Andrea Caliandro 1 Andrea Caliandro (INFN - Bari) on behalf the FERMI-LAT collaboration PSR J : the youngest gamma-ray pulsar in the Galaxy?

Andrea Caliandro 2 Prologue PSR J is the central compact object of the SNR G G is one of the brightest SNR in X-rays – It is recorded in the Green catalog as plerionic SNR (SNR + PWN) – This source was chosen as calibration target for Chandra X-ray observatory No radio pulsation was detected from PSR J until 2005 So far no significant X-ray pulsation is detected SNR G is detected by HESS at TeV energies

SNR G observed by Chandra PSR J not pulsing in X-rays Thermal northern knots Non thermal limb-brightened (Matheson & Safi-Harb 2005) PSR SNR PWN

Andrea Caliandro 4 Radio pulsation discovery Parkes discovery observation (Camilo et al. 2006) GMRT discovery observation (Gupta et al. 2005) Giant Metrewave Radio Telescope Parkes Radio Telescope Two independent discovery of PSR J pulsation were claimed on Camilo et al using Parkes and GBT telescope Gupta et al using GBMT telescope Characteristic parameters P = 61.8ms Pdot = 2.02 E-13s/s Edot = 3.3 E+37 ergs s-1 Age c = 4.8kyr One of the most powerful pulsars, second only to Crab in our Galaxy pulsars It is a very faint radio pulsar (flux density ~70  1.4GHz)

Andrea Caliandro 5 Different pulsar age estimations Characteristic age of 4800yr Despite the characteristic age of the pulsar, measurements of the expansion rate of the supernova remnant give an estimated age of less than 1000yr under the assumption of undecelerated expansion (Bietenholtz & Bartel 2008) There is good historical evidence from ancient Chinese records to believe that this pulsar is associated with a guest star supernova explosion that took place in BC 48, making the system just over 2050 years old (Wang et al. 2006) Copy of the ancient Chinese record of the BC 48 guest star in the Astronomical Chapter No.6 of Quian Han Shu (History of the Former Han Dynasty), originally written by Ban Gu AD 100 PSR J could be the youngest known pulsar in our Galaxy

Andrea Caliandro 6 With Delta-II rocket, From Cape Canaveral, Florida Launched on June 11, 2008 LAT turn on: June 24 Launch & Early Operation (L&EO) will end August 11, 2008

Andrea Caliandro 7 PSR J Light Curve with optimized cuts A very preliminary spectral analysis carry out a spectral index of ~1.7 and a flux of ~1e-7 ph/cm 2 s for the pulsed fraction of this source Using this results the S 2 /N ratio is evaluated for a grid of photon selection cuts (Energy Low Threshold, ROI radius) ‏ The plot shows that the optimal cuts are in a narrow region around: Energy low cut = 1.0 GeV Best Radius = 0.5 deg Ztest = 49.3 Z chance prob. = 5.12e-10 Htest = 69.1 H chance prob. = 4.00e-08 E>1GeV, 0.5° Preliminary

Andrea Caliandro 8 PSR J Light Curves The light curves in this slide are obtained collecting photons within 68% of the Point Spread Function 68%PSF  ~0.435 The ratio P1/P2 decrease with increasing energies Preliminary

Andrea Caliandro 9 Spectral analysis Likelihood spectral analysis n ij : number of counts in the pixel ij  ij : number of counts predicted by the model Galactic modelExtragalactic Neighboring sources Investigated source We would like to evaluate the contribute, in terms of differential flux, of our source in each energy bin – For each energy bin we apply the likelihood analysis in an energy range as large as the width of the bin – In this case the investigated source is modeled with a segment of power-law with fixed index (  = 2.0) for each energy bin – Minimized the Likelihood, the differential flux of our source in each bin is calculated from the term c a in the ‘investigated source’ model

Andrea Caliandro 10 keV–TeV multiwave spectrum SNR PWN PSR Chandra models INTEGRAL data FERMI data HESS spectral fit X-ray Chandra models (Safi-Harb et. al 2001)‏ ⁃ PSR:  1.4 ⁃ PWN:  2.3 ⁃ SNR:  2.4 INTEGRAL data (DeRosa et al. 2008) HESS model: (Djannati-Atai et al. 2007) ⁃ PWN:  2.08 Preliminary

Andrea Caliandro 11 Summary PSR J is a really interesting pulsar – It is a faint source in radio (flux density ~70  1.4GHz) – The pulsed signal is strong in gamma-ray( ~6  significance) – No X-rays pulsation detection – It is a young pulsar, maybe the youngest in our Galaxy – Its gamma-rays light curve show two peaks separated by ~ in phase and also the Interpulse – The ratio P1/P2 decrease with increasing energies – From the SED seems that the FERMI-LAT data points are well connected at low energy with the X-rays PSR spectrum and at high energy with the PWN HESS spectrum