars
97-102 F6.1 mJy Flux Mean HBA flux density in 110-188MHz
105-110 F6.1 mJy e_Flux ? rms uncertainty on mean HBA flux density
112-216 A105 --- Ref Literature flux references in refs.dat file
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Note (1): For PSR B2036+53, NE2001 model (2002astro.ph..7156C 2002astro.ph..7156C) predicts
scattering time of 486s, whereas census observations suggest the
scattering time to be approximately 0.2s.
Note (2): For PSR B2036+53, the expected modulation index was based
on census data estimate of the scattering time.
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Byte-by-byte Description of file: table1pl.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- PSR Name of pulsar as in ATNF catalogue v.1.51 (1)
13- 16 I4 MHz FreqRngLo Lower edge of the spectral frequency span
18- 22 I5 MHz FreqRngHi Upper edge of the spectral frequency span
24- 26 I3 --- N Number of data points in spectrum
28- 32 I5 MHz f0 Reference frequency
35- 38 F4.1 mJy S0 Fitted mean flux density at the reference
frequency
40- 44 F5.2 --- a Fitted spectral index
46- 49 F4.2 --- e_a Uncertainty in fitted spectral index
51- 54 F4.2 --- sigmalgS ? Fitted extra scatter of lg(S) (sigmaunknlgS)
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Note (1): PSRs J1238+21, J1741+2758, B1910+20, J2139+2242 have also 2PL fit,
with break frequency fixed at the frequency of the largest measured mean flux
density. See table2pl.dat for the values of fitted parameters.
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Byte-by-byte Description of file: table2pl.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- PSR Name of pulsar as in ATNF catalogue v. 1.51
13- 16 I4 MHz FreqRngLo Lower edge of the spectral frequency span
18- 22 I5 MHz FreqRngHi Upper edge of the spectral frequency span
24- 26 I3 --- N Number of data points in spectrum
28- 32 I5 MHz f0 Reference frequency
34- 38 F5.1 mJy S0 Fitted mean flux density at the reference
frequency
40- 44 F5.2 --- alo Fitted spectral index for f<fbr
46- 49 F4.2 --- e_alo Uncertainty in fitted spectral index for f<fbr
51- 54 I4 MHz frbr Fitted break frequency
56- 59 I4 MHz e_frbr ? Lower limit of 68% uncertainty range for
break frequency
61- 64 I4 MHz E_frbr ? Upper limit of 68% uncertainty range for
break frequency
66- 70 F5.2 --- ahi Fitted spectral index for f>fbr
72- 75 F4.2 --- e_ahi Uncertainty in fitted spectral index for f>fbr
77- 80 F4.2 --- sigmalgS ? Fitted extra scatter of lg(S) (sigmaunknlgS)
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Byte-by-byte Description of file: table3pl.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- PSR Name of pulsar as in ATNF catalogue v.1.51
15- 16 I2 MHz FreqRngLo Lower edge of the spectral frequency span
18- 22 I5 MHz FreqRngHi Upper edge of the spectral frequency span
24- 26 I3 --- N Number of data points in spectrum
30- 32 I3 MHz f0 Reference frequency
34- 38 F5.1 mJy S0 Fitted mean flux density at the reference
frequency
40- 44 F5.2 --- alo Fitted spectral index for f<fbr1
46- 49 F4.2 --- e_alo Uncertainty in fitted spectral index for f<fbr1
51- 54 I4 MHz frbr1 Fitted first break frequency
56- 59 I4 MHz e_frbr1 ? Lower limit of 68% uncertainty range for
the first break frequency
61- 64 I4 MHz E_frbr1 ? Upper limit of 68% uncertainty range for
the first break frequency
66- 70 F5.2 --- amid Fitted spectral index for frbr1<f<fbr2
72- 75 F4.2 --- e_amid Uncertainty in fitted spectral index for
frbr1 <f<fbr2
77- 80 I4 MHz frbr2 Fitted second break frequency
82- 85 I4 MHz e_frbr2 Lower limit of 68% uncertainty range for
the second break frequency
87- 90 I4 MHz E_frbr2 Upper limit of 68% uncertainty range for
the second break frequency
92- 96 F5.2 --- ahi Fitted spectral index for f>fbr2
98-101 F4.2 --- e_ahi Uncertainty in fitted spectral index for f>fbr2
103-106 F4.2 --- sigmalgS Fitted extra scatter of lg(S) (sigmaunknlgS)
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Byte-by-byte Description of file: refs.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Ref Reference number
4- 22 A19 --- BibCode BibCode
24- 48 A25 --- Aut Author's name
54-141 A88 --- Com Comments
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Acknowledgements:
Hanna Bilous, hanna.bilous(at)gmail.com
References:
Cordes & Lazio, 2002astro.ph..7156C 2002astro.ph..7156C
NE2001. I. A New Model for the Galactic Distribution of Free Electrons and
its Fluctuations
(End) Anna Bilous [UvA, the Netherlands], Patricia Vannier [CDS] 04-May-2016