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Vela Pulsar J0835-4510

Science Target Overview

Pulsars are steep-spectrum, significantly polarized radio sources and commonly discovered / studied at centimeter wavelengths. Observations at high frequencies will complement our understanding of pulsar emission physics and enable more effective pulsar searches in highly turbulent environments such as the center of our Galaxy (e.g., Cordes & Lazio 1997, Spitler et al. 2014). So far, all previous studies of pulsars above 30 GHz have been conducted with northern hemisphere radio telescopes (see Lohmer et al. 2008, Torne et al. 2017 and references therein). Located in the southern hemisphere of the sky, Vela (PSR J0835-4510) was one of the first pulsars discovered and is one of the brightest radio pulsars. An imaging detection of Vela has recently been made at millimeter wavelengths with ALMA using its standard interferometry observing mode (Mignani et al. 2017). This makes Vela an excellent target to explore the southern hemisphere pulsar population at high frequencies, studying the properties of their pulsed and polarised emissions and understanding the potential of pulsar searches at millimeter wavelengths. 

The ALMA development project, “ALMA Pulsar Mode Project” (referred to as APMP, hereafter, http://hosting.astro.cornell.edu/research/almapsr/#ProcessingSteps) made a test observation of the Vela pulsar as a first step in developing a new observing mode for the Observatory.  This mode would allow observations of similar targets for high-time resolution analyses of compact objects in the Galactic Center or elsewhere in the Galaxy.  The primary goal of the observation is to achieve a detection of the pulsar at a significance consistent with sensitivity (A/T) and bandwidth used, demonstrating the feasibility of pulsar and transient observations with ALMA. Exploring the feasibility of using pulsar observations for system tests and instrumental polarisation calibration is the secondary goal. Furthermore, comparing the properties of the Vela pulse profile with those obtained at lower frequencies allows us to study pulsar emission physics.

ALMA is an ideal instrument for probing neutron star populations in the Galactic Center and using detected objects for the study of spacetime around the central black hole, Sgr A* (Liu et al. 2012, Psaltis et al. 2016). Though no pulsar in a sufficiently close orbit to Sgr A* has yet been detected (Wharton et al. 2012), the recent discovery of a rare radio-loud magnetar (PSR J1745-2900) with a projected distance of only ~0.1 pc from the Sgr A* (Eatough et al. 2013), suggests the existence of an abundance of pulsars in the immediate vicinity of the Sgr A*. The APMP leverages the product from the development of the pulsar phased-array modes for the Very Large Array (https://science.nrao.edu/facilities/vla/docs/manuals/oss/performance/pulsar), the Event Horizon Telescope (Doeleman et al. 2008, Event Horizon Telescope Collaboration et al. 2019), the Black Hole Camera project (Goddi et al. 2017), and the ALMA Phasing Project (APP, Matthews et al. 2018).

 

ALMA Data Overview

The APMP Science verification data on the Vela pulsar (PSR J0835-4510) in Band 3 were obtained in conjunction with ALMA Phasing Project commissioning run on 2017 January 29, under excellent weather conditions. The observation lasted for approximately 40 min, when 37 12-m antennas were phased up to form a tied-array beam. There were in total eight individual scans where the telescope was alternately pointed at Vela and a bright phase calibrator (J0828-3731) close by. During the calibrator scans, the “active phasing mode” updated the phasing solution at 18.192 s intervals. This phasing solution was then applied at the beginning of each Vela scan and retained unchanged for the duration.  (This is the so-called “passive phasing” mode of operation.) The baseband data streams were recorded for all four spectral windows (centered at 86.268, 88.268, 98.268 and 100.268 GHz, respectively), each of which was subdivided into 32x62.5-MHz frequency channels. Then the data were processed with software tools dedicatedly developed for APMP to yield intensity detections for all stokes parameters, with a time resolution of 8 microsec and packed in PSRFITS format in search mode (channelized timeseries). The ALMA standard interferometric data have also been processed, following special procedures required for calibration and quality assurance of ALMA observations in APS mode, as outlined in Goddi et al., 2019, PASP, 31:075003. 

 

Using the data for publication

The following statement should be included in the acknowledgment of papers using the datasets listed above:

“This paper makes use of the following ALMA data:ADS/JAO.ALMA#2011.0.00004.E. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ."

 

Obtaining the Data

The data products are provided in the following two forms:

    Time-series data:

  • Search-mode pulsar data in PSRFITS format for each individual scan (No0001-0008 except 0007) and spectral window [=0,1,2,3]. Each file contains data of approximately 13-s observation. The calibrator scans are No0001,3,5 and the pulsar scans are No0002,4,6,8. 

  • A folder containing the software tool that was used to generate the data product with a brief manual.

    Interferometric data:

  • Raw data in ASDM format (uid___A002_Xbd27fa_Xbae)

  • Cleaned images in FITS and MS formats (one image per spw [=0,1,2,3] and per scan combinations [=1,2,3,4,5,6,7,8]). (vela.CLEAN_IMAGES.tar.gz)

  • An ascii file containing a gaussian fitting analysis to estimate fluxes and position of the pulsar (vela_fluxes_scans.zip)

  • A folder containing observing logs, ancillary metadata (e.g. Tsys), and diagnostic plots of gain tables (vela.APP.artifacts). 

The data along with the software / scripts that have been used to generate the data products can be downloaded here:  Vela ALMA Science Verification Data. N.B. instructions for retrieving the ALMA ASDM and the FITS images will be provided once the data are ingested in the ALMA archive.