Fermi-LAT and WMAP observations of the SNR Puppis A Marie-Hélène Grondin & Marianne Lemoine-Goumard Hewitt, J., Grondin, MH, et al. 2012, ApJ, accepted (arxiv:1210.4474) MODE-SNR-PWN workshop - November 2012 - Montpellier
A Text-book Type II Supernova Remnant Puppis A (G260.4-3.4) is a well-defined SNR: Distance of 2.2 ± 0.3 kpc CCO identified as RX J0822-4300 Physical diameter of 30 pc Age of 3700 ± 400 years (optical knots); 4450 ± 750 years (proper motion of CCO; Becker et al. 2012) Sedov phase In a well-known environment: Evolving into the ISM in the vicinity of a molecular cloud Non radiative shocks except at certain knots where small clumps are shocked X-ray/IR correlation indicates n ~ 4 cm -3 Arendt, et al. 2010, ApJ, 725, 585
Fermi-LAT analysis of a complex region! 3 years of Fermi-LAT data (2008-08-04 to 2011-08-20) P7 V6 Source IRFs Off-pulse Galactic background modeled by the LAT diffuse emission ring-hybrid model gal_2year_p7v6_v0.fits; Isotropic component modeled with the file iso_p7v6source.txt All sources listed in the 2FGL catalog within 15 around Puppis A + spatial model describing Vela-X (Grondin et al., 2012) and Vela Junior (Tanaka et al., 2011) Off-pulse photons from Vela for all analyses performed below 3 GeV Lightcurve of the Vela pulsar Abdo, A. A. et al. 2010, ApJ, 713, 154 0.1 < E < 2.3 kev E > 1.3 kev E > 1 GeV; off-pulse See Presentation by M-H Grondin
Our fnal model of the region (Galactic coordinates) E > 800 MeV E > 4 GeV Blue crosses: modified with respect to 2FGL White crosses: 2FGL sources
Fermi-LAT morphology Morphology performed above 800 MeV in the off-pulse: comparison of different spatial templates 2 nearby sources detected (BckgA and BckgB) not related to the SNR Best fit obtained with a uniform disk with R = 0.38 ± 0.04 Some marginal improvement of the fit obtained by dividing the template into 2 hemispheres TS map (E > 800 MeV; Off pulse) Hewitt, J., Grondin, MH, et al. 2012, ApJ, accepted Square root scale
Comparison to MWL data Excellent correlation with X-rays (ROSAT) and radio (VLA 1.4 GHz) which show enhancement to the East due to increasing density gradient TS maps Off pulse E > 800 MeV: ROSAT Contours VLA Contours
Fermi-LAT Spectrum Using off-pulse data above 200 MeV and the X-ray spatial template: Best fit simple power-law with index = 2.09 0.07 0.09 SED points are computed in the off-pulse below 3 GeV and all phase above 3 GeV for better statistics The two hemispheres show different spectra at 3 level: Western hemisphere is steeper by an index of 0.3 above 200 MeV More data or TeV observations may confirm this spectral/spatial difference Whole X-ray template = 2.09 0.07 0.09 Eastern hemisphere = 1.96 0.13 0.08 Western hemisphere = 2.28 0.14 0.10
Pulsation search PSR J0821-4300 is unlikely to provide soft-spectrum emission seen in the Western hemisphere Could the CCO explain the soft spectrum seen in the West? PSR J0821-4300 112ms X-ray pulsar, «antimagnetar» (Gotthelf et al., 2009) Proper motion gives projected velocity of ~1500 km/s placing it at the dynamical center of the SNR at t=0 Low Edot: not a good gamma-ray PSR candidate Blind search hardly feasible (low TS and few counts in the off-pulse of Vela). No significant pulsations using X-ray timing solution
WMAP extends the radio spectrum Puppis A is detected in the WMAP 7-year allsky data Analysis: 5 bands, 23-93 GHz; Template fit using 1.4 GHz VLA image + sloping-planar baseline Best fit 1 GHz flux density of 141 4 Jy and a radio spectral index of -0.56 0.01 Possible high frequency break Template fits to the WMAP data within a 2 radius around Puppis A
Non-thermal modeling & parameters used Assume only one particle population within R=15 pc Assume particle spectra follow power-law with exponential cut-off Account for energy losses during t=3700 years IR and X-ray observations constrain the density at the shock (4 cm -3 ) Dust emission from Puppis A fit by 2 black body (T = 150 K with n=12 cm -3 and T2 = 45 K with n= 20 cm -3 ) (Arendt et al 1991) Use local ISRF spectrum (Galactocentric radius comparable to Sun) => Shocked dust and optical background do not dominate over CMBR
Results of the non-thermal modeling All mechanisms are viable requiring W CR ~ (1-5) 10 49 erg but pion-decay is most reasonable: Brems dominates over pion-decay for e/p > 0.1 IC dominates for n < 0.3 cm -3 One-zone models have a great difficulty explaining radio break if confirmed (would need very high B field ~1 mg for synchrotron break)
Discussion Low luminosity: ~3 10 34 erg s -1 S. Funk, TeVPA (2011) Bulk of the large cloud not yet encountered but in the near future Transitional case between young SNRs evolving into a circumstellar medium (e.g. Cas A), and older SNRs which are interacting with large, dense molecular clouds (e.g. IC 443). Multi-zone modeling of Cas A: hadronic CR content of ~610 49 erg (Araya & Cui 2010), comparable to Puppis A. IC 443 has a luminosity one order of magnitude greater than Puppis A, with a total energy content in protons of only few times 10 49 erg (in hadronic models), similar to Puppis A. Difference may be explained by larger density in IC443
Summary Puppis A SNR is detected by Fermi as a significantly extended source with D ~0.8 ; excellent correlation with X-ray and radio observations Best fit obtained with a simple power-law with index = 2.09 0.07 0.09 Radio spectrum extended up to 93 GHz; possible high energy break to confirm SED modeling requires W CR ~ (1-5) 10 49 erg Pion-decay seems favored but none of the emission mechanisms are ruled out Interesting target for future observations in radio and TeV: could confirm the high energy break (in radio) and the spectral difference for the two hemispheres