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GRB 210112A

GCN Circular 29289

Subject
GRB 210112A: Swift detection of a burst with an optical counterpart
Date
2021-01-12T01:51:00Z (4 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
E. Ambrosi (INAF-IASFPA), S. D. Barthelmy (GSFC),
A. D'Ai (INAF-IASFPA), V. D'Elia (SSDC), J. A. Kennea (PSU),
N. J. Klingler (PSU), S. Laha (GSFC/UMBC/CRESST),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 01:37:03 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210112A (trigger=1016881).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 218.999, +33.070 which is 
   RA(J2000)  =  14h 36m 00s
   Dec(J2000) = +33d 04' 13"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows multiple peaks
with the larger peak at T+70 sec and duration of ~150 sec. The peak count rate
was ~20800 counts/sec (15-350 keV), at ~68 sec after the trigger. 

The XRT began observing the field at 01:38:18.0 UT, 74.2 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 219.0044, 33.0566 which is equivalent to:
   RA(J2000)  = 14h 36m 1.06s
   Dec(J2000) = +33d 03' 23.8"
with an uncertainty of 5.0 arcseconds (radius, 90% containment). This
location is 50 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

The initial flux in the 0.1 s image was 7.10e-08 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 82 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	14:36:01.45 = 219.00606
  DEC(J2000) = +33:03:15.4  =  33.05428
with a 90%-confidence error radius of about 0.66 arc sec. This position is 9.8
arc sec. from the center of the XRT error circle. The estimated magnitude is
19.52 with a 1-sigma error of about  0.16. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.014. 

Burst Advocate for this burst is E. Ambrosi (elena.ambrosi AT inaf.it). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/)

GCN Circular 29290

Subject
GRB 210112A: Enhanced Swift-XRT position
Date
2021-01-12T04:17:47Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 579 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 210112A, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 219.00603, +33.05415 which is equivalent
to:

RA (J2000): 14h 36m 1.45s
Dec (J2000): +33d 03' 15.0"

with an uncertainty of 1.7 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).

This circular was automatically generated, and is an official product of the
Swift-XRT team.

GCN Circular 29292

Subject
GRB 210112A: Kitab a optical upper limit
Date
2021-01-12T11:19:27Z (4 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
A. Novichonok (Petrozavodsk State University, KIAM), S. Belkin (IKI), 
A. Pozanenko (IKI), Sh. Ehgamberdiev (UBAI) report on behalf of GRB IKI FuN:

We observed the field of GRB 210112A (Ambrosi  et al., GCN 29289) with 
  Kitab-ISON RC-36  telescope starting on 2021-01-12 (UT) 01:54:30, i.e. 
447 seconds after trigger in Clear filter. We do not detect the 
afterglow candidate (Ambrosi  et al., GCN 29289) within enhanced 
Swift-XRT position (Goad et al., GCN 29290).
Preliminary photometry of the field is following

Date,      UT start, t-T0,   Exp.,  Filter,  OT,   Err., UL
                     (mid, days)
2021-01-12  01:54:30  0.01541 11*30 CR       n/d   n/d   18.5


The photometry is based on nearby USNO-B1.0 stars
USNO-B1.0_id R2
1231-0260671 14:35:00.70080 +33:06:09.4428 14.32
1229-0281658 14:34:57.67344 +32:58:13.0800 14.75



At 01:37:03 UT

GCN Circular 29293

Subject
GRB 210112A: AGILE detection
Date
2021-01-12T12:30:09Z (4 years ago)
From
Alessandro Ursi at INAF/IAPS <alessandro.ursi@gmail.com>
A. Ursi, M. Cardillo (INAF/IAPS), C. Pittori (SSDC, and INAF/OAR), M.
Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), A. Argan, C. Casentini, Y.
Evangelista, G. Piano (INAF/IAPS), F. Lucarelli, F. Verrecchia (SSDC, and
INAF/OAR), A. Bulgarelli, V. Fioretti, F. Fuschino, N. Parmiggiani
(INAF/OAS-Bologna), M. Marisaldi (INAF/OAS-Bologna, and Bergen University),
M. Pilia, A. Trois (INAF/OA-Cagliari), I. Donnarumma (ASI), F. Longo (Univ.
Trieste and INFN Trieste), A. Giuliani (INAF/IASF-Mi), report on behalf of
the AGILE Team:

The AGILE satellite detected GRB 210112A, reported by Swift (GCNs #29289,
#29290), at T0 = 2021-01-12 01:37:58 (UT).

The event is clearly visible in the scientific ratemeters of the SuperAGILE
(SA; 18-60 keV), MiniCALorimeter (MCAL; 0.4-100 MeV), and AntiCoincidence
(AC; 50-200 keV) detectors. The burst lasted about 25 s and released 1120
counts in the SA detector (above a background rate of 60 Hz), 25140 counts
in the MCAL detector (above a background rate of 1250 Hz), and 71500 counts
in the AC detector (above a background rate of 3570 Hz). The AGILE
ratemeters light curves can be found at:
http://www.agilescienceapp.it/notices/GRB210112A_AGILE_RM.png .

Additional analysis of AGILE data is in progress.

GCN Circular 29295

Subject
GRB 210112A: Swift-XRT refined Analysis
Date
2021-01-12T17:20:18Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), M. Capalbi
(INAF-IASFPA), M. Perri (SSDC & INAF-OAR), B. Sbarufatti (PSU), D.N.
Burrows (PSU), J. D. Gropp (PSU), K.L. Page (U. Leicester) and E.
Ambrosi report on behalf of the Swift-XRT team:

We have analysed 8.5 ks of XRT data for GRB 210112A (Ambrosi et al. GCN
Circ. 29289), from 77 s to 46.0 ks after the  BAT trigger. The data
comprise 859 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Goad et al. (GCN Circ. 29290).

The late-time light curve (from T0+6.4 ks) can be modelled with a
power-law decay with a decay index of alpha=1.36 (+/-0.06).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.56 (+/-0.03). The
best-fitting absorption column is  2.34 (+/-0.14) x 10^21 cm^-2, in
excess of the Galactic value of 9.5 x 10^19 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.01 (+0.10, -0.09)
and a best-fitting absorption column of 2.8 (+/-0.4) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.7 x 10^-11 (5.1 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.8 (+/-0.4) x 10^21 cm^-2
Galactic foreground: 9.5 x 10^19 cm^-2
Excess significance: 12.3 sigma
Photon index:	     2.01 (+0.10, -0.09)

If the light curve continues to decay with a power-law decay index of
1.36, the count rate at T+24 hours will be 0.046 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x
10^-12 (2.3 x 10^-12) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01016881.

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

GCN Circular 29296

Subject
GRB 210112A: OSN Reddened Afterglow Detection
Date
2021-01-12T19:28:59Z (4 years ago)
From
Alexander Kann at IAA-CSIC <kann@iaa.es>
D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, 
DARK/NBI), C. C. Thoene (HETH), M. Blazek, J. F. Agui Fernandez (both 
HETH/IAA-CSIC), and A. Sota (IAA-CSIC) report:

We observed the optical afterglow of GRB 210112A (Swfit detection: 
Ambrosi et al., GCN #29289; AGILE Detection: Ursi et al., GCN #29293) 
with the 1.5m telescope of the Observatorio de Sierra Nevada (OSN), 
Granada, Spain. We obtained 12 x 90 s exposures in B, Rc, Ic and 11 x 90 
s in V, between 2021-01-12 04:03:22.52 and 2021-01-12 05:21:34.99 UT. 
The afterglow is detected In the combined image of each band.

At 0.12587 days after the GRB, we measure Rc = 22.41 +/- 0.12 mag (AB 
mag, vs. a several nearby SDSS stars converted to Rc following the 
Lupton transformations, then transformed back to AB mag).

A preliminary analysis of all data reveals peculiar colors, the Rc - Ic 
color is large, whereas the colors between B, V, and Rc are quite flat. 
There is no source detected in either SDSS or PanSTARRS at the afterglow 
position, so this is probably not due to influence of the host galaxy. 
However, we are able to fit this SED with a large (A_V > 1 mag) amount 
of Milky-Way like dust at a redshift of z ~ 2 and an intrinsic slope in 
agreement with the one derived from X-ray observations. Such high 
extinction would be in line with the significant excess column density 
seen in the XRT observations (Evans et al., GCN #29295).

GCN Circular 29297

Subject
GRB 210112A: Swift-BAT refined analysis
Date
2021-01-13T01:45:13Z (4 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
M. Stamatikos (OSU), E. Ambrosi (INAF-IASFPA),
S. D. Barthelmy (GSFC), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):

Using the data set from T-239 to T+963 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 210112A (trigger #1016881)
(Ambrosi et al., GCN Circ. 29289).  The BAT ground-calculated position is
RA, Dec = 219.005, 33.058 deg which is
   RA(J2000)  =  14h 36m 01.3s
   Dec(J2000) = +33d 03' 30.4"
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 89%.

The mask-weighted light curve shows a multi-peaked structure that starts
at ~T-10 s and ends at ~T+220 s. The three main peaks occur at ~T+1 s,
~T+70 s, and ~T+105 s, respectively, and the one at ~T+70 s is the largest
peak.
T90 (15-350 keV) is 107.60 +- 13.02 sec (estimated error including
systematics).

The time-averaged spectrum from T-10.44 to T+218.47 sec is best fit by
a simple power-law model.  The power law index of the time-averaged
spectrum  is 1.45 +- 0.03.  The fluence in the 15-150 keV band is
2.33 +- 0.03 x 10^-5 erg/cm2. The 1-sec peak photon flux measured from
T+68.86 sec in the 15-150 keV band is 20.5 +- 0.6 ph/cm2/sec.
All the quoted errors are at the 90% confidence level.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/1016881/BA/

GCN Circular 29300

Subject
GRB 210112A: OSN second epoch, decay
Date
2021-01-13T19:50:01Z (4 years ago)
From
Alexander Kann at IAA-CSIC <kann@iaa.es>
D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, 
DARK/NBI), C. C. Thoene (HETH), M. Blazek, J. F. Agui Fernandez (both 
HETH/IAA-CSIC), and A. Sota (IAA-CSIC) report:

We observed again the optical afterglow of GRB 210112A (Swfit detection: 
Ambrosi et al., GCN #29289; AGILE Detection: Ursi et al., GCN #29293) 
with the 1.5m telescope of the Observatorio de Sierra Nevada (OSN), 
Granada, Spain. We obtained 3 x 450 s exposures in B, V, Rc each, and 8 
x 150 s in Ic, between 2021-01-13 04:29:28.99 and 2021-01-13 05:55:34.35 
UT.  The afterglow is now only detected in the combined Ic-band image. 
Together with the observations of the day before (Kann et al., GCN 
#29296), we measure (against the same SDSS comparison stars as before, 
in Vega mags):

Ic = 20.65 +/- 0.075 mag at 0.12587 days.

Ic = 22.57 +/- 0.217 mag at 1.12739 days.

This implies a decay index of alpha ~ 0.8.

GCN Circular 29301

Subject
GRB 210112A: 1.3m DFOT Optical upper limit
Date
2021-01-13T19:54:17Z (4 years ago)
From
Rahul Gupta at ARIES, India <rahulbhu.c157@gmail.com>
Rahul Gupta (ARIES),  Amit Kumar (ARIES), Dimple (ARIES), Ankur Ghosh
(ARIES), Krishan Chand (ARIES), Amar Aryan (ARIES), Shashi B. Pandey
(ARIES), and Kuntal Misra (ARIES) report:


We observed the filed of Swift and AGILE detected GRB 210112A (Ambrosi
et al., GCN 29289; and Ursi et al., GCN 29293) with 1.3m Devasthal
Fast Optical Telescope (DFOT) located at Devasthal observatory of
Aryabhatta Research Institute of Observational Sciences (ARIES),
India. The observations were started on 2021-01-13 at 00:06:18 UT i.e.
~ 22.49 hours after the BAT trigger. We have taken multiple frames
having an exposure time of 120 s in the R filter. We do not detect the
optical afterglow candidate (Ambrosi et al., GCN 29289; and Kann et
al., GCN 29296) within enhanced Swift-XRT position (Goad et al., GCN
29290).


We obtain the following 3-sigma upper limits in the stacked image.


Date Start_UT    T_start-T0 (hrs)        Filter   Exp time (s)
Limiting Magnitude

============================================================
2021-01-13   00:18:18      22.69              R              120*12
           > 22.0



The magnitude is not corrected for the Galactic extinction in the
direction of the burst. Photometric calibration is performed using the
standard stars from the USNO-B1.0 catalogue.

This circular may be cited.

GCN Circular 29302

Subject
GRB 210112A: Mondy optical observations
Date
2021-01-13T20:28:18Z (4 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
N. Pankov (HSE), A. Pozanenko (IKI), E. Klunko (ISTP), S. Belkin (IKI) 
report  on behalf of GRB IKI FuN:

We observed the field of GRB 210112A (Ambrosi  et al., GCN 29289; Ursi 
et al., GCN #9293) with AZT-33IK telescope of Sayan observatory (Mondy) 
starting on 2021-01-12 (UT) 20:41:40. The optical afterglow (Ambrosi  et 
al., GCN 29289; Kann  et al., GCNs 29296, 29300) is not detected in 
stacked  image in R-filter. The non detection of the afterlow is 
consistent with other non-detections in R-filter (Novichonok  et al., 
GCN 29292; Gupta et al., GCN 29301).

Preliminary photometry of the optical transient in a combined image is 
following

Date       UT start   t-T0       Filter Exp.    OT    Err.  UL(3sigma)
                       (mid, days)        (s)

2021-01-12 20:41:40   0.80738    R      18*120   n/d  n/d   22.4


The photometry is based on the nearby USNO-B1.0 stars.

GCN Circular 29303

Subject
GRB 210112A: Swift/UVOT Detection
Date
2021-01-15T03:50:43Z (4 years ago)
From
Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>
M. H. Siegel (PSU) and Ambrosi (INAF-IASFPA)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210112A
83 s after the BAT trigger (Ambrosi et al., GCN Circ. 29289).
A source consistent with the XRT position
(Goad et al. GCN Circ. 29290)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
  RA  (J2000) =  14:36:01.49 = 219.00619 (deg.)
  Dec (J2000) = +33:03:15.3  =  33.05424 (deg.)
with an estimated uncertainty of 0.50 arc sec. (radius, 90% confidence).

Preliminary detections and 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: 

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white               83          233          147         19.54 +/- 0.10
v                  626         1419           97        >18.5
b                  551         1517           97        >19.1
u                  296         1493          304        >20.2
w1                 675         1468           78        >19.1

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.014 in the direction of the burst
(Schlegel et al. 1998).

GCN Circular 29315

Subject
Konus-Wind detection of GRB 210112A
Date
2021-01-17T23:28:52Z (4 years ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
D. Svinkin, S. Golenetskii, D. Frederiks, M. Ulanov,
A. Tsvetkova, A. Lysenko, A. Ridnaia, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration GRB 210112A
(Swift-BAT detection: Ambrosi et al., GCN Circ. 29289;
AGILE detection: Ursi et al., GCN Circ. 29293)
triggered Konus-Wind at T0=5886.553 s UT (01:38:06.553).

The burst light curve shows a multipeaked structure
which starts at ~T0-73 s and has a total duration of ~143 s.
The emission is seen up to ~5 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB210112_T05886

As observed by Konus-Wind, the burst
had a fluence of 6.72(-0.65,+0.72)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+7.856 s,
of 1.02(-0.18,+0.19)x10^-5 erg/cm2/s
(both in the 20 keV - 16 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+68.608 s)
is best fit in the 20 keV - 16 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.96(-0.08,+0.08),
the high energy photon index beta = -2.71(-0.53,+0.25),
the peak energy Ep = 214(-16,+18) keV
(chi2 = 87/97 dof).

The spectrum near the maximum count rate
(measured from T0+7.168 s to T0+9.216 s)
is best fit in the 20 keV - 16 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.85(-0.12,+0.13),
the high energy photon index beta = -2.67(-0.57,+0.27),
the peak energy Ep = 219(-25,+28) keV
(chi2 = 38/65 dof).

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.

GCN Circular 29319

Subject
GRB 210112A: Deep CAHA 2.2m detection
Date
2021-01-18T15:53:55Z (4 years ago)
From
Alexander Kann at IAA-CSIC <kann@iaa.es>
D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, 
DARK/NBI), C. C. Thoene (HETH), M. Blazek, J. F. Agui Fernandez (both 
HETH/IAA-CSIC), and J. I. Vico Linares (CAHA) report:

We observed the afterglow position (Ambrosi et al., GCN #29289) of the 
bright Swift GRB 210112A (Swift detection: Ambrosi et al., GCN #29289; 
AGILE detection: Ursi et al., GCN #29293; Konus-Wind detection: Svinkin 
et al., GCN #29315) with CAFOS at the 2.2m telescope at Calar Alto, 
Almeria, Spain, in the Ic band. We obtained 10 x 360 s exposures, 
centered at 5.1696 days after the GRB, under good conditions but 
mediocre seeing.

The afterglow (Kann et al., GCNs #29296,29300; Siegel et al., GCN 
#29303) is faintly detected. We measure Ic = 23.69 +/- 0.24 mag. (AB 
mag, vs. a several nearby SDSS stars converted to Ic following the 
Lupton transformations, then transformed back to AB mag).

This magnitude lies slightly above the extrapolation of the decay found 
during the first two epochs (Kann et al., GCN #29300) and may indicate 
an underlying host galaxy. Indeed we also see another faint, possibly 
extended source about 2" to the East, at RA (J2000) = 14:36:01.453, Dec. 
(J2000) = +33:03:13.40, which may be the host galaxy or a system 
interacting with it. However, the rough redshift estimate of z ~ 2 (Kann 
et al., GCN #29296) would imply this must be a very luminous system, or 
a foreground interloper.

GCN Circular 29326

Subject
GRB 210112A: Insight-HXMT/HE detection
Date
2021-01-19T11:22:13Z (4 years ago)
From
Y Q Zhang at IHEP <yqzhang@ihep.ac.cn>
C. Zheng, C. Cai, J. C. Liu, Q. Luo, S. Xiao, 
W. C. Xue, Q. B. Yi, Y. Q. Zhang, Y. Huang, C. K. Li, 
G. Li, X. B. Li, J. Y. Liao, X. Y. Song, S. L. Xiong, C. Z. Liu, 
X. F. Li, Z. W. Li, Z. Chang, A. M. Zhang, Y. F. Zhang, 
X. F. Lu, C. L. Zou (IHEP), Y. J. Jin, Z. Zhang (THU), 
T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, 
M. Wu, Y. P. Xu, S. N. Zhang (IHEP), 
report on behalf of the Insight-HXMT team:

At 2021-01-12T01:38:13.400 (T0), Insight-HXMT/HE detected 
GRB 210112A (trigger ID: HEB210112068) in a routine search of the data, 
which also triggered Swift/BAT (E. Ambrosi (INAF-IASFPA) et al. ,GCN #29289).

The Insight-HXMT/HE light curve mainly consists of multiple 
pulses with a duration (T90) of 12.27 s measured from T0+0.91 s. 
The 1-ms peak rate, measured from T0+7.63 s, is 2134 cnts/sec. 
The total counts from this burst is 213416252 counts. 
URL_LC: http://twiki.ihep.ac.cn/pub/HXMT/GRBList/HEB210112068_lc.jpg

All measurements above are made with the CsI detectors operating in the 
regular mode with the energy range of about 80-800 keV (deposited energy). 
Only gamma-rays with energy greater than about 200 keV can penetrate 
the spacecraft and leave signals in the CsI detectors installed inside 
of the telescope. 

Insight-HXMT is the first Chinese space X-ray telescope, which was 
funded jointly by the China National Space Administration (CNSA) and 
the Chinese Academy of Sciences (CAS). 
More information about it could be found at: 
http://www.hxmt.org.

GCN Circular 29333

Subject
GRB 210112A: 3.6m DOT optical detection
Date
2021-01-20T06:14:31Z (4 years ago)
From
Dimple Panchal at ARIES, India <dimplepanchal96@gmail.com>
Dimple (ARIES), K. Misra (ARIES), A. Ghosh (ARIES), R. Gupta (ARIES),  A.
Kumar (ARIES), S.B. Pandey (ARIES) report:

We carried out the follow-up observations of GRB 210112A (Ambrosi et al.
GCN #29289) with Aries Devasthal Faint Object Spectrograph and Camera
(ADFOSC) mounted on the 3.6m Devasthal Optical Telescope (DOT) at Devasthal
observatory of Aryabhatta Research Institute of observational sciencES
(ARIES), India. The observations started on 2021-01-13 at 23:59:18 UT in
i-band (sdss). We observed a series of 6 images with an exposure time of
300 seconds each. We detect the afterglow at 1.933 days after the burst,
reported by Ambrosi et al. GCN #29289; Ursi et al. GCN #29293;  Kann et al.
GCNs #29296,29300; Siegel et al. GCN #29303, in i-band with a magnitude of
23.19 +- 0.166 (AB mag), calibrated with the nearby PanSTARRS field. Our
results are consistent with the power-law decay index of 0.8 reported by
Kann et al. #29296.

The magnitude is not corrected for Galactic extinction in the direction of
the burst.

GCN Circular 29456

Subject
GRB 210112A: LBT host detection and correction to GCN 29319 (CAHA observations)
Date
2021-02-10T15:12:35Z (4 years ago)
From
Alexander Kann at IAA-CSIC <kann@iaa.es>
A. Rossi (INAF-OAS), on behalf of the CIBO collaboration, and D. A. Kann 
(HETH/IAA-CSIC) report:

We observed the field of GRB210112A (Ambrosi et al., GCN #29289; Ursi et 
al., GCN #29293; Svinkin et al., GCN #29315) simultaneously in the r' 
and z' bands with the LBC imager mounted on the Large Binocular 
Telescope (LBT, Mt. Graham, AZ, USA). We obtained 20 min of imaging on 
2021-02-05, 24.3 days after the burst trigger. Observations were 
performed under mediocre seeing conditions and reached a depth of r' ~ 
26 mag.

At the position of the afterglow (Ambrosi et al., GCN #29289), we 
clearly detect the host galaxy in both filters and we measure the 
following AB magnitudes:

r' = 23.96 +/- 0.15 mag,
z' = 23.38 +/- 0.15 mag.

calibrated against SDSS field stars.

Therefore, we confirm that the flattening observed by Kann et al. (GCN 
#29319) was due to the host component.

However, we do not see the faint object detected by Kann et al. at RA, 
Dec. = 14:36:01.453, +33:03:13.40 (J2000). We have investigated the CAHA 
and OSN (Kann et al., GCN 29296) images and found that the source 
detected by Kann et al., GCN 29319, which should have been "South" of 
the afterglow position, not "East", is the actual afterglow (with the 
fainter, northern extension possibly stemming from image distortion or a 
slight mismatch when co-adding frames), the offset stemming from a small 
arcsecond-scale astrometry mismatch. For the afterglow position, we 
measure Ic = 23.52 �� 0.19 mag (AB), replacing the value given in GCN 
#29319. We estimate the underlying host to be Ic ~ 23.7 mag (AB) from 
the LBT photometry.

Correlating the OSN image with the LBT image, we find an afterglow 
position of RA, Dec. = 14:36:01.492 +33:03:14.945 (J2000), with errors 
of 0".2 in each coordinate, calibrated against Gaia DR2, in good 
agreement with the UVOT position (Ambrosi et al., GCN #29289).

In the LBT image, we furthermore detect a second, fainter, but probably 
also extended source just 2" north-north-east of the host (at RA, Dec. 
=14:36:01.54 +33:03:18.7; J2000) with r' = 24.5 �� 0.2 mag. It is unclear 
if this likely galaxy is related to the host galaxy.

We acknowledge the excellent support from the LBTO and LBT-INAF staff, 
particularly B. Rothberg and D. Paris, in obtaining these observations.

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