Survey of compact sources for pulsars and exotic objects -- I. Overview and initial discoveries

Abstract

Targeted searches for pulsars based on their counterparts in radio images have resulted in the discovery of interesting pulsars including the first ever discovered millisecond pulsar (MSP). We are conducting an image-based pulsar survey, survey of compact sources for pulsars and exotic objects (SCOPE), that utilizes interferometric as well as time-domain observations to search for radio pulsations as well as characterize the sources in the image-domain to identify their true nature. In the first stage of the SCOPE survey, we have used the Giant Metrewave Radio Telescope (GMRT) and the Green Bank Telescope (GBT) to follow up a sample of 31 compact and steep-spectrum sources. We provide an overview of the survey, the sample selection, the search procedures, and present discoveries of two MSPs -- J1840+1102 and J1827-0849. J1840+1102 is a 1.6 ms pulsar at the edge of the Scutum-Centaurus arm, while J1827-0849 is the radio counterpart of a gamma-ray pulsar that was earlier thought to be radio-quiet, and both the sources have very steep radio spectra. Using the interferometric data, we also provide a morphological classification of all the sources, model and characterize their spectra and identify the resolved, extragalactic sources in our sample. We discuss these results in the context of future image-based pulsar surveys.

Figures (9)

• Figure 1: Compact sources detected in band-3 and/or band-4. The color-scale is saturated at 10 times the local RMS noise. The lowest contour is at 4$\sigma_{local}$ level and the contour levels increase by factors of $\sqrt{2}$.
• Figure 2: Resolved sources detected in band-3 and/or band-4. The color-scale is saturated at 10 times the local RMS noise. The lowest contour represents 4$\sigma_{local}$ and the contour levels increase by factors of $\sqrt{2}$.
• Figure 3: Summary diagnostic plots for the newly discovered pulsar PSR J1840+1102 at the discovery epoch (left; at GMRT band-4) and from the follow-up confirmations at band-4 (middle) and band-3 (right) of GMRT. Each summary plot shows the folded pulse intensity in the 2D spaces, rotation phase vs. time (bottom panel) and rotation phase vs. frequency (middle panel) spaces, and the average profile (top panel).
• Figure 4: Summary diagnostic plots for the newly discovered pulsar PSR J1827$-$0849 at the discovery epoch (left; GBT 820 MHz band) and the rediscovery of PSR J1924+2027 (right; GMRT band-4). For the description of individual panels, please see Figure \ref{['fig-1840']} caption.
• Figure 5: Sub-banded profiles of PSR J1827$-$0849 are shown in the upper panels (black) at the center frequencies indicated in the title of each panel, along with the modeled profiles in red. The residuals are shown in the bottom panels.