Swift/UVOT photometry version 13.2

Swift has observed hundreds of supernovae over the last nine years, including dozens of very well sampled light curves published in many different papers (see post to Swift SN publication list here).  The calibration has been improved over the years, with the zeropoints of Poole et al. 2008 being updated in Breeveld et al. 2011.  As of 2010-11-30 these new zeropoints have been included in the Swift CALDB used with the HEASARC software (ie uvotsource and uvotmaghist).  A sensitivity loss of about 1% per year has also been discovered and is incorporated into the HEASARC software as of 2010-6-30.  Combining these effects could lead to a 0.1 magnitude error when comparing new and old photometry.

To allow an accurate comparison between new SNe and those published earlier in the mission, I have redone the photometry for using the latest calibration.  The photometry for the SNe Ia published in Brown et al. 2009 and 2012 have been redone and posted here.  The original references are given in the files, and I will be redoing other SNe as time allows.  I have also posted the reduction code here.  Please report any bugs, suspicious data, or deviations from ground photometry (for B and V, the Swift u band is quite different from ground-based u' or U) in the comments below or to uv dot supernova at gmail dot com.

A set of CC SN photometry from Pritchard et al. 2013 on the same system (but slightly different analysis) is posted here.

Notes:

The coincidence-loss saturation limit is currently set at 0.98 counts per frame.  This should be more rigorously tested.

There is something wrong with the three sigma upper limits, as the SN2006mr photometry lists magnitudes that are only 1-2 sigma detections.  I think the photometry is right, but there is an inconsistency in how the photometric errors are calculated and how the upper limits are calculated.  It might be the inclusion of the galaxy subtraction errors in the limit, as SN2006mr had the largest underlying galaxy count rate.

Swift Supernovae in the Future (2014-2018) Brainstorm List

Swift Supernovae in the Future (2014-2018) Brainstorm List

This post is intended as a brainstorming list to dump new ideas about what Swift should be doing in regards to supernovae over the next four years.  We don't need a list of all the wonderful science you could do, but how different target selection or observations can add to the science we are doing.  Adding something here doesn't necessarily mean you think we should do it, but that it could be done.  Adding something does not obligate you to do anything about it now, but we may ask for more details or ideas on implementation.  Suggestions do not need to be strongly justified on this page, but sometimes a brief clarification is useful.  Obviously we cannot do everything, but by airing these ideas we can probably find more synergistic observations which can benefit multiple projects.  Please add your ideas in the comments.

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SNe in the Hubble Flow -- a large fraction of the Swift SNe are at very low redshifts (z<0.02) where the peculiar velocity contribution to the absolute magnitude error is greater than 0.1 mag (in the absence of other distance measurements).  More SNe Ia could be targeted in the range 0.02 < z < 0.03 or so, and UV bright SNe II even farther out.  [ Peter B]

Early grism observations -- the updated grism software includes calibration for positions across much of the field.  A slew in place, while desirable in the planned schedules, is no longer necessary, so grism observations can be uploaded to Swift as immediate targets for earlier spectra.  [Peter B]

[ April 22, 2014 Update -- I only listed a few ideas so that others could contribute without having most ideas already listed.  Since there hasn't been much response, I'll go ahead and list the other ideas I have. ]

V grism observations of SNe Ia -- We've focused mostly on the UV grism since the V grism only extends a little past what can be done from the ground (to about 2900 Angstroms).  But there are interesting features there that might explain the difference between NUV-red and NUV-blue SNe, and using the V grism would allow for SNe to be targeted at higher redshifts than the UV grism.

Reddened SNe -- Now that we've got a large sample of low reddened SNe to compare with we should also target mildly reddened SNe (E(B-V) <~ 0.5) to understand the wavelength dependence of the extinction law(s?) applicable to SNe

V grism observations of reddened SNe?  We can't get much mid-UV flux anyway, but V grism observations could probe the extinction law down to 2900 Angstroms

UV light curves of SNe Ib/c -- we still don't have many good light curves of SNe Ib/c, especially in the mid-UV (uvm2 band).   There aren't many close enough to detect in short observations (2 ks) but we could take longer exposures to get light curves of SNe Ib/c a little farther away.

Distance-limited sample of SNe IIP -- IIn

Target all SLSN candidates brighter than g/B/V ~ 20 -- some might not be UV bright but we could get a feel for what fraction are and what the brightness distribution is in the UV

Swift Supernova Publications

I am trying to create a master list of all publications presenting or making significant use of Swift Supernova data.  Right now I am sticking to refereed (or arXiv papers in the refereeing process) papers but may add ATELs and IAU Circulars at some point -- there are quite a few.  Please alert me to any I am missing.  To minimize clutter I will delete comments after adding the reference.


https://docs.google.com/document/d/1V1WVF9--sWfTfV_4vjoXQ-KtzFNl13WVpUbDZEf4JS0/edit?usp=sharing

As of September 2015 I count 107 publications from 63 different authors.

Swift SN Timeline

Here is a timeline of Swift SN observations through mid-2012.  It demonstrates the continuity of our program, with the light curves of individual SNe being well sampled in time and multiple SNe being followed up at any given time.  The dynamic range for our observations in uvw1 is about 11 (the saturation point) down to a limiting magnitude of 21 for reasonable exposure times and typical galaxy contamination.

Swift Supernovae -- What are bad targets?

Which supernovae make good candidates for Swift observations is a very science-dependent question and has different answers to different people.  So I will start with things that make SNe poor targets for Swift as they are independent of the science.

UVOT Modes

The Swift UltraViolet/Optical Telescope (UVOT) has a different way of setting exposure times and filter combinations that I will attempt to explain below.

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."

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.

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.

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).