Radio counterparts of gamma-ray pulsars

Transcription

1 Radio counterparts of gamma-ray pulsars Lucas Guillemot, MPIfR Bonn on behalf of the Fermi LAT Collaboration IAU Symposium 2012, Beijing 20/08/12

2 117 gamma-ray pulsars! 41 young radio- and X-ray-selected (green circles, cyan crosses) 36 young gamma-selected (white squares) 40 radio-selected MSPs (red diamonds)

3 LAT-detected pulsars List available at L. Guillemot, IAU Symposium 2012, 20/08/12 3

4 LAT-detected pulsars List available at Distance and beaming also contributing! L. Guillemot, IAU Symposium 2012, 20/08/12 3

5 The LAT 2-year Point Source Catalog (2FGL) Nolan et al. (2012), and No association Possible association with SNR or PWN AGN Pulsar Globular cluster Starburst Gal PWN HMB Galaxy SNR Nova 1873 sources, including 1062 associated with blazars and other AGNs, 11 GCs, 5 binaries, 576 «unassociated» (~30%). Galactic plane: mainly pulsars and pulsar wind nebulae. L. Guillemot, IAU Symposium 2012, 20/08/12 4

6 Finding unknown pulsars with the LAT Based on the 2FGL Catalog, Nolan et al. (2012). Best targets have pulsar-like properties: low variability indices and curved spectra. Techniques used for ranking sources: visual inspection of light curves & spectra, or statistical studies of populations (cf. Ackermann et al., 2012; Lee et al. 2012; Mirabal et al. 2012) L. Guillemot, IAU Symposium 2012, 20/08/12 5

7 Gamma-ray blind search discoveries Cf. previous talk by Pablo Saz Parkinson LAT data sets are long and sparse, making pulsation searching extremely demanding. Atwood et al. 2006: time differencing search technique reducing computational costs. 26 discoveries in the first 2 years of LAT observations (Abdo et al. 2009, Saz Parkinson et al. 2010). Another 10 found in the 3 rd year with an improved technique originally used for searching for GW in LIGO data (Pletsch et al. 2012a & b). All 36 pulsars are «normal» energetic pulsars (Ė 3 x erg/s). L. Guillemot, IAU Symposium 2012, 20/08/12 6

8 Radio detections PSRs J & J , Camilo et al. (2009) PSR J , Pletsch et al. (2012) PSR J , Abdo et al. (2010) L. Guillemot, IAU Symposium 2012, 20/08/12 PSR J , Maan et al. (2012) 7

9 Radio fluxes and luminosities The radio-detected LAT-discovered pulsars have low radio fluxes: PSR J : S1400 = 8 µjy, d = 3 kpc (GBT) PSR J : S1400 = 0.16 mjy, d = 0.4 kpc (GBT) PSR J : S1400 = 3.4 µjy, d = 3.2 kpc (Arecibo) PSR J : S1400 = 0.34 mjy, d = 3.6 kpc (GBT) + Claimed detection of 10 aligned pulses from PSR J at 34.5 MHz in a 20- min observation at Gauribidanur (India). Radio detections distance estimates. Very low luminosities. Discovery made significantly easier by Fermi. What does «radio-faint» mean? L. Guillemot, IAU Symposium 2012, 20/08/12 8

10 Finding unknown radio pulsars with the LAT Searches for pulsars in EGRET unidentified sources had modest success, because of poor source localization. Typical localization accuracy (95% CL): <10. same size as radio telescope beams! Pulsars can be missed in radio surveys for several reasons: sensitivity, binary motion, dispersion & scintillation, eclipses, insufficient sky coverage... Top: radio pointings required to cover 3EG (from Crawford et al., ApJ 652, 1499, 2006) Bottom: distribution of 2FGL source localization accuracies. L. Guillemot, IAU Symposium 2012, 20/08/12 9

11 43 radio MSPs discovered! + 4 other young pulsars. See Ray et al. (2012), arxiv: L. Guillemot, IAU Symposium 2012, 20/08/12 10

12 Counts GeV < E < 1 GeV LAT detections of the new pulsars Counts 60 E > 0.1 GeV Radio Flux Counts Nançay 1.4 GHz E > 1 GeV Counts Pulse Phase PSR J , Cognard et al. (2011) 0.1 < E < 1 GeV PSR J , Keith et al. (2012) PSR J , Kerr et al. (2012) Weighted Counts Radio Flux E > 0.1 GeV Arecibo 1.4 GHz Westerbork 345 MHz PSR J , Ransom et al. (2011) Arecibo 345 MHz Pulse Phase PSR J , Guillemot et al. (2012) + other articles published (Camilo et al., 2012) or in preparation (Barr et al. 2012, etc.) L. Guillemot, IAU Symposium 2012, 20/08/12 11

13 Results & prospects Before Fermi, only ~70 Galactic field MSPs in 30 years of searching! At least 10 «Black Widow» systems (only ~4 previously outside of globular clusters) + at least 4 «Red Backs»: eclipsing pulsars with ~0.2 Msun companions. Several may be great additions to pulsar timing arrays. Shapiro delay measurement for PSR J , Guillemot et al. (2012) L. Guillemot, IAU Symposium 2012, 20/08/12 Future Fermi LAT catalogs will provide new targets. Re-observations are important: eclipses, scintillation, RFI, etc. Gamma-ray and radio fluxes uncorrelated (see next slide). 12

14 Radio vs gamma fluxes gamma-selected Preliminary B J L. Guillemot, IAU Symposium 2012, 20/08/12 13

15 Are there radio-quiet MSPs? Searches for isolated MSPs in a blind search of the LAT data yielded no detections. Two high-latitude 0FGL sources remain unidentified: J and J Optical and/or X-ray observations show hrscale variability! (Kong et al. 2012, Romani et al. 2011, Romani 2012). Orbital parameters indicate light companions. Likely black-widow MSPs. Deep radio searches unsuccessful so far. First radio-quiet MSPs? (see A. Belfiore s talk tomorrow) L. Guillemot, IAU Symposium 2012, 20/08/12 14

16 Radio-to-gamma-ray lag Gamma-ray pulse profiles generally have two sharp peaks, separated by ~ rotations. For radio-emitting pulsars, we can measure the phase-lag between the radio and the first gamma-ray peak, δ. Generally (not always: see next slide!) offset from the radio. Correlation between Δ and δ observed, as predicted in outer magnetosphere models, e.g. Outer Gap or Slot Gap models. From the 1 st LAT catalog of gamma-ray pulsars, Abdo et al. (2010) Vela (2 cycles, P=89.3 ms) δ Δ L. Guillemot, IAU Symposium 2012, 20/08/12 15

17 MSPs with aligned radio-gamma pulses A subclass of MSPs with aligned radio/gammaray pulses has been observed: B , B , J , J A,... Co-located caustic radio and gamma-ray 15 emission regions, in the outer magnetosphere? Counts Counts Radio Flux Radio Flux > 1 GeV > 0.1 GeV Westerbork 324 MHz PSR J Nançay 1398 MHz Pulse Phase L. Fig. Guillemot, 1. The topiau two panels Symposium show the phase-folded 2012, 20/08/12 light curve of PSR J for LAT events 16 above 1 GeV and above 0.1 GeV within 0.8 of the radio position. γ-ray light curves are shown across two rotations with 25 bins per rotation. The dashed horizontal lines correspond to the Counts Counts Counts Radio Flux Radio Flux LAT > 1 GeV PSR B LAT > 0.1 GeV 50 XMM kev Nançay 1.4 GHz Westerbork 0.35 GHz (Abdo et al. 2010, Freire et al. 2011, Guillemot et al. 2011) PSR B Pulse Phase

18 MSPs with aligned radio-gamma pulses From Espinoza et al., in preparation Preliminary Radio lag (!) Radio lag (!) Radio lag (!) x LC (G) index (s) (%) B LC (G) Radio spectral index <L/I> (%) MSPs with aligned radio and gamma-ray pulses have similar properties in terms of BLC, radio spectral index and radio polarization, contrasting with the rest of the MSP population. (low levels of radio polarization are predicted by models in which radio emission is generated at a range of altitude, cf. Venter et al. 2012, Guillemot et al. 2011). The Crab pulsar is the only radio/gamma-ray aligned young pulsar, and exhibits similar properties. L. Guillemot, IAU Symposium 2012, 20/08/12 17

19 Radio and gamma-ray beaming Selecting the 249 sources from the 2FGL catalog with >20 σ significance and average energy flux > 3 x erg cm -2 s -1 : 6 are unidentified. 41 are young pulsars, incl. 17 radio selected. 12 are MSPs, all radio selected. (See Romani, 2012) If all 6 unidentified sources are radio-quiet MSPs, then 66% of MSPs are radio-loud. 2x gamma-ray-selected young PSRs as radioselected: gamma-ray beams are likely larger. However, the most energetic gamma-ray pulsars are all detected in radio (Ravi et al. 2010). High altitude radio emission from high Ė pulsars, producing wider radio beams? From Romani (2012) L. Guillemot, IAU Symposium 2012, 20/08/12 18

20 Summary 4 (5?) / 36 LAT-discovered young pulsars are radio pulsars. 43 MSPs found in radio at the position of Fermi LAT unidentified sources. Importance of continued radio (multi-λ) observations of Fermi LAT pulsars and sources. In preparation: 2 nd Pulsar Catalog, with details on 117 pulsars. Radio & gamma-ray observations (phase lags, radio-loud vs radio-quiet ratio, etc.) provide constraints on models and beaming fractions. Thank you for your attention! L. Guillemot, IAU Symposium 2012, 20/08/12 19