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V1333 Aql outburst - AAVSO Alert Notice 718

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V1333 Aql outburst - AAVSO Alert Notice 718

AAVSO Alert Notice 718 announces an observing campaign on the outbursting X-ray binary V1333 Aql (Aquila X-1). Please see the notice for details and observing instructions.

To stay informed about this campaign, subscribe to this forum thread (option 1 under Subscribe below) -  see feedback from the PI,  comments and questions from observers, and notes from AAVSO HQ. Add a post yourself  -  join in the discussion about this interesting target!

Many thanks, and Good observing,

Elizabeth O. Waagen, AAVSO HQ

Observation Update

Hi All,

My apologies for the delay in getting back to you all.

First, thanks to DFS, SDM, NROA, and WKL for already getting data into the AAVSO on this source.

Optical Update

As of August 28, you all have shown the source to be at about V~16.5-16.7, R~15.8-16.5 (I'm not sure if the big drop was real, but given there is also a drop in V at the same time, it may well be) and B rising from 18.7 to 17.7.

I have not heard word back from the LCO team yet to see what they are seeing.

Ultraviolet Update

I apologize, but I have not heard word back from my UVOT person as to what they are seeing. But by eye, we are detecting the source in multiple filters.

X-ray Update

We've been monitoring the source with the Swift X-ray Telescope (XRT) and its Burst Alert Telescope. The former only gives us data when scheduled observations occur, while the latter monitors large swaths of the sky. The source is still in the early stage of an outburst, with X-ray luminosities around 1-4 e36 erg/s. It can get a hundred times brighter! Evolution has been slower than expected, and of course we had some bad luck. Scheduled Swift observations do not always occur as higher priority observations like Gamma Ray Bursts can shuffle what actually gets observed. Due to that, we did not get XRT observations on the 26 and 27. And when we did get XRT observations on the 28, the telescope did not slew onto target for the instrument mode we were using (another arcminute and we would have been great). But, for the first time today, the daily average of the BAT data is beginning to pick up the source!

Aql X-1 XRT Swift count rate /L_X (1-10) from the MCL / BAT count rate on that day / mCrab (from XRT)
08-20 16:21 12.4 1.4e36 0.0019+/-0.0017 13
08-21 19:31 27.7 2.3e36 0.0027+/-0.0016 29
08-22 22:43 43.0 4.9e36 0.0028+/-0.0020 45
08-23 22:35 28.8 3.3e36 0.0017+/-0.0022 30
08-24 19:10 27.5 3.2e36 0.0022+/-0.0022 29
08-25 03:19 33.9 3.9e36 0.0027+/-0.0019 35
08-26 XX:XX XX.X X.Xe36 0.0035+/-0.0028 XX
08-27 XX:XX XX.X X.Xe36 0.0034+/-0.0033 XX
08-28 12:13 XX.X X.Xe36 0.0082+/-0.0031 XX


Take the following with a grain of salt (because I may be predisposed to the answer). But given AAVSO measurements, the public LCO light curve, the recent Swift/BAT data and the historic Swift/BAT data, I expect that the source will get much brighter in optical.


Since there are two forums, I suggest all messages get posted in both


Clear Skies!



Bright source expected!

Hi All,

First off, keep up the great work (AAVSO lightcurve). I'm particularly thrilled with looking at Geoffrey Stone (SGEA)'s R band data as it shows a lot of variability --- 2 mag!! I'd have to check the literature to see if we've seen such extreme flickering on rapid time-scales for this source before.

And for all of you interested folks out there, the source is likely to be reaching peak brightness in the next week.

While we got some unlucky happenstances over the past week with the Swift X-ray observatory, the source was notably brighter the last few days (I'll try to keep the X-ray light curves updated). The source is now within a factor of about 2 of its peak in X-rays during the last few outbursts I have studied, although it never got bright at the hardest X-rays measured by the Swift BAT instrument.

So I think that the next week will be quite critical. After that, I'm likely to suggest skipping the rapid variability stuff on a daily basis. This will be picked up again when the source decline begins.

Thanks for all of your hard work!

Clear Skies,


The Plateau Stage & You

Hi All,


Thanks for your continued hard work. The outburst of Aql X-1 is in a plateau stage, from which we expect it to slowly decline. X-ray and matched extent optical lightcurves are presented offsite. Your data show the source is at approximately V~17-16, R ~16.5-15.5, and I~16-15.

We have begun to request observations from the Swift X-ray Observatory (getting both X-ray and Ultraviolet data) for observtions every 3-4 days. The next observations are nominally scheduled for some time on September 22 and September 26. These are the days when rapid cadence observations in one filter and observations across your filters are most useful.

But, because we need to know when this source goes into its rapid decline. I ask that if you can keep a daily eye on this source in one constant filter, that would be extra helpful. Given that many of you have seen 1 (to even 2) mag variability over a few hours, at least 4 snapshots over the night when the source is visible would be super useful.

Finally, if you have any questions about the campagin, both logistical and scientific, please feel free to ask!

Clear Skies,

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