| 1. |
- Kirsten, F., et al.
(författare)
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Precision astrometry of pulsars and other compact radio sources in the globular cluster M15
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 565
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Tidskriftsartikel (refereegranskat)abstract
- The globular cluster (GC) M15 (NGC 7078) is host to at least eight pulsars and two low mass X-ray binaries (LMXBs), one of which is also visible in the radio regime. Here we present the results of a multi-epoch global very long baseline interferometry (VLBI) campaign aiming at i) measuring the proper motion of the known compact radio sources; ii) finding and classifying thus far undetected compact radio sources in the GC; and iii) detecting a signature of the putative intermediate mass black hole (IMBH) proposed to reside at the core of M15. We measure the sky motion in right ascension (mu(alpha),) and declination (mu(delta)) of the pulsars M15A and M15C and of the LMXB AC211 to be (mu(alpha), mu(delta))(M15A) = (-0.54 +/- 0.14, -4.33 +/- 0.25) mas yr(-1), (mu(alpha), mu(delta))(M15A) = (-0.75 +/- 0.09, -3.52 +/- 0.13) mas yr(-1), and (mu(alpha), mu(delta))(AC211) = (-0.46 0.08, 4.31 0.20) mas yr-I, respectively. Based on these measurements we estimate the global proper motion of M15 to be (mu(alpha), mu(delta)) = (-0.58 +/- 0.18, -4.05 +/- 0.34) mas yr(-1). We detect two previously known but unclassified compact sotirces within our field of view. Our observations indicate that one them is of extragalactic origin while the other one is a foreground source, quite likely an LMXB. The double neutron star system M15C became fainter during the observations, disappeared for one year and is now observable again - an effect possibly caused by geodetic precession. The LMXB AC211 shows a double lobed structure in one of the observations indicative of an outburst during this campaign. With the inclusion of the last two of a total of seven observations we confirm the upper mass limit for a putative IMBH to be M-circle dot tau
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| 2. |
- Marti-Vidal, Ivan, 1980, et al.
(författare)
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On the calibration of full-polarization 86GHz global VLBI observations
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 542, s. A107-
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Tidskriftsartikel (refereegranskat)abstract
- We report the development of a semi-automatic pipeline for the calibration of 86GHz full-polarization observations performed with the Global Millimeter-VLBI array (GMVA) and describe the calibration strategy followed in the data reduction. Our calibration pipeline involves non-standard procedures, since VLBI polarimetry at frequencies above 43GHz has not yet been well established. We also present, for the first time, a full-polarization global-VLBI image at 86GHz (source 3C 345), as an example of the final product of our calibration pipeline, and discuss the effect of instrumental limitations on the fidelity of the polarization images. Our calibration strategy is not exclusive to the GMVA, and could be applied to other VLBI arrays at millimeter wavelengths. The use of this pipeline will allow GMVA observers to obtain fully calibrated datasets shortly after the data correlation.
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