Swift observations of Radio-quiet Fermi pulsars

Swift and the Surprising Sky 24th-25th November 2011

In collaboration with Patrizia Caraveo and Andrea de Luca

Martino Marelli

Fermi discovers PSRsThe Fermi/LAT

End of LEO: August 11, 2008

- 20MeV-300GeV (100MeV-10GeV)- Very Large FOV (more than 2sr)

and all-sky monitoring- Very high point source sensitivity (more

than 1800 sources in 2 years)- Very low deadtime (~6~65μμs)

Fermi/LAT pulsar sample

101 (public) pulsar

66 radio-loud39 classical

27 millisecond

34 discovered in BS (+Geminga), 32 “gamma-ray only” pulsars

How can the X-ray band help the gamma-ray one?Why should we search for X-ray counterparts of pulsars?

The position is fundamental for BS!

• Gamma-ray data are sparse. Thousands of rotations may occur between detected gamma rays. Months (years) of analysis are

necessary!• The motions of the spacecraft and the Earth are significant

compared to the time between pulses (msec to sec).• Solution: do the timing analysis in an intertial reference system,

not moving with respect to the pulsar.

Dormody et al., in preparation

With only 5 months of data and a bright pulsar.

The SWIFT fundamental contribution

Compared with Chandra and XMM-Newton, high PSF (~15”), low spectral and timing resolutions

BUT- rapidly re-pointed

- useful for short observations- part of the SWIFT collaboration

Counterparts of 4 RQ pulsars found (on 19 observed) few days after the Fermi discovery.

For them, the gamma-ray light curve and positioning have been improved (see e.g. J1958+2841)

X-ray spectrum:nH=3.9-2.6

+4.4*1022cm-2

p.i.=1.7-1.1+1.5F0.3-10=8.3-6.3

+1.8*10-13erg/cm2s

J1813-1256P = 48.1ms τ = 43 kyErot = 6.26*1036 erg/s

SWIFT first results

Published on:Abdo et al., 2009, Science, 325, 840

J1958+2841P = 290ms τ = 21 kyErot = 3.58*1035 erg/s

SWIFT first resultsPublished on:Abdo et al., 2009, Science, 325, 840

Are Swift observations useful also with no detection?

YES!To obtain an upper limit X-

ray flux, necessary for asking deeper observations(e.g. J0357)

To study all nearby bright

sources, necessary e.g.

for Suzaku analysis

(e.g. J1413)

Low Nh, powerlaw spectrum => pulsar counterpart

High Nh, powerlaw spectrum => pulsar counterpart?

So that, Swift can also be useful in combination with

other X-ray telescopes

Papers in preparation:2nd Fermi pulsar catalogMarelli et al. 2012

When possible, taken from the 1st pulsar catalogue (Abdo et al. ApJ 2011, 193,

22): exponential cutoff and off-pulse tractation.

Otherwise, pulsars' preliminary spectral analyses by the collaboration.

If both the results were unavailable, I used the 2FGL catalogue's parameters.

Gamma-rays X-rays- All the public Swift, Chandra and XMM-

Newton data - Processed by using the standard analysis

tools. Proton flares subtraction in XMM-Newton data where necessary

- Only the appropriate event patterns and energies between 0.3 and 10 keV

- Extraction regions in order to maximize the signal-to-noise ratio; a radial brillance

profile has been producted where necessary

- Spectra added by using ftools- XSPEC to simultaneously fit

Chandra/ACIS, XMM-Newton (PN, MOS1,2) and Swift/XRT spectra (where

available) by taking into account the different PSFs and cross-calibration

studies.- Standard model: absorbed powerlaw. When statistically needed, I added (or

used) a blackbody spectrum.

Type 0 : no X-ray counterpart detectionType 1 : counterpart detection but spectral shape unknown

Type 2 : PWN tractation, clear spectral results

Assess the X-ray behaviour of Fermi psrs

Marelli et al. 2011, ApJ, 733, 82

LogLx=0.7+0.9logE

rot

χ2red

=13

Distance Estimate?L=f*4πd2F, f dip α,ζPulsar geometrical factors?

The X-ray luminosities

-Marelli et al. 2011, ApJ, 733, 82

The γ-ray luminosities

LogLγ=2.6+1.5logE

rot , E

rot<4*1035erg/s

LogLγ=4.8+0.1logE

rot , E

rot>4*1035erg/s

χ2red

=7

-Marelli et al. 2011, ApJ, 733, 82

γ-to-X

Fγ/F

x=L

γ/L

x*f

x/f

γ

fx=f

γ

-Marelli et al. 2011, ApJ, 733, 82

High scatter

Low scatterX-ray underluminous

(fx>f

γ)

Low scatter

γ-to-X

Radio-Quiet Millisecond

Radio-Loud

-Marelli et al. 2011, ApJ, 733, 82

Assess the X-ray behaviourWe can conclude that:

- Lx dip E

rot with high scatter (distance or geometry?)

- Lγ dip E

rot with little lower scatter (distance or geometry?)

- X and γ-ray emissions are greatly dependent to geometry; moreover, they show no simple correlation good for each

pulsar- RQ pulsars are undeluminous in the X band: a geometry

different than RL ones could explain such behaviour- RL MS pulsars have a more uniform behaviour (geometry?)

than RL ones

(Our work is just a starting point)