(cba:news) possible riches in ATel 13257

Joe Patterson jop at astro.columbia.edu
Mon Nov 4 06:14:06 EST 2019

Hi CBAers,

The object described in ATel 13257 could be quite interesting to us. 
It's seasonally appropriate, and at a sufficient galactic latitude (-20) 
to suggest (probably) no great problems in identification and/or 
interstellar absorbtion.  It also gets more well-placed in the sky as 
time goes on.

  BUT since northern observers are shut out, it's important that 
southern observers jump to it!  Based on the example of Maxie and 
others, the key signature right now - other than the previously reported 
X-rays - is probably the very rapid variations (seconds).  Since 
*clouds* have a similar signature, it would be helpful if you included 
some comment about this worry, along with the time-series data you acquire.

joe p

-------- Forwarded Message --------
Subject: ATel  13257, 13258
Date: Mon, 4 Nov 2019 01:59:38 -0500
From: atel at astronomerstelegram.org
To: jop at astro.columbia.edu

The Astronomer's Telegram 
Posted: Within the last 24 hours
ATEL #13257							     ATEL #13257

Title:	MAXI J0637-430: Swift localization, optical counterpart
Author:	J. A. Kennea (PSU), A. Bahramian (ICRAR), P. A. Evans, A.
		P. Beardmore (U Leicester), H. A. Krimm (CRESST/GSFC/USRA), P. Romano
		(INAF-IASFPA), K. Yamaoka (Nagoya U.), M. Serino (RIKEN), H. Negoro
		(Nihon U.)
Queries:	jak51 at psu.edu
Posted:	3 Nov 2019; 19:10 UT
Subjects:X-ray, Black Hole, Transient

At 13:39UT on November 3, 2019, Swift performed a target of opportunity
observation to observe the location of the newly discovered soft X-ray
transient, MAXI J0637-430 (Negoro et al., ATEL #13256). Swift performed
a 7-point tiling of the MAXI error region with an exposure of 200s per
tile. In the Photon Counting mode data, we find a previously uncatalogued
bright X-ray source at the following location: RA/Dec(J2000) = 99.09828,
-42.86780, which is equivalent to:
RA(J2000) = 06h 36m 23.59s,
Dec(J2000) = -42d 52m 04.1s,
with an estimated uncertainty of 2.3 arc-seconds radius (90% confidence).
This position lies 28.4 arc-mins from the 2-4keV MAXI localization, and
18.5 arc-mins from the 4-10 keV band MAXI localization. We note that the
XRT position is consistent with the hard band localization, but not the
soft band. However, the XRT detected source is bright and uncatalogued,
suggesting that this is MAXI J0637-430.  This transient is bright, with
a count rate corrected for pile up of ~310 XRT count/s.
The pile-up corrected X-ray spectrum can be well fit by an absorbed 
+ disk blackbody spectrum, with kT_in = 0.9 +/- 0.1 keV, and photon index
= 2.3 +/- 0.8. Absorption with this model is ~8 x 10^20 cm^2. The observed
flux is 1 x 10^-8 erg/s/cm^2 (0.5 -10 keV).
In addition UVOT detects a source inside the XRT error circle, with a 
of u = 14.87 +/- 0.02 (Vega). A Vizier catalog search does not reveal a
known star at this localization, suggesting that this optical source has
brightened significantly. We note that significant brightening (~5 
of the optical counterpart during X-ray outburst is common for BH-LMXBs.
The UVOT position is RA/Dec(J2000) = 99.09881, -42.86785, which is 
RA(J2000) = 06h 36m 23.23s
Dec(J2000) = -42d 52m 04.25s.
We encourage further observations of this source in optical and X-ray in
order to determine the nature of the source.
This work was supported by NASA Grant 80NSSC19K1383, awarded by the Swift
Guest Investigator program.

Password Certification: Jamie A. Kennea (kennea at astro.psu.edu)

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