pulsar searches - naic.edunaic.edu/~astro/sdss7/talks/hoptalks/gb6_ao9_sdss7_presentation.pdf ·...

Pulsar SearchesPulsar Searches

● We began by taking new observations of We began by taking new observations of unassociated Fermi sources with the GBT.unassociated Fermi sources with the GBT.

● In addition to our observations, we also In addition to our observations, we also analyzed an additional data set taken at analyzed an additional data set taken at Arecibo pre-meltdown.Arecibo pre-meltdown.

● Since pulsars also emit in gamma rays, we Since pulsars also emit in gamma rays, we can use the gamma ray SED to try and can use the gamma ray SED to try and choose the best sources to analyze.choose the best sources to analyze.

Source Selection

● Fermi unassociated sources are typically faint Fermi unassociated sources are typically faint and have ambiguous SEDsand have ambiguous SEDs

Strong gamma-ray pulsarStrong gamma-ray pulsar Our sourceOur source

Many sources unsearchedMany sources unsearched

● 575 unassociated after 2 years of all-sky data575 unassociated after 2 years of all-sky data

Analyzed Fermi SourcesAnalyzed Fermi Sources

RFI RemovalRFI Removal

De-DispersionDe-Dispersion

FoldingFolding

Candidate SearchCandidate Search

ProcedureProcedure


● We need to remove excess power in the We need to remove excess power in the Fourier domain due to RFI.Fourier domain due to RFI.

● We produce a median filter mask for the data We produce a median filter mask for the data that zaps channels with strong RFI. that zaps channels with strong RFI.

● We then inspect the power spectrum by eye to We then inspect the power spectrum by eye to remove RFI in the power spectrum.remove RFI in the power spectrum.

Example of the power spectrum at DM 0 for GBT Example of the power spectrum at DM 0 for GBT source SEEDH-127.source SEEDH-127.

60 Hz AC RFI

200 Hz RFI

2nd Harmonic of200 Hz


Example of the power spectrum for J2317+1439 Example of the power spectrum for J2317+1439 at DM 21.9, the known DM for a bright pulsar.at DM 21.9, the known DM for a bright pulsar.




FoldingFolding


ProcedureProcedure


● Different frequencies in the ISM arrive at Different frequencies in the ISM arrive at different times due to free electrons between different times due to free electrons between us the the source. We must correct for this to us the the source. We must correct for this to find a pulsar.find a pulsar.

● Since the distance is not known a-priori, we Since the distance is not known a-priori, we need to determine the best way to search need to determine the best way to search dispersion measures as quickly as possible so dispersion measures as quickly as possible so we don't miss the pulsar.we don't miss the pulsar.

Example of how de-dispersion works.Example of how de-dispersion works.




FoldingFolding


ProcedureProcedure

FoldingFolding

● At this point, we begin folding over the At this point, we begin folding over the strongest peaks in the power spectrum for a strongest peaks in the power spectrum for a number of potential dispersion measures.number of potential dispersion measures.

● For a 15 minute observation with Arecibo at For a 15 minute observation with Arecibo at 327 Mhz, this step takes ~8 hours to run with 327 Mhz, this step takes ~8 hours to run with 128 processors.128 processors.



FoldingFolding


ProcedureProcedure


● The output of folding leaves thousands of The output of folding leaves thousands of candidates. To make this manageable, we candidates. To make this manageable, we remove either bad candidates, or visible remove either bad candidates, or visible harmonics.harmonics.

● We then fold over the best candidates to We then fold over the best candidates to inspect by eye.inspect by eye.

● A vast majority of the candidates are low-level A vast majority of the candidates are low-level RFI, but a human eye is still needed to RFI, but a human eye is still needed to recognize a pulsar.recognize a pulsar.


● The output of folding leaves thousands of The output of folding leaves thousands of candidates. To make this manageable, we candidates. To make this manageable, we remove either bad candidates, or visible remove either bad candidates, or visible harmonics.harmonics.

● We then fold over the best candidates to We then fold over the best candidates to inspect by eye.inspect by eye.

● A vast majority of the candidates are low-level A vast majority of the candidates are low-level RFI, but a human eye is still needed to RFI, but a human eye is still needed to recognize a pulsar.recognize a pulsar.

After After searching for searching for

too long....too long....

RFIRFI

Obvious RFI from SEEDH-127 that we Obvious RFI from SEEDH-127 that we can discard out of hand.can discard out of hand.

Intermediate

Example of a potential candidate Example of a potential candidate in P74RJ2052+1217. It has a in P74RJ2052+1217. It has a narrow pulse shape, and no narrow pulse shape, and no

obvious RFI.obvious RFI.

Raw time series folded by the Raw time series folded by the potential candidate potential candidate

characteristics. No pulsar in the characteristics. No pulsar in the data. data.

PULSAR!PULSAR!

An actual pulsar found in recent Arecibo An actual pulsar found in recent Arecibo observations and analyzed by the SDSS observations and analyzed by the SDSS

students. Go us!students. Go us!

Fermi Source LocationFermi Source Location

ResultsResults

● We found a pulsar in the unassociated Fermi We found a pulsar in the unassociated Fermi sources. Yay!sources. Yay!

● Now we have to wait to make sure no one else Now we have to wait to make sure no one else has discovered this with other telescopes has discovered this with other telescopes around the world.around the world.

● The pulsar has already been confirmed in The pulsar has already been confirmed in other data sets, and appears to be a highly other data sets, and appears to be a highly accelerated binary.accelerated binary.

pulsar searches - naic.edunaic.edu/~astro/sdss7/talks/hoptalks/gb6_ao9_sdss7_presentation.pdf ·...

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