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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').
Advanced Search

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.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"
  1. GRB 250314A: VLA detection
  2. LIGO/Virgo/KAGRA S250331o: Identification of a GW compact binary merger candidate
  3. Fermi GRB 250330B: Global MASTER-Net observations report
  4. GRB 250330B: Fermi GBM Final Real-time Localization
  5. Fermi GRB 250330A: Global MASTER-Net observations report
  6. GRB 250330A: BOOTES-7 early optical upper limit
  7. GRB 250330A: Swift/UVOT Upper Limits
  8. GRB 250330A: Swift-XRT afterglow detection
  9. GRB 250328A: 1.6m Mephisto optical observations
  10. GRB 250329B: SVOM/COLIBRÍ (F-GFT) optical upper limit
  11. GRB 250330A: Fermi GBM Final Localization
  12. IceCube-250330A - IceCube observation of a high-energy neutrino candidate track-like event
  13. IceCube Alert 250330.35: Global MASTER-Net observations report
  14. GRB 250330A: VLT/FORS2 Optical Observations
  15. GRB 250330A: Prompt Swift-XRT position
  16. GRB 250329B: Swift-XRT afterglow detection
  17. GRB 250330A: Swift detection of a burst
  18. Swift GRB250330.26: Global MASTER-Net observations report
  19. GRB 250328A: A fading optical afterglow confirmed by SVOM/VT
  20. GRB 250329B: SVOM/C-GFT optical upper limit
  21. LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 1)
  22. GRB 250327B: ALMA detection
  23. GRB 250327B: VLA detection
  24. GRB 250329B: SVOM/VT optical upper limit
  25. GRB 250327B: SVOM/COLIBRÍ (F-GFT) Further Observations
  26. GRB 250329B: 1.6m Mephisto Optical Upper Limits
  27. LIGO/Virgo/KAGRA S250329fl: 2 counterpart neutrino candidate events from an IceCube neutrino search
  28. GRB250329A: REM optical afterglow detection
  29. GRB 250329B: GWAC-F50A optical upper limit
  30. GRB 250329B: SVOM detection of a faint transient
  31. GRB 250329A: Swift-XRT afterglow detection
  32. GRB 250328A: SVOM/VT optical observation
  33. GRB 250329A: Fading optical counterpart detection by LCO.
  34. GRB 250328A: SVOM/C-GFT optical upper limit
  35. GRB 250328A: SVOM/COLIBRÍ (F-GFT) optical afterglow candidate
  36. GRB 250328A: VLT/HAWK-I near-infrared afterglow candidate
  37. GRB 250329A: VLT/X-shooter redshift z = 2.921
  38. GRB 250329A: SVOM/VT optical counterpart confirmation
  39. GRB 250329A: SVOM detection of a burst
  40. GRB 250329A: SVOM/COLIBRÍ (F-GFT) Detection of a Bright Optical Counterpart Candidate
  41. GRB 250327B: J-band observations with WINTER
  42. GRB 250327B: MASTER detection of OT rebrightening
  43. GRB 250327B: LCO optical counterpart detection
  44. GRB 250328A: GWAC-F50A optical upper limit
  45. GRB 250328A: SVOM detection of a burst
  46. FRB 20250316A: FTW optical observations
  47. LIGO/Virgo/KAGRA S250328ae: NED Galaxies in the 4-Update Localization Volume
  48. EP250302a: SPI-ACS/INTEGRAL Upper Limit
  49. GRB 250327B: CrAO and SAO RAS Optical Observations
  50. GRB 250327B: OHP/T193 spectroscopic observations and redshift confirmation
  51. GRB 250327B: further optical observations by LCOGT
  52. EP250315a: Pan-STARRS r and i-band imaging and photometry
  53. GRB 250327b: Liverpool Telescope optical observations
  54. GRB 250322A: GRANDMA/TNOT optical upper limits
  55. LIGO/Virgo/KAGRA S250328ae: Updated Sky localization
  56. GRB 250327A: SVOM/VT upper limits on the XRT position
  57. LIGO/Virgo/KAGRA S250328ae: Identification of a GW compact binary merger candidate
  58. GRB 250327B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  59. GRB 250327B: Las Cumbres optical counterpart detection
  60. GRB 250327B: Swift-XRT detection of the X-ray afterglow
  61. GRB 250327B: 1.6m Mephisto optical observations
  62. GRB 250327B: NOT spectroscopic redshift z = 3.035
  63. GRB 250327A: Swift-XRT refined Analysis
  64. GRB 250327B: GOTO optical counterpart detection
  65. GRB 250327B: SVOM/VT optically bright counterpart
  66. GRB 250327B: SAO RAS optical candidate
  67. GRB 250327B: SVOM detection of a burst
  68. FRB 20250316A: Gemini Imaging and Spectroscopy of the Sub-arcsecond Localization Region of FRB 20250316A
  69. FRB 20250316A: The sub-arcsecond localization of FRB 20250316A using CHIME/FRB Outriggers coincides with reported X-ray counterparts
  70. GRB 250327A: J-band observations with WINTER
  71. GRB 250327A: SVOM/VT optical candidate
  72. FRB 20250316A: Pan-STARRS r and i-band imaging and photometry
  73. GRB 250327A: Fermi GBM observation
  74. Fermi GRB 250327A: Global MASTER-Net observations report
  75. Swift GRB 250327A: Global MASTER-Net observations report
  76. GRB 250327A: DDOTI Optical Observations
  77. GRB 250327A: COLIBRÍ optical upper limit
  78. GRB 250327A: Swift detection of a burst
  79. GRB 250327A: Fermi GBM Final Real-time Localization
  80. Fermi trigger No 764700395: Global MASTER-Net observations report
  81. LIGO/Virgo/KAGRA S250326y: Updated Sky localization
  82. Konus-Wind detection of GRB 250322A (short)
  83. IPN triangulation of GRB 250322B
  84. LIGO/Virgo/KAGRA S250326y: Identification of a GW compact binary merger candidate
  85. EP250321a: Mondy AZT-33IK Continued Optical Observations
  86. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  87. GRB 250322A: third epoch of NOT optical observations
  88. GRB 250322A: Swift-BAT refined analysis
  89. The EP-WXT trigger 01709133021 (designated as EP250324a) is not a real source
  90. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  91. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  92. GRB 250322A: further NOT optical observations
  93. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  94. GRB 250322A: Swift/UVOT Upper Limits
  95. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  96. GRB 250322A: VLT/X-shooter redshift confirmation of the putative host galaxy
  97. FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
  98. GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst
  99. GRB 250321B: Swift-XRT observations
  100. GRB 250322A: Swift-XRT refined Analysis

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