Les Pulsars gamma avec GLAST

David Smith

Centre d’Etudes Nucléaires de Bordeaux-

Gradignan

( CENBG - in2p3 - CNRS )

Moriond4 February 2009

GeV Galactic Sources GeV Galactic Sources with the Large Area with the Large Area Telescope on Telescope on FermiFermi

(formerly GLAST)

David A. Smith for the LAT Collaboration Centre d’Études Nucléaires de Bordeaux-Gradignan (CENBG / IN2P3 / CNRS) smith@cenbg.in2p3.fr

Who cares about Galactic gamma-ray sources?

• Detail-loving astrophysicists, who study the shocks within winds or jets, or with the surrounding medium the electric dynamos around rotating, magnetized stars

• « Big picture » folks, mastering the Galactic energy budget ( ¼ starlight ; ¼ cosmics ; ¼ 3°K ; ¼ B-fields*)

• Particle physicists, for whom all of the above is just foreground garbage masking a sexy susy dark matter signal.

Practically everybody!

Better instruments at new wavelengths open new windows.Example from the year 1609…

* Improvements due from J.L. Han

Galactic sources

• SNRs & PWNs• OB associations ; WR stars ; Globular clusters ; open clusters• X-Ray Binaries ( µQuasars, binary pulsars )• Pulsars

known pulsars, with known rotation parameters blind period search

• Other • A component of diffuse emission is unresolved all-of-the-above.

Implicit in all of the above – identifying the EGRET unid’s.

Impression after some months of Fermi LAT data:It’s all as intertwined as you thought, and pulsars play a central role in many types of sources.

Discovery instrument par excellence.

LAT

EGRET

Continuous sky survey means We don’t have to squabble about who looks at what first (no TAC!). We record things no one thought to squabble about. We can perform « complete » surveys, in the statistical sense.

Supernova Remnants & Pulsar Wind NebulaeSNRs & PWNs

• The distinction between the two can be fuzzy: e.g. our first pulsar discovery in SNR CTA 1, and Cygni (See F. Giordano’s talk)

• Will nearly all known PWNs have a -pulsar? Too early in the mission to say…

• See PWN+pulsar talk by Marie-Hélène Grondin Crab – Vela – Kookaburra

• but note that the PWN upper limits for the other young pulsars are not yet very constraining – see these talks:

Andrea Caliandro PSR J1833-1034/G21.5-0.9 Damien Parent PSR J0205+6449, PSR J2229+6114 and more Matthew Kerr PSR J2021+3651/Dragonfly Max Razzano PSR J1048-5832, PSR J1028-5819 poster

• X-ray images of the PWN can give you the angle of the pulsar rotation axis relative to the Earth line-of-sight.

• Fermi LAT sees pulsations for 7 of these.

Image Model

9

-

From R. Romani. Discussion in K. Watters et al., ApJ accepted 2008, arXiv/0812.3931

Hypothesis: particle acceleration could occur via Fermi shocks between the winds from hot young stars in dense environments.

This was predicted: “On gamma-ray sources, supernova remnants, OB associations, and the origin of the cosmic rays”, Thierry Montmerle, ApJ 231, 95-110 (1979)

“Local gamma rays and cosmic ray acceleration by supersonic stellar winds”, Michel Cassé & Jacques Paul, ApJ 237, 236-243 (1980)

Provides an alternative to the “cosmic rays must come from SNRs” monopoly:

1. E-2 argument still works2. energy budget argument still (almost) works

OB associationsOBAFGKM « only boys accepting feminism get kissed meaningfully » O & B type stars are the hottest.

At « Moriond » in 2002 Hegra announced TeV ’s from near Cyg OB2. Aharonian…Horns…Rowell, A&A 393 L37-40 (2002)

• OB stars are the progenitors of neutron stars.

• «Stellar nurseries » : Stars are close together, so even more binary systems than else where. Lots of stardust and gas leftover from exploded stars, and forming new stars.

• OB, WR, Be companions… see Adam Hill’s talk.

* * Berkeley 87

~3.5°

Open clusters• The open cluster Berkeley 87 was proposed to be the hadron accelerator that would explain the EGRET unidentified source(s) 3EG J2021+3716 and/or 3EG J2016+3657. (e.g. shocks from winds from WR star(s) in the cluster)

see W. Bednarek MNRAS 382, 367 (2007) and references therein

• HEGRA searched, to no avail… F. Aharonian A&A 454, 775 (2006)

• The LAT gamma pulsations identify 3EG J2021+3716 as a pulsar! (See Matthew Kerr’s talk).

• But! Berkeley 87 skims the line-of-sight to the pulsar. The pulsar Dispersion Measure distance is too big (i.e. more electrons on that LOS than expected from the galactic model). Berkeley 87 may account for part of the discrepancy.

• Off-pulse upper limit near Bednarek’s prediction wait for more statistics.

• Whether they emit gammas or not, open clusters remain objects of interest.

Globular clusters

• We now know that many millisecond pulsars are gamma-ray emitters.

• We know that globular clusters are full of MSPs.http://www.naic.edu/~pfreire/GCpsr.html is a nice resource.

• See Lucas’ Guillemot’s talk.

Wolf-Rayet stars Professor Rayet founded the Bordeaux observatory, by the way. 

• Not to be confused with the -pulsar PSR J1028-5819, which is 0FGL J1028.6−5817 (M. Razzano poster).

• WR stars can be TeV emitters, and can be found in OB assc’s, in open clusters, and elsewhere. • Study of Fermi LAT source 0FGL J1024.0-5754 is in progress…

X-ray binariesThe following question is intriguing:

The jury is still out! See Adam Hill’s talk.

Galactic transients

• « the static sky » is an outdated concept.

• From both EGRET and AGILE we know they’re there.

• Recall the animated 3-month sky shown by Jean Ballet.• Recall also « Vela stable 3% » in his talk.

•LAT automated pipeline routinely searches for flares AGN driven, but also used by Milky Way afficionados

See (once again!) Adam Hill, Thursday evening.

Pulsars

There’s so much that I could say…

« Hertzsprung - Russell » Diagram Crab nebula , with its pulsar in the middle

« pulsar wind nebula = PWN »Seen by Chinese astronomers in 1054

Endpoint of massive star evolution

Make heavy elements.

Make GRBs, SNs, & n.s.’s.

Make stars reincarnate.

Make EBL.

10 km radius.

1.4 solar masses.

Iron crust (probably).

Superfluid neutron interior.

Some pulsars spin faster than a blender!

The link from pulsar observables to the nuclear equation of state is not easy… Having a large high energy pulsar sample is good start.

for gamma pulsars:

gamma flux is a fraction O (0.1 to 10) % of spin-down power. most power in gammas Rotational kinetic energy transformed into gammas via electromagnetic braking.

True for both young pulsars and MSPs.

From Thompson via Kanbach

Vela pulsar

Pow

er

Pulsars

Two points that I will make:

1) Synergy with the radio (and X-ray) astronomers

2) Implications of the discovery of the populations

Astronomy & Astrophysics 492 (2008) 293

Parkes (Australia)

Nançay (France)

Jodrell Bank (England)

RXTE

Green Bank (West Virginia)

Arecibo (Puerto Rico)

Spin-down power Edot = 4²Pdot/P3.

“Recycled”, or millisecond pulsars

newborn pulsars(The EGRET pulsars are here)

In middle age, they become invisible, but can accrete a binary companion’s spin, to live again.

Fermi so far:~21 young radio pulsars~15 new young pulsars~9 MSPs-----------------~45 gamma pulsars in all(figure not up-to-date)

Increasing as ~ Time

Pulses at1/10th true rate

Why a priori radio measurements of the neutron star rotation and slow-down? (P and Pdot)

1. Relative phases of the radio versus gamma-ray phase help determine relative locations of the emission regions absolute timing for both.

2. Better detection sensitivity, since • not N statistical trials from searching over P,Pdot space.• Gamma photons come in real slow*. Can take years to stack a light curve.

With known period, see pulsations even with low statistics.

And furthermore: Highest Edot pulsars are young & turbulent. Starquakes! “Glitches”. Timing noise.“blind searches” weaken after several months…

*Crab – a gamma photon every ~15 seconds in the LAT => ~500 rotations of the neutron star

In the simplest model, the emission should depend on 4 parameters: spin period, magnetic field, magnetic dipole inclination, and viewing angle

luminosity derived from rotational energy

Erot = ½ I 2

E = - B2R64 / c3.

derived parameters:

rotational age : = /2

B field: B = 3.2x1019 (PP)1/2 G

spin-down power: L = I

..

.

radio emission cone

-ray emission fan beam

Pulsar geometry

• Stated previously: X-ray PWN image can give orientation angle .• Sweep of the polarization angle versus rotation phase can give the angle between the rotation and magnetic axes.

• For a given , the Polar Cap and Outer Gap predictions for the light curves in radio versus gamma rays help see which signal comes from which region.

J.L Han’s talk yesterday – extensive pulsar radio polarization data, to determine magnetic fields via Faraday rotation.

Ap J accepted, arXiv/0812.3931

Typical values for f:• Polar cap, f= 1/4 ~ 0.1 (1 sr!)• Outer gap, slot gap, f~ 1

For a measured energy flux h, find versus Edot.

Pulsar distance• Interstellar medium has an index of refraction at radio frequencies f (MHz) due to free electrons: t = DM/2.41x10-4/f² with Dispersion Measure DM in units of electrons per pc/cm3 .

• Cordes & Lazio NE2001 models the galactic electron distributions, allowing translation of DM into distance for a given direction.

(+/- 40% uncertainty when things go well.)

• Parallax for close pulsars ( <several hundred pc ).• X-ray data? black-body absorption distance

• Generally, distance from radio DM.

Radio pulse arrival time

Rad

io f

requ

ency

bin

Pulse dispersion

1. Radio-gamma synergy

• Pre-launch agreement with radio and X-ray pulsar astronomers to time 224 pulsars with Edot > 1E34 erg/s, ranked by Edot / d².

• Bearing wonderful fruit.

• We’re also seeing Edot < 1E34 erg/s pulsars! In consequence, they’re also sending us rotation parameters (« timing solutions ») for a broad variety of pulsars.

Soon over 1000 pulsars in our ephemeris database!

==============================They’re also searching for radio & X-ray signals for « blind period » -pulsars

They’ll also be searching for radio & X-ray pulsations for some of the Fermi catalog unidentified sources

• Blind period search weak for >64 Hz rotations, and for binaries.• If radio pulsations found, will then phase-fold the gamma data.

2. Implications

• Geometrical (i.e. light curves) and spectral data combined, over a large sample: we will progress on the old « polar cap versus outer gap » question.

• Predicted by some, not believed by most – very many pulsars, both young & old, emit gamma-rays.• Rotational kinetic energy being converted into high energy radiation.

• First ever large scale uniform survey – towards statistical completeness and rigorous population studies.

• Contribution of resolved and unresolved pulsars to the diffuse emission will be better constrained (Gulli Johannesson’s talk)

• Pulsar contribution to the cosmic electrons will be better constrained.

Figure: ApJ 604:775-790 (2004) "Role of Beam Geometry in Population Statistics and Pulse Profiles of Radio and Gamma-Ray Pulsars", Gonthier, Van Guilder, & Harding

• Population synthesis requires many input factors, including « typical » beam sizes and L vs Edot.• Better inputs will yield better predictions of the neutron star content of the Galaxy, supernova rates, massive star populations, et cetera.

Conclusions

• The Fermi LAT is indeed resolving sources that were confused for previous missions, and is allowing localization adequate to find associations at other wavelengths.

• The gamma ray sources reveal a variety of cosmic accelerators: such as shocks in a variety of jets and winds, and dynamos.

• New populations of pulsars being discovered, in a variety of systems.

• The radio-assisted and the blind period pulsar searches yield complementary information that will assist improved population studies and will greatly enhance understanding of pulsar radiation.

• Only months into the mission and we’ve seen a lot. Digesting it all will take a little longer.

Look us up on You Tube!

Search for « glastcenbg » (one word, no spaces)

It’s 7 minutes long, fun, and in your choice of French or English.

http://fr.youtube.com/watch?v=54IBWt-O8Co

http://www.dailymotion.com/relevance/search/glastcenbg/video/x5lfbo_le-satellite-glast_tech

It’s also on Daily Motion…

~september…

After a year?

Histogram of Edot / d² from the ATNF pulsar data

After one month of survey: we see N, with a minimum F ~ L/d²

After a year: Fmin Fmin /12 = 0.3 Fmin =10-

0.54

(essentially logN-logS.)