The Swift UltraViolet/Optical Telescope (UVOT) has a different way of setting exposure times and filter combinations that I will attempt to explain below.
Tuesday, July 30, 2013
UVOT mode recommendations
This page is intended to suggest observing modes for Swift's UVOT. A discussion of the uvot modes is on this page.
The mode below are especially recommended for red objects (ie low UV flux
compared to their optical flux), but because the UV filters have lower
sensitivity and the optical data can be obtained from the ground,
weighting the time heavily to the UV is rarely a bad thing. The optical filters are useful for estimating the reddening as well as
for estimating the optical contribution to the uvw2 and uvw1 filters,
and with these modes the optical uses a small fraction of the time. The uvm2 is particularly important since it is the narrowest UV filter and doesn't have a long red tail, thereby giving the best measurement of the UV flux.
Default recommended observing mode for Supernovae in the PPST
6 UVOT filters heavily weighted to the UV -- 0x223f [time weighting w2:m2:w1:u:b:v::5:8:3:1:1:1]
Default recommended observing mode for Supernovae as an uploaded AT
6 UVOT filters heavily weighted to the UV -- 0x0270 (this will do all 6 filters in that ratio for a 1000 second snapshot. If the snapshot is longer, any extra time is dumped into the uvm2 exposure which is almost always a good thing.
uvw1+u+b+v (ie a target is too faint for the mid-UV filters) -- 0x2238 [w1:u:b:v::6:2:1:1]
There are also special modes for if the SN is too bright (m<13), taking grism spectra (m_uv < 15 or so) or for other filter combinations, but it is probably better to work with a UVOT team member or an ODS to figure out what is appropriate rather than me listing the hundreds of modes that are available.
One should state the filters and weighting desired rather than just the mode (in case you get the mode number wrong or the observing sequence won't give what you think it will give using that mode).
There might be better modes to get the data you want, but if the mode than the ODS might not know if there is a better way to get what you want. For most SN observations I recommend adding the following to the filter justification.
"We would like to use the 6 broadband filters (uvw2,uvm2,uvw1,u,b,v) heavily weighted to the uvm2 for better mid-UV sensitivity. If appropriate, please use UVOT mode 0x0270 for a ToO upload (needs some snapshots longer than 1000 sec to get all six filters) and 0x223f in the PPST to weight the time heavily to the UV."
Default recommended observing mode for Supernovae in the PPST
6 UVOT filters heavily weighted to the UV -- 0x223f [time weighting w2:m2:w1:u:b:v::5:8:3:1:1:1]
Default recommended observing mode for Supernovae as an uploaded AT
6 UVOT filters heavily weighted to the UV -- 0x0270 (this will do all 6 filters in that ratio for a 1000 second snapshot. If the snapshot is longer, any extra time is dumped into the uvm2 exposure which is almost always a good thing.
uvw1+u+b+v (ie a target is too faint for the mid-UV filters) -- 0x2238 [w1:u:b:v::6:2:1:1]
There are also special modes for if the SN is too bright (m<13), taking grism spectra (m_uv < 15 or so) or for other filter combinations, but it is probably better to work with a UVOT team member or an ODS to figure out what is appropriate rather than me listing the hundreds of modes that are available.
One should state the filters and weighting desired rather than just the mode (in case you get the mode number wrong or the observing sequence won't give what you think it will give using that mode).
There might be better modes to get the data you want, but if the mode than the ODS might not know if there is a better way to get what you want. For most SN observations I recommend adding the following to the filter justification.
"We would like to use the 6 broadband filters (uvw2,uvm2,uvw1,u,b,v) heavily weighted to the uvm2 for better mid-UV sensitivity. If appropriate, please use UVOT mode 0x0270 for a ToO upload (needs some snapshots longer than 1000 sec to get all six filters) and 0x223f in the PPST to weight the time heavily to the UV."
Monday, July 15, 2013
Swift ToOs (Targets of Opportunity)
This post is designed to take you through the steps of submitting a Swift TOO request. This site tells you what ToO requests have been made and their status. Specific recommendations for Supernova ToOs are here which will make more sense after you see the form below.
First you need a user account, which requires your name, institution, contact information, and accepting a user agreement that you will only submit real sources.
The site to set up a user account is here.
Then login and proceed to Submit a ToO Request. The request form is composed of multiple pages that depend somewhat on previous answers (UVOT modes, monitoring). Below are those pages so that you know what will be asked before you start. Farther below that are the instructions one would see after logging in but before submitting a new ToO request.
First you need a user account, which requires your name, institution, contact information, and accepting a user agreement that you will only submit real sources.
The site to set up a user account is here.
Then login and proceed to Submit a ToO Request. The request form is composed of multiple pages that depend somewhat on previous answers (UVOT modes, monitoring). Below are those pages so that you know what will be asked before you start. Farther below that are the instructions one would see after logging in but before submitting a new ToO request.
Swift SN TOO recommendations
This post gives you some of the background of Swift Targets of Opportunity (ToOs). Below I give some recommendations for SN ToOs.
Friday, July 12, 2013
ULTRAVIOLET EXPLOSION!!
The title does not refer to the actual explosion of a star or the ultraviolet emission that results, but the recent, dramatic increase in ultraviolet (UV) observations of supernovae (SNe) over the past several years.
The launch of the Swift spacecraft in late 2004 enabled a ten-fold increase in the number of SNe observed each year in the UV utilizing the UltraViolet/Optical Telescope (UVOT). Interestingly, the Hubble Space Telescope (HST) has observed more SNe in the UV during the Swift era than it did previously. These high quality spectroscopic observations complement nicely the well sampled photometric UV light curves and low resolution UV spectra from Swift. There are likely many SNe missing from this plot, in particular from XMM which likely observed in the UV simultaneous to the primary X-ray observations. The list is posted here, and you can alert me to any missing SNe by e-mailing me at uv dot supernova at g mail dot com. Likewise for the Swift SNe, I used the same list as for this website, so please let me know if I am missing any (in particular, PTF and other project designated transient objects may not be listed unless I have found out it was a SN).
The launch of the Swift spacecraft in late 2004 enabled a ten-fold increase in the number of SNe observed each year in the UV utilizing the UltraViolet/Optical Telescope (UVOT). Interestingly, the Hubble Space Telescope (HST) has observed more SNe in the UV during the Swift era than it did previously. These high quality spectroscopic observations complement nicely the well sampled photometric UV light curves and low resolution UV spectra from Swift. There are likely many SNe missing from this plot, in particular from XMM which likely observed in the UV simultaneous to the primary X-ray observations. The list is posted here, and you can alert me to any missing SNe by e-mailing me at uv dot supernova at g mail dot com. Likewise for the Swift SNe, I used the same list as for this website, so please let me know if I am missing any (in particular, PTF and other project designated transient objects may not be listed unless I have found out it was a SN).
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