where are the neutron star candidates?lpc2e.cnrs-orleans.fr/~pulsar/psrworkshop/workshop2008/... ·...
TRANSCRIPT
1
Where are the neutron Where are the neutron star candidates?star candidates?
M.H. GrondinM.H. Grondin
for the CENBGfor the CENBG
2
Detection of pulsars with Fermi• Before Fermi : 7 pulsars known in gammarays, only Geminga is radio
quiet
• ~100 pulsars expected before the launch• Two types of searches for gammaray pulsars :
– using known ephemeris at other wavelengths for radio/Xray pulsars– blind searches for Gemingatype pulsars
Here, we consider sources that may be neutron stars but without any evidence of pulsed emission.
3
Implications of the detection of Gemingatype pulsars
• Knowing the “Geminga fraction” of pulsars can constrain the mechanisms of gammaray emission
cf. 1st GLAST symposium, Stanford, 2007 Harding et al, 2007, astroph/0706.1542
4
Pulsar blind search in the Fermi collaboration
A blind search is performed on the Fermi gammaray photons :
– Position of the source wellknown
– Spin parameters (F0,F1,F2) unknown
– Sources of interest:• sources from the LAT catalog• « known pulsars », in parallel with the studies performed using
the radio/X/optical ephemeris• promising « Geminga candidates » (CCO of PWN, MILAGRO
sources, …)
5
Methods used for the blind search (UCSC, NRL)
A blind search is performed on the gammaray photons using :
Fast Fourier Transforms : very expensive computationnally, needs a long observation time (with possibility of glitch) because of the low flux of the sources can not be used on Fermi data
TimeDifferencing Technique : analysis the differences of photon arrival times, with a better sensitivity than FFT
reduce the computational time, the effects of frequency derivatives and glitches
For more details, please see :Atwood et. al., ApJ Lett., 652, 49 (2006)Ziegler et. al., ApJ 680, 620 (2008)
6
The LAT catalog
Every month, a complete analysis is performed on the whole sky : Source detection, using MRfilter (Haar wavelet transform) Spectral analysis, using the likelihood method Source association, using catalogs from other wavelengths
experimentsThe LAT internal catalog is updated and improved because of the
increasing statistics, a better knowledge of the Instrument Response Functions (effective area, energy resolution, point spread function) and of the diffuse emission.
The two first public versions of the LAT catalog should be published in february and august 2009. This catalog will contain : the position of the source spectral (flux, pivot energy, …) and spatial (radius of ellipse at
68% and 90% confidence, …) informations the name(s) of potential counterparts (if they exist)
7
Detection of a glitch in PSR B170644
Preglitch ephemeris
Postglitchephemeris
A search around a narrow range of frequencies centered on the known ephemeris results in two highly significant peaks in the power spectrum.
Glitch occurred between 08:00 on 14 Aug and 06:00 on 15 Aug
This pulsar has been known to glitch (e.g. 1992, 1995). This is the first detection in gamma rays. Radio followup observations are planned.
8
Central Compact Objects of PWNe
• CCO of PWNe are very interesting candidates for the blind search, as neutron star candidates (detectable in gammarays?)
• Study in the framework of the « plerion candidates for Fermi » : list and bibliography of PWNe with and without known pulsars
• Selection of PWNe without any detected pulsar but with a Central Compact Object (CCO) detected in Xrays (no pulsation observed)
9
CCO of PWNe (2)
29:04:13 17:45:39.6 G359.890.08 37:54 18:56.5 G358.617.2 G327.11.1 MSH 1556 G326.31.8 G293.8+0.6 MSH 1162 G291.00.1 05:27:12 19:04:04.7 3C 396 G39.20.3
3EG J18092328 23:32:23 18:09:50.2 Taz G7.42.0 3EG J0010+7309 +73:03:08.17 00:07:01.537 CTA 1 G119.5+0.2
13:00:55 18:28:48 G18.951.1 17:49:57.48 18:13:35.17 G12.820.02
3EG J14206048 60:57:56.514:18:39.9 Rabbit G313.3+0.1 3EG J0617+2238 +22:21:27.3 06:17:05.31 IC 443 G189.1+3.0
28:52:56.5 17:46:21.5 G0.130.11
EGRET coïncidence
Dec of the CCO
(°:':".d)
Ra of the CCO
(hh:mm:ss.d)
Other name PWN
10
Other compact objectscf. Kaspi, Roberts and Harding, astroph/0402136v2 (2004). see also contributions to AIP Conf. Proc. Montreal, Canada (2007).
• Isolated neutron stars:– RX J0420.05022– RX J0720.43125– RX J0806.44132– RX J1308.6+2127– RX J1605.3+3249
• CCO of SNR– CXOU J082157.5430017 (Puppis A)– CXOU J085201.4461753 (Vela Jr.)– RX J121000.8522625 (G296.5+10.0)– CXOU J161736.3510225 (RCW 103)– CXOU J232327.9+584843 (Cas A)– Pointlike source in RCW 86 (ra=14:40:31.05, dec=62:38:16.9)– 1WGA 1713.43949 (RX J1713.73946)– CXOU J185238.6+004020 (Kes 79)
11
Discovery of a pulsar in the young supernova remnant CTA1
CTA1
Fermi first lights (June, 30. – July, 4. 2008)
12
Before Fermi launch SNR observed in radio in the 1960’s (Harris & Roberts, 1960) : young
SNR in the Sedov phase, distance ~ 1.4 kpc, diameter ~ 90’ Synchrotron pulsar wind nebula detected in Xrays (Seward et al, 1995,
Slane et al, 1997, 2004), diameter ~ 18’ Pointlike source detected by Chandra (Halpern et al, 2004) in the SNR.
No evidence of pulsation but spectral characteristics of a neutron star This pointlike source is a good pulsar candidate
An EGRET error box is located in the SNR A detection is highly expected with Fermi
Pointlike source observed by Chandra
SNR as seen in radioEGRET contours (violine) and
synchrotron nebula Xray emission
13Phase histogram
(two cycles are represented)
The first postlaunch Fermi paper, published in Science deals with the discovery of a pulsar (no pulsation observed either in radio or in Xrays) in the SNR CTA1
Discovery of a pulsar in the young supernova remnant CTA1
14
The Fermi detection (red circle) is spatially coïncident with the pointlike Xray source (black cross). It is also compatible with the 95% error box of EGRET (blue circle).
30/06/08 – 30/07/08 : 900 photons above 100 MeV
Flux (>100 MeV) ~ 3.8e7 cm2.s1
Pulsar informations from Fermi data:• P ~ 317 ms• dP/dt ~ 3.6e13• Ė = 4.5e35 ergs/s• B = 1.1e13 G• Characteristic age ~ 10,000 yr
Discovery of a pulsar in the young supernova remnant CTA1
15
Conclusions
• Different types of neutron star candidates: CCO of PWN, SNR, isolated neutron stars, …
• A pulsar blind search can be performed, in particular when a Fermi source is spatially coincident with such candidate.
• The detection of radioquiet pulsars has an implication on the emission mecanisms.
• A new radioquiet gammaray pulsar has been discovered in the SNR CTA1... and more are on the way!