Title TOO Observations of Energetic Particles in Stellar Superflares Pi R. A. Osten Time 2 hrs 1. Name of program and authors TOO Observations of Energetic Particles in Stellar Superflares R. A. Osten S. Drake 2. One short paragraph with science goal(s) The recent detection of nonthermal hard X-ray emission from a stellar superflare (Osten et al., astro-ph/0609205) has made possible the study of energetics of accelerated particles during stellar flares. This is a project to investigate the time and spectral variability of the MeV particles which produce optically thin gyrosynchrotron emission at mm wavelengths. Simultaneous observations of the ~100 keV electrons producing the hard X-ray emission will be obtained through the use of triggered observations from an appropriate spacecraft (e.g. Swift). Comparison of the spectral index from radio observations and the spectral index derived by analysis of hard X-ray spectra will allow an investigation into whether there is a change in the distribution of electrons at these energies; their joint time variations can also be used to diagnose magnetic trapping and precipitation from the trap. 3. Number of sources (e.g., 1 deep field of 4'x4', 50 YSO's, 300 T Tauri stars with disks, ...; do NOT list individual sources or your "pet object", except in special cases like LMC, Cen A, HDFS) Initially, only two triggers will be requested. Sample includes all nearby active stars capable of producing stellar superflares. 4. Coordinates: 4.1. Rough RA and DEC (e.g., 30 sources in Taurus, 30 in Oph, 20 in Cha, 30 in Lupus) Indicate if there is significant clustering in a particular RA/DEC range (e.g., if objects in one particular RA range take 90% of the time) distributed in RA and DEC 4.2. Moving target: yes/no (e.g. comet, planet, ...) no 4.3. Time critical: yes/no (e.g. SN, GRB, ...) yes, TOO 4.4. Scheduling constraints: (optional) need rapid response (<0.5 hour) to get on source and take data. 5. Spatial scales: 5.1. Angular resolution (arcsec): pt. src. 5.2. Range of spatial scales/FOV (arcsec): (optional: indicate whether single-field, small mosaic, wide-field mosaic...) 5.3. Required pointing accuracy: (arcsec) 1 6. Observational setup 6.1. Single dish total power data: no/beneficial/required no Observing modes for single dish total power: (e.g., nutator switch; frequency switch; position switch; on-the-fly mapping; and combinations of the above) 6.2. Stand-alone ACA: no/beneficial/required no 6.3. Cross-correlation of 7m ACA and 12m baseline-ALMA antennas: no/beneficial/required no 6.4. Subarrays of 12m baseline-ALMA antennas: yes/no no 7. Frequencies: 7.1. Receiver band: Band 3, 4, 5, 6, 7, 8, or 9 3 7.2. Lines and Frequencies (GHz): (approximate; do _not_ go into detail of correlator set-up but indicate whether multi-line or single line; apply redshift correction yourself; for multi-line observations in a single band requiring different frequency settings, indicate e.g. "3 frequency settings in Band 7" without specifying each frequency (or give dummies: 340., 350., 360. GHz). For projects of high-z sources with a range of redshifts, specify, e.g., "6 frequency settings in Band 3". Apply redshift correction yourself.) 7.3. Spectral resolution (km/s): n/a 7.4. Bandwidth or spectral coverage (km/s or GHz): few GHz 8. Continuum flux density: 8.1. Typical value (Jy): Based on extrapolations from SXR-microwave relations for active stars (Guedel & Benz 1993 ApJ 405, L63) we expect cm-wavelength fluxes to be several hundred mJy. Extrapolating to mm wavelengths with spectral index of -3, expected for a very soft electron distribution (and thus somewhat pessimistic, as solar flares and the nonthermal hard X-ray detection of a stellar flare indicate harder distributions), leads to expected flux densities of ~100 microJy or larger. More optimistic values assume alpha=-1.3, with extrapolated flux then ~5 mJy. (take average value of set of objects) (optional: provide range of fluxes for set of objects) 8.2. Required continuum rms (Jy or K): For the numbers given above, a detection can be achieved at the > 5$sigma$ level with 20 microJy rms. 8.3. Dynamic range within image: (from 7.1 and 7.2, but also indicate whether, e.g., weak objects next to bright objects) >5 8.4. Calibration requirements: absolute ( 10% ) repeatability ( 5% ) relative ( 1-3% ) 9. Line intensity: 9.1. Typical value (K or Jy): (take average value of set of objects) (optional: provide range of values for set of objects) 9.2. Required rms per channel (K or Jy): 9.3. Spectral dynamic range: 9.4. Calibration requirements: absolute ( 1-3% / 5% / 10% / n/a ) repeatability ( 1-3% / 5% / 10% / n/a ) relative ( 1-3% / 5% / 10% / n/a ) 10. Polarization: yes/no (optional) yes 10.1. Required Stokes parameters: I,V 10.2. Total polarized flux density (Jy): unknown, likely small (<10% Stokes I). Circular polarization at cm wavelengths in stellar flares is typically less than what is seen during quiescence, and we assume the same behavior here. 10.3. Required polarization rms and/or dynamic range: Unless polarization is larger than V/I =10% (or flare is brighter than minimum predicted flux), this will not be feasible within the 1 hour time frame. For 1 sigma rms similar to Stokes I, V/I can be constrained to <60% (3 sigma) for the pessimistic case, or <1\% for the more optimistic case. 10.4. Polarization fidelity: don't expect any linear polarization, but polarization leakage should be small. 10.5. Required calibration accuracy: 11. Integration time for each observing mode/receiver setting (hr): Follow the source for an hour. Detection can be achieved in about 5 minutes (or less, for the more optimistic scenario), allowing for a study of temporal change in spectral index. This timescale is not set by ALMA's sensitivity constraints, but rather by the intrinsic properties of stellar flares. The activation phase of the flare, when particle acceleration is most important, can last for tens of minutes. 12. Total integration time for program (hr): Two triggers, one hour each trigger, total=2 hr 13. Comments on observing strategy : (optional) Target of Opportunity proposal, requiring rapid turn-around time. (e.g. line surveys, Target of Opportunity, Sun, ...): -------------------------------------------------- Review v2.0: 1. Name of program and authors TOO Observations of Energetic Particles in Stellar Superflares R. A. Osten S. Drake DRSP2.0 Review Leonardo Testi: Interesting Rapid Response ToO. Only one frequency required? May be feasible to sacrify some sensitivity in favour of simultaneous multifrequency observations. e.g. 2 subarrays of 25 antennas observing at 100 and 140 (bands 3 and 4) could achieve ~0.05mJy rms in 5 minutes. If sources are bright enough, otherwise it may require coordination with longer wavelength facility (I assume that the radio spectral index is an interesting quantity here). Reply: Yes, spectral index is an interesting quantity. I assumed, but did not state explicitly, that coordination with cm-wave facility would describe emission at lower frequencies. We have such a TOO program at the VLA now. Splitting the ALMA observations into two subarrays is interesting, but will depend on the sources being bright. While large radio flares from active stars have produced significant (>100 mJy) flux at mm wavelengths, it is unknown at this point what the response in the mm region would be from a superflare diagnosed from X-ray observations. Based on the L_X/L_R relation (Gudel & Benz 1993 ApJ 405, L63) we expect that there would be large enhancements. For now, we will leave the proposal as having coordination with cm-wave facilities to provide the spectral index constraints, but a future proposal might want to pursue the sub-array capabilities of ALMA for spectral index measurement, based on experience with high-frequency stellar flare behavior.