Global Millimeter VLBI: Where do we stand ? T.P.Krichbaum Max-Planck-Institut für Radioastronomie Bonn, Germany tkrichbaum@mpifr.de This is the final version

people involved in Global Millimeter VLBI (GMVA): MPIfR: W. Alef, U. Bach, A. Bertarini, T. Krichbaum, R. Porcas, J.A. Zensus, et al. IRAM: M. Bremer, A. Grosz, S. Sanchez, K. Schuster, et al. OSO: J. Conway, M. Lindqvist, I. Marti-Vidal, et al. OAN: P. Colomer, P. de Vicente, et al. INAF: S. Buttaccio, G. Tuccari, et al. NRAO: W. Brisken, C. Chandler, M. Claussen, V. Dhawan, C. Walker, et al. KVN: B.W. Sohn, T. Jung, S.S. Lee, et al. 1mm VLBI, EHT collaboration (in 2013) : APEX: R. Güsten, K. Menten, D. Muders, A. Roy, J. Wagner, et al. Haystack: S. Doeleman, V. Fish, R. Lu, M. Titus, R. Capallo, et al. CARMA: G. Bower, R. Plambeck, M. Wright, et al. JCMT: P. Friberg, R. Tilanus, et al. SMA: R. Blundell, J. Weintroub, K. Young, et al. SMTO: R. Freund, D. Marrone, P. Strittmatter, L. Ziurys et al. plus: A. Marscher's BU group since 2015: + BHC Team: C. Brinkerink, H. Falcke, R. Tilanus, et al.

The Origin of Jets: Understanding BH – Disk – Jet coupling Image Credit: Astronomy/Roen Kelly - VLBI at mm- l overcomes opacity barrier - mm-VLBI and space-VLBI probe jet origin

How are jets made – a sketch of present knowledge image: Rani@MPIfR, Marscher@BU this region can be probed by mm-VLBI and by variability studies (at high energies) with mm-VLBI we can measure: jet brightness temperature as function of BH separation for r < 1000 RS opacity and radial dependence of t=1 surface (core shift) polarization / magnetic field vs. r BH mass and spin, respectively set observational limits to these

BP: BZ: BP versus BZ mechanism Blandford – Payne mechanism: centrifugal acceleration by magnetized accretion disk wind BP versus BZ mechanism Blandford – Znajek mechanism: electromagnetic extraction of rotational energy from Kerr BH measure Jet speed f(r,z) Jet width f(z) TB f(z) → Shape of Nozzle Magnetic Field BH Spin etc. need to reach scale of a few RG Light cylinder BP: Jet B-field BZ:

A 3mm VLBI survey of 127 AGN: Brightness temperature decreasing with increasing frequency ? Lee et al. 2008, 2015 86 GHz data M87 Figure adopted from A. Marscher (1995) Brightness temperature increasing along jet; evidence for intrinsic acceleration ? mm-VLBI imaging of AGN can discriminate between fundamental models of jet formation VLBI with ALMA Lee et al. 2008 (AJ)

3C279 @ 230 GHz: compactness: 10-15 % !! 86 GHz (GMVA) APEX EHT @ 230 GHz SMA-SMTO Apex-SMTO Apex-SMA SNR ~ 10-20 beam: 37 x 15 mas APEX compactness: 10-15 % !! 3c279, z=0.5362, 1 mas=6.31pc, 0.1 mas= 0.63pc=6476 Rs9, 0.15 muas= 0.095pc=973 rs (1pc =10280 Rs9)

VLB-Arrays observing at mm-wavelength 43 GHz: VLBA(10), EVN (5), KaVa (7), HSA (12+) 86 GHz: GMVA(15), VLBA(8), HSA(10) KVN(3) 129 GHz: KVN(3), PV, PdB, SMTO, .... no joined activity yet 230 GHz: PV, APEX, SMTO, SMA/JCMT, LMT, planned: ALMA, SPT, NOEMA, GLT, .... future: 350 GHz: PV, PdB, SMTO, SMA/JCMT, APEX, ALMA, SPT, KP12m

The Global Millimeter VLBI Array (GMVA) Imaging with ~45 mas resolution at 86 GHz Baseline Sensitivities in Europe: 30 – 250 mJy in US with GBT: 50 – 250 mJy best transatlantic: 30 – 100 mJy Array: 0.5 – 1 mJy / hr (assume 7s, 100 sec, 2 Gbps) GBT100m Yebes (OAN) http://www.mpifr-bonn.mpg.de/div/vlbi/globalmm Europe: Effelsberg (100m), Pico Veleta (30m), Plateau de Bure (35m), Onsala (20m), Metsähovi (14m), Yebes (40m), KVN (3 x 21m), planned: SRT, NOEMA, ... America: 8 x VLBA (25m), GBT (100m), planned: LMT, ALMA, ... Proposal deadlines: February 1st, August 1st

3mm VLBI sensitivity enhanced by inclusion of large European mm-telescopes: Effelsberg 100 m (MPIfR) Plateau de Bure, 6 x 15 m (IRAM, France) Yebes 40 m (OAN, Spain) Pico Veleta 30 m (IRAM, Spain) Baseline lengths (km): participating since 2011 fringe spacing: 0.4 – 1.8 mas, sensitivity > 15 - 50 mJy (7s, 2Gbps)

POSSM plot after FRING: Green Bank 100m telescope participates in GMVA 3mm VLBI observations 1st test observations in Feb. 2013 2 Gbps, 1 RDBE, PFB mode SEFD ~ 164 K app. eff ~ 0.26 (for s = 173 mm) POSSM plot after FRING: (solint 2min) RR LL

Polarized sub-structure in jet of BLLac on 0.1 mas scales 43 GHz VLBA 86 GHz GMVA Jan. 15 Feb. 18 polarized jet emission on scales down to 50 mas

3mm VLBI Array Sensitivities assuming: 512 MHz bandwidth (2 Gbit/s), t=20 sec, 7sigma fringe detection, 2 bit sampling Combining European mm-telescopes with the VLBA improves the angular resolution by factor ~ 2 and imaging sensitivity by a factor of ~2 - 3. The addition of telescopes with large collecting area (GBT, LMT,SRT, ...) will give another factor of 2 - 3. Participation of ALMA leads to mJy sensitivities and will improves the overall sensitivity by a factor of 5 over present day values. Another factor of sqrt(rate/2Gbps) in sensitivity can be obtained via a further increase of the observing bandwidth.

First Fringes between KVN and GMVA (86 GHz, May 2012) 3 x 21 m, baselines 305 – 478 km 0716+714 KVN – PdBI: SNR ~ 11 on 1 Jy source PB-KU 256 Mbps KY-KU RR LL

86 GHz VLBI Fringes VLBA to KVN GMVA Session May 2015 (PFB, now 1 Gbps) LCP 90 mas RCP KVN Yonsei – VLBA Brewster: B= 7860 km SNR ~ 22 on 0716+714 (Stot ~ 2 Jy) tint = 388 sec, 1 Gbps

S. Koyama+ S. Koyama+ 2015

KVN stations improve uv-coverage and resolution of GMVA Dec +20 Dec +50 KVN stations improve uv-coverage and resolution of GMVA KVN VLBA Europe long baselines with Europe at start long baselines with VLBA at end baseline sensitivities: KVN – GBT ~ 0.07 Jy KVN – IRAM ~ 0.15 Jy KVN – VLBA ~ 0.35 Jy (7 s, t=10 sec, 1024 Mbps)

OJ 287: Spectral decomposition of core using GMVA VLBA 43 GHz GMVA 86 GHz VLBA 15 GHz beam: 0.22 x 0.043 mas Rcore < 0.04 mas (180 Rs9) TB ~ 2.4 E11 K The core is South! modelfit: 0.21 x 0.043 mas beam total spectrum from FGAMMA monitoring program VLBI component spectra from VLBI at 15 + 43 + 86 GHz, need to add 230 GHz

The next step towards truly global 1.3 mm VLBI array (EHT) Status March 2013 with APEX added APEX/ALMA LMT SMTO CARMA JCMT+SMA Pico Veleta PdBure SPT GLT existing planned fringes established

M87 at 86 and 230 GHz GMVA @ 86 GHz (11 stations) EHT @ 230 GHz: beam (290 x 50) mas = (37 x 6) RS May 2009 GMVA @ 86 GHz (11 stations) EHT @ 230 GHz: (4 stations) Modelfit + Clean Map uvtaper 0.3@6Gl Mar. 2013 1mas = 126 Rs Core jet structure traced down to ~25 mas scale small core size indicates BH spin a > 0 beam 59 x 24 mas = (7.4 x 3.9 RS)

M87's core size is smaller than previously thought VLBI core size at 86 GHz, new VLBI core size at 230 GHz, new I new data point core size: 23 mas or 2.9 Rs This is smaller than the photon ring for an a=1 BH ! 1 mas = 126 Rs, photon ring size for max. spinning BH APEX baselines are more N-S oriented, than the E-W orientation of the US-array: the above numbers may measure the N-S jet width or sheath rather than the core !

last stable orbit radius: 1 → 6 Rs for BH spin a = 1 → 0 Competing Jet Models synchrotron self-absorbed conical jet plus relativistic shocks (Blandford-Königl jet) stratified (MHD) jet with moving hot spots/shocks or filamentary patterns 2 R0 ≥ 10 RS (a=0) Figure from Hada et al. 2011, Nat. last stable orbit radius: 1 → 6 Rs for BH spin a = 1 → 0 still unclear of what is seen at 1mm, need complementary imaging with GMVA

230 GHz structure may trace edge-brightening in 3C279 Krichbaum+2013, Wagner+ 2015 GMVA 86 GHz beam: 274 x 73 mas May 17, 2012 EHT 230 GHz beam: 37 x 15 mas May 7, 2012 0.6 pc core < ~1300 RS 3c279, z=0.5362, 1 mas=6.31pc, 0.1 mas= 0.63pc=6476 Rs9, 1pc=10289 Rs9 base of jet is transversely resolved and has a width of ~1 pc (~104 RS) size of individual components (emission regions) < 0.1 pc (1000 RS)

Cygnus A: stacked VLBI image at 86 GHz (3 epochs, 2009 – 2010, 512 Mbps) 1 mas = 1.1pc 0.1 mas ↔ 0.11 pc ↔ 440 Rs9 core size: ≤ 46 mas or 200 Rs9 jet transversely resolved on pc-scales evidence for conical jet opening on jet side (at r < 1pc) c-jet opening angle more narrow by factor 2 Boccardi et al. 2015

Ridgeline at 86 GHz, Oct. 2009 (work in progress) Cyg A core ridgeline separation : ~ 0.1 mas (~ 400 Rs9) for jet & cjet evidence for conical opening both in jet and c-jet Boccardi et al., in prep

Astrometry at mm-wavelength Because of phase self-calibration in VLBI, the absolute position information is lost. Due to rapid atmospheric phase-variations classical phase-referencing VLBI via position switch is limited to close source pairs. With the phase-transfer method applied to 2 or more frequencies observed simultaneously, VLBI maps at different frequencies could be aligned. The positional accuracy of the alignment will be of order of a fraction of the beam (< 50 micro-arcseconds at 86 GHz). An accurate image alignement is required for: spectral index measurements of cores and jets source kinematics at different frequencies (stratification) measurement of opacity shifts in RA and DEC determination of rotation measure

Phase-referencing at 86 GHz is possible for close source pairs Phase vs. time 1308+326, 709 mJy hybrid map of calibrator 1308+328, 85 mJy phase-reference map of target distance: 14'.3 cycle: 10 – 20 s rate: 256 Mbps Porcas & Rioja, 2002 VLBA supports rapid enough switching

VLBI frequency agility between 22-129 GHz (preliminary) note: consider hybrid phase transfer: some stations observe only at one frequency need to develop strategies how to tie in phases for these stations

Summary and Outlook the Origin of Jets in AGN can be studied at 7mm, 3mm and now also at 1mm 3mm and 7mm VLBI is almost standard (< 2 Gbps), VLBI @ 1mm is non- standard (16 Gbps in 2015, aim at 32 Gbps) participation of large collecting area dishes now provide much higher sensitivity (IRAM, GBT, Effelsberg, Yebes, soon: LMT, ALMA, ...) VLBA provides important uv-coverage and frequency agility (43/86 GHz) calibration limitations due to weather are over-come with an increased antenna number, which facilitates the use of closure amplitudes (N > 12) advanced methods in global-fringe fitting could be implemented to further optimize the array sensitivity (incoherent averaging, etc.) a further increase of the observing bandwidth beyond 2 Gbps at 3mm/7mm is highly desirable (ALMA: 32 Gbps) dual/multi frequency phase transfer capabilities are not yet in place a denser time sampling is necessary to better trace rapidly evolving sources 1.3 mm-VLBI (EHT) is limited and requires complementary global 7 & 3 mm VLBI (better uv-coverage, sensitivity, beam size within a factor of 2)

End