GRB 180224A

A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), J.D. Gropp (PSU),
H. A. Krimm (NSF/USRA), S. J. LaPorte (PSU),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL) and A. Tohuvavohu (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 22:21:07 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180224A (trigger=811561).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 202.661, +38.088 which is 
   RA(J2000)  =  13h 30m 39s
   Dec(J2000) = +38d 05' 17"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single FRED peak
with a duration of about 15 sec.  The peak count rate
was ~2200 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 22:22:28.1 UT, 80.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 202.68324, 38.07881 which is equivalent
to:
   RA(J2000)  = 13h 30m 43.98s
   Dec(J2000) = +38d 04' 43.7"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 71 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at http://www.swift.ac.uk/sper.  We
cannot determine whether the source is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 8.24
x 10^19 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 85 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	13:30:44.09 = 202.68370
  DEC(J2000) = +38:04:44.6  =  38.07906
with a 90%-confidence error radius of about 0.63 arc sec. This position is 0.9
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.94 with a 1-sigma error of about  0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.01. 

Burst Advocate for this burst is A. Y. Lien (amy.y.lien AT nasa.gov). 
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/too.html.)

P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 1326 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 180224A, 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 = 202.68383, +38.07876 which is equivalent
to:

RA (J2000): 13h 30m 44.12s
Dec (J2000): +38d 04' 43.5"

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.

V.Vladimirov, V. Lipunov, E.Gorbovskoy, N.Tyurina, V.Kornilov, 
D.Zimnukhov,   A.Krylov, I.Gorbunov, P.Balanutsa, A.Kuznetsov, V.Chazov, 
D. Kuvshinov (Lomonosov Moscow State University, SAI)

A. Tlatov, V.Senik, D. Dormidontov
(Kislovodsk Solar Station of the Pulkovo Observatory)

D.Buckley, S. Potter
(South African Astronomical Observatory),

O.Gres,  N.M.Budnev
(Irkutsk State University),

V.Yurkov, A.Gabovich, Yu.Sergienko
(Blagoveschensk Educational State University, Blagoveschensk),

R.Podesta, C.Lopez, F. Podesta
(Observatorio Astronomico Felix Aguilar (OAFA),
National University of San Juan,  Argentina),

H. Levato, C. Saffe
(Instituto de Ciencias Astronomicas,de la Tierra y del Espacio (ICATE), 
San
Juan, Argentina),

R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres
(The Instituto de Astrofisica de Canarias),



MASTER-Kislovodsk (Russia)  robotic telescope (MASTER-Net: 
http://observ.pereplet.ru) located in Kislovodsk was pointed to
the  GRB180224.93 21 sec after  notice time and 37 sec after trigger time 
at 2018-02-24 22:21:44 UT. On our  unfiltered polarizing  exposures
set we  found 1 bright optical transient within  SWIFT
error-box (ra=202.658 dec=38.0878 r=0.05) 
brighter then 18.1.

RA,DEC  = 13h 30m 44.057s , +38d  04m 44.55 s
Error = 0.1 arcsec
maximal magnitute ~ 16.7


The 5-sigma upper limit has been about 18.1mag
The message may be cited.


====================================================================



The observations made on zenit distance = 23 degrees, galaxy latitude b = 
76 degree.
The moon (68 % bright part) is 16 degrees above the horizon. The distance 
between  moon and  object is 97 degrees.
The sun  altitude  is -53.0 degree.
The object can be observed till sunrise at 2018-02-25 03:53:29 UT.


MASTER-SAAO  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in SAAO was pointed to the  GRB180224.94 92 sec after notice time 
and 176 sec after trigger time at 2018-02-24 22:24:12 UT. On our first
  set we  not found optical transient within SWIFT error-box 
(ra=202.638 dec=38.0819 r=0.1) brighter then 15.8.

The 5-sigma upper limit has been about 15.8 mag
The message may be cited.


The observations made on high zenit distance = 82 degrees, galaxy latitude 
b = 76 degree.
The moon (68 % bright part) is  6 degrees above the horizon. The distance 
between  moon and  object is 97
The sun  altitude  is -48.3 degree.
The object can be observed till sunrise at 2018-02-25 04:21:26.


This message can be cited.

A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), B. Sbarufatti
(INAF-OAB/PSU), D.N. Burrows (PSU), A. Tohuvavohu (PSU), S.L. Gibson
(U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester),
V. D'Elia (ASDC) and A.Y. Lien report on behalf of the Swift-XRT team:

We have analysed 7.2 ks of XRT data for GRB 180224A (Lien et al. GCN
Circ. 22442
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 ), from 84 s to 47.4 ks after the  BAT trigger. The data
comprise 35 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. The enhanced XRT position for this burst was given
by Evans et al. (GCN Circ. 22443
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 ).

The light curve can be modelled with an initial power-law decay with an
index of alpha=0.70 (+/-0.08), followed by a break at T+3451 s to an
alpha of 2.00 (+0.30, -0.25).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.65 (+0.17, -0.16). The
best-fitting absorption column is  9.2 (+5.4, -4.7) x 10^20 cm^-2, in
excess of the Galactic value of 8.2 x 10^19 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 4.1 x 10^-11 (4.6 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     9.2 (+5.4, -4.7) x 10^20 cm^-2
Galactic foreground: 8.2 x 10^19 cm^-2
Excess significance: 2.9 sigma
Photon index:	     1.65 (+0.17, -0.16)

If the light curve continues to decay with a power-law decay index of
2.00, the count rate at T+24 hours will be 5.7 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.3 x
10^-14 (2.6 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00811561.

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

Alan M. Watson (UNAM), Nat Butler (ASU), Alexander Kutyrev (GSFC),
William H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J.
Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UVI),
Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz
(UCSC), Jes��s Gonz��lez (UNAM), Carlos Rom��n-Z����iga (UNAM), Harvey
Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (U. Wash.), and Vicki
Toy (UMD) report:

We observed the field of GRB 180224A (Lien et al., GCN 22442
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 ) with the
Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on
the 1.5m Harold Johnson Telescope at the Observatorio Astron��mico
Nacional on Sierra San Pedro M��rtir from 2018/02 25.23 to 2018/02 25.53
UTC (7.24 to 14.42 hours after the BAT trigger), obtaining a total of
3.91 hours exposure in the r and i bands.

We detect a source at 13:30:44.11 38:04:44.2 (J2000, �� 0.5 arcsec),
within the Swift-XRT error circle, in comparison with the SDSS DR9, with
the following magnitudes:

  r	= 22.94 +/- 0.13
  i	= 22.08 +/- 0.06

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.

The position and magnitudes of this source are consistent with the SDSS
DR9 galaxy SDSS J133044.06+380443.0, which has r = 22.56 +/- 0.18 and i
= 21.83 +/- 0.14. We suggest that this might be the host galaxy of the
GRB.

Vladimirov et al. (GCN 22444
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 ) report a early 16.1 mag transient in the
Swift XRT error circle. Our non-detection 7 hours later suggests that
the afterglow faded extremely quickly.

We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir.

T. Sakamoto (AGU), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF/USRA),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), M. Stamatikos (OSU),
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 180224A (trigger #811561)
(Lien et al., GCN Circ. 22442
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 ).  The BAT ground-calculated position is
RA, Dec = 202.675, 38.073 deg which is
  RA(J2000)  =  13h 30m 41.9s
  Dec(J2000) = +38d 04' 23.0"
with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 93%.

The mask-weighted light curve shows a FRED-like pulse that starts at ~ T0,
peaks at ~ T+1 s, and ends at ~T+15 s. T90 (15-350 keV) is 10.9 +- 3.6 sec
(estimated error including systematics).

The time-averaged spectrum from T-0.48 to T+14.57 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.11 +- 0.18.  The fluence in the 15-150 keV band is 4.7 +- 0.5 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.40 sec in the 15-150 keV band
is 1.4 +- 0.2 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/811561/BA/

E. Mazaeva (IKI),  A. Pozanenko (IKI),  A. Volnova  (IKI), R. Inasaridze 
(AbAO),  V. Ayvazian  (AbAO),  O. Kvaratskhelia (AbAO), G. Inasaridze 
(AbAO),  I. Molotov (KIAM), report on behalf of larger GRB follow-up 
collaboration:

We observed the field of GRB 180224A  (Lien  et al., GCN 22442
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 ) with AS-32 
(0.7m) telescope of Abastumani Observatory starting on Feb. 25  (UT) 
01:07:37.   The afterglow of GRB 180224A (Lien  et al., GCN 22442
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 ; 
Vladimirov et al., GCN 22444
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 ) is  clearly detected in a stacked image. 
Preliminary photometry is following.

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

2018-02-25  01:07:37   0.15162   CR     60*60  21.88   0.15  22.6

The photometry is based on nearby SDSS DR9 stars

SDSS_id                            R_Lupton
J133038.17+380528.6    17.45
J133040.16+380535.7    17.10
J133051.85+380146.4    17.91

We confirm the fast decay of the afterglow and possible host galaxy 
association  SDSS DR9 J133044.06+380443.0 with the afterglow source (Watson 
et al., GCN 22446
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 ).

L. Izzo (IAA-CSIC), A. Noschese (AC-OASDG) report:

We observed the field of GRB 180224A (Lien et al. GCN 22442
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 ) with the 0.5m telescope of the Osservatorio Astronomico S. Di Giacomo located in Agerola, Italy ( http://acgo.it/oa ). 
We obtained a series of 9x180 s images in the Rc filter, starting at 23:33:36 UT, ~ 1.21 hrs after the GRB detection. In our stacked image, we find no source at the position of the observed optical counterpart (Vladimirov  et al. GCN 22444
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 , Watson et al. GCN 22446
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 , Mazaeva et al. GCN 22448
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 ) down to a 3-sigma limit of Rc (Vega) > 20.2.  The calibration was performed using nearby stars in the USNO B1 catalog.

GRB 180224A: Swift/UVOT Detection

S. J. LaPorte (PSU) and A. Y. Lien (GSFC/UMBC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180224A
85 s after the BAT trigger (Lien et al., GCN Circ. 22442
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 ).
A fading source consistent with the XRT position
(Evans et al. GCN Circ. 22443
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 ) also detected by (Lipunov et al. GCN Circ.
22444
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 ; Watson et al. GCN Circ. 22446
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 ; Pozanenko et al. GCN Circ. 22448
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 )
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  13:30:44.10 = 202.68377 (deg.)
    Dec (J2000) = +38:04:44.5  =  38.07902 (deg.)
with an estimated uncertainty of 0.46 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               61          211          294         18.9 +/- 0.07
white              553         5337          287         20.7 +/- 0.33
v                  603         1397           97        >18.4
b                  552         1348           78        >19.5
u                  273         5063          500        >20.3
w1                 652         1446           97        >18.7
m2                 824          844           19        >18.2
w2                 751          771           19        >17.6

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.01 in the direction of the burst
(Schlegel et al. 1998).