Emmision of the remarkable pulsar B0943+10: Continual changes in the subpulse drift rate and in integrated pulse shape, intensity and polarization at frequencies of 327, 112, 62 and 42 MHz.

Svetlana A. Suleymanova (PRAO , Pushchino)Joanna M. Rankin (University of Vermont, Vermont)

We present data of new observations carried out at the Pushchino Radio Astronomy

Observatory (PRAO) at low radio frequencies 42, 62 and 112 MHz of a well known

mode switcher B0943+10. Earlier observations at 327 MHz (Arecibo) have shown

remarkably continual changes in subpulse drift rate and in the integrated-profile shape

with duration of several hours in its ‘B’urst mode. Observations at PRAO have shown

that the changes in the pulse shape during B-mode life-time are strongly frequency

dependent, namely: the changes in components amplitude ratio are more dramatic at

327 & 112 MHz as compared with those at 62 & 42 MHz.

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Subbem "carouse l" c ircu la tion tim e as a function o f tim e from B -m ode onset a t in terva ls o f 256 P1. C ircu la tion tim es for th ree Q /B transitions are a ligned a t the orig in (vertica l dotted line) and fitted w ith exponentia lcurve (so lid line). The characteris tic tim e is 73 m in or som e 4000 pu lses. Va lues fo r 3 "pure" B -m ode days are sh ifted to beg in a t p rofile num bers 18, 24 and 22, respective ly.

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System atic changes in B0943+10's average profile fo rmas a function o f tim e a fte r the B -m ode onset.( The am plituderatio A (2 /1) o f the com ponents peaks, separa ted by 6 deg,as a function o f averaged pulse num ber). Each averageis com prised o f 256 ind iv idua l pu lses, o r 280 seconds (4 .7 m in).

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B 0943+10 in tegra ted pu lse evo lu tion from B -m ode onset (top)to B -m ode o ffse t (bo ttom ) a t frequencies 42 M H z (on le ft) and 112 M H z (on righ t). R (2/1) changes in the range 0 .46-0 .26 a t 42 M H z and1.5-0 .27 a t 112 M H z. C orrespondent da tes and 20-subbeam carouse lC ircu la tion T im e is g iven on right

The component's peak intensity ratio- A(2/1) histograms in B-mode of the pulsar B0943+10 at near 42, 62, 112 MHz (PRAO, 2005-2008) and 327 MHz (Arecibo, 2003). It is obvious that components amplitude ratio A(2/1) changes in the wider range at higher frequencies.

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Integrated-pulse profile evolution during the ‘B’urst –mode lifetime for pulsar B0943+10. The profile component-amplitude ratio A(2/1) as a function of the circulation time of the 20-subbeam "carousel" at 327 MHz (stars), 112 MHz (crosses), 62 MHz (open circles) and 42 MHz (diamonds). Each averaged profile is comprised of 256 individual pulses (IP) at 327 MHz, 190 IP at 112 MHz, and 860 IP at 42 & 62 MHz. The vertical dashed line indicates the B-mode onset time.

3 6 3 6 . 5 3 7 3 7 . 5 3 8Subbeam "C arousel" C ircu lation T im e, P1

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Amplitude-fluctuation spectra of the individual pulse sequence following the B-mode onset at pulse #101 detected in the observations at PRAO 02 December 2007 at 62 MHz. The spectrum of the whole sequence has three maxima (left panel) resulting from three groups of pulses drifting with different rates (right panel). This example show that the subpulse-drift rate changes very rapidly over the first 15 minutes after B-mode onset.

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Systematic changes in B0943+10's average profile form as a function of time at the frequencies 112 MHz (crosses), 62 MHz (open circles) and 42 MHz (diamonds). The “ turbulent ” stage of the pulse shape evolution lasts nearly 40 minutes after the B-mode onset. The vertical dashed line indicates the B-mode onset time.

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The linear polarization percentage at the peak of the first component as a function of amplitude ratio A(2/1) of the two component peaks at 327 MHz (crosses) and 62 MHz (circles). The data fit to exponential functions which are marked by dashed line (62 MHz) and solid line (327 MHz). The X-axis is given in descending order with A(2/1)=1.34 at B-mode onset and A(2/1)=0.12 at B-mode offset.

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Systematic increasing of the linear polarization percentage at the peak of the first component as a function of time at 327 MHz. The linear percentage was calculated as a ratio of the linear–to-total power amplitudes at the longitude of the main (first) component of the average profile. Each average is comprises of 512 individual pulses, or 9.4 min. The average profile linear polarization varies markedly within the range between 3% and 50% during 4+ hours between onset and offset of B-mode. Since P3 has been measured from intensity-fluctuation spectra for each individual pulse sequence, the corresponding time has been derived from the CT-Time dependence.

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Histograms of the CT data based on Arecibo-2003 observations (dark columns) at 327 MHz and PRAO-2005-2008 observations (open columns) at 112 MHz. The turnover of the tendency at CT between 37.75 and 38 is caused increased probability of B-offsets here. The arrows mark the CTs at the time preceding the B-mode offset (1h 20m, 1992, 430 MHz, Arecibo and 3h 50m, 2006, 112 MHz, PRAO).

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Summary

1. Recent observations at PRAO (2005-2007) at the low frequencies of 112, 62 and 42 MHz have shown that the changes in the pulse shape during B-mode life-time are strongly frequency dependent, namely:

The changes in the component-amplitude ratio are less at 62 and 42 MHz as compared with those at 327 and 112 MHz .

The (A2/A1)-CT relation at lowest frequency of 42 MHz can be approximated by two linear functions implying different behaviors of A2/A1 above and below some critical CT.

Question: Can refraction cause this frequency dependence?

2. The duration of each individual event of the B-mode may vary significantly.

T= 1h20m, 1992, 430 MHz, Arecibo; T= 3h50m, 2006,112 MHz, PRAO

Question: What is the critical condition in pulsar magnetosphere that cause the

offset of the B-mode at so different “age” ?

3. The pulsar exhibits the utmost difference in the pulse shape at frequency range 327-42 MHz during 30 minutes after B-mode onset.

Question: What is happening in the pulsar magnetosphere during these 40 minutes?f

4. A measurements at 62 and 327 MHz have shown that the linear polarization of the stronger (first) component of the integrated profile continually increases during B-mode lifetime.

Question: We have reasons to suggest that the increasing of linear polarization percentage is connected with redistribution of the energy between polarization modes in favor of PPM which is mostly characteristic of the strong intensities. Can we then to propose that the pulsar B0943+10 in its B-mode continually flares up? Is it B-mode or F-mode?

Interpretation

The frequency dependence of the phenomenon suggests that propagation effects in the

magnetospheric plasma play a marked role. Petrova (2002) has shown that refraction can

cause a significant redistribution of the intensity in the emission beam. As the refraction is

determined mainly by the plasma-density gradient within the polar flux tube, the

continuous B-mode pulse-shape changes may imply a correspondingly slow

redistribution of the plasma outflow. The refraction is expected to be more intense at

higher frequencies (Lyubarskii & Petrova 1998)—i.e.,> 1 GHz—where rays are emitted

nearly parallel to the local magnetic field. To explain B0943+10’s observed pulse

changes at low frequencies (327-40 MHz) by refraction, some exotic magnetic field

geometry is needed like the ‘twisted up” one suggested by initially Rankin, Suleymanova

& Deshpande (2003).