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Register a new userDiscovery of three new pulsars in a 610 MHz pulsar survey with the GMRT
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B. C. Joshi
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We report on the discovery of three new pulsars in the first blind survey of the north Galactic plane (45 degrees < l < 135 degrees; |b| < 1 degrees with the Giant Meterwave Radio telescope (GMRT) at an intermediate frequency of 610 MHz. The survey covered 106 square degrees with a sensitivity of roughly 1 mJy to long-period pulsars (pulsars with period longer than 1 s). The three new pulsars have periods of 318, 933, and 1056 ms. Their timing parameters and flux densities, obtained in follow up observations with the Lovell Telescope at Jodrell Bank and the GMRT, are presented. We also report on pulse nulling behaviour in one of the newly discovered pulsars, PSR J2208+5500.
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In this paper we present a wide-area 610 MHz survey of the ELAIS,N1 field with the GMRT, covering an area of 12.8 deg$^2$ at a resolution of 6 arcsec and with an rms noise of $sim 40$ $mu$Jy beam$^{-1}$. This is equivalent to $sim 20$ $mu$Jy beam$^{-1}$ rms noise at 1.4 GHz for a spectral index of $-0.75$. The primary goal of the survey was to study the polarised sky at sub-mJy flux densities at $<$ GHz frequencies. In addition, a range of other science goals, such as investigations in to the nature of the low-frequency $mu$Jy source populations and alignments of radio jets. A total of 6,400 sources were found in this region, the vast majority of them compact. The sample jointly detected by GMRT at 610 MHz and by VLA FIRST at 1.4,GHz has a median spectral index of $-0.85 pm 0.05$ and a median 610 MHz flux density of 4.5 mJy. This region has a wealth of ancillary data which is useful to characterize the detected sources. The multi-wavelength cross matching resulted optical/IR counterparts to $sim 90$ per~cent of the radio sources, with a significant fraction having at least photometric redshift. Due to the improved sensitivity of this survey over preceding ones, we have discovered six giant radio sources (GRS), with three of them at $z sim 1$ or higher. This implies that the population of GRS may be more abundant and common than known to date and if true this has implications for the luminosity function and the evolution of radio sources. We have also identified several candidate extended relic sources.
We report the discovery of a fourth eastern arc (Arc E) towards the cool-core cluster Abell 2626 using 610 MHz Giant Metrewave Radio Telescope observations. Three arcs towards north, west and south were known from earlier works at 1400 MHz and proposed to have originated in precessing radio jets of the central active galactic nucleus. The 610 - 1400 MHz integrated spectral indices of the arcs are in the range 3.2 - 3.6 and the spectral index map shows uniform distribution along the lengths of the arcs. If associated with A2626, the arcs have linear extents in the range 79 - 152 kpc. The detection of Arc E favours the scenario in which a pair of bipolar precessing jets were active and halted to produce the arc system. Based on the morphological symmetry and spectral similarity, we indicate a possible role of gravitational lensing. Further high resolution low frequency observations and measurements of the mass of the system are needed to disentangle the mystery of this source.
We study the space density evolution of active galactic nuclei (AGN) using the $610 mathrm{MHz}$ radio survey of the XXL-North field, performed with the Giant Metrewave Radio Telescope (GMRT). The survey covers an area of $30.4 mathrm{deg}^2$, with a beamsize of $6.5 mathrm{arcsec}$. The survey is divided into two parts, one covering an area of $11.9 mathrm{deg}^2$ with $1 sigma$ rms noise of $200 mathrm{mu Jy beam^{-1}}$ and the other spanning $18.5 mathrm{deg}^2$ with rms noise of $45 mathrm{mu Jy beam^{-1}}$. We extracted the catalog of radio components above $7 sigma$. The catalog was cross-matched with a multi-wavelength catalog of the XXL-North field (covering about $80 %$ of the radio XXL-North field) using a likelihood ratio method, which determines the counterparts based on their positions and their optical properties. The multi-component sources were matched visually with the aid of a computer code: Multi-Catalog Visual Cross-Matching (MCVCM). A flux density cut above $1 mathrm{mJy}$ selects AGN hosts with a high purity in terms of star formation contamination based on the available source counts. After cross-matching and elimination of observational biases arising from survey incompletenesses, the number of remaining sources was $1150$. We constructed the rest-frame $1.4 mathrm{GHz}$ radio luminosity functions of these sources using the maximum volume method. This survey allows us to probe luminosities of $ 23 lesssim log(L_{1.4 mathrm{GHz}}[mathrm{W/Hz}]) lesssim 28$ up to redshifts of $z approx 2.1$. Our results are consistent with the results from the literature in which AGN are comprised of two differently evolving populations, where the high luminosity end of the luminosity functions evolves more strongly than the low-luminosity end.
We present Giant Metrewave Radio Telescope 610 MHz observations of 14 Atacama Cosmology Telescope (ACT) clusters, including new data for nine. The sample includes 73% of ACT equatorial clusters with $M_{500} > 5 times 10^{14};M_odot$. We detect diffuse emission in three of these (27$^{+20}_{-14}$%): we detect a radio mini-halo in ACT-CL J0022.2$-$0036 at $z=0.8$, making it the highest-redshift mini-halo known; we detect potential radio relic emission in ACT-CL J0014.9$-$0057 ($z=0.533$); and we confirm the presence of a radio halo in low-mass cluster ACT-CL J0256.5+0006, with flux density $S_{610} = 6.3;pm;0.4$ mJy. We also detect residual diffuse emission in ACT-CL J0045.9$-$0152 ($z=0.545$), which we cannot conclusively classify. For systems lacking diffuse radio emission, we determine radio halo upper limits in two ways and find via survival analysis that these limits do not significantly affect radio power scaling relations. Several clusters with no diffuse emission detection are known or suspected mergers, based on archival X-ray and/or optical measures; given the limited sensitivity of our observations, deeper observations of these disturbed systems are required in order to rule out the presence of diffuse emission consistent with known scaling relations. In parallel with our diffuse emission results, we present catalogs of individual radio sources, including a few interesting extended sources. Our study represents the first step towards probing the occurrence of diffuse emission in high-redshift ($zgtrsim0.5$) clusters, and serves as a pilot for statistical studies of larger cluster samples with the new radio telescopes available in the pre-SKA era.
Recycled pulsars are old ($gtrsim10^{8}$ yr) neutron stars that are descendants from close, interacting stellar systems. In order to understand their evolution and population, we must find and study the largest number possible of recycled pulsars in a way that is as unbiased as possible. In this work, we present the discovery and timing solutions of five recycled pulsars in binary systems (PSRs J0509$+$0856, J0709$+$0458, J0732$+$2314, J0824$+$0028, J2204$+$2700) and one isolated millisecond pulsar (PSR J0154$+$1833). These were found in data from the Arecibo 327-MHz Drift-Scan Pulsar Survey (AO327). All these pulsars have a low dispersion measure (DM) ($lesssim 45 , rm{pc}, cm^{-3}$), and have a DM-determined distance of $lesssim$ 3 kpc. Their timing solutions, have data spans ranging from 1 to $sim$ 7 years, include precise estimates of their spin and astrometric parameters, and for the binaries, precise estimates of their Keplerian binary parameters. Their orbital periods range from about 4 to 815 days and the minimum companion masses (assuming a pulsar mass of 1.4 $rm{M_{odot}}$) range from $sim$ 0.06--1.11 $rm{M_{odot}}$. For two of the binaries we detect post-Keplerian parameters; in the case of PSR~J0709$+$0458 we measure the component masses but with a low precision, in the not too distant future the measurement of the rate of advance of periastron and the Shapiro delay will allow very precise mass measurements for this system. Like several other systems found in the AO327 data, PSRs J0509$+$0854, J0709$+$0458 and J0732$+$2314 are now part of the NANOGrav timing array for gravitational wave detection.
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