<p>While I am not really familiar with Kepler, there is the following paper by <a href="https://arxiv.org/abs/1408.3853" rel="nofollow noreferrer">Vanderburg &amp; Johnson</a>, where they explain:</p>
<blockquote>
<p>Extracting raw photometry and centroid positions
from the K2 images results in flux and position time series characterized by jagged features occurring several
times a day. Figure 1 shows an example of a “raw” light
curve and image centroid positions for a 10th magnitude
K2 target. The position of the star on the detector drifts
on time scales of hours and then is quickly corrected back
to its starting point when the spacecraft thrusters fire.
The changes in position introduce significant artifacts
into the raw K2 photometry, which must be corrected in
order to achieve the photometric precision characteristic
of the original Kepler Mission.</p>
</blockquote>
<p><a href="https://i.sstatic.net/1IbcO.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/1IbcO.png" alt="enter image description here" /></a></p>
<p>So it seems that this is just a result of the reduced pointing accuracy introduced after Keppler lost two of its four reaction wheels.
The paper also goes into detail how to correct for this behavior.</p>

CC BY-SA 4.0
2022-03-23T15:23:24.007Z
2022-03-23T15:23:24.007Z
SpaceCore
<p>I obtained the optical light curve of 3C 273 QSO from the MAST repository off the K2 mission and plotted it by making the FITS into a CSV file through Pandas dataframe and plotting the obtained columns using <em>lightkurve</em> package in Python.</p>
<p>The SAP_FLUX and the PDCSAP_FLUX vs the Time gives a gradual steep slope but when the steepness is over and the slope is climbing up, the steepness is very dramatic, in the sense, that it's very precipitous and not gradual like how it should be.</p>
<p>I am attaching the image of a part of the light curve. My teacher was quick to spot that but I totally missed it while including it in my project. Thanks.</p>
<p><strong>EDIT:</strong> Since my question is not clear as pointed out in the comments (apologies for it!), I will reformulate it.
My question is that why are the curves rising so precipitously (as seen in the image) and when they are coming down from the peak the change is gradual and slow. Shouldn't both of them be rising and falling gradually?
<a href="https://i.sstatic.net/hofA0.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/hofA0.jpg" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2021-10-14T15:24:49.370Z
Can you edit your question to actually provide a concrete question you'd like someone to answer? As is, you have no actual question for someone to address in your post.
zephyr
CC BY-SA 4.0
2021-10-14T17:26:46.850Z
If your question is about the origin of this, you'd habe to understand whether such brightness - changes would be normal when symmetric and what processes drive brightness variations in such objects. If neither seems to provide an answer look for instrumental effects, possible only affecting this observations or a few around that time or region
planetmaker
CC BY-SA 4.0
2021-10-15T14:04:42.427Z
I made an edit to address the question directly. Thanks for pointing out.
mnuizhre
CC BY-SA 4.0
2021-10-15T16:20:01.507Z
I see that the light curve has been smoothed out to some extent, how separated are the individual data points? Is the steep jumps transition from one data point to another?
Justin T
CC BY-SA 4.0
2021-10-16T03:38:13.547Z
QSOs show variability in flux in the observer's frame the spikes indicate the variability in the optical regime. The gradual fall show the decrease and the rise show the increase in the observed fluxes.
mnuizhre
CC BY-SA 4.0
2021-10-16T03:39:17.540Z
To answer the first question, I don't know. I obtained the processed FITS off MAST archive K2 mission. I didnt carry out any processing in the raw data myself.
mnuizhre
<observational-astronomy><quasars><light-curve>
Sudden spikes on the light curve of a Quasar from K2 mission
mnuizhre
# Sudden spikes on the light curve of a Quasar from K2 mission

(Asked by: username_0 on 2021-10-14)

I obtained the optical light curve of 3C 273 QSO from the MAST repository off the K2 mission and plotted it by making the FITS into a CSV file through Pandas dataframe and plotting the obtained columns using *lightkurve* package in Python.

The SAP\_FLUX and the PDCSAP\_FLUX vs the Time gives a gradual steep slope but when the steepness is over and the slope is climbing up, the steepness is very dramatic, in the sense, that it's very precipitous and not gradual like how it should be.

I am attaching the image of a part of the light curve. My teacher was quick to spot that but I totally missed it while including it in my project. Thanks.

**EDIT:** Since my question is not clear as pointed out in the comments (apologies for it!), I will reformulate it.
My question is that why are the curves rising so precipitously (as seen in the image) and when they are coming down from the peak the change is gradual and slow. Shouldn't both of them be rising and falling gradually?
[![enter image description here](https://i.sstatic.net/hofA0.jpg)](https://i.sstatic.net/hofA0.jpg)

**Tags:** observational-astronomy, quasars, light-curve

> **Comments:**
> **username_1**: Can you edit your question to actually provide a concrete question you'd like someone to answer? As is, you have no actual question for someone to address in your post.  
> **username_2**: If your question is about the origin of this, you'd habe to understand whether such brightness - changes would be normal when symmetric and what processes drive brightness variations in such objects. If neither seems to provide an answer look for instrumental effects, possible only affecting this observations or a few around that time or region  
> **username_0**: I made an edit to address the question directly. Thanks for pointing out.  
> **username_3**: I see that the light curve has been smoothed out to some extent, how separated are the individual data points? Is the steep jumps transition from one data point to another?  
> **username_0**: QSOs show variability in flux in the observer's frame the spikes indicate the variability in the optical regime. The gradual fall show the decrease and the rise show the increase in the observed fluxes.  
> **username_0**: To answer the first question, I don't know. I obtained the processed FITS off MAST archive K2 mission. I didnt carry out any processing in the raw data myself.  

---

## 1 answers

### Answer by username_4 on 2022-03-23. Score: 2 | Accepted answer

While I am not really familiar with Kepler, there is the following paper by [Vanderburg & Johnson](https://arxiv.org/abs/1408.3853), where they explain:

> Extracting raw photometry and centroid positions
> from the K2 images results in flux and position time series characterized by jagged features occurring several
> times a day. Figure 1 shows an example of a “raw” light
> curve and image centroid positions for a 10th magnitude
> K2 target. The position of the star on the detector drifts
> on time scales of hours and then is quickly corrected back
> to its starting point when the spacecraft thrusters fire.
> The changes in position introduce significant artifacts
> into the raw K2 photometry, which must be corrected in
> order to achieve the photometric precision characteristic
> of the original Kepler Mission.

[![enter image description here](https://i.sstatic.net/1IbcO.png)](https://i.sstatic.net/1IbcO.png)

So it seems that this is just a result of the reduced pointing accuracy introduced after Keppler lost two of its four reaction wheels.
The paper also goes into detail how to correct for this behavior.


---

