Radio pulsar studies in Poland and prospects for the POLFAR - PowerPoint PPT Presentation

Radio pulsar studies in Poland and prospects for the POLFAR telescopes. Wojciech Lewandowski Janusz Gil Institute for Astronomy, University of Zielona Góra

Pulsar Group at the Janusz Gil Institute of Astronomy Prof. Giorgi Melikidze Collaborators: Dr hab. Jarosław Kijak Dipanjan Mitra (NCRA Pune, India) Dr hab. Wojciech Lewandowski Rahul Basu (IUCAA Pune, India) Dr Andrzej Szary Yashvant Gupta (NCRA Pune, India) Dr Krzysztof Maciesiak Axel Jessner (MPIfR, Bonn) Duncan Lorimer (West Virginia U.) PhD students Kaustubh Rajwade (WVU/Manchester Univ.) Karolina Rożko Olga Koralewska Main Topics of study: • Pulsar radio emission mechanism – observations and theory • Pulsar spectra • Iinterstellar medium (ISM) studies using pulsar observations

Studies of the pulsar emission mechanism using single pulse analysis Edwards & Stappers (2002) PSR B1857-26, Mitra & Rankin (2004)

Characteristics of single pulses: • Drifting subpulses • Large/giant pulses • Nulling P 4 Characteristic P 3 periodicities: • P 2 – distance between P 2 subpulses • P 3 – subpulse re- appearance at the same phase • P 4 – carousel rotation time (?) van Leeuwen et al. (2002)

Fourier Based methods used to analyse pulse stacks: Longitude Resolved Fluctuation Spectrum (LRFS) From: Meterwavelength Single-pulse Polarimetric Emission Survey. II. The Phenomenon of drifting Subpulses; Basu, Mitra, Melikidze, Maciesiak, Skrzypczak, Szary, ApJ, (2016)

Important results: the P 3 – luminosity dependence Result from MSPES: pulsars with luminosities above a certain limit (right side of the picture) would have P 3 lower than 1 pulse period – which is undetectable due to the aliasing effect (Basu et al., 2016)

Observations of PSR B1133+16 (8 GHz Effelsberg Data) LRFS ~30 P 1 periodicity visible in both fluctuation spectrum as well as in the periodic nulls. From: Single-pulse analysis of PSR B1133+16 at 8.35 GHz and carousel circulation time, Honnappa, Lewandowski, Kijak et a. MNRAS (2012) Periodic null folding

Pulsar magnetosphere studies – Partially Screened Gap in a non-dipole polar cap More details of the model in the next talk by Andrzej Szary From: Two modes of Partially Screened Gap, Szary, Melikidze and Gil, ApJ, 2015

2. Pulsars spectra study Most pulsars radio spectra can be described by a single power-law with a an average spectra index of a = -1.8 (Maron et al. 2000) or a = -1.60 (Jankowski et al., 2018) Distribution of puslar spectra indices from Jankowski et al. (2018) – Spectral properties of 441 radio pulsars

What are the Gigahertz-Peaked Spectra pulsars? A few percent of sources were classified as "broken spectra" – two power-laws, steeper spectra at higher frequencies Timeline: 1995 – Lorimer et al., spectra of 280 pulsars, some of them nearly flat 2000 – Maron et al. - an extension of the above with new observations. Pulsars with broken spectra, a hint of a high frequency beaks 2007 – Kijak et al. – two pulsars with a high frequency turn-overs 2011 – Kijak et al. - another three objects with a turn-over above 1 GHz. The name Gigahertz-Peaked Spectra pulsars ( GPS ) was introduced. These objects: • tend to adjoin various peculiar surroundings, i.e. PWNe and dense HII regions • preffer large DMs • are usually relatively young Kijak, Lewandowski, Maron, Gupta, Jessner, 2011, A&A, 521 A16 Kijak, Dembska, Lewandowski, Melikidze, Sendyk, 2011, MNRAS, 418, L114

2013 – Kijak et al. – based on literature data: two radio magnetars with GPS! 2013 – Allen et al. – PSR J2007+2722 (Einstein@Home X-ray discovery) – spectrum peaks at 1.5 GHz 2014. 2015 – Dembska et al. – PSR J1740+1000 2015 – Lewandowski et al. – SgrA* radio-magnetar is a GPS source 2017 – Kijak et al. – 17 known GPS pulsars; 2018 – Jankowski et al. (2018) – another four GPS pulsars in the study of the spectra of 441 sources Kijak, Tarczewski, Lewandowski, Melikidze, 2013, ApJ, 722, 4

What causes the GPS phenomenon? PSR B1259-63 may hold a key to the puzzle. A pulsar- Be star binary with a long-period (1237 day), eccentric orbit (e=0.87). Be stars are known to have strong stellar wind, both equatorial and polar. The disk formed from the equatorial wind causes the pulsar eclipses. Thermal absorption in the polar wind may be enough to cause B1259-63 spectra to bend.

Kijak, Dembska, Lewandowski, Melikidze, Sendyk, 2011, MNRAS, 418, L114 The radio spectrum evolves with the orbital phase.

How does B1259-63 relate to isolated GPS pulsars? Pulsars in or behind HII regions: same case as B1259-63, only the matter is lower density, but the several-parsec sizes make up for it. (this is true in the case of GPS pulsar B1054-62) Pulsar Wind Nebulae – may they cause similar effects? Weak GPS/broken spectrum (?) Seems that some PWNs may have GPS? large enough densities (up to n e =2000 cm -3 ) and sizes (up to 1 parsec) for the thermal free-free absorption to kick in. SNR filaments which may by another candidate (densities up to 8000 cm -3 ) and sizes up to a fraction of a parsec. No GPS PWN simulation (Bucciantini, 2002, A&A, 387, 1066)

Comet-shaped Pulsar Wind Nebulae PWN structure from Buccantini et al. (2002) Lewandowski, Rożko , Kijak, Melikidze (2015).

The current state of GPS pulsar studies: Around 30 sources known including 3 of 5 known radio-magnetars: 17 + 5 published (Kijak et al. 2017 + Allen et al., 2013, Jankowski et al. 2017), 8 in press, 5- 8 good candidates that require some additional observations A sample of 4 GPS pulsars from Kijak et al., ApJ, 2017

Two radio-magnetars with GPS. Spectral modeling: Free fit parameters: A – pulsar intrinsic flux scale a – intrinsic pulsar spectra index B – frequency-independent optical Optical depth: depth parameter Modeling of the spectra provides constrains on the physical parameters of potential absorbers.

Interesting GPS neutron stars: Radio pulse profiles from Thorne, SgrA* magnetar (SGR J1745-2900) Eatough et al. (2015) Outburst on April 26, 2013, visible as radio pulsar until 2017(?) Picture: NASA, Chandra X-ray Observatory

Modeled spectra of SGR J1745-2900 using: • Absorption in the expanding shell of an outburst • External absorption: N e = 290 cm -3 , S = 1.5 pc, T= 100 K Spectral data from ATCA (8- Expanding shell: 20 GHz (Shannon & • Density decreasing like 1/r 2 Johnston 2013) ( 1/t 2 assuming constant expansion velocity) • Temperature decreasing like t -1 • Required initial density: 2∙10 4 of Goldreich-Julian co-rotation density • Initial temperature: 10 9 K Absorption parameters on May 1st: • T = 900 K, • Ne = 7∙10 5 cm -3 , d = 0.7 light-day (6∙10 -4 pc) • Lewandowski et al. 2015

3. The study of Interstellar Medium: Interstellar Scattering Scattering is frequency dependant, and is clearly more noticeable at lower frequencies. This frequency dependance gives us a way to estimate the energy spectrum of the turbulence in the ISM. For Kolmogorov's turbulence spectrum ( b= 11/3 ) the expected a= 4.4 . Lewandowski et al. (2013), MNRAS

Scatter time frequency scaling index vesrus the dispersion measure. Theory predicts the values of α between 4.0 (the critical spectrum) and 4.4 (Kolmogorov's spectrum). Most of the pulsars lie beyond this range, and lower values of α dominate! Strangely, the average values for the whole population are relatively close Until 2013 : multi-frequency scattering to 4.0. and scintillation observations available only for 27 objects (out of 2400 pulsars Only for sources with the known). largest DM (the most distant objects) a significant deviation can be seen.

Scatter time frequency scaling index vesrus the dispersion measure. Theory predicts the values of α between 4.0 (the critical spectrum) and 4.4 (Kolmogorov's spectrum). Most of the pulsars lie beyond this range, and lower values of α dominate! Strangely, the average values for the whole population are relatively close Until 2013 : multi-frequency scattering to 4.0. and scintillation observations available only for 27 objects (out of 2400 pulsars Only for sources with the known). largest DM (the most distant objects) a significant deviation can be seen.

The amount of scattering (cont.) Normalized amount of scattering versus disperssion measure (DM). Why are the scintillation based measurements lower than the trend indicated by the scattering estimates? Is the theoretical scatter time versus decorrelation bandwidth relation true? ? For two pulsars (the Vela pulsar and PSR B1933+16) we have both the scattering based and the scintillation based measurements. They indicate C 1 ≈5 ! Lewandowski, Dembska, Kijak, Kowalinska (2013) Lewandowski, Kowalińska , Kijak (2015a) Lewandowski, Rożko , Kijak, Bhattacharya, Roy (2015b)

LOFAR in Poland is already working and observing pulsars!

LOFAR in Poland: POLFAR consortium Members of the POLFAR consortium imvolved in pulsar observations using polish LOFAR Statiions: UZ, Zielona Góra: Jarosław Kijak, Wojciech Lewandowski, Marek Sendyk UWM, Olsztyn: Andrzej Krankowski , Leszek Błaszkiewicz, Tomasz Sidorowicz UJ, Kraków: Krzysztof Chyży, Marian Soida, Bartosz Śmierciak, Małgorzata Curyło CBK Warszawa : Hanna Rothkaehl , Mariusz Pożoga, Barbara Matyjasik