206th AAS Meeting, San Diego, 04/22/23 1

ALFA/Arecibo pulsar surveys

First Results and Future Plans

Paulo César C. FreireCornell University / Arecibo Observatory

andTHE ALFA PULSAR CONSORTIUM

http://alfa.naic.edu/~pulsar

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In This Talk…

Pulsar surveys with and without multi-beam systems The ALFA system The preliminary Arecibo survey Near future plans

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Pulsar Surveys

Pulsars are brighter at lower frequencies. At lower frequencies, beams are larger, so more of the sky

is searched at once! Ideal frequencies for surveys at high Galactic latitudes are around 300-600 MHz!

However, most pulsars are found near the Galactic disk. This makes the use of lower frequencies inconvenient because:

1. Sky temperatures are very large for the low frequencies,2. There is a lot of plasma in the paths to the pulsars, therefore

increasing dispersive smearing per spectral channel,3. Scattering due to multi-path propagation smooths pulsations!

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Pulsar Surveys

Dispersive smearing can be combated by building better back-ends, but scattering or the sky noise can not be eliminated!

These three problems of pulsar surveys in the Galaxy can be circumvented by using high frequencies:

1. Sky temperatures are lower by a factor of F-1.6

2. Dispersive smearing per MHz scales with F-3

3. Scattering times scale with F-4.4

However, the problems associated with high-frequency surveys (the pulsars are fainter and the beams are small) persist. This is only partly compensated by the fact that the survey area (the Galactic disk) is quite small.

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Pulsar Surveys

The use of L-band also allows us to compensate the lower brightness of the pulsars: large bandwidths (BW ~ 300 MHz) and very low system temperatures are possible.

Large integration times are also desirable to increase sensitivity. The resulting inconvenience of the small sky area covered per unit time can be circumvented by using multiple beams, i.e., several simultaneous pixels.

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Pulsar Surveys

From 1997 to 2002, the Parkes multi-beam pulsar survey used a set of 13 beams to search the Galaxy from –5º < b < 5º and 260º < l < 50º.

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Pulsar Surveys

Using a set of thirteen 2 x 96 x 3 MHz filterbanks, and using 1-bit digitization, this survey found 728 pulsars so far!

Despite its tremendous success (doubling the number of known pulsars!), the 3 MHz channels make this survey unable to detect millisecond pulsars at DMs >~ 100 cm–3 pc. Most new objects are “boring” slow pulsars.

The beams are quite wide, so the lower gain can be compensated by large integration times (35 minutes). However, the discovery of compact binary systems in such long integrations requires the use of very complex and computer intensive techniques.

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The ALFA system

In 2002, the Arecibo Observatory purchased from the ATNF the Arecibo L-band Feed Array. This consists of a set of seven beams, adapted to the smaller focal plane of the Arecibo telescope (Jim!).

This was delivered to Arecibo in April 1st 2004, and is now working

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The ALFA system

The gain of the central beam is 11 K/Jy, the system temperature is about 25 K at 1400 MHz

The gain of the outer beams is about 8 K/Jy

The average beam size is 204 x 232 arcseconds. The six outer beams sit on an ellipse of 329 x 384 arcseconds.

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The ALFA system

We can cover the sky almost completely with three interlaced pointings. Using this strategy, one needs 50 pointings per square degree.

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The ALFA system

The back-ends used to detect the spectra (for pulsar and continuum purposes) are now the Wideband Arecibo Pulsar processors. Each of the eight boards can deal with bandwidths of up to 100 MHz. For the L-band searches, this is divided in 256 channels, samples every 64.

Eventually, these will be replaced (for the purpose of pulsar searches with ALFA) with the new PALFA spectrometers. These will be able to detect 300 MHz, with a total of 1536 channels, sampled every 64 μs.

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The ALFA system

This will address a fundamental limitation of the PMB survey; we will be able to detect MSPs at DMs 16 times larger, and be able to detect sub-millisecond pulsars (if they exist).

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The ALFA system

The Galactic coverage possible at Arecibo is unfortunately quite limited (32° < l < 75°). But having such a smaller part of the sky to cover means that one can cover it quite deeply! With integration times of 5 minutes, an Arecibo survey can be about 7 times deeper than the PMB survey.

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The ALFA system

Because the Arecibo dish is so much larger than Parkes, one can reach much improved sensitivity with much smaller integration times for a similar sky coverage per unit time. This means that this survey will be much more sensitive to binary pulsars: no complex and CPU-intensive algorithms are needed to detect fast binary systems.

This, coupled with the much increased sensitivity to MSPs, should enable us to detect a much larger number of pulsars in binary systems than the PMB survey.

These are precisely the objects one wants to discover for GR testing, probing the EOS for nuclear matter, etc.

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Results of preliminary survey

The aim of this survey is testing the observing system, establishing a data reduction pipeline and testing some new concepts.

The scientific aim is to find some bright MSPs! A shallow survey can only detect good timers!

The bandwidth was only 100 MHz (we used the WAPPs) and the integration times were 134 seconds for the Galactic center region and 67 seconds away from the Galaxy.

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Results of preliminary survey Data was taken the 1st of August to early October.

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Results of preliminary survey

Everything working perfectly: GUI observing mode, ALFA IF/LO system, WAPPs. Feed rotation now working.

Pulsar MySQL database (J. Hessels) and python scripts used to interface with it (Ramachandran, Nice, Hessels, Reid, et al.) were installed, tested.

Fast processing software (D. Lorimer) was installed and successfully tested. Degradation factor used so far: 16.

PHP/MySQL web browsing programs (D. Champion) made viewing of results of fast processing very easy.

The region covered was 40° < l < 75º and –1º < b < 1º. This was covered in sparse mode, another of the

innovations of this survey.

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Results of preliminary survey

The sparse mode searches the same area for faint pulsars as a dense survey, but three times as much area for bright pulsars!

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Results of preliminary survey

29 known pulsars were re-detected and 11 new pulsars were found to date, using degraded data only.

We used about ~37 hours (21 sq. degrees) of telescope time to observe the center and 19 in the anti-center (20 sq. deg.)

The first new pulsar is a relatively young 68-ms object, not detectable at 430 MHz!

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Results of preliminary survey

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Results of preliminary survey

This first new pulsar is an oddball: its spectrum is flat!

It is a young, energetic pulsar with an age of ~80 kyr.

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Results of preliminary survey

Also, one of the new pulsars (discovered in the anti-center region) was found in a single-pulse search of these data (McLaughlin, Cordes).

Periodicity not yet well established!

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Near-term plans

Understand the observing system better, like survey sensitivity (are we finding as many pulsars as we should? Apparently so!)

Incrementally improve survey software, implement processing software for full resolution data.

Increase data storage and handling capacity and computing, in order to prepare full-scale surveys

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Near-term plans Test 300-MHz back-ends Start 300-s, 300-MHz “Main” survey of the Galactic

plane – most recent simulations indicate that there is some slight advantage in doing this as compared to two 150-second passes

First two years – make a sparse covering of the 19-20H Galactic plane visible from Arecibo with |b| < 5°. Simulations indicate that we will be able to make 600 of the total expected 900 detections. Spend following 4 years filling in the holes.

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It will be challenging to make the 900 detections we proposed ourselves to do…

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The pulsar consortium thanks…

…the people that made it possible: Jeff Hagen and Bill Sisk for the magnificent work with the

WAPP and CIMA gui Avinash Deshpande, and the electronics department for all

their great work on the ALFA system and its characterization Arun Venkataraman, for all of his efficient data transferring and

archiving Steve Torchinsky, for managing it all and maintaining the

irreplaceable ALFA website NAIC and Bob Brown for pursuing ALFA, a great research

instrument, and ATNF for building it.

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The National Astronomy and Ionosphere Center is operated by Cornell University, under a cooperative agreement with the National Science Foundation.

Contact me at: pfreire@naic.edu, or visit my website at http://www.naic.edu/~pfreire.

Thank you for your time!