Blind period search gamma ray pulsar by fermi lat
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Blind Period Search gamma-ray pulsar by Fermi-LAT. F. Giordano Dipartimento Interateneo di Fisica and INFN Sez. Bari for the Fermi LAT collaboration. Where we were: the EGRET Pulsars. Vela, Crab & Geminga are the brightest sources in the Gamma-ray sky

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Blind Period Search gamma-ray pulsar by Fermi-LAT

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Blind Period Search gamma-ray pulsar by Fermi-LAT

F. Giordano

Dipartimento Interateneo di Fisica


INFN Sez. Bari

for the

Fermi LAT collaboration

Where we were: the EGRET Pulsars

Vela, Crab & Geminga are the brightest sources in the Gamma-ray sky

Their Flux for E>100MeV 10-5÷10-6ph/cm2s

  • PSR B1706-44

    • Flux ~1.1 ∙10-6ph/cm2s

  • PSR B1951+32 & PSR B1055-52

    • Flux for E>100MeV ~10-7ph/cm2s

Where we started…

Vela (16 days)

PSR B1951+32 (25 days)

Geminga (16 days)

Crab (16 days)

PSR B1055-52 (25 days)

PSR B1706-44 (25 days)

Where we are…

Pulses at

1/10th true rate

Search for new -ray pulsars

The Geminga candidates

1. Radio-quiet gamma-ray sources list generated pre-Launch, with very accurate source locations from other wavelengths.

a. 3EG J1835+5918 (possibly the “next Geminga”)

b. CTA1 (recently published in Science)

c. Compact objects of Pulsar Wind Nebulae (PWNe)

d. Milagro sources (e.g. MGROJ2019+37)

2. Fermi-LAT sources – a list of gamma-ray sources generated post-Launch with a Fermi localization

The Blind Period Search

The spin parameters (frequency, spin-down) are unknown, so to resolve the phase plot, a search over f, df/dt parameter space has to be implemented to find the timing solution.


1. Gamma-ray photon data is exceptionally sparse (103104 photons per yr ).

2. Such long datasets make fully coherent methods like FFTs require large numbers of fdot trials to prevent smearing of the signal. This large number of trials would also greatly reduce the significance of the signal.

3. FFTs of this magnitude require large amounts of memory:

1 month @ 64 Hz = 331 million bins = 5.3 GB of memory!

4. If the pulsar were to glitch (suddenly change its frequency), then the signal power would diminish greatly.

The “Time-Differencing” Technique

Periodicity in photon arrival times will also show up in differences of photon arrival times.

Time differences cancel out long term phase slips because differencing starts the "clock" over (and over, and over...)

Despite the reduced frequency resolution (and therefore number of bins), the sensitivity is not much reduced because of a compensating reduction in the number of fdot trials

The First Candidate

The First discovery

Science, Volume 322, Issue 5905, pp. 1218- (2008).

CTA 1 pulsar (2 cycles, P=315.86 ms)

  • -ray source at l,b = 119.652, 10.468;

  • 95% error circle radius =0.038° contains the X-ray source RX J00070+7302, central to the PWN superimposed on the radio map at 1420 MHz.

  • Pulsar off-set from center of radio SNR; rough estimate of the lateral speed of the pulsar is ~450 km/s

  • Exhibits all characteristics of a young high-energy pulsar (characteristic age ~1.4 x 104 yr), which powers a synchrotron pulsar wind nebula embedded in a larger SNR.

  • Spin-down luminosity ~1036 erg s-1, sufficient to supply the PWN with magnetic fields and energetic electrons.

  • The -ray flux from the CTA 1 pulsar corresponds to about 1-10% of Erot (depending on beam geometry)

P 315.8 ms



EG UnID sources

3EG J1734-3232

3EG J1826-1302 (Eel)

3EG J1420-6038 (Rabbit)

3EG1809.5 (Taz)

3EG J1741-2050

3EG J0631+0642

3EG J1958+2909

3EGJ2020 Gamma-Cigny

3EG J2033+4118

More Blind Search Pulsars (not in 3EG )

1 MGRO + 2 new Fermi Sources

PSR J2238+5852

PSR J1907.5+0601

MGRO J1908+06

PSR J0357.5+3211

First population study

Blind search pulsars

ATNF pulsars













Flux (Ph/cm2s)

Age (yr)

Edot (erg/s)














Age (yr)


B Strength (Gauss)


- 13 new (potentially radio-quiet) gamma-ray pulsars have been discovered in 3 months of Fermi-LAT data

- 10 out of 13 of these blind period search pulsars have an EGRET source location (3EG). Since two-thirds of EGRET sources remain unidentified, and this is a good step in identifying them.

- These pulsars have an age distribution 10 kyr - 1.8 Myr and spin-down luminosity distribution: 1033 erg/s - 1036 erg/s

- These new pulsar discoveries will enable a population study of radio-quiet vs. radio-loud pulsars which will provide new information on the emission geometry in these sources and the galactic populations of these high energy emitters.

- Deep radio pulsar searches of the new gamma-ray only pulsars have begun, in order to get strong constraints on the radio luminosity.

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