GRB 220506A

S. Urabe, J. Kohara (Chuo U.), H. Negoro (Nihon U.),
M. Nakajima, K. Kobayashi, K. Asakura, K. Seino (Nihon U.),
T. Mihara, T. Kawamuro, S. Yamada, T. Tamagawa, M. Matsuoka (RIKEN),
T. Sakamoto, M. Serino, S. Sugita, H. Hiramatsu, A. Yoshida (AGU),
Y. Tsuboi, W. Iwakiri, H. Kawai, Y. Okamoto, S. Kitakoga (Chuo U.),
M. Shidatsu, M. Iwasaki (Ehime U.),
N. Kawai, M. Niwano, R. Hosokawa, Y. Imai, N. Ito, Y. Takamatsu (Tokyo Tech),
S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, M. Tominaga, T. Nagatsuka, M. Kurihara (JAXA),
Y. Ueda, S. Ogawa, K. Setoguchi, T. Yoshitake, Y. Goto, R. Uematsu, K. Inaba (Kyoto U.),
H. Tsunemi (Osaka U.),
M. Yamauchi, Y. Nonaka, T. Sato, R. Hatsuda, R. Fukuoka (Miyazaki U.), K. Yamaoka (Nagoya U.),
Y. Kawakubo (LSU),
M. Sugizaki (NAOC) 
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray 
transient source at 06:28:15 UT on 2022 May 6.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (239.698 deg, -26.668 deg) = (15 58 47, -26 40 04) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.34 deg and 0.27 deg, respectively.
The roll angle of long axis from the north direction is 64.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 103 +- 22 mCrab
(4.0-10.0keV, 1 sigma error).
Without assumptions on the source constancy, we obtain a rectangular error
box for the transient source with the following corners:
(R.A., Dec) = (239.079, -27.388) deg = (15 56 18, -27 23 16) (J2000)
(R.A., Dec) = (239.660, -27.603) deg = (15 58 38, -27 36 10) (J2000)
(R.A., Dec) = (240.203, -26.432) deg = (16 00 48, -26 25 55) (J2000)
(R.A., Dec) = (239.626, -26.218) deg = (15 58 30, -26 13 04) (J2000)
There was no significant excess flux in the previous transit at 00:45 UT
and in the next transit at 08:01 UT with an upper limit of 20 mCrab for each.

P. A. Evans (U. Leicester) reports on behalf of the Swift team:

Swift has initiated a series of observations, tiled on the sky, of the
MAXI GRB 220506A. Automated analysis of the XRT data will
be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00105

Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. The probability of finding
serendipitous sources, unrelated to the MAXI event is high: any X-ray source
considered to be a probable afterglow candidate will be reported via a GCN Circular
after manual consideration.

Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).

This circular is an official product of the Swift-XRT team.

J.P. Osborne (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC &
INAF-OAR), V. D'Elia (SSDC & INAF-OAR), A. Tohuvavohu (U. Toronto), B.
Sbarufatti (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P.
Beardmore (U. Leicester) and P.A. Evans (U. Leicester) report on behalf
of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the MAXI-detected
burst GRB 220506A (Urabe et al. GCN Circ. 32001
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 ) in a series of
observations tiled on the sky. The total exposure time is 1.2 ks,
distributed over 6 tiles; the maximum exposure at a single sky location
was 463 s. The data were collected between T0+38.2 ks and T0+55.6 ks,
and are entirely in Photon Counting (PC) mode. 

An uncatalogued X-ray source is detected and is above the RASS 3-sigma
upper limit at this position, and is therefore likely the GRB
afterglow.  The position of this source is RA, Dec=239.7257, -26.4186
which is equivalent to:

RA (J2000): 15:58:54.18
Dec(J2000): -26:25:06.9

with an uncertainty of 7.2 arcsec (radius, 90% confidence).  This
position is 15.0 arcmin from the MAXI position.  We cannot determine at
the present time whether the source is fading.

The results of the XRT-team automatic analysis of the likely afterglow
are at https://www.swift.ac.uk/xrt_products/TILED_GRB00105/Source1.php.

The results of the full analysis of the tiled XRT observations are
available at https://www.swift.ac.uk/xrt_products/TILED_GRB00105.

This circular is an official product of the Swift-XRT team.

Y.-D. Hu, E. Fernandez-Garcia, I. Perez-Garcia, T.-R. Sun, A. J. Castro-Tirado, M.D. Caballero-Garcia, R. Sanchez-Ramirez (IAA-CSIC), D. Hiriart and W. H. Lee (UNAM), C. J. Perez del Pulgar and I. Carrasco (UMA), I. H. Park (SKKU) on behalf of a larger collaboration, report:

Following the detection of GRB 220506A by MAXI/GSC (Urabe et al. GCNC 32001) and Swift (Evans et al. GCNC 32005), the BOOTES-5/JGT 0.6m robotic telescope at Observatorio Astronomico Nacional in San Pedro Martir (Mexico) observed the GRB location starting on May 7, 10:36 UT (~1.2 days after trigger) at high airmass. In the co-added image (15 x 60 s exposures in the clear filter), no optical afterglow is detected within the Swift/XRT error region (Osborne et al. GCNC 32006) down to 19.0 mag.

We thank the staff at Observatorio Astronomico Nacional in San Pedro Martir for their excellent support.

V. Swain (IITB), H. Kumar (IITB), K. Angail (IAO), V. Bhalerao (IITB), G.
C. Anupama (IIA), S. Barway (IIA) report on behalf of the GIT team:

We observed GRB 220506A detected by MAXI/GSC (Urabe et al. GCN #32001
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 ) and
Swift (Phil Evans et al. GCN #32005
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 ), with a 0.7m GROWTH-India Telescope
(GIT). The observation started at 19:08:47 UT on 2022-05-06, 12.68 hours
after the MAXI/GSC trigger. We obtained multiple 300-sec exposures in the
r' filter. We did not detect any new source in our stacked image within the
7.2 arcsec radius circle around R.A.= 15h 58m 54.18s, Dec.= -26d 25' 06.9"
(Phil Evans et al. GCN #32006
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 ). The obtained upper limit follows as:
----------------------------------------------------------------------------------
 JD (mid) | T_mid-T0(hrs) | Exposure (sec) | Filter | Lim_mag (5-sigma) |
----------------------------------------------------------------------------------
 2459706.327602595 | 13.39 | 7 x 300 (stacked) | r' | >20.38 |
----------------------------------------------------------------------------------

The magnitudes are calibrated against PanSTARRS DR1 (Chambers et al., 2016)
and not corrected for Galactic extinction.


The GROWTH India Telescope (GIT) is a 70-cm telescope with a 0.7-degree
field of view, set up by the Indian Institute of Astrophysics (IIA) and the
Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and
IUSSTF. It is located at the Indian Astronomical Observatory (Hanle),
operated by IIA. We acknowledge funding by the IITB alumni batch of 1994,
which partially supports operations of the telescope. Telescope technical
details are available at https://sites.google.com/view/growthindia/.

N. Ito, M. Sasada, Y. Imai, K. L. Murata, M. Niwano, Y. Takamatsu, S.
Sato, M. Tateda, T. Hattori, R. Hosokawa, Y. Yatsu, and N. Kawai
(Tokyo Tech) report on behalf of the MITSuME collaboration:

We observed the field of GRB 220506A (Urabe et al. GCN Circular
#32001
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 , Evans et al. GCN Circular #32005
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 , Osborne et al. GCN Circular
#32006
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 , Hu et al. GCN Circular #32008
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 , Swain et al. GCN Circular
#32012
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 ) with the optical three color (g', Rc, and Ic) CCD cameras
attached to the MITSuME 50 cm telescope Akeno.

The observation with a series of 60 sec exposures started at
2022-05-06 13:00:47 UT (6.5 hours after the MAXI/GSC trigger). We
stacked the images with good conditions. Additionally, we performed
the other follow-up observation starting at 2022-05-09 16:12:56 UT. We
did not detect any uncatalogued sources within the XRT error region
(Osborne et al. GCN Circular #32006
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 ). We obtained the 5-sigma limits
of the stacked images as follows.

T0+[hour] MID-UT T-EXP[sec] 5-sigma limits
------------------------------------------------------------------------------------------------
8.2 2022-05-06 14:42:28 240 g'>16.9, Rc>17.0, Ic>16.6
34.2 2022-05-07 16:37:41 8580 g'>18.9, Rc>19.5, Ic>18.8
82.9 2022-05-09 17:21:47 6660 g'>19.0, Rc>19.4, Ic>19.0
------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time

We used PS1 catalog for flux calibration.
The magnitudes are expressed in the AB system.
The images were processed in real-time through the MITSuME GPU
reduction pipeline (Niwano et al. 2021, PASJ, Vol.73, Issue 1, Pages
4-24; https://github.com/MNiwano/Eclaire).

D. Svinkin, D. Frederiks, A.Lysenko, A.Ridnaia,
A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long-duration GRB 220506A
(MAXI/GSC detection: Urabe et al., GCN Circ. 32001
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 )
was detected by Konus-Wind (KW) in the waiting mode.

A Bayesian block analysis of the KW waiting mode data in
the 20-1500 keV band reveals a ~6 sigma count rate increase
over background in the interval from ~T0-115 s to ~T0-89 s,
where T0 = T0(MAXI) = 23295 s UT (06:28:15).

The K-W light curve of this burst is available at
http://www.ioffe.ru/LEA/GRBs/GRB220506A/

As observed by Konus-Wind, the burst had a fluence of
1.46(-0.10,+1.13)x10^-6 erg/cm2 and a 2.944-s peak flux,
measured from ~T0-112 s, of 1.14(-0.28,+0.92)x10^-7 erg/cm2/s
(both in the 20 - 1500 keV energy range).

Modeling the K-W 3-channel time-integrated spectrum
(from ~T0-115 s to ~T0-89 s)
by a power law with exponential cutoff (CPL) model
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha > -1.0 and Ep = 110(-16,+70) keV.

All the quoted errors are estimated at the 1 sigma confidence level.
All the presented results are preliminary.