The Galaxy Viewed at Very Short Time-Scales with the Berkeley Visible Image Tube (BVIT) Barry Y. Welsh, O.H.W. Siegmund, J. McPhate, D. Rogers & J.V. Vallerga Space Sciences Laboratory University of California, Berkeley, CA 510-642-0305 (bwelsh@ssl.berkeley.edu)
What is BVIT? The Berkeley Visible Imaging Tube (BVIT) is a visible microchannel plate photon counting detector designed to provide observers with very high time resolution imaging photometry. Enables a new time domain for astronomical observations with full imaging capability Time resolution (for each detected photon) ~ 100 picosec BVIT is a simple instrument with minimal observational setup requirements and a high degree of post acquisition data flexibility. Designed as a user facility instrument only available at the 10m South African Large Telescope (SALT)
Microchannel Plate Detectors γ Tube Window with photocathode MCP stack Charge distribution on strips Charge Cloud Very similar detectors are currently in-orbit on NASA s GALEX UV astronomy mission and COS on Hubble
Microchannel Plate Detectors Photocathode converts photon to electron γ Tube Window with photocathode MCP stack Charge distribution on strips Charge Cloud Very similar detectors are currently in-orbit on NASA s GALEX UV astronomy mission and COS on Hubble
Microchannel Plate Detectors Photocathode converts photon to electron γ Tube Window with photocathode MCP(s) amplify electron by 10 4 to 10 8 MCP stack Charge distribution on strips Charge Cloud Very similar detectors are currently in-orbit on NASA s GALEX UV astronomy mission and COS on Hubble
Microchannel Plate Detectors Photocathode converts photon to electron γ Tube Window with photocathode MCP(s) amplify electron by 10 4 to 10 8 Rear field accelerates electrons to anode MCP stack Charge distribution on strips Charge Cloud Very similar detectors are currently in-orbit on NASA s GALEX UV astronomy mission and COS on Hubble
Microchannel Plate Detectors Photocathode converts photon to electron γ Tube Window with photocathode MCP(s) amplify electron by 10 4 to 10 8 Rear field accelerates electrons to anode MCP stack Patterned anode measures charge centroid (X,Y) and time of photon arrival Charge distribution on strips Charge Cloud Very similar detectors are currently in-orbit on NASA s GALEX UV astronomy mission and COS on Hubble
Cross Delay-Line Anode Image Tube GaAs SuperGenII Photocathode Q.E. Cross-Delay Line Anode Test mask 10µm pinholes on 500µm centers. 30µm resolution.
BVIT Demo System on SALT (Jan 2009) The Berkeley-SAAO team carried out a commissioning/ engineering test-run with the BVIT installed on SALT for 10 nights in January 2009. A further 7 nights observations were performed by SAAO staff in March 2009. The BVIT detector The BVIT on SALT at prime focus
THE BVIT Instrument Package on SALT B &V + ND Filter Wheels + Shutter & BVIT HVPS Filter wheel controllers TDC electronics PC LVPS BVIT F.O.V = 1.9 arc min (enables source & comparison star observations)
The BVIT Demo Detector System Resolution Command, Control & real time Display Software for BVIT BVIT 25mm tube with amp and (in rack) TDC and HVPS
BVIT Observations on SALT Observations were carried out for a wide variety of astronomical objects in order to investigate which types were best suited for future in-depth study Objects included QSO s, AGN, Spiral galaxies, Globular Clusters, Flare Stars, CV systems, Low-Mass X-ray Binaries, Pulsars, asteroid transits Observational & instrumental constraints restricted observations to targets with 12.5 < Vmag < 22.0 Some objects (CV systems) were simultaneously observed with the SAAO 74 inch telescope + hi-speed photometer by Dr. Steve Potter During the March run, the black hole candidate GX 339-4 (Vmag =15.5) was also observed with SALTICAM in order to compare data sets The BVIT+SALT observing efficiency was 58%, which is the highest value yet achieved with the SALT 10m telescope!
The SALT facility Both the Hobby-Eberly and SALT telescopes have had more than their fair share of engineering problems. SALT is presently closed for 3 months to re-engineer its tracking system Our data was taken when the tracking system had glitches and the multisegment mirror focus system had problems The effect of these facility problems resulted in stellar images suddenly going in and out of focus, and the stellar image sometimes moving several arc seconds during an exposure. The photon counting capability of BVIT, in which every photon is assigned an X,Y and t, meant that neither of these instrumental anomalies was a problem for data reduction. Note that SALT cannot produce accurate photometric fluxes
Source, Background and Comparison Star Plots (time versus counts)
Samples of BVIT Reduced Data: X-ray Transients Low-mass X-ray binaries are systems that include a low-mass companion that transfers material onto a neutron star or black hole. Most LMXRB systems have orbital periods of a few hours to days and XRT s undergo significant X-ray, optical and radio outbursts separated by long periods of quiescence Little information is currently known about short-time scale non-orbital emission variations in the optical. Although optical bursts generally lag behind those observed in X-rays (by re-processing), in several cases the optical burst emission LEADS the X-ray emission (perhaps due to synchrotron emission from a jet). (see Gandhi et al 2008) We observed the X-ray nova GX 339-4 in the B-band with BVIT on SALT for ~ 500sec with the data shown here in 0.1 sec bins
GX 339-4: Black Hole candidate data binned at 0.1 sec X-ray Transients with BVIT Short period flare event on the BH accretion disk Power spectrum
Samples of BVIT Reduced Data: M-star flares CN Leo: dme Flare Star: emission structure observed < 0.1 sec
Samples of BVIT Reduced Data: CV Systems Magnetic cataclysmic variables (CVs) contain a white dwarf that is accreting material from a secondary (red dwarf) star down the field lines. In these polar systems the strong magnetic field of the white dwarf causes it to rotate synchronously with the orbital motion. We observed the UZ For system in the B-band with BVIT for ~ 2000sec and captured an entire an eclipse event. We show the BVIT data in time bins of 0.5s and compare it with similar (white light) data recorded with an STJ device by Perryman et al (2001)
Samples of BVIT Reduced Data: CV Systems
Optical pulsars and isolated neutron Stars Only 3 optical pulsars are sufficiently bright enough to be observed with BVIT: the Crab, PSR B0540-69 and Vela. Light curve of the Crab pulsar recorded with BVIT on the Lick 1m Nickel Telescope in 2007 We have searched the ~ 2 hrs of pulsar data for the presence of giant optical pulses with no success.
Optical pulsars and isolated Neutron Stars In future observing runs we shall point the center of the BVIT f.o.v. at the radio position of several Rotating Radio Transients (RRATs) To date, ~ 20 RRATs have been detected and are characterized by short bursts of 2 to 30ms duration (100mJ to 10Jy) with time intervals between recurrent bursts ranging from 3 min to 3 hours. Obtaining a ratio of the optical-to-radio flux can place limits on the spectral slope of any proposed emission mechanism from a plausible magnetar. We shall also perform limited optical follow-up observations of gamma-ray bursts to search for very fast time-structure in their optical light curve emission
New BVIT tube for SALT New detectors for BVIT are in production, the detection efficiency is considerably better than our first detector, particularly in the red. We expect to upgrade the BVIT detector in mid-2010. New BVIT detector Comparison of detector photocathode efficiency
Photon counting counts EVERYTHING!! 1.2413 sec events with rise times of only 2 milli-sec?? Meteor Detection
Peak* Performance of the BVIT on SALT Detector FOV = 25mm circular, 1.9 arc min diam Spatial Resolution = 30 microns (0.14 ) Photocathode = S20 (replace with Supergen2) Timing Resolution = Time-stamped to 25 ns Filter selection = U, B or V-band Neutral Density Filter = ND0 to ND4 Max BVIT count rate = 2 MHz (whole detector) Max local count rate = 20 khz per arc sec 2 Stellar magnitude count rates U = 17.5 mag (1500 cts/sec) U = 22.0 mag (25 cts/sec) B = 17.0 mag (11000 cts/sec) B = 21.6 mag (170 cts/sec) Sky background count rates (Dark) = 25 cts/sec (U-band) (in 1 arc sec 2 ) (Grey) = 170 cts/sec (B-band) * Actual performance numbers depend on observing conditions etc etc