Multi-Telescope Studies of Neutron Stars

Neutron stars are unique stellar remnants with extreme properties, as their density and magnetic field. Their study can be the key to a number of unanswered problems in fundamental physics and astronomy, ranging from stellar evolution to strong field gravity. One of the best ways of studying these objects is with observations at radio wavelengths, the efficiency of which can be vastly improved with the combination of data from multiple radiotelescopes. In this thesis, we use the largest European radiotelescopes for performing high quality studies of the properties of objects belonging into two separate categories of neutron stars, millisecond pulsars and magnetars. In the first part of this thesis, a complete description of the observing systems and calibration procedures for the multiple telescopes used is presented. Specifically, all observations were made with the European Pulsar Timing Array (EPTA) telescopes, which are the Effelsberg 100m radiotelescope in Germany, the Lovell 76m radiotelescope in UK, the Westerbork 94m equivalent synthesis radiotelescope in the Netherlands and the Nan\c cay 94m equivalent decimetric radiotelescope in France. In addition, the different procedures for the data acquisition and improvement of the latest and archival data of the Effelsberg radiotelescope are described. Finally, the techniques and advantages of the combination of multi-telescope data sets are being presented. In the second part of the thesis we concentrate on the study of millisecond pulsars using the pulsar timing technique. Specifically, we analyse a set of 15 millisecond pulsars from the Effelsberg source list, showing that most of them are good candidate sources for the EPTA efforts to detect gravitational waves in the nano-Hertz regime. We present, in most cases only for the Effelsberg data set, improved preliminary results for their astrometric, spin and binary parameters. Finally, we report on the complete timing analysis of one of these sources. Specifically, we present results from the high precision timing analysis of the pulsar-white dwarf binary PSR J1012+5307 using 15 years of EPTA multi-telescope data. All the timing parameters have been improved from the previously published values, at least by an order of magnitude. In addition, a parallax measurement is obtained for the first time for PSR J1012+5307, being consistent with previous optical estimations from the WD companion. Combining improved 3D velocity information and models for the Galactic potential the complete evolutionary Galactic path of the system is obtained. While a new intrinsic eccentricity upper limit is acquired, being one of the smallest calculated for a binary system and providing evidence for the stellar evolution of this system, a measurement of the variation of the projected semi-major is also constraining the systems orbital orientation for the first time. Finally, combining the fact that PSR J1012+5307 is an ideal laboratory for testing alternative theories of gravity, with a measurement for the first time of the change of the orbital period of the system, stringent, general, theory independent upper limits for the dipole gravitational wave emission and the variation of the gravitational constant are being derived. In the final part of this thesis, we study the category of magnetars and specifically the case of the first radio emitting anomalous X-ray pulsar (AXP) J1810-197. With a simultaneous and quasi-simultaneous multi-frequency and multi-telescope campaign from July 2006 until July 2007 we obtained flux density measurements and spectral features of this 5.5-sec radio-emitting magnetar. We monitored the spectral evolution of its pulse shape which consists of a main pulse (MP) and an interpulse (IP). We present the flux density spectrum of the average profile and of the separate pulse components. We observe a decrease of the flux density by a factor of 10 within 8 months and follow the disappearance of one of the two main components. Although the spectrum is generally flat, we observe large fluctuations of the spectral index with time. We conclude that AXP J1810-197 is not like any other radio pulsar we know with spectral properties and temporal fluctuations differing remarkably from normal pulsars. Significant variability exists on all considered time scales, from pulse to pulse, day-to-day and over the time of weeks and months. Analysis of the interstellar scintillation for AXP J1810-197 shows that only some of the variability is affected by scintillations and most of it is due to intrinsic variations, better described by a model of turbulent magnetosphere. Further analysis on the single pulse properties of AXP J1810-197 confirms these results

Simultaneous X-ray and Radio Observations of Rotating Radio Transient J1819-1458

We present the results of simultaneous radio and X-ray observations of PSR J1819-1458. Our 94-ks XMM-Newton observation of the high magnetic field 5*10^13 G pulsar reveals a blackbody spectrum (kT~130 eV) with a broad absorption feature, possibly composed of two lines at ~1.0 and ~1.3 keV. We performed a correlation analysis of the X-ray photons with radio pulses detected in 16.2 hours of simultaneous observations at 1-2 GHz with the Green Bank, Effelsberg, and Parkes telescopes, respectively. Both the detected X-ray photons and radio pulses appear to be randomly distributed in time. We find tentative evidence for a correlation between the detected radio pulses and X-ray photons on timescales of less than 10 pulsar spin periods, with the probability of this occurring by chance being 0.46%. This suggests that the physical process producing the radio pulses may also heat the polar-cap.Comment: 12 pages, 5 figures, Accepted to Ap

Multiwavelength Studies of Rotating Radio Transients

We describe our studies of the radio and high-energy properties of Rotating Radio Transients (RRATs). We find that the radio pulse intensity distributions are log-normal, with power-law tails evident in two cases. For the three RRATs with coverage over a wide range of frequency, the mean spectral index is -1.7\pm0.1, roughly in the range of normal pulsars. We do not observe anomalous magnetar-like spectra for any RRATs. Our 94-ks XMM-Newton observation of the high magnetic field RRAT J1819-1458 reveals a blackbody spectrum (kT ~130 eV) with an unusual absorption feature at ~1 keV. We find no evidence for X-ray bursts or other X-ray variability. We performed a correlation analysis of the X-ray photons with radio pulses detected in concurrent observations with the Green Bank, Effelsberg, and Parkes telescopes. We find no evidence for any correlations between radio pulse emission and X-ray photons, perhaps suggesting that sporadicity is not due to variations in magnetospheric particle density but to changes in beaming or coherence.Comment: 4 pages, 2 figures, to appear in AIP Conference Proceedings of Pulsar Conference 2010 "Radio Pulsars: a key to unlock the secrets of the Universe", Sardinia, October 201

Precision timing of PSR J1012+5307 and strong-field GR tests

We report on the high precision timing analysis of the pulsar-white dwarf binary PSR J1012+5307. Using 15 years of multi-telescope data from the European Pulsar Timing Array (EPTA) network, a significant measurement of the variation of the orbital period is obtained. Using this ideal strong-field gravity laboratory we derive theory independent limits for both the dipole radiation and the variation of the gravitational constant.Comment: 3 pages, Proceedings of the 12th Marcel Grossmann Meeting on General Relativity (MG 12

Enhancement of intratumoral chemotherapy with cisplatin with or without microwave ablation and lipiodol : future concept for local treatment in lung cancer

Novel therapies for lung cancer are being explored nowadays with local therapies being the tip of the arrow. Intratumoral chemotherapy administration and local microwave ablation have been investigated in several studies. It has been previously proposed that lipiodol has the ability to modify the microenvironment matrix. In our current study we investigated this theory in BALBC mice. In total 160 BALBC mice were divided in eight groups: a) control, b) cisplatin, c) microwave, d) microwave and lipiodol, e) cisplatin and lipiodol, f) microwave and cisplatin, g) lipiodol and h) lipiodol, cisplatin and microwave. Lewis lung carcinoma cell lines (106) were injected into the right back leg of each mouse. After the 8th day, when the tumor volume was about 100mm3 the therapy application was initiated, once per week for four weeks. Magnetic resonance imaging was performed for each tumor when a mouse died or when sacrificed if they were still alive by the end of the experiment (8-Canal multifunctional spool; NORAS MRI products, Gmbh, Germany). Imaging and survival revealed efficient tumor apoptosis for the groups b,c,d,e and f. However; severe toxicity was observed in group h and no follow up was available for this group after the second week of therapy administration. Lipiodol in its current form does assist in a more efficient way the distribution of cisplatin, as the microwave apoptotic effect. Future modification of lipiodol might provide a more efficient method of therapy enhancement. Combination of drug and microwave ablation is possible and has an efficient apoptotic effect