GLAST Large Area Telescope: First Light

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GeV Galactic Sources with the Large Area
Telescope on Fermi (formerly GLAST)
David A. Smith for the LAT Collaboration Centre
dÉtudes Nucléaires de Bordeaux-Gradignan
(CENBG / IN2P3 / CNRS) smith_at_cenbg.in2p3.fr
Les Pulsars gamma avec GLAST
David Smith Centre dEtudes Nucléaires de
Bordeaux-Gradignan ( CENBG - in2p3 - CNRS )
Moriond 4 February 2009
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• 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 3K ¼ B-fields)
• Particle physicists, for whom all of the above
  is just foreground garbage masking a sexy susy
  dark matter signal.
• Practically everybody!

Improvements due from J.L. Han
Better instruments at new wavelengths open new
windows. Example from the year 1609 ?
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• 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 unids.
• Impression after some months of Fermi LAT data
• Its all as intertwined as you thought, and
  pulsars play a central role in many types of
  sources.

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Discovery instrument par excellence.

• Continuous sky survey means
• We dont 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.

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• Supernova Remnants Pulsar Wind Nebulae
• SNRs PWNs
• The distinction between the two can be fuzzy
  e.g. our first pulsar discovery in SNR CTA 1, and
  g Cygni (See F. Giordanos talk)
• Will nearly all known PWNs have a g-pulsar? Too
  early in the mission to say
• See PWNpulsar 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 J02056449, PSR
  J22296114 and more
• Matthew Kerr PSR J20213651/Dragonfly
• Max Razzano PSR J1048-5832, PSR
  J1028-5819 poster

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• 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

From R. Romani. Discussion in K. Watters et al.,
ApJ accepted 2008, arXiv/0812.3931
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OB associations OBAFGKM  only boys accepting
feminism get kissed meaningfully  O B type
stars are the hottest. At  Moriond  in 2002
Hegra announced TeV gs from near Cyg OB2.
AharonianHornsRowell, AA 393 L37-40 (2002)

• 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
• E-2 argument still works
• energy budget argument still (almost) works

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• 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 Hills talk.

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Open clusters

• The open cluster Berkeley 87 was proposed to be
  the hadron accelerator that would explain the
  EGRET unidentified source(s) 3EG J20213716
  and/or 3EG J20163657. (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 AA
  454, 775 (2006)
• The LAT gamma pulsations identify 3EG J20213716
  as a pulsar!
• (See Matthew Kerrs 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 Bednareks prediction
  ? wait for more statistics.
• Whether they emit gammas or not, open clusters
  remain objects of interest.

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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 Guillemots talk.

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

• Not to be confused with the
• g-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 asscs, in open clusters, and elsewhere.
• Study of Fermi LAT source 0FGL J1024.0-5754 is
  in progress

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X-ray binaries
The following question is intriguing
The jury is still out! See Adam Hills
talk.
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Galactic transients

•  the static sky  is an outdated concept.
• From both EGRET and AGILE we know theyre 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.

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Pulsars
Theres so much that I could say
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Endpoint of massive star evolution
Make heavy elements. Make GRBs, SNs,
n.s.s. Make stars reincarnate. Make EBL.
Crab nebula , with its pulsar in the middle
 pulsar wind nebula PWN  Seen by Chinese
astronomers in 1054
 Hertzsprung - Russell  Diagram
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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.
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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.
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Pulsars

• Two points that I will make
• Synergy with the radio (and X-ray) astronomers
• Implications of the discovery of the populations

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Astronomy Astrophysics 492 (2008) 293
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Parkes (Australia)
RXTE
Jodrell Bank (England)
Nançay (France)
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Arecibo (Puerto Rico)
Green Bank (West Virginia)
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Spin-down power Edot 4p²Pdot/P3.
newborn pulsars (The EGRET pulsars are here)
Recycled, or millisecond pulsars
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
In middle age, they become invisible, but can
accrete a binary companions spin, to live again.
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Pulses at 1/10th true rate
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• Why a priori radio measurements of the neutron
  star rotation and slow-down?
• (P and Pdot)
• Relative phases of the radio versus gamma-ray
  phase help determine relative locations of the
  emission regions ? absolute timing for both.
• 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 gt 500 rotations of the neutron star

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Pulsar emission
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 W2

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Pulsar geometry

• Stated previously X-ray PWN image can give
  orientation angle ?.
• Sweep of the polarization angle versus rotation
  phase can give the angle a between the rotation
  and magnetic axes.
• For a given a, ? 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 Hans talk yesterday extensive pulsar radio
  polarization data, to determine magnetic fields
  via Faraday rotation.

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Ap J accepted, arXiv/0812.3931
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versus Edot.
For a measured energy flux h, find

• Typical values for fW
• Polar cap, fW 1/4p 0.1 (1 sr!)
• Outer gap, slot gap, fW 1

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Pulsar distance

• Interstellar medium has an index of refraction
  at radio frequencies f (MHz) due to free
  electrons Dt 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
• ( ltseveral hundred pc ).
• X-ray data?
• black-body absorption distance
• Generally, distance from radio DM.

Pulse dispersion
Radio frequency bin
Radio pulse arrival time
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1. Radio-gamma synergy

• Pre-launch agreement with radio and X-ray pulsar
  astronomers to time 224 pulsars with Edot gt 1E34
  erg/s, ranked by ?Edot / d².
• Bearing wonderful fruit.
• Were also seeing Edot lt 1E34 erg/s pulsars!
• In consequence, theyre also sending us rotation
  parameters ( timing solutions ) for a broad
  variety of pulsars.
• Soon over 1000 pulsars in our ephemeris database!
• Theyre also searching for radio X-ray signals
  for  blind period  g-pulsars
• Theyll also be searching for radio X-ray
  pulsations for some of the Fermi catalog
  unidentified sources
• Blind period search weak for gt64 Hz rotations,
  and for binaries.
• If radio pulsations found, will then phase-fold
  the gamma data.

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

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

Figure ApJ 604775-790 (2004) "Role of Beam
Geometry in Population Statistics and Pulse
Profiles of Radio and Gamma-Ray Pulsars",
Gonthier, Van Guilder, Harding
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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 weve seen a
  lot. Digesting it all will take a little longer.

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Look us up on You Tube! Search for
 glastcenbg  (one word, no spaces) Its 7
minutes long, fun, and in your choice of French
or English.
http//fr.youtube.com/watch?v54IBWt-O8Co
Its also on Daily Motion
http//www.dailymotion.com/relevance/search/glastc
enbg/video/x5lfbo_le-satellite-glast_tech
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Histogram of ?Edot / d² from the ATNF pulsar data
After one month of survey we see N, with a
minimum F Lg/d² After a year Fmin ? Fmin /?12
0.3 Fmin 10-0.54 (essentially logN-logS.)
After a year?
september