IBEX Time Series Data ===================== The files in these directories are readable representations of a compact binary format which encodes the details of the various IBEX event types. The "meta event" includes both direct events, which is the appearance of a single ENA detection and histogram bins, which are collections of such events over some well-defined part of the sky within some period of time. Common to all meta events is the a timestamp (MET) which derived from the s/c clock which is set to the number of seconds in the GPS epoch near the perigee of each orbit. (The GPS epoch starts at Sat->Sun midnight on Jan 6, 1980 when the Global Positioning System was activated.) The IBEX clock is not well regulated, so the correlation with the times on other s/c or the ground is not likely to be better than a few minutes. For a DE, this time is the arrival time of the event. For a HB or the BM, it is the start of the interval over which the events were collected. Note that during this time, the electrostatic analyzer (ESA) sweeps through several energy steps (6 for Hi, 8 for Lo). The celestial source (assuming a straight line-trajectory from the HS) of a single direct event (DE) or histogram bin (HB) is given as R.A. and Decl. in the J2000 celestial coordiate system. Obviously the trajectory is not a straight-line, so these are really statements about arrival direction, bearing in mind that the collimator FWHM is about 14 degrees and the event timing limits accuracy to 0.1 deg or so. For the case of histogram bins, this is the center of a 6-deg sky bin. The "ch" and "ty" columns provide more detailed information about the type of event represented on each line. More detail on this is given below. The "count" column is 1 for a DE; for the HB and background monitor (BM), it is the approximate number of counts. (The telemetry system uses a compression scheme.) The "selnbits" column is not used in this release. The "phase" column expresses the arrival time of the event (or center of a sky bin) expressed as the fraction of a spin between spin pulses. The spin pulse is triggered 3 deg before IBEX-Hi is pointed at the North Ecliptic Pole (NEP) and IBEX-Lo is pointed at the South Ecliptic Pole (SEP). Thus the NEP is phase = 0.0083 in IBEX-Hi and 0.5083 for IBEX-Lo. (The R.A. and Decl values are derived from this together with the detailed s/c attitude information.) The "loc-?-RE" columns record the position of IBEX relative to the Earth in Earth Radii in the same J2000 inertial reference frame as R.A. and Decl. The events are segregated by type and ESA for these files, so the "ch" and "ty" columns are largely redundant with the file names. However, since you're probably curious these are hexadecimal (base 16) bytes constructed from upper and lower nibbles (4-bits) as: ch = SPECIES | ESA ty = SENSOR_TYPE | COINCIDENCE_TYPE where for HiDE SPECIES: 10 (almost certainly H) ESA: 1,2,3,4,5, or 6 SENSOR_TYPE: 00 COINCIDENCE_TYPE: one of 16 coincidence types, see table below. LoDE SPECIES: 20,40 for H,O ESA: 1,2,3,4,5,6,7, or 8 SENSOR_TYPE: 40 COINCIDENCE_TYPE: one of 16 absent types, see table below HiHB SPECIES: 10 (almost certainly H) ESA: 1,2,3,4,5, or 6 SENSOR_TYPE: 10 COINCIDENCE_TYPE: groups of the coincidence type, see table below LoHB SPECIES: 20,40 for H,O ESA: 1,2,3,4,5,6,7, or 8 SENSOR_TYPE: 80 for 6-deg histograms, C0 for 60-deg monitors COINCIDENCE_TYPE: see table below BM ch is always 0F ty is always 1F Note that calibrations only exist for the collective groupings of the events in each file so that knowing the details of the types is probably not useful at this time. IBEX Hi Event types and histograms ---------------------------------- There are 16 IBEX-Hi direct event coincidence types. These are grouped into 8 groups for histogram purposes as shown in the following table. coincidence names histograms Hex type oct binary abcABC LongH QualH --- ---- --- ------ ------ ----- ----- 0A 10 047 100111 a--ABC L-ABC Q-ABC 05 5 027 010111 -b-ABC L-ABC Q-ABC 0E 14 067 110111 ab-ABC L-ABC Q-ABC 0C 12 057 101111 a-cABC L-ABC - 0F 15 077 111111 abcABC L-ABC - 07 7 037 011111 -bcABC L-ABC - 02 2 017 001111 --cABC L-ABC - --- ---- --- ------ ------ ----- ----- 09 9 046 100110 a--AB- L-AB Q-AB 0D 13 066 110110 ab-AB- L-AB Q-AB 04 4 026 010110 -b-AB- L-AB Q-AB --- ---- --- ------ ------ ----- ----- 03 3 023 010011 -b--BC L-BC Q-BC 06 6 033 011011 -bc-BC L-BC - 00 0 013 001011 --c-BC L-BC - --- ---- --- ------ ------ ----- ----- 08 8 045 100101 a--A-C L-AC Q-AC 0B 11 055 101101 a-cA-C L-AC - 01 1 015 001101 --cA-C L-AC - --- ---- --- ------ ------ ----- ----- Events are named according to the bits present at the end of the short and long windows. The binary and abcABC are both in use; the type numbers are the order of the events expressed in octal (base 8), but appear in Hex in the event listings. Here: abc the ABC pulses latched after the short window (3 bits) ABC the ABC pulses latched after the long window (3 bits) L-??? Long count coincidence histogram group (named after the set of CEMs bits present at the end of the long window, and independent of the bits present at the end of the short window)) Q-??? Qualified count coincidence histogram group (named after the set of CEMs bits present at the end of the long window) The Hex (meta-event) representations for the histogram types are Hex Hist --- ----- 10 Q-ABC 11 Q-AB 12 Q-BC 13 Q-AC 14 L-ABC 15 L-AB 16 L-BC 17 L-AC IBEX Lo Direct Events Classified by Absent Bits ----------------------------------------------- There are 16 IBEX-Lo direct event coincidence types. They are classified based on whether the corresponding time-of-flight (TOF) measurement between the start/stop points in the detector are valid. There are 4 such points: a is a start, b0 and b3 are stops, and c is an intermediate surface where both stops and starts may be generated. +------ TOF0 not absent => a & b0 present & TOF valid |+----- TOF1 not absent => b3 & c present & TOF valid ||+---- TOF2 not absent => a & c present & TOF valid |||+--- TOF3 not absent => b0 & b3 present & TOF valid |||| Hex 0123 --- ---- 40 0000 $ Triple (=> a,b0,b3,c; golden/allvalid) 41 0001 - Triple (=> a,b0,b3,c; TOF3 invalid) 42 0010 - Triple (=> a,b0,b3,c; TOF2 invalid) 43 0011 - Triple (=> a,b0,b3,c; TOF2 & TOF3 invalid) 44 0100 - Triple (=> a,b0,b3,c; TOF1 invalid) 45 0101 . Triple (=> a,b0, c; TOF1 & TOF3 invalid) 46 0110 $ Double (=> a,b0,b3 ; TOF1 & TOF2 invalid) 47 0111 . Double (=> a,b0 ; only TOF0 valid) 48 1000 - Triple (=> a,b0,b3,c; TOF0 invalid) 49 1001 . Triple (=> a, b3,c; TOF0 & TOF3 invalid) 4A 1010 + Double (=> b0,b3,c; TOF0 & TOF2 invalid) 4B 1011 . Double (=> b3,c; only TOF1 valid) 4C 1100 - Triple (=> a,b0,b3,c; TOF0 & TOF1 invalid) 4D 1101 $ Double (=> a, c; only TOF2 valid) 4E 1110 x Single (=> b0,b3 ; only TOF3 valid) 4F 1111 x Absent (=> ; nothing valid) - == not likely, but still physical . == one of b0 or b3 missing, not likely but still physical x == useless events $ == the most likely possibilities The 4F type is not possible (and indeed the 4F type is reserved for future use); the 4E type is a common single which is not included in the telemetry stream. The absent class is or-ed with 0x40 to make a unique event type in the meta-event classification scheme. When a species classification can be made onboard, histograms of hydrogen and oxygen are constructed from the golden triples (0000) events.