----- Attempting Submission 1 (Fri May 11 17:58:24 GMT 2007) ----- Resubmission of ACS proposal #629. Assigned ID: 1300 ----- Attempting Submission 1 (Fri Feb 09 18:03:29 GMT 2007) ----- The nature of radio transients We have conducted the first ever blind, wide-field survey for radio transients (Levinson et al. 2002; Gal-Yam et al. 2006). We have discovered four radio transients and explored their nature using radio and optical follow-up observations. One is a known pulsar, one is a z~0.1 AGN, and one is most probably an optically obscured radio supernova (SN) in the nearby galaxy NGC 4216 (the first such event to be discovered by a wide field radio survey). The last source appears not to be associated with a bright host galaxy (to a limit of R < 24.5 mag). We request 4 orbits of WFPC2 F606W imaging to check whether we can establish an association between this radio transient and any of three nearby faint resolved galaxies we have detected from the ground. If the source is associated with any of these galaxies it would represent a new type of extra-galactic radio bursts, more luminous than, e.g., radio afterglows of gamma-ray bursts. Alternatively, ruling out an association with these galaxies would disfavor an extra-galactic nature of this object, and suggest instead that this is a radio outburst of a faint Galactic compact object, probably a new type of radio-flaring neutron star. If this is the case, the high luminosity (9 mJy) and relatively high galactic latitude (33 degrees) of this source may indicate it is relatively nearby. This single source represents a large population (comparable in sky density to AGN, pulsars, and radio SNe) and thus merits intensive study. A modest investment of HST time, leveraged by massive ground-based radio and optical efforts, will allow us to identify a new class of radio sources, and complete a census of the variable radio sky down to ~6 mJy, leaving no unidentifed objects. This result can be directly scaled to predict the number and type of transient sources expected to be detected by future surveys with the next generation radio arrays, such as ATA and SKA.Since our science critically requires HST's spatial resolution (rather than sensitivity) it is perfectly suited to be carried out with WFPC2.
We will image the location of the unidentified radio transient RTC9 to look for optical counterparts and examine its association with putative nearby host galaxies. AGN/QUASARS 12 false 0.0 false false false false false false SUPPORTED UNIDENTIFIED RADIO EMITTER J2000 17 20 59.9000 +38 52 27.00 J2000 WFPC2 Imaging No F606W /tmp/OPVisit52811.xml Single visit in this proposal (Tic-Visit :proposal-id 11104 :visit-id "01" :proposal-version -1 :trans-version "20070325" :date "11-May-2007 10:52:59.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 358528 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11104 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11104 :visit-id "01" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2720 :al-overhead-at-end 160 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3159 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11104 :visit-id "01" :orbit-number 2 :pcs-time 355 :si-vis-utilization 2722 :al-overhead-at-end 158 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3159 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11104 :visit-id "01" :orbit-number 3 :pcs-time 355 :si-vis-utilization 2722 :al-overhead-at-end 158 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3159 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11104 :visit-id "01" :orbit-number 4 :pcs-time 355 :si-vis-utilization 2700 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3159 :pcs-gap 0 ) true 4 0