Early Fermi LAT
observations of the
Vela pulsar
Massimiliano Razzano
on behalf of the Fermi LAT Collaboration
INFN-Pisa
[email protected]
M.Razzano - 44th Rencontres de Moriond
ID of Vela pulsar

Radio pulsation discovered in 1968 in the Vela SNR, bright pulsar: S1.4Ghz~1.5 Jy

Located RA=08:35:20.61,dec=-45:10:34.87 (near the Galactic plane @b~-2.8˚)

D~287+19-17 pc (VLBI parallax in 2003)


P:~89 ms; Pdot ~3x10-13 s/s
Young pulsar tc~11 kyr

Energetic Edot~7x1036 erg/s

Bsurf ~3.4x1012 G
7 high confidence gamma-ray pulsars
Low confidence gamma-ray pulsars
(D. Thompson, 2003)
A huge gamma-ray telescope !
Events
Collected photons from Vela
at different g-ray telescopes
200000
180000
160000
140000
120000
100000
80000
60000
40000
20000
0
SAS-2
COS-B
EGRET
AGILE
Fermi
LAT
LAT
expected
(~1 yr)
A huge teamwork !
•Large collaborative
effort of
scientific/instrumental
analysis!
•See Abdo et al. 2009
ApJ in press,
arXiv:0812.2960
Point Spread Function
• Flight data on Vela used for testing the pre-launch expectations
• The PSF is very sharp at high energy
Excellent agreement
with pre-launch
expectations below
few GeV
Stefano Germani’s talk
about on-orbit performance
verifications & monitoring
First Fermi Vela light curve
100 MeV < E < 10 GeV
~50000 photons !
Remarkably
sharp peaks;
features to
~0.3 ms
Turns almost
completely off
between the
double pulses
Light curve evolution with energy
Large LAT energy
window puts Vela
pulsar in
multiwavelength
context !
Vela in Radio
• Coherent radio emission
– Parkes 64m telescope
– RMS residuals 90s
log nFn
(Jy Hz)
log E2 dN/dE
(erg cm-2 s-1)
Vela in UV
• Synchrotron optical/uv
– HST STIS/MAMA
– 4.1-6.5 eV
(Romani et al., ApJ 2005)
log nFn
(Jy Hz)
log E2 dN/dE
(erg cm-2 s-1)
Soft X-rays
• Thermal soft X-rays
–XMM PN
log nFn
(Jy Hz)
log E2 dN/dE
(erg cm-2 s-1)
Hard X-rays
• Synchrotron hard X-rays
–RXTE PCA
(Harding et al., ApJ 2002)
log nFn
(Jy Hz)
log E2 dN/dE
(erg cm-2 s-1)
Vela in g-rays
• Curvature g-rays
– Fermi LAT
– Energy dependent pulses
• First peak softer than
second
– Known from EGRET
log nFn
(Jy Hz)
log E2 dN/dE
(erg cm-2 s-1)
Vela in g-rays
• Curvature g-rays
– Fermi LAT
– Energy dependent pulses
• First peak softer than
second
– Known from EGRET
log nFn
(Jy Hz)
log E2 dN/dE
(erg cm-2 s-1)
Vela in g-rays
• Curvature g-rays
– Fermi LAT
– Energy dependent pulses
• First peak softer than
second
– Known from EGRET
– 3rd Peak, which
shift in energy
– New result !
log nFn
(Jy Hz)
log E2 dN/dE
(erg cm-2 s-1)
Vela in g-rays
• Curvature g-rays
– Fermi LAT
– Energy dependent pulses
• First peak softer than
second
– Known from EGRET
– 3rd Peak, which
shift in energy
– New result !
log nFn
(Jy Hz)
log E2 dN/dE
(erg cm-2 s-1)
Vela in g-rays
• Curvature g-rays
– Fermi LAT
– Energy dependent pulses
• First peak softer than
second
– Known from EGRET
– 3rd Peak, which
shift in energy
– New result !
log nFn
(Jy Hz)
log E2 dN/dE
(erg cm-2 s-1)
Vela in g-rays
• Curvature g-rays
– Fermi LAT
– Energy dependent pulses
• First peak softer than
second
– Known from EGRET
– Trailing peak survives
(known from EGRET)
log nFn
(Jy Hz)
log E2 dN/dE
(erg cm-2 s-1)
Phase-averaged spectrum
 (E / Ec )b
N(E)  N 0 E e
Consistent with b=1
(simple exponential)
  1.510.04
0.05

E c  2.9  0.1 GeV

b=2 (super-exponential)
rejected at 16.5s
No evidence for
magnetic pair
attenuation:
Near-surface emission
ruled out
The Vela pulsar movie
E<300MeV (red)
300MeV<E<1GeV(Green)
E>1GeV (blue)


Summary of key results
•
•
Vela pulsar
– Phase-averaged spectrum
• Simple exponential cutoff Ec = 2.9 ± 0.1 GeV
• Inconsistent with magnetic pair attenuation, thus favoring outer
magnetosphere emission models
– Energy-dependent pulse profile
• First peak is softer than second peak (confirming EGRET)
• Sharpest features to ~0.3 ms.
• Peak in bridge region (phase ~ 0.3) shifts to later phase with increasing g-ray
energy
– Upper limit on unpulsed emission (>100 MeV)
• 1.8x10-7 ph/cm2/s 95% C.L. upper limit on unpulsed emission, e.g. PWN
(Talk of Marie-Helene Grondin)
• Stringent limits or measurement will be available with more livetime
– See Abdo et al. 2009 ApJ in press, arXiv:0812.2960
• Contact authors R. Romani and M. Razzano
Fermi LAT & Vela
– Working as designed, performance as expected
• e.g. Vela results demonstrate timing and angular resolution below few GeV
(Talk of Stefano Germani)