### Pulsar Searching

Pulsar Searching is one of the Research Themes of the Pulsars and Time Domain Astrophysics group. You may be interested to read a list of all major pulsar surveys conducted since 1967. Further information on notable pulsar research can be found below:

• ### with Parkes

The High Time Resolution Universe in the southern sky (HTRU-South) was a survey for pulsars and fast transients, running between November 2008 and January 2014 at the 64-metre Parkes radio telescope in Australia. Combined with its sister survey covering the northern sky, HTRU-North, currently underway at the 100-metre Effelsberg radio telescope in Germany, the HTRU survey is a true all-sky pulsar survey. With some data processing still on-going, HTRU-South has discovered over 200 previously unknown pulsars, including more than 30 of the most rapidly-rotating pulsars, known as millisecond pulsars (MSPs). More about the survey in general, and the low-latitude part in particular, can be found on HTRU-South low-latitude Galactic plane website created by Cherry Ng. The site also contains a list of all published HTRU-South papers and PhD theses.

One of the most interesting of the HTRU MSPs is in a binary system with a companion whose mass is similar to that of Jupiter. It is thought that this companion was once the star which spun up the pulsar, but has now been transformed into a planet over the lifetime of the system. You can read more about this discovery in the University's press release 'A Planet Made of Diamonds'

• ### with LOFAR

The Low Frequency Array (LOFAR) is a new-generation radio interferometer based in the north of the Netherlands with further stations across Europe. It will operate in the relatively unexplored frequency range 30-240 MHz. With its dense core and long baselines, LOFAR has unparalleled sensitivity and angular resolution in the low-frequency radio regime. LOFAR's capabilities make it an important pathfinder to the Square Kilometer Array (SKA).

‌‌LOFAR consists of 1000's of antenna grouped into stations across a large area thus creating the perfect tool for pulsar surveys. During the comissioning stages of LOFAR, 2 new pulsar discoveries were made leading to a full Northern sky survey. The LOFAR Tied-Array All Sky Survey(LOTAAS) began taking data 01 December 2012 and as of 29 January 2016 has almost completed the first out of three sparse coverage of the sky. The survey is expected to uncover over 1,000 pulsars in the Northern sky which will add significantly to the Galactic pulsar catalogue. 'Observing Pulsars and Fast Transients with LOFAR' - a paper published on the Astronomy & Astrophysics website contains more detailed information on the LOFAR pulsar survey.

Aerial view of the LOFAR core. (C) ASTRON

LOTAAS uses the 12 HBA substations of the LOFAR core to form three sub-array incoherent beams for each survey pointing that cover ~30 square degrees of the sky. Within each incoherent beam, a hexagonal grid of 61 tied-array beams are formed. The three sets of tied-array beams cover ~10 square degrees of the sky. The arrangement of the beams can be seen on the figure below. An additional 12 tied-array beams are formed for each incoherent beam to point towards any known pulsars that falls within the field of view of the incoherent beam but outside of the grid. This results in a total of 222 beams per survey pointing. The survey has a central observing frequency of 139 MHz with a bandwidth of 32 MHz, spectral resolution of 12kHz and sampling time of 492 μs. This generates data at a rate of 35 Gbps and each 1-hour pointing produces 16 TB of raw data.

The new increased sample of pulsars will add many new lines of sight through the Galaxy, which will be valuable for studying the ISM and Galactic magnetic field using dispersion and rotation measures. The newly discovered population will also be useful for studying pulsar birth rates, the velocities and distributions of pulsars and core collapse physics. It is also likely that several interesting new objects will be found, perhaps even the first pulsar-black hole binary which could be used to test General Relativity.

LOFAR will also be able to utilise long baselines (~100 km) in order to perform deep surveys with very high resolution. By looking at other galaxies with long integration times, it is likely that LOFAR will detect the first pulsar from another galaxy.

• ### with GMRT

We are conducting a survey for pulsars and transients using the Giant Metrewave Radio Telescope (GMRT). The GMRT High Resolution Southern Sky (GHRSS) survey is an off-Galactic-plane (|b|>5) survey in the declination range -40 degrees to 54 degrees at 322 MHz. With the high time (up to 30.72 micro-sec) and frequency (up to 0.016275 MHz) resolution observing modes, the 5-sigma detection limit is 0.5 mJy for a 2 ms pulsar with 10% duty cycle at 322 MHz. Total GHRSS sky coverage of 2866 square-deg, will result from 1953 pointings, each covering 1.8 square-deg. The 10-sigma detection limit for a 5 ms transient burst is 1.6 Jy for the GHRSS survey. In addition, the GHRSS survey can reveal transient events like rotating radio transients or fast radio bursts.

With 35 % of the survey completed (i.e. 1000 square-deg), we report the discovery of 10 pulsars, one of which is a millisecond pulsar (MSP), one of the highest pulsar per square degree discovery rates for any off-Galactic plane survey. We re-detected 23 known in-beam pulsars. Utilising the imaging capability of the GMRT we also localised 4 of the GHRSS pulsars (including the MSP) in the gated image plane within $\pm$ 10 arcsec. We demonstrated rapid convergence in pulsar timing with a more precise position than is possible with single dish discoveries. We also exhibited that we can localise the brightest transient sources with simultaneously obtained lower time resolution imaging data, demonstrating a technique that may have application in the SKA.