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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
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To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

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subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

21772 results found.

  1. EP 250827B: Detection of supernova counterpart by LCO.
  2. GRB 250902B: SVOM/GRM observation
  3. EP250827b: SVOM/VT observation of AT 2025wkm
  4. LIGO/VIRGO/KAGRA S250818k: No evidence for radio variability of AT2025ulz in MeerKAT 3 GHz data
  5. GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
  6. GRB 250901A: Swift/UVOT Upper Limit
  7. GRB 250830B: Swift-XRT afterglow detection
  8. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  9. GRB 250902A: SVOM/GRM observation
  10. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  11. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  12. GRB 250901A: EP-FXT follow-up observation
  13. GRB 250901A: SVOM/VT optical afterglow with VHF data
  14. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  15. GRB 250901A: LCO optical upper limit
  16. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  17. EP250831a: NOT optical observations and tentative afterglow candidate
  18. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  19. GRB 250901A: SVOM detection of a burst
  20. EP250901a: Mephisto optical upper limits
  21. GRB 250830C: AstroSat CZTI detection of a long burst
  22. EP250901a: Einstein Probe detection of an X-ray transient
  23. IceCube Alert 250831.75: Global MASTER-Net observations report
  24. EP250831a: EP-WXT detection of a fast X-ray transient
  25. GRB 250831A: Swift-XRT counterpart detection
  26. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  27. GRB 250831A: SVOM/VT upper limit with VHF data
  28. GRB 250831A: SVOM detection of a soft burst
  29. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  30. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  31. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  32. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  33. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  34. GRB 250828B: Swift-BAT refined analysis
  35. EP250821a: SOAR observations
  36. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  37. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  38. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  39. GRB 250808B: SVOM detection of a burst through offline search
  40. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  41. EP250828a: Optical counterpart detection with Kinder observations
  42. EP250828a: Liverpool Telescope upper limits
  43. EP-WXT trigger 01709200800 : KAIT optical observations
  44. EP250828a: KAIT optical upper limit
  45. EP250827a: Swift/UVOT Detection
  46. EP250828a: NOT optical counterpart confirmation
  47. EP250828a: SVOM/VT optical candidate
  48. EP250828a: Seimei/TriCCS optical counterpart detection
  49. EP250828a: Optical upper limit with Kinder observations
  50. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  51. EP250828a: Einstein Probe detection of an X-ray transient
  52. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  53. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  54. EP250827a: confirmation of optical rebrightening with LCO
  55. EP250827a: GOTO observation of the optical afterglow
  56. GRB 250826A: SVOM/GRM observation
  57. EP250827A: An optical rebrightening was detected by LCO.
  58. EP250827a: TRT optical observations
  59. EP250827a: BOOTES-7 early optical dectection
  60. EP250827a: Las Cumbres independent detection of the optical counterpart
  61. EP250827a: Einstein Probe detection of an X-ray transient
  62. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  63. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  64. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  65. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  66. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  67. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  68. EP250821a: MeerKAT radio counterpart
  69. GRB 250823A: COLIBRÍ optical observations
  70. GRB 250823A: SVOM/VT optical observation
  71. GRB 250823A: Swift/UVOT Detection
  72. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  73. GRB 250818B: MeerKAT Detection
  74. GRB 250823A: Enhanced Swift-XRT position
  75. GRB 250823A: LCOGT Optical Detection
  76. GRB 250823A: Liverpool Telescope optical detection
  77. GRB 250823A: Swift detection of a burst
  78. Konus-Wind detection of GRB 250821B
  79. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  80. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  81. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  82. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  83. GRB 250821A: Kilonova-Catcher optical upper limits
  84. GRB 250821A: VLT/FORS2 Optical Observation
  85. GRB 250821B: SVOM/GRM observation
  86. EP250821a: SVOM/VT optical observation
  87. GRB 250821A: NOT z-band upper limit
  88. GRB 250821A: KAIT optical upper limit
  89. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  90. GRB 250821A: Enhanced Swift-XRT position
  91. GRB 250821A: Swift/UVOT Upper Limits
  92. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  93. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  94. GRB 250821A: LCOGT Optical Upper Limits
  95. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  96. GRB 250821A: Swift detection of a burst
  97. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  98. EP250821a: Einstein Probe detection of an X-ray transient
  99. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  100. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz

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