Targets, Alerts & Follow-ups

Target and Alert Team

Team Leaders: Ting-Wan (Janet) Chen (NCU ; from 01/04/2019)

Team members - revised list : Kate Maguire (Trinity College Dublin; was TAT leader until 01/04/2019), Andrea Pastorello (INAF-OAPd; was TAT leader until 01/09/2014),  Joe Anderson (ESO Chile), Cristina Barbarino (Stockholm), Maria Teresa Botticella (INAF-Capodimonte), Regis Cartier (CTIO), Annalisa De Cia (ESO Garching), Michel Dennefeld (IAP, Paris), Nancy Elias-Rosa (INAF-OAPd/ICE-CSIC), Morgan Fraser (University College Dublin), Lluís Galbany (Barcelona), Cosimo Inserra (Cardiff), Giorgos Leloudas (DTU), Joe Lyman (Warwick), Stephen Smartt (QUB), Mark Sullivan (Southampton), Stefan Taubenberger (MPA), Steve C. Williams (Turku), Mariusz Gromadzki (Univ. Warsaw), Hanin Kuncarayakti (Turku), Claudia Gutierrez (Turku), Priscila Pessi (IALP), Simon Prentice (TCD), Takashi Nagao (ESO), Priscila Pessi (CONICET), Ilya Mandel (Birmingham), Giuliano Pignata (UNAB/MAS), Roberta Carini (INAF), Shubham Srivastav (QUB), Phil Wiseman (Southampton).

Classification and Target and Alert Team duties

Guideline of Target and Alert Team for each sub-run (2023.10 updated)

This is quantitive guideline for TAT work for each sub-run.  

1. TAT members start to clean the inbox two days before the subrun. 

2. The inbox should be clean one night before the observing night, because this is the time the observers make a plan for their first night.

3. The maximum number in the classification queue is 40 (no mater for 3n or 4n subrun, because one of 4n is likely to use SOFI). Ideally 10 high - 20 medium -10 low priority, with an eye on the second part of the night.

4. No fainter than 19 mag targets with “HIGH” priority, as our main goal is for further follow-up. Except young, new, expect rising objects. For those targets need very convincing (1-3 days before) non-detection. Add scientific comments for high priority objects in the marshall. 

5. When on duty please keep watching and discussing on the ePESSTO “TAT” Slack channel. 

   1. (2021.09) In order to coordinate the job in between 3 TAT members, we can separate inbox objects by different RA ranges.

6. (2019.08) test-mode: One person is in charge of "classification targets" queue for overall number and priority. Two persons clean out the inbox and also pay attention on priority if there is any special concern.  

7. (2020.01) Each TAT focus on different surveys, select objects from inbox to classification and decide their priorities. One TAT will additionally do final number control. 

8. (2021.09) We do NOT need to make a finder anymore!  (2020.10) There is only the telescope operator on site, our observers will "remote" observe. Therefore we need to provide finders for classification objects as well. One TAT will collect and make finders to: https://sites.google.com/a/pessto.org/wiki/pessto-wiki/home/finder-chart-repo/classification_finders

9. (2023.10) Here are the additional classification criteria:

   1. Classify everything at < 100 MPc with a trustworthy non-detection 24 hours before (mainly ATLAS but also ZTF and others). Classify with a Gr11

   2. Classify possible bumps/blips/precursors in SLSNe/Ia/II-IIn. These usually have slightly different timescales/increases in mag and will span from 2 mag rise in 2 days (blip) to 2 mag in 20 days (precursors) with the SLSN bump in-between.

   3. Colours span from -1 < g-r < -0.2. These will be classified with Gr11. All of those will be tried to be follow-up photometrically for 15 days with BHTOM

Target and Alert Team duty overview

The aim of the TAT is to identify suitable targets for spectroscopic classification with ePESSTO+ during an upcoming observing subrun. Discovery information from feeder surveys is ingested by the Marshall and appears firstly in the 'Inbox'. The duty of the TAT is to prioritise the targets appearing in the inbox in the days leading up to an observing subrun. Usually, the TAT is most active in the days preceding observing nights and one to two days before the start of the subrun. Nevertheless, in the ZTF and ATLAS era more discoveries are made and hence the TAT has to handle the 'inbox' targets also between runs and subruns.

Scheduling of targets for classification (adding them to the 'classification targets' queue) is best done no more than one to two days before the start of the observing subrun. This is because otherwise objects can be added for classification for which more data appears that makes them less interesting and then have to be downgraded but can sometimes be missed. Generally, it is fine to 'snooze' objects (see below) well in advance of the subrun because these objects will reappear in the inbox if further information is obtained. TAT tip courtesy of Stefan Taubenberger: "In the inbox, you can sort the objects by various criteria. What I find extremely useful is sorting by last reported non-detection, because this is the best bet to give you young objects. And with ZTF and ATLAS there are actually plenty with non-detections within the last week."

For ZTF targets, It might be useful to check the RB scores in Lasair  (click on candidate object link). Especially if it’s only a single detection as ZTF revisits the field 2 or 3 times a night. ZTF recommends objects with RB>0.65 for astrophysical. Tip courtesy of Chris Frohmaier and Dan Perley. The other parameter in the Lasair is isdiffpos, if this flag is "f", which means the difference flux is "negative", i.e. it is going down in brightness rather than up (but you can't assess this from the lightcurve because it has a single detection). For example, ZTF19acssnul, when we took a spectrum we saw just the galaxy.

TAT team should coordinate their work through the PESSTO Slack Channel '#TAT'. If you are not a member of this channel, please email the TAT leader (Chen) to get an invitation.

A general (but not-exhaustive) strategy for a TAT member on duty would be to go through the inbox and ask a number of initial questions about each target:

• 1. Is the target bright enough for classification at NTT (approx. 19.5-20.0 mag)? Otherwise can be snoozed. Exception for fainter targets can be done if the redshift is well known or object has a reliable non-detection a few days earlier or light curve might suggest that the target will still rise considerably (at least up to 18.5-19.0 mag)

  2. Does the target appear to be real (not an artefact)?

  3. Is it centred on a point source i.e. likely variable star?

  4. Is it a target without a host galaxy that is close to the Galactic plane (see general tips below) i.e. likely variable star?

  5. Is the object currently visible from La Silla? Using e.g. http://catserver.ing.iac.es/staralt/ As noted above, please don't archive targets that are >+30 deg if you are also looking at the northern targets.

  6. It can be difficult to observe transients at the centres of galaxies due to the strong background contamination of the host galaxy. This should be taken into account when prioritising candidates for classification.

  7. Will the target be visible from La Silla for enough time to obtain a good follow-up?

If it appears likely to be a true extragalactic transient, then the criteria defined in Section 2 below can be applied to determine the priority.

The snooze button is there to be used for objects where their current light curve evolution is unclear or they are currently too faint for an NTT classification spectrum (>20-20.5 mag). Snoozing an object means that it is removed from the inbox and placed in the 'snoozed' list. When an additional light curve point becomes available that shows the transient to be rising, the object is automatically added back into the inbox for reevaluation by the TAT team on duty.

IMPORTANT - Cleaning of ‘classification targets’ queue: check the targets in the 'classification targets' list before the beginning of a subrun and downgrade them if necessary. It is likely that most of the targets from the previous subrun will be too old to be considered high priority anymore. It’s no problem if they remain there with low priority as backup targets, but old targets should not have high priority unless there is something very special about them.

Priority classification targets

Some science topics will require a "Must classify” targets (i.e. done as soon as possible since science is very timely). Each science PI can send such a request to observers@pessto.org for approval by the TAT chair or survey PI. The email list comprises the observers, the survey PI and the TAT chair.

Criteria for selecting targets for classification

Light curve and discovery properties for approved ePESSTO+ science projects available here: Object properties

For nearly all transient events that fall into an ePESSTO+ science group, our aim is to observe them as soon as possible after explosion. In most cases (with some notable exceptions), old declining transients are not of interest to us.

Targets that are suitable for classification are added to the 'classification queue' using the top button on the righthand side of the target. A comment should be included describing why it is of interest (or not) e.g 'Offset from z=0.005 galaxy. Deep non-detection three days ago and rising over past two nights. Currently -16 mag. High priority. ' The priority of the target is assigned on the 'classification queue using the 'flame' symbol dropdown menu on the righthand side of the target ('high', 'medium' or 'low'). 'High priority' for classifications should be reserved for the youngest, brightest, faintest, etc. transients to make it easier for the observers to prioritise during the night.

The ATLAS rates project :  we are aiming to classify all, or most, transients for the "ATLAS Volumetric Rate Survey" (AVS) project. This is aiming at all transients within 100 Mpc or z = 0.024 (mu = 35.0 ; all assuming H_o = 73). Transients after peak are still worth classifying, but at medium priority. Guidelines for the TAT and observers for this classification project (note the young transients or otherwise interesting ones should over-ride the AVS priority 

• If host has a spectroscopic redshift and  z < 0.03 and current mag < 19.0 then set priority as medium; current mag > 19.0 then set priority as low

• If host has a spectroscopic redshift and  z > 0.03 and the object does not fulfil our other criteria (intrinsically bright, faint, fast or unusual) then put it into archive  

• For older ATLAS objects, they might become somewhat hidden for us when scanning targets in the marshall. Therefore, the ATLAS team should directly add these older objects to the classification queue and include comments with "classification requested for ATLAS rates project." This will help us to keep them in the classification and not remove them.

Old version of selection criteria for targets can be found here: (Criteria for selecting targets for classification up to mag 20.5)

Latest news

2023 October 21

• • Updating the strategy of the ATLAS rates project. 

2023 October 18

• • Following the discussion in the Warsaw workshop, it was decided to make some changes to our classification policies. This is driven by the large number of observing nights we have this semester (P112) and the motivation to obtain higher quality classification spectra for events that have a high probability of being scientifically interesting.

  • New slack channel 'must-high-priority- classifications'. This channel is to be used for TAT but also those directly connected with discovery surveys (mainly ATLAS, but also any others) to quickly communicate to observing teams that there is an object that should be classified *now*. In contrast to previous policy, such classifications can take higher priority than 'critical' followup - especially if the the latter can be done e.g. on the next observing night.

2021 October 15

• • For those ZTF objects without IAU names (not reported to TNS), should be more careful, they maybe possible not real. 

2021 April 03

• • The GSNST survey candidates are not reliable. We don't add those objects to the classification queue. 

2020 October 20

• • Note the ZTF page that Dan set up which lists for example "latest transients" and  SNe that need classification, https://sites.astro.caltech.edu/ztf/bts/bts.php#classify

2019 October 25

• • Access to the ASASSN 'SNIPER' web pages is now active through the PESSTO Marshall.

  • While SNIPER also gives one access to ASASSN photometry, the use of that photometry has to be requested on a case-by-case basis as outline in the ePESSTO+ publication policy.

2019 August 29

• Follow-up objects with  V > 19.5 mag will be observed only with GR#13 unless a strong case is made to the Survey PI.

• OBs lasting from more than 2*2700s would need a waiver sent to the Survey PI (C Inserra) and Science Board Chair (J. Anderson)

• SOFI RG observations are, in general, no longer offered unless the object is very bright and there is a clear scientific gain. To request such observation, please contact the Survey PI (C. Inserra) and the Chair of the Science Board (j. Anderson)

2019 June 07

• Finding different context (host redshift) from marshall and ATLAS page?

  • The ATLAS pages have a rogue spec-z from GLADE. The Marshall associates with a NED galaxy and z - which you can trace and verify by clicking through to NED. We know GLADE has some errors - always trust a NED association above it, and one you can verify by following the links. Until you hear otherwise, trust the PESSTO marshall as the more reliable source (over the ATLAS pages).

2019 May 13

• Facing problems with marshall?

  • If anyone finds a problem or issue with marshall, don't struggle along, please add bugs to the marshall issues queue: here, and/or email Dave directly.

2019 Apr 29

• For the "Spectral homogeneity of SNe Ia in the Hubble flow and a subset of SNe Ib/c" project  (PI: Ariel Goobar), the project PI will add targets to classification list with medium priority. With a typical comment: "Target for ZTF Ia program, please classify ASAP" will help the project having a priority among the medium ones. Transients after peak are still worth classifying at medium priority. 

2019 Apr 16

• • If TAT members are in a pinch due to too many targets ingested by ZTF and both the snooze option and the TAT tips reported above are of no help, please use the LASAIR broker 

2019 Feb 08

• • Cleaning of ‘classification targets’ queue: check the targets in the 'classification targets' list before the beginning of a subrun and downgrade them if necessary. It is likely that most of the targets from the previous subrun will be too old to be considered high priority anymore. It’s no problem if they remain there with low priority as backup targets, but old targets should not have high priority unless there is something very special about them.

  • Top TAT tip courtesy of Stefan T.: "In the inbox, you can sort the objects by various criteria. What I find extremely useful is sorting by last reported non-detection, because this is the best bet to give you young objects. And with ZTF and ATLAS there are actually plenty with non-detections within the last week."

2019 Jan 18

• • There are a lot of ZTF objects coming through so two additional cuts were made in November that removes objects with abs(galactic latitude) < 10 degrees and are fainter than 20 mag. There are still a large number of objects but generally priority should be given to objects with official TNS names. Ones with only ZTF names were deemed less likely to real astrophysical transients than those registered on the TNS.

2018 Sept 17

• • Evolving ZTF light curve data can be obtained from LCO via https://mars.lco.global/ Just enter the object of interest's name under objectId on the lefthand side and the light curve data is returned. Good for seeing if the object is rising or not .

2018 Jan 03

• • Targets marked as 'NT' by the Marshall contextual classifier (visible under the reference image for 'host info' on the Marshall ticket for each object) should NOT be moved to the classification queue during the period Jan - May 2018.

  • The PUNTS team will prioritise 'NT' objects according to their selection criteria and move to the classification queue where appropriate. 

Selection of the TAT for ePESSTO runs

The dates of upcoming observing runs are available here: Observing Runs. A request email for volunteers will be sent by the TAT chair to alerts_@_pessto.org about one week prior to the start of the next observing run (generally made up of three subruns). Responses received by email within 24 hours will be included for consideration in the TAT schedule. Note: requests for inclusion in the TAT for future observing runs are also possible in advance of this email by emailing the TAT chair, Janet Chen (jchen_at_mpe.mpg.de) with details of your availability. Preference will be given to people who haven't served in the TAT recently (if they so wish).

ePESSTO Marshall

http://www.pessto.org/marshall

The Marshall is the interface through which targets are compiled from the feeder surveys, scheduled for classification, classifications are added and follow-up scheduling is overseen. Bugs & improvement/development requests can be reported via the 'bug' symbol on the right-hand side of the top menu bar on the Marshall - this takes you to the github issues page

Note on Northern targets in the Marshall:

By default, northern targets are not visible on the Marshall pages. At the top of the page there is a button “NTT” which you can use to turn on >+30deg northern targets. The reason for this is that we have northern targets from ATLAS and PS1 we want to keep track of, and don’t really want to code up another Marshall. Many of you have access to northern facilities so feel free to take spectra of these, but please do put in a comment and/or classify them with the usual Marshall tool.

• • Do NOT archive something just because it is >+30deg. 

  • Feel free to comment and push them into the classification queue. 

  • Other Users can turn them on/off if they want to with the NTT button 

The Pan-STARRS data points you see are generally public (from PSST), so can be used freely. The ATLAS light curve data points you see (for the northern targets) are not public. You can view the PNG plot to guide you if you want to classify things, but ask the ATLAS team at QUB if you want to use data for any papers/analysis.

Tips and tricks (including understanding the feeder survey webpages)

General tips:

1. Beware of Galactic transients e.g. variable stars that are generally located near the Galactic plane. They usually appear like orphan candidates without a visible host galaxy. The Galactic coordinates are available on the ATLAS and PS webpages for their transients. For a quick check of the sky position, an image like this can be useful (Credit: D. Coe (STScI), D. Schlegel (LBNL), D. P. Finkbeiner (Harvard), M. Davis (Berkeley))

Survey specific tips:

1. Pan-STARRS (Example: https://star.pst.qub.ac.uk/sne/ps13pi/psdb/candidate/1142016661152029700/):

   1.  Due to the large chips gaps in PS images, non-detections do not mean what you typically might think. They are calculated from the limiting magnitude for each particular skycell for that night. However, they are also displayed for objects that fall on a chip gap or are masked for some reason so a non-detection arrow does not necessarily mean that a true non-detection occurred on that night.

   2.  Galactic coordinates are given on the right-hand side in the top info panel.

   3.  Objects that Ken Smith is confident are real transients and likely SNe are added to the TNS. If a PS1 object has no ‘AT’ designation, treat it with more suspicion.

2. ATLAS  (Example: https://star.pst.qub.ac.uk/sne/atlas4/candidate/1135706051275938400/):

• 1. The ATLAS filters are non-standard. Broadly cyan corresponds to ‘g+r’ and orange to ‘r+i’. More details on the ATLAS filters can be found here: ATLAS filters

  2. The second light curve plot on ATLAS pages is from forced photometry so should be more accurate.

  3. Galactic coordinates are given on the right-hand side in the top info panel.

  4. Comments (added mainly by Ken Smith) are available in the top box. Objects that Ken is confident are real transients and likely SNe are added to the TNS. If an ATLAS object has no ‘AT’ designation, treat it with more suspicion.

3. Gaia (Example: http://gsaweb.ast.cam.ac.uk/alerts/alert/Gaia19bml/):

• 1. Underneath the image, there is generally a comment detailing the Gaia scanner’s impression of the target. ‘GS-TEC predicts’ relates to the Gaia spectrophotometry transient events classifier of Blagorodnova et al. (2014, MNRAS, 442, 327). It uses the blue and red grism spectra to estimate the most likely type.

  2. A low-res spectrum is obtained for each epoch. You can scroll through by clicking on the arrows to the right and left of the spectrum.

  3. The spectra are not flux calibrated. For details on interpreting Gaia spectra, see https://gaia.ac.uk/alerts/what-and-why/gaia-spectra

  4. Gaia is not a SN survey - there will be CVs, YSOs and other transients there too! Checking the galactic latitude of a candidate is probably a good idea!

4. ZTF (Example: https://lasair.roe.ac.uk/object/ZTF19aagqkrq/):  it might be useful to check the RB scores in Lasair  (click on candidate object link). Especially if it’s only a single detection as ZTF revisits the field 2 or 3 times a night. ZTF recommends objects with RB>0.65 for astrophysical.

5. ASASSN: http://www.astronomy.ohio-state.edu/asassn/index.shtml

Information on follow-up target requests

Follow-up objects with  V > 19.5 mag will be observed only with GR#13 (no GR#11+GR#16), unless a strong case is made to the Survey PI (C. Inserra).

OBs lasting from more than 2*2700s would need a waiver sent to the Survey PI (C. Inserra) and Science Board Chair (J. Anderson)

When a classification spectrum identifies an interesting target for follow-up, the science lead of the relevant science group has first refusal on this target. If they are not interested or not able to lead a full follow-up campaign, others may take the lead following an open call within the relevant science group.

Targets can only become follow-up targets with the approval of the Survey P.I., the Science Board chair and the TAT chair. For each science target, a science P.I. is assigned (and their contact details must be listed on the Marshall). Once this is achieved, a summary of the target, Science Group and Science PI must be sent to alerts@pessto.org by the science group lead or his/her delegate.

The science targets can be added to the 'follow-up targets' list on the Marshall. The P.I. is responsible for scheduling follow-up observations. All requests and their details should be entered via the Marshall (not via email!) including a recent estimate of the magnitude of the target. Details on typical exposure times are available at: OBs information  Since SOFI spectroscopy is very time-consuming, requests for follow-up SOFI spectra must be made to the Survey P.I., the Science Board chair and the TAT chair with a justification of the science case.

There are three classes of priority for follow-up: (i) CRITICAL, (ii) IMPORTANT, and (iii) USEFUL. There has been an overuse of 'critical' in the past, this should only be used when the resulting publication is expected to significantly suffer for the lack of these data. A justification on why the target is CRITICAL has to be provided in the marshall. Once the data have been obtained or the time period of the request expires, the priority will be reset to 'NONE'.