# Copyright (c) 2016 Weitian LI # MIT license """ Galactic supernova remnants (SNRs) emission simulations. """ import os import logging from datetime import datetime, timezone import numpy as np from astropy.io import fits import astropy.units as au import healpy as hp import pandas as pd from ..utils import write_fits_healpix from ..utils.convert import Fnu_to_Tb from ..utils.grid import make_grid_ellipse, map_grid_to_healpix logger = logging.getLogger(__name__) class SuperNovaRemnants: """ Simulate the Galactic supernova remnants emission. The simulation is based on the Galactic SNRs catalog maintained by *D. A. Green* [GreenSNRDataWeb]_, which contains 294 SNRs (2014-May). However, some SNRs have incomplete data which are excluded, while some SNRs with uncertain properties are currently kept. Every SNR is simulated as an *ellipse* of *uniform brightness* on a local coordinate grid with relatively higher resolution compared to the output HEALPix map, which is then mapped to the output HEALPix map by down-sampling. Parameters ---------- configs : ConfigManager object An `ConfigManager` object contains default and user configurations. For more details, see the example config specification. Attributes ---------- ??? References ---------- .. [Green2014] Green, D. A., "A catalogue of 294 Galactic supernova remnants", 2014, Bulletin of the Astronomical Society of India, 42, 47-58, http://adsabs.harvard.edu/abs/2014BASI...42...47G .. [GreenSNRDataWeb] A Catalogue of Galactic Supernova Remnants http://www.mrao.cam.ac.uk/surveys/snrs/ """ def __init__(self, configs): self.configs = configs self._set_configs() self._load_catalog() def _set_configs(self): """Load the configs and set the corresponding class attributes.""" comp = "galactic/snr" self.catalog_path = self.configs.get_path(comp+"/catalog") self.catalog_outfile = self.configs.get_path(comp+"/catalog_outfile") self.resolution = self.configs.getn(comp+"/resolution") * au.arcmin self.prefix = self.configs.getn(comp+"/prefix") self.save = self.configs.getn(comp+"/save") self.output_dir = self.configs.get_path(comp+"/output_dir") # self.filename_pattern = self.configs.getn("output/filename_pattern") self.use_float = self.configs.getn("output/use_float") self.clobber = self.configs.getn("output/clobber") self.nside = self.configs.getn("common/nside") self.freq_unit = au.Unit(self.configs.getn("frequency/unit")) # logger.info("Loaded and set up configurations") def _load_catalog(self): """Load the Galactic SNRs catalog data.""" self.catalog = pd.read_csv(self.catalog_path) nrow, ncol = self.catalog.shape logger.info("Loaded SNRs catalog data from: {0}".format( self.catalog_path)) logger.info("SNRs catalog data: {0} objects, {1} columns".format( nrow, ncol)) # Set the units for columns self.units = { "glon": au.deg, "glat": au.deg, "size": au.arcmin, "flux": au.Jy, } # The flux densities are given at 1 GHz self.catalog_flux_freq = 1.0 * au.GHz def _save_catalog_inuse(self): """Save the effective/inuse SNRs catalog data to a CSV file. NOTE ---- - Only the effective/inuse SNRs are saved (i.e., without the ones that are filtered out). - Also save the simulated rotation column. - The unnecessary columns are striped. """ if self.catalog_outfile is None: logger.warning("Catalog output file not set, so do NOT save.") return # Save catalog data colnames = ["name", "glon", "glat", "ra", "dec", "size_major", "size_minor", "flux", "specindex", "rotation"] self.catalog.to_csv(self.catalog_outfile, columns=colnames, header=True, index=False) logger.info("Save SNRs catalog in use to: %s" % self.catalog_outfile) def _filter_catalog(self): """Filter the catalog data to remove the objects with incomplete data. The following cases are filtered out: - Missing angular size - Missing flux density data - Missing spectral index value NOTE ---- The objects with uncertain data are currently kept. """ if hasattr(self, "catalog_filtered") and self.catalog_filtered: return # cond1 = pd.isnull(self.catalog["size_major"]) cond2 = pd.isnull(self.catalog["size_minor"]) cond3 = pd.isnull(self.catalog["flux"]) cond4 = pd.isnull(self.catalog["specindex"]) cond_keep = ~(cond1 | cond2 | cond3 | cond4) n_total = len(cond_keep) n_remain = cond_keep.sum() n_delete = n_total - n_remain n_delete_p = n_delete / n_total * 100 self.catalog = self.catalog[cond_keep] # Drop the index self.catalog.reset_index(drop=True, inplace=True) self.catalog_filtered = True logger.info("SNRs catalog: filtered out " + "{0:d} ({1:.1f}%) objects".format(n_delete, n_delete_p)) logger.info("SNRs catalog: remaining {0} objects".format(n_remain)) def _add_random_rotation(self): """Add random rotation angles for each SNR as column "rotation" within the `catalog` data frame. The rotation angles are uniformly distributed within [0, 360). The rotation happens on the spherical surface, i.e., not with respect to the line of sight, but to the Galactic frame coordinate axes. """ if "rotation" in self.catalog.columns: return # num = len(self.catalog) angles = np.random.uniform(low=0.0, high=360.0, size=num) rotation = pd.Series(data=angles, name="rotation") self.catalog["rotation"] = rotation self.units["rotation"] = au.deg logger.info("Added random rotation angles as the 'rotation' column") def _calc_Tb(self, flux, specindex, frequency, size): """Calculate the brightness temperature at requested frequency by assuming a power-law spectral shape. Parameters ---------- flux : float The flux density (unit: `self.units["flux"]`) at the reference frequency (i.e., `self.catalog_flux_freq`). specindex : float The spectral index of the power-law spectrum frequency : float The frequency (unit: `self.freq_unit`) where the brightness temperature requested. size : 2-float tuple The (major, minor) axes of the SNR (unit: `self.units["size"]`). The order of major and minor can be arbitrary. Returns ------- Tb : float Brightness temperature at the requested frequency, unit [ K ] NOTE ---- The power-law spectral shape is assumed for *flux density* other than the *brightness temperature*. Therefore, the flux density at the requested frequency should first be calculated by extrapolating the spectrum, then convert the flux density to derive the brightness temperature. """ freq = frequency * self.freq_unit flux = flux * self.units["flux"] Fnu = flux * (freq / self.catalog_flux_freq).value ** (-specindex) omega = size[0]*self.units["size"] * size[1]*self.units["size"] Tb = Fnu_to_Tb(Fnu, omega, freq) return Tb.value def _simulate_templates(self): """Simulate the template (HEALPix) images for each SNR, and cache these templates within the class. The template images/maps have values of (or approximate) ones for these effective pixels, excluding the pixels corresponding to the edges of original rotated ellipse, which may have values of significantly less than 1 due to the rotation. Therefore, simulating the HEALPix map of one SNR at a requested frequency is simply multiplying the cached template image by the calculated brightness temperature (Tb) at that frequency. Furthermore, the total HEALPix map of all SNRs are straightforward additions of all the maps of each SNR. Attributes ---------- templates : dict A dictionary containing the simulated templates for each SNR. The dictionary keys are the names (`self.catalog["name"]`) of the SNRs, and the values are `(hpidx, hpval)` tuples with `hpidx` the indexes of effective HEALPix pixels (RING ordering) and `hpval` the values of the corresponding pixels. e.g., ``{ name1: (hpidx1, hpval1), name2: (hpidx2, hpval2), ... }`` """ templates = {} resolution = self.resolution.to(au.deg).value for row in self.catalog.itertuples(): name = row.name logger.info("Simulate HEALPix template for SNR: {0}".format(name)) center = (row.glon, row.glat) size = ((row.size_major * self.units["size"]).to(au.deg).value, (row.size_minor * self.units["size"]).to(au.deg).value) rotation = row.rotation grid = make_grid_ellipse(center, size, resolution, rotation) hpidx, hpval = map_grid_to_healpix(grid, self.nside) templates[name] = (hpidx, hpval) logger.info("Done simulate {0} SNR templates".format(len(templates))) self.templates = templates def _simulate_single(self, data, frequency): """Simulate one single SNR at the specified frequency. Parameters ---------- data : namedtuple The data of the SNR to be simulated, given in a `namedtuple` object, from which can get the required properties by `data.key`. e.g., elements of `self.catalog.itertuples()` frequency : float The simulation frequency (unit: `self.freq_unit`). Returns ------- hpidx : 1D `~numpy.ndarray` The indexes (in RING ordering) of the effective HEALPix pixels for the SNR. hpval : 1D `~numpy.ndarray` The values (i.e., brightness temperature) of each HEALPix pixel with respect the above indexes. See Also -------- `self._simulate_template()` for more detailed description. """ if not hasattr(self, "templates"): self._simulate_templates() # name = data.name hpidx, hpval = self.templates[name] # Calculate the brightness temperature flux = data.flux specindex = data.specindex size = (data.size_major, data.size_minor) Tb = self._calc_Tb(flux, specindex, frequency, size) # Multiply the brightness temperature to the template map hpval = hpval * Tb return (hpidx, hpval) def _simulate_frequency(self, frequency): """Simulate the emission (HEALPix) map of all Galactic SNRs at the specified frequency. Parameters ---------- frequency : float The simulation frequency (unit: `self.freq_unit`). Returns ------- hpmap_f : 1D `~numpy.ndarray` HEALPix map data in RING ordering See Also -------- `self._simulate_template()` for more detailed description. """ # Filter the catalog first self._filter_catalog() # Assign a random rotation angle for each SNR self._add_random_rotation() # hpmap_f = np.zeros(hp.nside2npix(self.nside)) for row in self.catalog.itertuples(): hpidx, hpval = self._simulate_single(row, frequency) hpmap_f[hpidx] += hpval return hpmap_f def simulate(self, frequencies): """Simulate the emission (HEALPix) maps of all Galactic SNRs for every specified frequency. Parameters ---------- frequency : list[float] List of frequencies (unit: `self.freq_unit`) where the simulation performed. Returns ------- hpmaps : list[1D `~numpy.ndarray`] List of HEALPix maps (in RING ordering) at each frequency. """ hpmaps = [] for f in np.array(frequencies, ndmin=1): logger.info("Simulating Galactic SNRs emission map " "at {0} ({1}) ...".format(f, self.freq_unit)) hpmap_f = self._simulate_frequency(f) hpmaps.append(hpmap_f) if self.save: self.output(hpmap_f, f) # Also save the catalog in use. self._save_catalog_inuse() return hpmaps def _make_filepath(self, **kwargs): """Make the path of output file according to the filename pattern and output directory loaded from configurations. """ data = { "prefix": self.prefix, } data.update(kwargs) filename = self.filename_pattern.format(**data) filetype = self.configs.getn("output/filetype") if filetype == "fits": filename += ".fits" else: raise NotImplementedError("unsupported filetype: %s" % filetype) filepath = os.path.join(self.output_dir, filename) return filepath def _make_header(self): """Make the header with detail information (e.g., parameters and history) for the simulated products. """ header = fits.Header() header["COMP"] = ("Galactic supernova remnants (SNRs)", "Emission component") header["UNIT"] = ("Kelvin", "Map unit") header["CREATOR"] = (__name__, "File creator") # TODO: history = [] comments = [] for hist in history: header.add_history(hist) for cmt in comments: header.add_comment(cmt) self.header = header logger.info("Created FITS header") def output(self, hpmap, frequency): """Write the simulated free-free map to disk with proper header keywords and history. """ if not os.path.exists(self.output_dir): os.mkdir(self.output_dir) logger.info("Created output dir: {0}".format(self.output_dir)) # filepath = self._make_filepath(frequency=frequency) if not hasattr(self, "header"): self._make_header() header = self.header.copy() header["FREQ"] = (frequency, "Frequency [ MHz ]") header["DATE"] = ( datetime.now(timezone.utc).astimezone().isoformat(), "File creation date" ) if self.use_float: hpmap = hpmap.astype(np.float32) write_fits_healpix(filepath, hpmap, header=header, clobber=self.clobber) logger.info("Write simulated map to file: {0}".format(filepath))