Hello all!
I observed an optical afterglow of GRB 210306A with remote telescope T24 of iTelescope.Net on March 6, 2021. Shooting started 49 minutes after the burst. Two images were obtained with exposures of 300 seconds, in which I detected the afterglow and measured its brightness: 17.80 (+/- 0.057) and 17.97 (+/- 0.038) mag. - from comparison to r magnitudes of nearby stars from Pan-STARRS DR1 catalogue.
More information published in the GCN circular №29599: https://gcn.gsfc.nasa.gov/gcn3/29599.gcn3 I am attaching the stacked image.
This is the third optical afterglow of GRB that I was able to photograph (after GRB 191221B and GRB 201223A). In addition, four more times (GRB 191029A, GRB 191123A, GRB 210104A, GRB 210226A) I received only upper limits.
With best regards,
Filipp.
Congratulations, this is awesome given how fast those things can fade!!
I'd like to know more about how you select GRBs of interest for going after them with e.g. iTelescope, but maybe that's something that better belongs in the "High Energy Network" forum section. The HEN section was originally primarily focused on GRB afterglows (it now has a bit of a wider focus, but GRB afterglows are still super interesting and a major challenge to observe).
Clear Skies!
HB
Thank you for your congratulations to me!
I'll answer here: I read the GCN Circulars https://gcn.gsfc.nasa.gov/gcn3_archive.html and if I see information about GRB then I watch how much time has passed since the burst. If not more than a few hours, then I try to shoot. But I do not always have access to the Internet, so I cannot often track such information.
With best regards,
Filipp.
Ah I see, thanks for the explanation.
If you ever want to react even quicker, there are also the GCN notices which are machine generated and machine-readable. Those are sometimes triggered within seconds of the burst being detected, with most of the logic for triggering happeing on-board the spaceprobes .You could set up some computer (anywhere, even a Raspberry Pi would do) that listens for those events and if it's something interesting for you, it could sent you an email or text message perhaps. There would be some work involved tho in parsing the machine readable notices from different detectors (FERMI, SWIFT I guess) and filter out those that are well localized I guess. I did something similar for gravitational wave events furing the LIGO/VIRGO detectors science run from 2019..2020 (sadly no really interesting optical followup opportunity for amateurs happend). It was a few lines of python using the pygcn library.
Clear Skies
HB
Do the GCN notices duplicate GCN VOevents?
George
Hi George,
It depends. You can enable various classes of GCN notices for either email or VOEvent, such as GCN/SWIFT_XRT_POSITION. After the automated alerts come out, they usually post a human-readable "alert" as a GCN Circular within a few minutes. Each class of alert from SWIFT, for example, has a different localization error, so which one you want to trigger on depends on your ability to pick out a new object (if an optical transient exists). Since BAT and XRT, the gamma-ray and X-ray telescopes on board SWIFT, come first, I usually trigger on them as their localization is good enough to fit in the field of view of a typical telescope. Then I wait for the UVOT localization and detection/nondetection alert to see if I should continue to observe (when an optical candidate was seen) or return to my normal program. If you just trigger on the UVOT_POSITION alert, you lose 6-8 minutes of imaging time, as it takes them that long to take the UVOT image, download it and check for a transient. An optical transient fades very quickly, so waiting 8 minutes before you even begin to slew means the transient may be a magnitude or two fainter than at the beginning.
Arne
(crossing with Arne's message..beat me to it)
Technically speaking, GCN Notices for FERMI and Swift are (also transmitted as) VOevents
There's a lot of terminology to be unpacked here, so let's define some terms:
VOevent : This is a standardized language used to describe astronomical transients in a structured, machine readable and well defined way, the definition can be found here : https://www.ivoa.net/documents/VOEvent/ . I guess it's also common to refer to a message written in the VOevents language as a "VOevent"
GCN: Gamma-ray Coordinates Network: a network used to broadcast news about certain kinds of astronomical transients to interested researchers (it started with gamma ray bursts but is now used for other events with similar follow-up needs like neutrino and gravitational wave transients). It's run by NASA https://gcn.gsfc.nasa.gov/ . The idea is to use it in a publish-subscribe paradigm: the messages are produced by the different science missions and researchers can subscribe to certain message types if they want to be notified in a timely fashion.
GCN circulars: messages that are usually written my humans and are meant for human consumptions. A bit like Twitter but without the "likes" and "retweets" and "comments" and BS ... These are just prose, ASCII text messages. Typically these messages are about follow-up observations, not just about the initial event detections.
GCN notices: messages that are generated, usually in real time, when a transient is detected, or when data for a detection is updated subsequently. These are structured and machine readable , meant to be digested by computers rather than humans. Every mission has its own definitions of the content of those messages, and the message syntax often depends on the protocol used to transfer them. In the old days, you could find messages distributed by e-mail as a list of key-value pairs. Nowadays, the better way is VOevent messages.
Event brokers: As someone who wants to receive those messages about transients, you can use a service that lets you subscribe to certain messages. That service will then make sure that those particular messages are delivered to you via a means of transport that you support. One such event broker is 4PiSky https://4pisky.org/voevents/ . The service reads events for different sources, including GCN, and re-transmits them to subscribers. So for the gamma ray events in question here, GCN is the actual data source for 4pisky and they forward them to "subscribers".
But GCN itself is also acting as a broker, you can subcribe to get e.g. email messages with quite some functionality of filtering out what is interesting for your site. However, the way perhaps most people access GCN these days is to connect via some software directly to one of the public servers of GCN as described here:
https://gcn.gsfc.nasa.gov/voevent.html
This way, you get ALL (!!) GCN events in VOevent format, from ALL (public) event sources, which can be up to a few messages every minute, and it is the responsibility of the software listening to the GCN server on your side to filter out stuff that is interesting for you. The advantage is that this happens with the minumum time delay possible. You don't need to write that client-side software from scratch, there are libraries like this one written in Python that make it easy to listen for specific messages only (by dopping all other received messages):
https://github.com/lpsinger/pygcn
With a bit of Python programming, you can write your own message handlers that decide automatically which events are interesting for you, and execute whatever commands are necessary to get your attention or otherwise react to such events (send an email to you, text you, sound a klaxon at your home, point your telescope automatically....)
Clear Skies
HB