III. NEOWISE Single-exposure Images

III.2. Cautionary Notes

III.2.c. Image Anomalies and Features

III.2.c.ii. The Resonant Pixel in W2 (4.6 micron) Data

III.2.c.ii.1. Introduction

On rare occasions, WISE data exhibit an interesting phenomenon whose nature is unknown. A large annulus of W2 pixels, centered roughly on the pixel at coordinates [912,568] (0-indexed, as in IDL) and hereafter referred to as the "resonant pixel," appears then subsequently decays in later frames. This halo is usually preceded by a dramatic elevation of signal, colloquially referred to as a "TV test pattern" (also of unknown origin), that appears in both W1 and W2. The phenomenon is often accompanied by a W1 latent at approximately the same row as the W2 resonant pixel halo, but on the left side of the array. This W1 latent is generally present in strong instances of the W2 phenomenon.

The following figures illustrate, in chronological order, the forty-two recorded instances of this W2 resonant pixel phenomenon. In all figures, each row represents a simultaneously taken set of frames that, from left to right, represent W1, W2, W3, W4, and a three-color image formed using the W1+W2(+W3+W4) frames. The frame number in the scan is shown to the far left. Icons with open white squares or question marks indicate missing bands of data. For example, data taken during the NEOWISE Reactivation period lack W3 and W4 data.

The first instance of the resonant pixel phenomenon occurred during the WISE 4-band cryogenic period (Figure 1), followed by one instance in the WISE 3-band cryogenic period (Figure 2), three instances during the WISE post-cryogenic period (Figures 3-5), and thirty-seven instances so far during NEOWISE reactivation (Figures 6-18x).

Figure 1 - Scan 06405b, framesets 218-224. Frameset 218, which failed to complete processing and therefore has no color-composite image, shows elevated backgrounds in all four observed bands, which led to most pixels being NaN'ed in W1, W2, and W3. The following framesets, 219-224, show the resonant pixel halo in W2 (second image from the left in each row).

Figure 2 - Scan 07949b, framesets 230-231. Frameset 230, which failed to complete processing and therefore has no color-composite image, shows elevated backgrounds in all three observed bands. The following frameset, 231, shows the resonant pixel halo in W2 (second row, second image from the left).

Figure 3 - Scan 10897b, framesets 118-124. Frameset 118 shows elevated backgrounds that led to most of its pixels being NaN'ed. The arrays exhibit evidence of the "TV test pattern," where rectangular blocks (horizontal in W1 and vertical in W2, orthogonal in each case to the read-out channels) show elevated signal; in this case, at the top edge of W1 and on the left edge of W2. Frameset 119 shows the W2 resonant pixel halo, which decays throughout framesets 120-124.

Figure 4 - Scan 11984a, framesets 146-154. Frameset 146 appears normal. Frameset 147 shows elevated backgrounds but fails in processing and is not illustrated here. Framesets 148-154 show the appearance and decay of the W2 resonant pixel halo.

Figure 5 - Scan 12125b, framesets 146-153. Frameset 146 appears normal. Frameset 148 has elevated backgrounds and an unusual illumination pattern. Framesets 149-153 show the appearance and decay of the W2 resonant pixel halo.

Figure 6 - Scan 48672a, framesets 105-109. Frameset 105 has high backgrounds and an unusual illumination pattern caused in part by saturation. This frameset also failed to complete processing, so its color-composite image is not available. Framesets 106-109 show the decay of the W2 resonant pixel halo.

Figure 7 - Scan 67842b, framesets 097-098. Frameset 097 exhibits a "TV test pattern". Frameset 098 shows a weak W2 resonant pixel halo.

Figure 8 - Scan 70877b, framesets 177-178. Frameset 177 exhibits a "TV test pattern," and frameset 178 shows a weak W2 resonant pixel halo.

Figure 9 - Scan 73648a, framesets 135-136. Like Figures 7 and 8 above, the first frameset shows a "TV test pattern" followed in the second frameset by a weak W2 resonant pixel halo.

Figure 10 - Scan 77064a, framesets 142-146. The first frameset shows a "TV test pattern" followed in subsequent framesets by a W2 resonant pixel halo.

Figure 11 - Scan 77978a, framesets 254-256. The first frameset shows a "TV test pattern" followed in subsequent framesets by a W2 resonant pixel halo.

Figure 12 - Scan 78569a, framesets 148-150. The first frameset shows a "TV test pattern" followed in subsequent framesets by a W2 resonant pixel halo.

Figure 13 - Scan 79980a, framesets 134-135. The first frameset shows a "TV test pattern" followed in subsequent framesets by a W2 resonant pixel halo.

Figure 14 - Scan 80992a, framesets 152-159. Frameset 153, where a "TV test pattern" would be seen, failed processing. It is followed in subsequent framesets by a W2 resonant pixel halo.

Figure 15 - Scan 81074a, framesets 225-227. The first frameset shows a "TV test pattern" followed in subsequent framesets by a W2 resonant pixel halo. The diffuse, double-lobed blue feature in frameset 226, coincidentally near the resonant pixel, is the galaxy IC 2574, also known as Coddington's Nebula.

Figure 16 - Scan 82157b, framesets 151-153. The first frameset shows a "TV test pattern" followed in subsequent framesets by a W2 resonant pixel halo.

Figure 17 - Scan 84826a, framesets 146-148. The first frameset shows a "TV test pattern" followed in subsequent framesets by a W2 resonant pixel halo.

Figure 18 - Scan 87990a, framesets 023-026. The first frameset shows a "TV test pattern" followed in subsequent framesets by a W2 resonant pixel halo.

Figure 18a - Scan 91539a, framesets 187-188. The first frameset shows a "TV test pattern" followed in the subsequent frameset by a W2 resonant pixel halo.

Figure 18b - Scan 93691a, framesets 014-015. The first frameset shows a "TV test pattern" followed in the subsequent frameset by a weak W2 resonant pixel halo. The latter can be seen more convincingly in Figure 18bb below.

Figure 18bb - Scan 93691a, frameset 015. The weak resonant pixel halo in Figure 18b is also shown here, in the W2 frame, after heavily stretching the image scale. The green box is centered at the coordinates of the halo.

Figure 18c - Scan 94036a, framesets 115-120. Frameset 115 has high backgrounds and an unusual illumination pattern caused in part by saturation. This frameset also failed to complete processing, so its color-composite image is not available. Framesets 116-120 show a W2 resonant pixel halo.

Figure 18d - Scan 94908a, framesets 038-039. The first frameset shows a "TV test pattern" followed in frameset 039 by a weak W2 resonant pixel halo. Frameset 039 also shows a curious small W2-only (red) feature, near the center. It resembles a latent, but no astrophysical object is found in preceding framesets. Its asymmetric shape also resembles that of an optical ghost.

Figure 18e - Scan 05442r, framesets 163-164. The first frameset shows a "TV test pattern" followed in the second frameset by a (very) weak W2 resonant pixel halo that is more obvious in a hard stretch of the FITS image.

Figure 18f - Scan 05932r, framesets 045-047. The first frameset shows a "TV test pattern" followed in the second frameset by a (very) weak W2 resonant pixel halo.

Figure 18g - Scan 10546r, framesets 142-150. In this sequence, frameset 143 (not shown) was completely saturated in both bands in what the raw images confirm was an unusually bright "TV test pattern" phenomenon. This frameset failed processing. Subsequent framesets 145-150 show a slowly decaying resonant pixel halo in W2.

Figure 18h - Scan 11960r, framesets 036-038. The first frameset shows a "TV test pattern" followed in the next two framesets by a decaying W2 resonant pixel halo.

Figure 18i - Scan 27520r, framesets 225-227. The first frameset shows a "TV test pattern" followed in the next two framesets by a decaying W2 resonant pixel halo. The TV test pattern is unusual in that the W2 frameset shows a vertical rectangular area of lower signal in the middle of the array, instead of at one of the edges.

Figure 18j - Scan 27578r, framesets 128-130. The first frameset shows a "TV test pattern" followed in the next frameset by a decaying W2 resonant pixel halo, which is no longer discernible in frameset 130.

Figure 18k - Scan 28226r, framesets 152-154. The first frameset shows a "TV test pattern" followed in the next two framesets by a decaying W2 resonant pixel halo.

Figure 18l - Scan 29492r, framesets 134-136. Frameset 134 has high backgrounds and an unusual illumination pattern caused in part by saturation. This frameset also failed to complete processing, so its color-composite image is not available. Framesets 135-136 show a W2 resonant pixel halo.

Figure 18m - Scan 33862r, framesets 139-142. The first frameset shows a "TV test pattern" followed in the next two framesets by a decaying W2 resonant pixel halo.

Figure 18n - Scan 37872r, framesets 052-056. The first frameset shows a "TV test pattern" followed in the next three framesets by a decaying W2 resonant pixel halo. The first frameset itself is unusual because it exhibits the W2 resonant pixel halo in the TV test pattern. The TV test pattern also lacks a sharp jump in the backgrounds but instead shows a generally smooth gradient in addition to the jump itself.

Figure 18na - Scan 37872r, frameset 052. Signal medians over columns and over rows are shown for the W1 (left panel) and W2 (right panel) arrays described in Figure 18n, above. The left panel shows that the median row signal in W1 (red line) drops gradually from the bottom of the array to the top, with a 15 DN jump partway through. The right panel shows that the median column signal in W2 (green line) rises gradually towards the right side of the array, with a 10 DN jump partway through.

Figure 18o - Scan 37942r, framesets 205-211. A very extreme "TV test pattern" was present in frameset 206, but the frameset is not shown because its almost total saturation caused it to fail processing. Glow patterns and a hint of the W2 resonant pixel halo are seen in framesets 207-211.

Figure 18p - Scan 39449r, framesets 065-067. The first frameset shows a "TV test pattern" followed in the next frameset by a decaying W2 resonant pixel halo, which is no longer visible in frameset 067.

Figure 18q - Scan 43962r, framesets 092-096. Frameset 093 shows a "TV test pattern" followed in the next frameset by a decaying W2 resonant pixel halo, which is no longer visible in frameset 096. Frameset 093 also shows at least three features which could be reflections from one or more out-of-focus nearby objects that passed through the field of view.

Figure 18r - Scan 44657r, framesets 183-188. The first frameset (183) shows a "TV test pattern" followed in the next four framesets by a decaying W2 resonant pixel halo. The second frameset (184) shows an unusual latent of the TV test pattern itself, in addition to the resonant pixel halo.

Figure 18s - Scan 50265r, framesets 146-147. The first frameset shows a "TV test pattern" followed in the subsequent frameset by a W2 resonant pixel halo.

Figure 18t - Scan 50396r, framesets 157-159. The first frameset shows a "TV test pattern" followed in the next two framesets by a decaying W2 resonant pixel halo. The TV test pattern lacks a sharp jump in the backgrounds but instead shows a generally smooth gradient in addition to the jump itself.

Figure 18u - Scan 51630r, framesets 226-233. Frameset 226 has high backgrounds and an unusual illumination pattern caused in part by saturation. This frameset also failed to complete processing, so its color-composite image is not available. Framesets 227-233 show the decay of the W2 resonant pixel halo.

Figure 18v - Scan 52920r, framesets 151-152. The first frameset shows a "TV test pattern" followed in the subsequent frameset by a W2 resonant pixel halo.

Figure 18w - Scan 53461r, framesets 214-215. The first frameset shows a "TV test pattern" followed in the subsequent frameset by a W2 resonant pixel halo.

Figure 18x - Scan 56724r, framesets 105-106. The first frameset shows a "TV test pattern" followed in the subsequent frameset by a W2 resonant pixel halo. A W1 counterpart of the resonant pixel halo in the form of a latent is also visible at approximately the same row as the W2 feature but on the left side of the array. The W1 latent is seen in other instances of the resonant pixel halo such as in Figures 3-6, 8, 10, 12, 14, 18, 18c, 18g, 18k, 18l, 18m, 18o, 18q, 18r, 18s, 18t, 18u, 18v, and 18w.

III.2.c.ii.2. Nature of Masked Pixels in the Center of the W2 Resonant Pixel Region

Figures 19 and 20 show 31×31 pixel cut-outs centered at the nominal resonant pixel, for each of the first framesets in Figures 1-10 that show the feature. The resonant pixel itself seems to have very low responsivity, but is also transient. Pixels in its vicinity are also transient, are excessively noisy, or have very low responsivity. Note that dead pixels have constant signal at the digital saturation level. The figures show that the nominal resonant pixel itself is not unique but more likely is a member of a tight cluster of masked pixels. Color coding on the figures is explained in the legend below:

Table 1: Color Coding of Masked Pixels

Figure 19 - Zoom-ins centered at the resonant pixel feature from Figures 1-6. See Table 1 for an explanation of the color coding of masked pixels.

Figure 20 - Zoom-ins centered at the resonant pixel feature from Figures 7-10. See Table 1 for an explanation of the color coding of masked pixels.

III.2.c.ii.3. Relation between the Resonant Pixel and Longer-Duration Short-Term Latents

It has been observed that bright objects falling near the right edge of the W2 array tend to produce longer-lasting latents than bright objects falling elsewhere, as discussed in IV.4.g.iv.1.e. Figure 21 shows an example of this effect. The bright satellite trail in this figure leaves a W2 latent but only in the vicinity of the resonant pixel. Figure 21a shows a similar instance where a brighter satellite trail leaves W2 latents in the subsequent four framesets, but markedly brighter at the resonant pixel position. That the resonant pixel falls within this region, where bright stars and satellite trails leave more prominent latents than elsewhere in the array, suggests that the two effects may be related. This point is further illustrated in Figures 22 and 23, which are zoomed versions of satellite trails and of the resonant pixel, with 100-pixel-radius circles centered at the latter.

Figure 21 - Scan 77602a, frameset 063, exhibits a satellite trail that coincidentally crossed the W2 resonant pixel. The corresponding latent in the subsequent frameset, 064, is brightest in the region of the W2 resonant pixel.

Figure 21a - Scan 57227r, framesets 058-062. The bright satellite trail in frameset 058 leaves W2 latents in framesets 059-062. These latents are pronouncedly brighter at the position of the W2 resonant pixel, thus further suggesting that the latter is related to the phenomenon of longer-duration short-term latents in this region of the array.

Figure 22 - Zoomed illustration of four of the resonant pixels from Figures 1-10. The 100-pixel radius circles are centered on each instance of the resonant pixel.

Figure 23 - Zoomed illustration in W2 of two satellite trails that coincidentally crossed the resonant pixel. The left panel is from frameset 70774a164, and the right panel is 77602a063, also illustrated in Figure 21. The 100-pixel radius circles are centered on the resonant pixel, as in Figure 22.

III.2.c.ii.4. Correlation of Signal in the Resonant Pixel with Signal in the Precursor Frameset

We looked for a correlation between the intensity of the resonant pixel feature, and the signal in the illuminated frameset preceding it. To this end, we carried out aperture photometry with the ATV tool in IDL, centered at the nominal resonant pixel position, and using the radii for aperture and sky annuli illustrated in Figure 24. We separately calculated the centroid of the feature, via its first moment of inertia, and found out that it is reasonably constant, except for the faintest examples, due to noise.

Figure 24 - GUI for ATV photometry centered at the resonant pixel position, illustrated for frameset 148 in scan 11984a.

Table 2 lists our measurements for the first 22 instances of the resonant pixel. We obtained the mean signal of the illuminated frameset (the one that often shows a "TV test pattern"). For the framesets in Figures 9 and 16, we could not obtain reliable aperture photometry of the resonant pixel feature, because of its faintness. For the framesets in Figures 1, 2, 4, 6, 14, and 18c, there were no level-1b data available for the illuminated frameset, so we used level-1a data instead. In cases where a TV test pattern was discernible, we also measured the W2 signal jump between the elevated region and the rest of the array. Figure 25 illustrates an example estimate of signal jump in a TV test pattern.

Table 2: Measured Signal in the Resonant Pixel Halo and in the Preceding Frame

Figure 25 - (Left panel) Illustration of a "TV test pattern" (scan 67842b, frame 097, Fig. 7) in W2. The red line shows the location of the row cut shown in the right-hand panel. (Right panel) Row cut illustrating the rise in counts. The signal jumped from an average of 300 DN on most of the row, to about 1200 DN at the elevated region on the right.

Figure 26 shows both the mean signal of the preceding illuminated frameset, and the typical signal jump in a TV test pattern, as a function of aperture photometry of the resonant pixel halo. Figure 26 shows that there may be a correlation between the signal jump in the preceding frame and the signal in the resonant pixel halo. We do not see a solid correlation with the mean signal of this preceding frameset. Our measurements of the latter are compromised by the lack of level-1b data for them (due, for instance, to failure to complete processing) or by our inability to measure the peak signal if this preceding frameset already represents the signal in decay.

Figure 26 - The x-axis shows the aperture photometry in the W2 resonant pixel halo, and the y-axis shows either the mean signal in the W2 frame immediately preceding the resonant pixel instance (blue circles), or the signal jump in the TV test pattern (red circles).

III.2.c.ii.5. Summary

The resonant pixel halo is related not to a single pixel, but to a cluster of them in W2, and it is located in a region of the array where long-term latents are observed. Instances are rare and are preceded by a frameset with a dramatically elevated signal, often with a "TV test pattern" effect.

Last update: 23 February 2024