(cba:news) Fwd: AAVSO Alert Notice 630: Coverage needed TONIGHT for ASASSN-18ey = MAXI J1820+070

Joe Patterson jop at astro.columbia.edu
Wed Apr 11 18:42:18 EDT 2018

Hi CBAers,

You know the target.  A multi-wavelength blitz!  So let's do it. Not 
very well positioned in the sky, but they don't have much choice 
(usually because of the orientation of the spacecraft solar panels, the 
observing windows favor +/- 6 hours of the Sun).  Good for all hemispheres!

joe p

-------- Forwarded Message --------
Subject: 	AAVSO Alert Notice 630: Coverage needed TONIGHT for 
ASASSN-18ey = MAXI J1820+070
Date: 	Wed, 11 Apr 2018 22:35:09 +0000
From: 	AAVSO <aavso at aavso.org>
Reply-To: 	AAVSO <aavso at aavso.org>
To: 	jop at astro.columbia.edu

AAVSO Alert Notice 630: Coverage needed TONIGHT for ASASSN-18ey = MAXI 

   AAVSO Alert Notice 630

     *Coverage needed TONIGHT for ASASSN-18ey = MAXI J1820+070*

/*April 11, 2018*/: Dr. Gregory Sivakoff (University of Alberta), on 
behalf of a large number of collaborators, has requested AAVSO 
observers' assistance in monitoring the outbursting black hole X-ray 
binary ASASSN-18ey = MAXI J1820+070 in support of a multiwavelength 
"blitz" campaign *taking place tonight and into tomorrow*.

Dr. Sivakoff writes: "Black hole X-ray binaries tend to undergo one of 
two types of outbursts. The first (often called a "canonical outburst") 
involves a variety of changes in the properties of the disk that feeds 
the black hole and the jets/winds that can escape before they fall 
within the black hole's event horizon. The second (often called a 
"hard-state-only outburst") only involves the "hard" and the 
"hard-intermediate" accretion states. Each outburst provides different 
opportunities for studying the connection between accretion inflows and 

"MAXI J1820+070/ASASSN-18ey (hereafter MAXI J1820+070 to save a few 
characters) has appeared to have stalled its evolution in the "hard" 
state. This behaviour tends to occur in "hard-state-only" outbursts. For 
observers, the stalled behaviour means an extended opportunity to study 
the "hard" accretion state (which has an analogue with the accretion 
state of the vast majority of accreting supermassive black holes). While 
many of our observational programs were hoping to catch that transition 
from the "hard" state through the "intermediate" states to the "soft" 
state, we have adapted our plans to this outburst's behaviour. (And to 
be fair, many observational programs were already designed for the 
"hard" state).

"A second implication of the stalled behaviour at its current bright 
levels is that MAXI J1820+070 may be atypically close for a black hole 
X-ray binary. I have estimated that the source could be only 1 kpc (3260 
light-years) away, which would make it one of the nearest black hole 
X-ray binaries. This possibility has many of us quite excited; GAIA 
should provide the distance measurement via parallax soon."

He continues: "I am leading what I like to call a "blitz" campaign on 
the source. I use this term for a significant multiwavelength campaign 
focussed on a single day. My collaborators and I have planned this blitz 
for the night of April 11th. (Again I apologize for the short delay, but 
putting this together has taken all of my time recently). The campaign 
is designed to measure both rapid variability features (0.01 - 100 Hz) 
from X-ray to radio frequencies and the (quasi-)simultaneous broad-band 
spectral energy distribution. *Since the campaign is focusing on 
facilities that can see MAXI J1820+070 at some time within the window of 
April 12th 05:00 - 15:00 UTC, we strongly encourage multiwavelength 
observations (and communication of those observations) within that 
window. Observations within approximately 24 hours on either side of the 
window will also be useful for this campaign.*

*"For those with the capacity to do many high cadence CCD/CMOS 
observations on this bright source, we have been using the following 
comparison star:  URAT1 486-270264 (Zacharias et al. 2015) at 
RA=18h20m26.43s, Dec=+07d10m11.8s. For an example, see 
http://www.astronomerstelegram.org/?read=11437 . [Note: In the 
photometry table for the AAVSO sequence for ASASSN-18ey, the URAT1 star 
has the AUID 000-BMQ-477.]*

"I have reports that 1 Hz (1-second exposure) imaging can be done on a 
12" telescope with a fairly standard CCD. Although I cannot verify what 
the readout time or the what type of shutter was used. If you are going 
to try high cadence observations, be aware that both readout time and 
your shutter may be a limiting factor. Some detectors are capable of 
sub-array modes that reduce readout time at the sacrifice of your field 
of view."

*Beginning now and continuing through 2018 April 13, V time series are 
requested, with as short a cadence as possible (ideally, a time 
resolution of 0.1 second or better). If doing high-cadence time series, 
please see above regarding the comp star to use.*

Please see /AAVSO Alert Notice 624/ 
for more information about this object.

ASASSN-18ey = MAXI J1820+070 has a published optical range of 12.5 CV - 
18.3: V. The most recent observations submitted to the AAVSO 
International Database are:
   2018 Apr. 11.38536 UT, 12.249 CV +/-0.008 (F.-J. Hambsch, Mol, Belgium);
11.38548, 12.302 CV +/-0.008 (Hambsch);
11.38561, 12.384 CV +/-0.008 (Hambsch);
11.38572, 12.248 CV +/-0.009 (Hambsch);
11.38584, 12.190 CV +/-0.008 (Hambsch);
11.38597, 12.226 CV +/-0.008 (Hambsch);
11.38608, 12.375 CV +/-0.009 (Hambsch);

Coordinates (2000.0):  R.A. 18 20 21.95   Dec. +07 11 07.3

Charts with a comparison star sequence for ASASSN-18ey may be created 
using the AAVSO Variable Star Plotter (VSP) 
You may use either ASASSN-18ey or MAXI J1820+070 as the name when 
creating a chart. Note the comment above regarding choice of comparison 
star if carrying high-cadence time series observations.

Please submit observations to the AAVSO International Database using the 
name ASASSN-18ey.

This observing campaign is being followed on the AAVSO Time Sensitive 
Alerts online forum at

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.

Information on submitting observations to the AAVSO may be found at:


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