GRB 180324A

E. Sonbas (Adiyaman Univ.), A. D'Ai (INAF-IASFPA), V. D'Elia (ASDC),
A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL), M. H. Siegel (PSU) and
A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 04:37:09 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180324A (trigger=817345).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 76.585, +56.725 which is 
   RA(J2000) = 05h 06m 20s
   Dec(J2000) = +56d 43' 29"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a small 
precursor about 5 seconds before the main, short, peak for a 
total duration of about 6 sec.  The peak count rate
was ~8000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 04:38:17.4 UT, 67.8 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 76.52896, 56.71298 which is equivalent
to:
   RA(J2000)  = 05h 06m 06.95s
   Dec(J2000) = +56d 42' 46.7"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 118 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 in excess of the Galactic value (3.81 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 7.1
(+6.82/-5.48) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 71 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers none of
the XRT error circle. The 8'x8' region for the list of sources generated
on-board covers 100% of the XRT error circle. The list of sources is typically
complete to about 18 mag. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.90. 

Burst Advocate for this burst is E. Sonbas (edasonbas AT yahoo.com). 
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 (U. Leicester) reports on behalf of the Swift-XRT team:

Using  promptly downlinked XRT event data for GRB 180324A, we find an
enhanced XRT position of the afterglow: RA, Dec: 76.5270, 56.7137 which
is equivalent to:
   RA (J2000)  = 05 06 06.49
   Dec (J2000) = +56 42 49.2
with an uncertainty of 2.0 arcseconds (radius, 90% confidence).
Analysis of the promptly available data is online at
http://www.swift.ac.uk/sper/817345.

Position enhancement is is described by Goad et al. (2007, A&A, 476,
1401) and Evans et al. (2009, MNRAS, 397, 1177).

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

WeiKang Zheng and Alexei V. Filippenko (UC Berkeley) report on
behalf of the KAIT GRB team:

The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, responded to Swift GRB 180324A (Sonbas et al.,
GCN 22524
Loading...
 
 ) starting at 04:54:12 UT, ~17 minutes after the burst,
and lasted ~10 minutes before it reached the physical limit of the
telescope.
Observations were performed with an automatic sequence in the
clear (roughly R), and I filters, and the exposure time was 20 s
per image. We do not detect any optical afterglow candidate within
the enhanced XRT position error circle (Evans et al., GCN 22525
Loading...
 
 ).
The typical limiting magnitude of our single clear image is about
19.0 mag calibrated to the APASS catalog.

Nat Butler (ASU), Alan M. Watson (UNAM), 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 180324A (Sonbas, et al., GCN 22524
Loading...
 
 ) 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 2018/03 24.19 to 2018/03 24.23 UTC (2.4
minutes to 0.92 hours after the BAT trigger), obtaining a total of 0.66
hours exposure in the r and i bands.

We detect a weak source within the Swift-XRT error circle (Evans, et al.,
GCN 22525
Loading...
 
 ) in our first 80 s exposure, i-band image only.  In comparison
with the USNO-B1 catalog, we find i=20.15+/-0.37.

The source is not on the frame in the subsequent image and is not detected
in the next possible frame 3.5 minutes later.  In our full 0.66 hour
exposure time, the source is not detected with the following upper limits
(3-sigma):

  r > 22.08
  i > 22.04

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.  If the detection in the first
frame is due to the afterglow, then the afterglow faded rapidly.

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

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

Using 2334 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 180324A, 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 = 76.52652, +56.71430 which is equivalent
to:

RA (J2000): 05h 06m 6.37s
Dec (J2000): +56d 42' 51.5"

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.

J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), V. D'Elia
(ASDC), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), D.N. Burrows
(PSU), A. Tohuvavohu (PSU), S. J. LaPorte (PSU), A.P. Beardmore (U.
Leicester) and E. Sonbas report on behalf of the Swift-XRT team:

We have analysed 7.1 ks of XRT data for GRB 180324A (Sonbas et al. GCN
Circ. 22524
Loading...
 
 ), from 80 s to 13.9 ks after the  BAT trigger. The data are
entirely in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Goad et al. (GCN Circ. 22525
Loading...
 
 ).

The late-time light curve (from T0+5.7 ks) can be modelled with a
power-law decay with a decay index of alpha=1.07 (+/-0.16).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.36 (+0.13, -0.12). The
best-fitting absorption column is  9.0 (+1.6, -1.4) x 10^21 cm^-2, in
excess of the Galactic value of 3.8 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 6.7 x 10^-11 (8.7 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     9.0 (+1.6, -1.4) x 10^21 cm^-2
Galactic foreground: 3.8 x 10^21 cm^-2
Excess significance: 5.9 sigma
Photon index:	     1.36 (+0.13, -0.12)

If the light curve continues to decay with a power-law decay index of
1.07, the count rate at T+24 hours will be 0.032 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.2 x
10^-12 (2.8 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/00817345.

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

GRB 180324A: Swift/UVOT Upper Limits

S. J. Laporte (PSU) and E. Sonbas (Adiyaman Univ.)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180324A
72 s after the BAT trigger (Sonbas et al., GCN Circ. 22524
Loading...
 
 ).
No optical afterglow consistent with the XRT position
(Goad et al. GCN Circ. 22529
Loading...
 
 ) or RATIR position (Butler et al. GCN Circ. 22528
Loading...
 
 )
is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

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

white_FC            72          221          147         >19.8
u_FC               284          534          246         >19.3
white               72        12383         1552         >21.3
v                  614        13894         1172         >19.5
b                  539         8158          549         >20.9
u                  284         7992          814         >20.3
w1                 664         7787          471         >20.2
w2                6970        13290         1082         >21.5

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.90 in the direction of the burst
(Schlegel et al. 1998).

H. A. Krimm (NSF/USRA), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), J. P. Norris (BSU),
D. M. Palmer (LANL), T. Sakamoto (AGU),
E. Sonbas (Adiyaman Univ.), 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 180324A (trigger #817345)
(Sonbas et al., GCN Circ. 22524
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 76.581, 56.744 deg which is
  RA(J2000)  =  05h 06m 19.4s
  Dec(J2000) = +56d 44' 36.8"
with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 78%.

The mask-weighted light curve shows a small precursor at ~T-5 s, followed
by the main pulse that starts at ~T-0.2, peaks at ~T+0.3 s, and ends at ~T+1 s.
There is also some weak emission that lasts till ~T+4 s. T90 (15-350 keV)
is 7.2 +- 1.3 sec (estimated error including systematics).

The lag analysis for the main pulse finds a lag of 48 +- 18 ms for the
100-350 keV to 25-100 keV band. This value is consistent with that of a
long GRB. In addition, no extended emission is found after ~T+4 s.

The time-averaged spectrum from T-5.4 to T+3.7 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.45 +- 0.14.  The fluence in the 15-150 keV band is 5.6 +- 0.5 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.13 sec in the 15-150 keV band
is 4.4 +- 0.3 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/817345/BA/

D. Frederiks, S. Golenetskii, R.Aptekar, M. Ulanov, D. Svinkin,
A. Tsvetkova, A.Lysenko, A. Kozlova, and T. Cline,
on behalf of the Konus-Wind team, report:

GRB 180324A (Swift-BAT trigger 817345:
Sonbas et al., GCN 22524
Loading...
 
 ; Krimm et al., GCN 22533
Loading...
 
 )
triggered Konus-Wind at T0=16629.939 s UT (04:37:09.939)

The burst light curve shows a weak pulse,
which started at ~T0-0.4 s and peaked at ~T0 s.
The total duration of the burst is ~0.7 s.
The emission is seen up to ~0.5 MeV.

As observed by Konus-Wind, the burst had a fluence of
(7.4 �� 2.1)x10^-7 erg/cm2 and a 64-ms peak energy flux,
measured from T0, of (1.8 �� 0.5)x10^-6 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The burst spectrum (measured from T0 to T0+0.256 s)
is best fit in the 20 keV - 15 MeV range by a cutoff power-law
(CPL) function with the following model parameters:
the photon index alpha = -0.56(-0.71,+1.16),
and the peak energy Ep = 154(-38,+77) keV,
chi2 = 22/19 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep, and an upper limit on beta of ~-2.2

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180324_T16629/

All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.