One solar cycle of heliosphere observations with IBEX-Lo
André Galli (University of Bern)
The Interstellar Boundary Explorer (IBEX) is a NASA satellite in Earth orbit, dedicated to observing both interstellar neutral atoms entering the heliosphere and energetic neutral atoms (ENAs) from the interstellar boundaries from roughly 10 eV to 6 keV. This work presents the averaged maps, energy spectra, and temporal variability of heliospheric ENA intensities measured with the IBEX-Lo instrument at 1 au at energies between 10 eV and 2 keV, covering one entire solar cycle from 2009 through 2019. These results expand the range in time and energy for studying the globally distributed ENA flux and the IBEX Ribbon. The observed ENA intensities exceed model predictions, in particular below 500 eV. Moreover, the ENA intensities between 50–200 eV energy show an unexpected rise and fall around the year 2015 in most sky regions.
To download the entire data release as a zip file click the link above. To learn more about the structure and content of the files contained within the release, a detailed description follows. For questions about this or any other release, please email [email protected].
A detailed description and initial analysis of these maps is presented in Galli et al. 2022 (ApJS). Click here to access the paper.
Data Directory Structure and Naming Conventions
The data in this release are separated into one-year segments. The annual allsky maps represent the following IBEX orbits and dates:
|Year||Skymap Name||Start-End Orbits or Arcs||Dates|
|1||Map2009||11-58 (excluding 32 - 48)||12/25/2008 – 12/25/2009|
|2||Map2010||59-106 (excluding 62, 81 - 101)||12/25/2009 – 12/26/2010|
|3||Map2011||107-150a (excluding 110 - 114, 128 - 144)||12/26/2010 – 12/24/2011|
|4||Map2012||150b-190b (excluding 150b - 155, 170 - 182)||12/24/2011 – 12/26/2012|
|5||Map2013||191a-230b (excluding 207, 210 - 222)||12/26/2012 – 12/26/2013|
|6||Map2014||231a-270b (excluding 250 - 261)||12/26/2013 – 12/24/2014|
|7||Map2015||271a-310b (excluding 289 - 300, 303, 304)||12/24/2014 – 12/23/2015|
|8||Map2016||311a-351a (excluding 316 - 317, 323, 329 - 339)||12/24/2015 – 12/26/2016|
|9||Map2017||351b-391a (excluding 368 - 380, 390)||12/26/2016 – 12/25/2017|
|10||Map2018||391b-431b (excluding 405, 408 - 418)||12/25/2017 – 12/26/2018|
|11||Map2019||432a-471b (excluding 441, 446, 448 - 460)||12/27/2018 – 12/26/2019|
Some orbits are excluded due to Super Good Times criteria (see the paper for more details).
Map directories are named using keywords that indicate the type of data they contain:
- antiram - data were collected when the spacecraft was moving away from the incoming ENAs.
- cg - Compton-Getting corrections have been applied to transform the ENA intensities from the spacecraft reference frame to the solar inertial reference frame.
- noSP - no survival probability corrections have been applied to the data.
- ram - data were collected when the spacecraft was ramming into the incoming ENAs.
- tabular - survival probability corrections have been applied to the ENA intensities to account for the loss of ENAs due to account due to radiation pressure, photoionization and ionization via charge exchange with solar wind protons as they stream through the heliosphere. This correction scales the ENA intensities from the IBEX heliocentric distance at 1 AU out to ~100 AU.
- yyyy - identifies a particular set of orbits spanning year yyyy.
Data and map files are named using additional keywords that indicate the type of data they contain:
- cnts - total counts data
- desc - description of processing details
- ener - energies data
- fexp - total time exposure data
- ffsn - flux exceeding S/N threshold
- flux - flux data
- fraw - raw orbit data
- fsnr - signal/noise (S/N) data
- fvar - flux variances
- hstransport-chan-0n-surv - survival probability for nth IBEX-Lo energy bin
- lo-n - data from the nth IBEX-Lo energy bin
- lohb - IBEX Lo histogram events
- numb - samples per pixel
- trp - triple coincidence
The first number in the first line of each data file gives the number of lines taken up by the header followed by the number of rows times the number of columns in the data (i.e. 30x60 indicates 30 rows of declination by 60 columns of right ascension values). Row 1 corresponds to the South Ecliptic Pole, while row 30 corresponds to the North Ecliptic Pole. The columns start at ecliptic longitude 0 and step through to ecliptic longitude 360; the values of the first and last columns in each map are identical. The layout of the columns corresponds to Solar Ecliptic East Longitude, right to left as seen outward by IBEX. The keyword “h_title” gives the description of the data and the units used.
Calculation Notes for Users to Combine Multiple Maps:
Combining different maps can be done by accounting for the statistical uncertainties and time exposure weighting. This approach works well if the ENA intensities do not vary with time. Below is an example of combining three different maps in this manner.
ENA Exposure times for the three ENA maps: tau1, tau2, tau3;
ENA fluxes for the three ENA maps: flux1, flux2, flux3;
ENA flux variances for the three ENA maps: var1, var2, var3;
We now calculate the weights from the exposure times as,
Combined fluxes and propagated variances are then determined using:
combined_flux=flux1*wt1 + flux2*wt2 + flux3*wt3
combined_var=var1*(wt1)^2 + var2*(wt2)^2 + var3*(wt3)^2
If there is real variation with time, the above approach will bias the average to those years where there is more measurement time. This seems to be the case if the evolution over all 11 years, in particular at medium energies, is examined. For the 11-year average maps in the paper, unweighted means were calculated and only individual pixels with insufficient coverage or with an anomalously high variability or with an anomalously low exposure weight were excluded.