Aristeidis Noutsos

1
Aristeidis Noutsos University of Manchester
2
The LOFAR Ionosphere

• See Gers talk, in Hamburg last year.

• The ionospheric RM contribution can be as much as
  5 rad m2.

• Ionospheric TEC fluctuations can
• hamper accurate RM determination
• relative TEC varies in short time scales
• absolute TEC varies more slowly (responsible for
  RM variations)

• Strong, highly polarised pulsars can be used to
  calibrate LOFAR
• we need to average a number of pulses, depending
  on pulsar strength.

3
Observation proposal
We have put together a WSRT proposal to observe
13 highly polarised, northern pulsars in the LFFE
band (115-180 MHz). Requested time 48
h. (Noutsos, Stappers, de Bruyn, Haverkorn)

• We would like to record simultaneously
• Full-Stokes filterbank data with PuMa II (?f
  20 MHz)
• this will allow us to perform high-time-resolution
  
• phase-resolved analysis (dt lt 50 µs)
• Aperture synthesis data
• this will allow us to perform RM synthesis on
  pulsars
• with no detectable radio pulsation
• e.g. the ms-binary PSR J02184232 and the
  scattered PSR B193721

4
Goals (I)
Establish a number of physical properties that
remain largely unexplored at low frequencies
total flux degree of polarization
phase-resolved RM etc.
5
Goals (II)
Investigate their suitability as LOFAR
polarization calibrators we would like to use
them regularly for polarization calibration

• What makes a good pulsar calibrator?
• Only pulsars with Decgt0º were considered.
• LOFAR sensitivity diminishes at large ?º
• DM had to be small (lt100 pc cm3)
• At low frequencies scattering smears the pulse
  profiles
• Linear flux gt 100 mJy
• A flat PA profile is desirable
• steep PAs / OPM may cause RM variation
• Increasing L towards low frequencies
• Candidate PSRs have to produce a high-S/N
  integrated profile in 1 min (or even faster!)

6
LOFAR sensitivity
The integration time needed for good polarization
s/n depends on S. For LOFAR 1818,
60s / Lchan is actually easy to achieve for
strong, highly polarised pulsars e.g. B192910
produces it in 3 sec! That s/n gives sPA 0.9º.
We need such low errors for phase-resolved RM
variations and GFR tests.
7
PSR B053121
S100 104 mJy
(L/I)600 0.3
a ?
DM 71 pc cm3
?t60s 0.3 s

• Notes
• S100 from Malofeev et al. (2000)
• L/I from Gould Lyne (1998)
• a from Lorimer et al. (1995)
• profiles from EPN database

8
PSR B080974
S100 1080 mJy
(L/I)230 0.11
a 1.7
DM 6 pc cm3
?t60s 52 s
L
f (MHz)
9
PSR B082326
S100 620 mJy
(L/I)400 0.29
a 1.6
DM 20 pc cm3
?t60s 7 s
Beware! It switches off some times.
L
f (MHz)
10
PSR J08370610
S100 1040 mJy
(L/I)400 0.03
a 2.7
DM 13 pc cm3
?t60s 501 s
L
f (MHz)
11
PSR B095008
S100 2030 mJy
(L/I)230 0.31
a 1.7
DM 3 pc cm3
?t60s 3 s
L
f (MHz)
12
PSR B113316
S100 1280 mJy
(L/I)230 0.25
a 1.5
DM 5 pc cm3
?t60s 7 s
L
f (MHz)
13
PSR B123725
S100 260 mJy
(L/I)230 0.44
a 1.8
DM 9 pc cm3
?t60s 76 s
L
f (MHz)
14
PSR B150855
S100 1280 mJy
(L/I)400 0.15
a 1.5
DM 20 pc cm3
?t60s 10 s
L
f (MHz)
15
PSR B154109
S100 400 mJy
(L/I)230 0.57
a 2.1
DM 35 pc cm3
?t60s 29 s
L
f (MHz)
16
PSR B191921
S100 1900 mJy
(L/I)400 0.29
a 1.9
DM 12 pc cm3
?t60s 2 s
L
f (MHz)
17
PSR B192910
S100 660 mJy
(L/I)400 0.79
a 1.7
DM 3 pc cm3
?t60s 3 s
L
f (MHz)
18
PSR B202151
S100 60 mJy
(L/I)230 0.49
a 0.7
DM 23 pc cm3
?t60s 421 s
L
f (MHz)
19
PSR B221747
S100 1200 mJy
(L/I)400 0.05
a 2.8
DM 44 pc cm3
?t60s 67 s
L
f (MHz)
20
psr ?tint (sec) pL (L/I) S100 (mJy) d (W/P)
053121 0.3 0.30 10000 0.09
080974 52 0.11 1080 0.03
082326 7 0.29 620 0.01
08370610 501 0.03 1040 0.02
095008 3 0.31 2030 0.04
113316 7 0.25 1280 0.03
123725 76 0.44 260 0.04
150855 10 0.15 1280 0.015
154109 29 0.57 400 0.06
191921 2 0.29 1900 0.02
192910 3 0.79 660 0.03
202151 421 0.49 60 0.015
221747 67 0.05 1200 0.01
21
LOFAR 1818 RM-sensitivity Simulation
RMfit 5 rad m2
22
LOFAR 1818 RM-sensitivity Simulation
23
RM determination issues
In the LOFAR observing band, scattering will play
an important role (see my science talk?)
PA profile
pulsar
observer
Scattering screen
24
RM determination issues
?RMpp 25 rad m2
A number of high-DM pulsars show large RM
variation across the pulse Scattering But, we
still see significant variation in a few lower-DM
pulsars PSR J20481616 DM 12 pc cm3 ?RMpp
17 rad m2
PSR J1644 4559
1.4 GHz
DM 478 pc cm3
Noutsos et al. (2009 accepted)
25
RM determination issues