e-vlbi follow-up of Galactic, unidentified TeV sources

Transcription

1 e-vlbi follow-up of Galactic, unidentified TeV sources Zsolt Paragi (JIVE) And in collaboration with: Krisztina Gabányi (FOMI SGO), Gloria Dubner, Elsa Giacani (IAFE) Yurii Pridopryhora (JIVE), Sándor Frey (FOMI SGO) Presented at the 10 th e-vlbi Workshop at Amazingwe, near Hartebeesthoek, South Africa, November 2011

2 Outline First attempts on 3EG J , triggered by AGILE (just before Fermi time) A new gamma-ray binary (e-evn: Moldon, Ribo & Paredes 2011) A known source but unidentified flaring region in the Crab nebula (e-evn: Lobanov, Horns & Muxlow 2011) The new, unidentified TeV source HESS J : a new case of a pulsar wind nebula, surrounded by a lost SNR? (e-evn, our group: Gabanyi, Dubner, Giacani, Paragi, Pidopryhora & Frey 2011) Conclusions

3 Observing VHE sources with the e-evn: a bit of history VLBI observations of unidentified EGRET sources was thought to be a good idea in the beginning of e-vlbi, especially when they flare For example, AGILE detected a -ray transient in the very busy Cygnus region in April 2008 near 3EG J , that showed renewed activity in June There was only one hard X-ray source in the large error circle, that had IR and radio counterparts: IGR J / 2MASX J We did observe this source with the e-evn as well

4 Observing VHE sources with the e-evn a bit of history and did publish the results Trejo, Giacani, Paragi, Langevelde, Dubner & Bykov, ATel #1597, 2008 Paragi, Trejo, Giacani, Dubner, Bykov & Langevelde, PoS(MQW7) 105, 2008 But the identification was completely wrong! This is a very complex region in the gamma-ray sky (as well), removing background was not straightforward

5 Observing VHE sources with the e-evn a bit of history But we were convinced that this should work some day, and it did (as we will see )!

6 Gamma-ray binaries Binary systems with compact object, detected in GeV/TeV regime, SED peak is at the MeV-GeV energies Three classical examples: PSR B , LS 5039 and LSI (e.g. Paredes 2008) Two main scenarios proposed: Particles accelerated by microquasar jet (e.g. Bosch-Ramon & Khangulyan 2009) Particles accelerated in the shock between the relativistic pulsar wind and the wind from the massive companion star (Tavani & Arons 1997; Dubus 2006) Microquasar scenario challenged by VLBA monitoring results of LSI (Dhawan et al. 2006)

7 HESS J , -ray BH binary candidate Point like, variable TeV source discovered by the HESS team (Aharonian et al. 2007; Acciari et al. 2009) Variable counterparts in the X-rays and in the radio band (Hinton et al and Skilton et al. 2009, respectively) Propsed counterpart is the massive B0pe star MWC 148, d~1.5 kpc; SED similar to LSI , but order of mag. fainter (Hinton et al. 2009) Swift/XRT: 321 5d periodicity (Bongiorno et al. 2011) supports binary nature, but binarity with optical spectroscopy not confirmed yet X-ray outburst in Feb (Falcone et al. 2011) VERITAS and MAGIC reported increased activity at >200 GeV between 7-9 Feb (Ong 2011; Mariotti 2011) e-evn: first VLBI detection! Moldon, Ribo & Paredes (2011), ATel #3180

8 e-evn: -ray BH binary scenario confirmed Radio emission within 20 AU of MWC 148: confirming optical counterpart and indicating a compact object in close orbit T b >10 6 K nonthermal radio emission Follow-up observations during the normal EVN session, 30 days later: extended structure seen ~20 AU off the first epoch position, size ~75 AU Peak: Jy/bm Total: Jy Peak: Jy/bm Total: Jy Moldon, Ribo & Paredes (2011), A&A 533, L7

9 Congratulations to our colleagues! HEPRO-III, Barcelona, 2011 Sun reflects from a window of Barcelona University, shining like a TeV source in the Sky Castells: Katalan demonstration of the formation of astrophysical jets

10 A surprise from the Crab-nebula VLA (NRAO) HST (NASA/ESA) Chandra (NASA) Radio Optical X-rays

11 A gamma-ray flare detected by AGILE A pulsar wind nebula: highly magnetized plasma of relativistic particles collide with ISM AGILE lightcurve, 2010 Until now has thought to be very stable (at large) in the X-rays and -rays (standard candle) Early AGILE data showed a flare calibration or instrumental errors? HST September 2010 another flare (~4 days), later confirmed by Fermi Chandra Short duration small size, L cm Wisps, knots and the anvil feature known to vary (days to months); interesting features, A in particular, marked to the right (HST/Chandra follow-up) Pulsar itself did not change where is the flaring region and what is the mechanism? Tavani et al. 2011, Science HST Chandra

12 The Crab-flare with the e-evn Normal CLEAN, uv-tapered, restoring beam 150 mas Multi-resolution CLEAN, uv-tapered, 500 mas e-evn + 3 Merlin telescopes, 1.6 GHz observations on 5 Nov Detected pulsar, C1 and C2 components plus extended emission Bright optical knot HST-1 not detected C mjy, ~ ; C mjy, 0.2 SNR<4 for both, but simulations show that they are real Lobanov et al. 2011, Astron. Astrophys 533, A10

13 The Crab-flare with the e-evn Pulsar removed, restored with 1.5 beam (color image) Overlaid VLA image with same resolution (Bietenholz et al. 2004) Structure changes with time, but similarities suggest the emission the EVN picked up is real: largest structure ever imaged with VLBI Lobanov et al. 2011, Astron. Astrophys. 533, A10

14 The Crab-flare with the e-evn e-evn HST e-evn Chandra e-evn multi-scale image in contours, restored with 0.7 beam C1, C2 significant offset from jet axis (jet collimation beyond C1???) C1 close to (but not coincident with) knot A related to flare? In this case the injection power generated the burst would be 0.2% of the pulsar spin-down power Lobanov et al. 2011, Astron. Astrophys. 533, A10

15 The Crab-flare with the e-evn In spite of the difficulties (Crab nebula 900 Jy in the primary beam, limited short spacings uv-covarege), most amazing imaging results Future observations needed confirm these findings and shed more light on the outflow and on the flaring region Great potentials in future e-merlin plus e-evn observations or SKA precursors with excellent short baseline coverage but working in VLBI mode as well (MeerKAT, ASKAP+LBA)!

16 HESS J : a new TeV source HESS Galactic plane survey for VHE sources (>100 GeV): found J , data Dedicated observations between May-Aug. 2009, after rejection of bad weather data left with 24.8h on-source time Statistical significance is 7.9 ; fitted point source and convolved HESS PSF RA (J2000) 19h 43m 55s 1s (stat) 1s (sys) DEC (J2000) (stat) 20 (sys) In the Galactic Plane: l=57.76, b=-1.29 HESS PSF: 68% containment radius of degrees Distribution of gamma-like events plus normalized background; dashed line denotes a point source profile Extension smaller than 2.8 at the 3 level (Abramowski et al. 2011)

17 HESS J : a new TeV source Lightcurve (up) and periodogram (below) do not show significant variability (Abramowski et al. 2011) Power-law pectrum (470 GeV 6 TeV) Flux ( (stat) (sys) ) cm --2 s --1 corresponding to 2% Crab

18 HESS J : counterparts Black dot-dashed lines show HESS confidence levels 68%, 95% and 99% Large green circle: INTEGRAL error circle for IGR Red circle is the NVSS beamsize, while NVSS J itself is indicated by the red triangle. Blue dashed circle is the NRT position (Nancay Radio Telescope) Magenta circle is ROSAT 90% confidence for 1RXH J Blue square: Swift BAT position Star indicates both CXOU J (Chandra) 2MASS J (Abramowski et al. 2011) Only one radio source within HESS 90% errors Out of 19 IR sources only one within 90% errors

19 HESS J : counterparts But CHANDRA NVSS source offset is 3.5 outside the 0.5 radio error circle There is no optical detection There is no Fermi source coincident with HESS, indicating a break in the HE/VHE spectrum between GeV or even higher (Abramowski et al. 2011)

20 HESS J scenarios Gamma-ray binary OK BUT (Like HESS J , but much more far away) Lies in the Galactic Plane Matching HE/VHE properties No massive star seen OK if D>22 25 kpc, but then X-ray luminosity too high Pulsar-wind nebula (Like the Crab Nebula; abundant class of Galactic VHE sources) Extreme BL Lac object (High-frequency peak BL Lac have two peaks in the SED, one around kev, the other near 100 GeV. They constitute the majority of VHE sources.) Gamma to X-ray flux ratio implies a very young age of ~1000 years PWN age and P similar to the Crab Nebula; if similar luminosity, D~<16 kpc VHE properties would agree with this scenario All unresolved VHE PWNe are extended in the X-rays VHE spectrum significantly softer than typical X-ray spectrum is hard with no cutoff till 195 kev, indicating an extreme BL Lac with synchrotron peak higher than 10 kev (Abramowski et al. 2011)

21 HESS J : a different view with EVN Short e-evn observations on 18 May 2011, 2h of e-vlbi at 1024 Mbps with Effelsberg, Jodrell Bank (Lovell), Medicina, Onsala, Torun, Hartebeesthoek and the WSRT. EVN at 1.6 GHz Did detect the source, but very far off the NVSS position!!! RA(J2000) 19h 43m s DEC(J2000) Featureless but resolved, T B ~ K However, these agree very well with the Chandra position But only a fraction of the NVSS flux is seen: is this a high proper motion variable Galactic object, or is it simply resolved between NVSS- EVN scales? In any case, the measured brightness temperature is much lower than typical in BL Lacs (beamed AGN) (Gabanyi et al., A&A, accepted)

22 HESS J : a resolved radio source Source total flux density (WSRT data during VLBI run) agrees well with NVSS, i.e. source not variable, but resolved: VLA C-array WSRT: 95 5 mjy (1.6 GHz) NVSS: mjy (1.4 GHz) While e-evn recovered only 30 2 mjy VLA C-array archival data confirm this, and show extended structure on arcminute scales => all these facts exclude the BL Lac origin 2 NVSS HESS 3 Chandra, EVN (Gabanyi et al., A&A, accepted)

23 HESS J : a Galactic source VLA Galactic Plane Survey (VGPS) data (Stil et al. 2006) HI HI emission likely from warped Galactic disk further behind the HESS source HI absorption at 16 km/s HI emission at ~ 45 km/s Distance within kpc (Gabanyi et al., A&A, accepted) HI, subtracted HI absorption from a cloud in front of the HESS source

24 HESS J : large-scale HI emission (b) (l) HI cube shows a shell-like feature between +50 and +57 km/s

25 HESS J : large-scale HI emission V max ~35 km/s HI absorption (b) km/s (l) HI shell appears at velocities too high for Galactic rotation in this direction

26 Forbidden Velocity Wings FVWs are known from Galactic HI surveys (e.g. Leiden/Dwingeloo Survey) 85% of these not coincident with known SNR, galaxies or High Vel. Clouds FVW believed to be related to energetic phenomena: old SNR that are too faint to be detected in radio continuum or X-rays, but revealed by HI emission Koo & Kang (2004); Kang & Koo (2007); Kang et al. (2010)

27 HESS J : a PWN surrounded by SNR? VGPS continuum No large scale continuum emission at 1.4 GHz, but prominent shell-like structure in HI in emission, like proposed for the old, missing SNRs (Kang et al. 2010) Derived parameters for the SN explosion: Dynamic age ~ years E SN = n R 3.16 S v 1.35 exp ξ erg erg initial energy! VGPS HI, km/s (Alternative explanation could be that the HI shell is a result of winds from several massive stars) In the SNR scenario the NVSS source could be powered by the pulsar left over from the supernova explosion a PWN Apparent size of 1 and spectral index of -0.3 supports this interpretation (Gabanyi et al., A&A, accepted)

28 But are there other SNR with HI shells? HESS Kes 79 (Giacani et al. 2010) G (Giacani et al. 2011) The above examples have normal velocity HI shells, but there is an example of high-velocity HI shell as well: W44 (Giacani et al. 1996) HI shell XMM Spitzer Images for G Green contours show ATCA+VLA continuum radio emission

29 And are there PWNe without SNR in the radio? Deep search for radio SNR around PWN G with the VLA Note there is X-ray detection of the SNR, still, the VLA does not detect it with a surface brightness upper limit W m 2 Hz 1 sr 1 The authors note that G is not unique, in fact most young PWNe seem to show little continuum radio emission from the putative shell; The best example is the Crab nebula itself! (Bietenholz et al. 2011)

30 Conclusions for HESS J HESS J is most likely related to a PWN (radio source on VLA scales) But what is the source detected by VLBI? May look for pulsed emission in the radio (although seems to be too bright for a pulsar at this distance) and further details with full-track, high resolution VLBI If the SNR scenario is true, the HI shell represents the long-sought missing SNR population

31 General conclusions Great results from e-evn follow-up of high energy sources (see also next talk by Marcello Giroletti on a -ray nova! ) e-vlbi operations mode and flexible proposal options (ToO/triggered/short-exploratory proposals) make things much easier for us As shown in this talk, these three projects observed in late 2010 and early 2011 are already published in main journals (and already getting cited!) It is fun to do e-vlbi!

32 The world of e-vlbi Some things never change Morpheus But some things do Niobe e-vlbi! PI PI

33 e-vlbi rocks Holy antipodes, Batman! Well-known VLBI astronomer on EVNtech, after the announcement of the detection of real-time fringes between Mopra (AU) and Jodrell Bank (UK). Happy PI #2 All hail to e-vlbi