GRB 240730A

S. B. Cenko (GSFC), P. A. Evans (U Leicester),
R. A. J. Eyles-Ferris (U Leicester), K. L. Page (U Leicester) and
D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 07:52:06 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 240730A (trigger=1245636).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 37.829, +59.074 which is 
   RA(J2000) = 02h 31m 19s
   Dec(J2000) = +59d 04' 27"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 80 sec.  The peak count rate
was ~300 counts/sec (15-350 keV), at ~30 sec after the trigger. 

The XRT began observing the field at 07:54:14.8 UT, 128.7 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 37.83844,
59.02878 which is equivalent to:
   RA(J2000)  = 02h 31m 21.22s
   Dec(J2000) = +59d 01' 43.6"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 163 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
https://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 7.80
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 133 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 coverage of the XRT error circle by the 8'x8' region
for the list of sources generated on-board is uncertain because the large
number of sources filled the available telemetry. The list of sources is
typically complete to about 18 mag. No correction has been made for the large,
but uncertain, extinction expected. 

Although this appears to be a long GRB, its long duration and
its position near the Galactic plane (lat=-1.35) raise the possibility
that this is a Galactic transient instead.  If that is the case
then we give it the name Swift J0231.3+5902 . 

Burst Advocate for this burst is S. B. Cenko (brad.cenko 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/)

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

Using 915 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 240730A, 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 = 37.83822, +59.02875 which is equivalent
to:

RA (J2000): 02h 31m 21.17s
Dec (J2000): +59d 01' 43.5"

with an uncertainty of 2.6 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.

Paul Kuin (MSSL/UCL), R. Caputo and S. B. Cenko (GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 240730A
133 s after the BAT trigger (Cenko et al., GCN Circ. 36976
Loading...
 
 ).
No optical afterglow consistent with the XRT position in Evans et al.,
GCN Circ. 36977
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           133          283          147         >19.1
u_FC               291          541          246         >19.2
white              133         1026          295         >19.1
u                  291          541          246         >19.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 1.146 in the direction of the burst
(Schlegel et al. 1998).

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 240730A (Cenko et al.,

GCN 36976
Loading...
 
 ) starting at 10:24UT, ~2.53 hours after the burst. A

total of 50x60s images were obtained in the clear (roughly R)

filters.  We do not detect any optical afterglow candidate within

the enhanced XRT position error circle (Evans et al., GCN 36977
Loading...
 
 ),

neither in single image, nor in the co-add images. The typical

limiting magnitude of our single clear image is about 19.5 mag

calibrated to the PS1 catalog.

S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), A. D'Ai
(INAF-IASFPA), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto) and P.A.
Evans report on behalf of the Swift-XRT team:

We have analysed 7.2 ks of XRT data for GRB 240730A, from 113 s to 23.5
ks after the  BAT trigger. The data comprise 14 s in Windowed Timing
(WT) mode (the first 9 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=2.04 (+/-0.24).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.6 (+/-0.4). The
best-fitting absorption column is  1.4 (+0.6, -0.5) x 10^22 cm^-2, in
excess of the Galactic value of 7.8 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 6.8 x 10^-11 (1.0 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.4 (+0.6, -0.5) x 10^22 cm^-2
Galactic foreground: 7.8 x 10^21 cm^-2
Excess significance: 2.1 sigma
Photon index:	     1.6 (+/-0.4)

If the light curve continues to decay with a power-law decay index of
2.04, the count rate at T+24 hours will be 5.4 x 10^-6 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.6 x
10^-16 (5.7 x 10^-16) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01245636.

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

V. Lipunov, V.Kornilov, E. Gorbovskoy, K. Zhirkov, N.Tyurina, P.Balanutsa, A.Kuznetsov, V.Senik,  D. Vlasenko,
G.Antipov, D.Zimnukhov, E.Minkina, A.Chasovnikov, V.Topolev, D.Kuvshinov, D. Cheryasov, Ya.Kechin, Yu.Tselik, A. Sosnovskij
(Lomonosov Moscow State University, SAI, Physics Department),

R. Podesta, C.Lopez, F. Podesta, C.Francile
(Observatorio Astronomico Felix Aguilar OAFA),

R. Rebolo, M. Serra
(The Instituto de Astrofisica de Canarias),

D. Buckley
(South African Astronomical Observatory),

O.A. Gress, N.M. Budnev, O.Ershova
(Irkutsk State University, API),

L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez
(INAOE, Guillermo Haro Astrophysics Observatory),

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

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

MASTER-Tavrida robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the Swift GRB 240730A ( S. B. Cenko et al., GCN 36976
Loading...
 
 ) errorbox  37782 sec after notice time and 37859 sec after trigger time at 2024-07-30 18:23:05 UT, with upper limit up to  16.8 mag. Observations started at twilight.  The observations began at zenith distance = 71 deg. The sun  altitude  is -11.9 deg. 

The galactic latitude b = -1 deg., longitude l = 136 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2545484

We obtain a following upper limits.  

Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

   32544 |             MASTER- |   C |    30 | 18.9 |        
   32585 |             MASTER- |   C |    30 | 18.8 |        
   32627 |             MASTER- |   C |    30 | 18.8 |        
   32671 |             MASTER- |   C |    30 | 18.8 |        
   32719 |             MASTER- |   C |    30 | 18.6 |        
   32762 |             MASTER- |   C |    30 | 19.0 |        
   33359 |             MASTER- |   C |    30 | 18.8 |        
   33403 |             MASTER- |   C |    30 | 18.9 |        
   34542 |             MASTER- |   C |   180 | 19.4 |        
   34735 |             MASTER- |   C |   180 | 19.5 |        
   34928 |             MASTER- |   C |   180 | 19.4 |        
   35120 |             MASTER- |   C |   180 | 19.3 |        
   35313 |             MASTER- |   C |   180 | 19.4 |        
   35509 |             MASTER- |   C |   180 | 19.1 |        
   35703 |             MASTER- |   C |   180 | 19.3 |        
   35821 |             MASTER- |   C |    30 | 19.1 |        
   35868 |             MASTER- |   C |    30 | 19.1 |        
   35915 |             MASTER- |   C |    30 | 19.1 |        
   35957 |             MASTER- |   C |    30 | 19.1 |        
   36000 |             MASTER- |   C |    30 | 19.1 |        
   36042 |             MASTER- |   C |    30 | 19.1 |        
   36085 |             MASTER- |   C |    30 | 18.9 |        
   36121 |             MASTER- |   C |    30 | 19.1 |        
   36163 |             MASTER- |   C |    30 | 19.1 |        
   36206 |             MASTER- |   C |    30 | 19.1 |        
   36248 |             MASTER- |   C |    30 | 19.1 |        
   36291 |             MASTER- |   C |    30 | 18.8 |        
   36970 |             MASTER- |   C |   180 | 18.9 |        
   37949 |      MASTER-Tavrida |   C |   180 | 16.8 |        
   38248 |             MASTER- |   C |   180 | 19.3 |        
   39462 |             MASTER- |   C |   180 | 19.2 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

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

Following the detection of GRB 240730A by Swift (Cenko et al. GCNC 36976), the BOOTES-5/JGT 0.6m robotic telescope at Observatorio Astronomico Nacional in San Pedro Martir (Mexico) automatically observed the GRB location starting on Jul. 30, 07:53:50 UT (~ 104 s after trigger). No new optical source is detected on the co-added images (57 x 1 s, clear-filter) within the enhanced Swift/XRT error box (Evans et al. GCNC 36977) down to 18.7 mag.  which is consistent with reports from UVOT (Kuin et al., GCNC 36978), KAIT (Zheng et al., GCNC 36980) and MASTER (Lipunov et al. GCNC 36983).

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

Nello Ruocco at Osservatorio Nastro Verde - Sorrento (Naples) - Italy
in a large collaboration with:
M.G. Dainotti (National Astronomical Observatory of Japan), 
Y. Niino (Tokyo University, Institute of Astronomy), 
K. Kalinowski (Aarhus University, Department of Physics and Astronomy),
B. De Simone (Universita' degli Studi Di Salerno)
report: 

We image the field of GRB 240730A (Trigger 1245636 S. B. Cenko (GSFC), P. A. Evans (U Leicester),
R. A. J. Eyles-Ferris (U Leicester), K. L. Page (U Leicester) and
D. M. Palmer (LANL) GCN Circular 36976
Loading...
 
 )
with telescope of Nastro Verde Observatory - Sorrento (Naples), Italy. Member of: 
AAVSO - American Association of Variable Star Observers.
UAI/SSV - Unione Astrofili Italiani/sezione stelle variabili.
AstroCampania Associazione

The observations started at 22:08 UT of 2024/07/30, after about 14.20 hours after the GRB trigger, with clear sky,
with principal telescope  SC 0.35 f/10 with focal reduced + CCD Sbig ST10 XME
I took 20 image of 60 sec each. All images are unfiltered, calibrated with masterdark and masterflat,stacked with Tycho Tracker software
We have not detected any clearly visible sources, up to 19.5th magnitude with clear skies.
 Start T0+                End T0+       Rlim
22:08:20 UT             22:32:39 UT     19.5

We did not found any optical counterpart in the error box of the XRTcandidate.




Magnitudes were estimated with the Gaia DR2 cat. and 
are not corrected for galactic dust extinction.



The message may be cited.

D. Sadaula (GSFC/UMBC), S. D. Barthelmy (GSFC), 
S. B. Cenko (GSFC), R. Gupta (GSFC),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC),
A. Y. Lien (U Tampa), C. B. Markwardt (GSFC),
M. J. Moss (GSFC), D. M. Palmer (LANL),
T. Parsotan (GSFC), T. Sakamoto (AGU)
(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 240730A (trigger #1245636)
(Cenko, et al., GCN Circ. 36976
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 37.841, 59.045 deg which is 
   RA(J2000)  =  02h 31m 21.9s 
   Dec(J2000) = +59d 02' 43.5" 
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 98%.
 
The BAT mask-weighted light curve displays two spectrally soft peaks.  
The T90 (15-350 keV) is 50.13 +- 7.60 sec (estimated error including systematics).
 
The time-averaged spectrum from T-6.06 to T+53.43 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.50 +- 0.19.  The fluence in the 15-150 keV band is 6.8 +- 0.9 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T+5.80 sec in the 15-150 keV band
is 0.4 +- 0.1 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 
 
The results of the batgrbproduct analysis are available at
https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1245636

The long duration and proximity to the Galactic plane raised the initial 
possibility that this was a Galactic transient.  However, its subsequent behavior, 
including a lack of later BAT detections, is consistent with a GRB, making the 
Galactic transient interpretation less likely.