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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"

20514 results found.

  1. GRB 250331D: Swift/BAT-GUANO arcminute localization of a burst during slew
  2. LIGO/Virgo/KAGRA S250331o: NED Galaxies in the 3-Initial Localization Volume
  3. LIGO/Virgo/KAGRA S250328ae: Swift XRT observations, 34 possible X-ray sources
  4. GRB 250330A: VLT/FORS2 Afterglow Detection
  5. GRB20250327B: 45th Parallel Observatory upper limit
  6. GRB 250328A: Swift/UVOT Detection
  7. Fermi-LAT gamma-ray observations of IceCube-250330A
  8. GRB 250330A: SVOM/VT optical upper limit
  9. GRB 250314A: VLA detection
  10. Fermi GRB 250330B: Global MASTER-Net observations report
  11. Fermi GRB 250330A: Global MASTER-Net observations report
  12. GRB 250330A: BOOTES-7 early optical upper limit
  13. GRB 250330A: Swift/UVOT Upper Limits
  14. GRB 250330A: Swift-XRT afterglow detection
  15. GRB 250328A: 1.6m Mephisto optical observations
  16. IceCube Alert 250330.35: Global MASTER-Net observations report
  17. GRB 250330A: VLT/FORS2 Optical Observations
  18. Swift GRB250330.26: Global MASTER-Net observations report
  19. GRB 250329B: SVOM/C-GFT optical upper limit
  20. LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 1)
  21. GRB 250327B: ALMA detection
  22. GRB 250327B: VLA detection
  23. GRB 250327B: SVOM/COLIBRÍ (F-GFT) Further Observations
  24. GRB 250329B: 1.6m Mephisto Optical Upper Limits
  25. GRB250329A: REM optical afterglow detection
  26. GRB 250329B: GWAC-F50A optical upper limit
  27. GRB 250328A: SVOM/VT optical observation
  28. GRB 250329A: Fading optical counterpart detection by LCO.
  29. GRB 250328A: SVOM/C-GFT optical upper limit
  30. GRB 250328A: SVOM/COLIBRÍ (F-GFT) optical afterglow candidate
  31. GRB 250328A: VLT/HAWK-I near-infrared afterglow candidate
  32. GRB 250329A: SVOM/COLIBRÍ (F-GFT) Detection of a Bright Optical Counterpart Candidate
  33. GRB 250327B: J-band observations with WINTER
  34. GRB 250327B: LCO optical counterpart detection
  35. GRB 250328A: GWAC-F50A optical upper limit
  36. FRB 20250316A: FTW optical observations
  37. LIGO/Virgo/KAGRA S250328ae: NED Galaxies in the 4-Update Localization Volume
  38. GRB 250327B: CrAO and SAO RAS Optical Observations
  39. GRB 250327B: OHP/T193 spectroscopic observations and redshift confirmation
  40. GRB 250327B: further optical observations by LCOGT
  41. GRB 250327b: Liverpool Telescope optical observations
  42. GRB 250327A: SVOM/VT upper limits on the XRT position
  43. GRB 250327B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  44. GRB 250327B: 1.6m Mephisto optical observations
  45. GRB 250327B: GOTO optical counterpart detection
  46. GRB 250327B: SAO RAS optical candidate
  47. FRB 20250316A: Gemini Imaging and Spectroscopy of the Sub-arcsecond Localization Region of FRB 20250316A
  48. FRB 20250316A: The sub-arcsecond localization of FRB 20250316A using CHIME/FRB Outriggers coincides with reported X-ray counterparts
  49. GRB 250327A: J-band observations with WINTER
  50. FRB 20250316A: Pan-STARRS r and i-band imaging and photometry
  51. Fermi GRB 250327A: Global MASTER-Net observations report
  52. Swift GRB 250327A: Global MASTER-Net observations report
  53. GRB 250327A: DDOTI Optical Observations
  54. GRB 250327A: COLIBRÍ optical upper limit
  55. Fermi trigger No 764700395: Global MASTER-Net observations report
  56. EP250321a: Mondy AZT-33IK Continued Optical Observations
  57. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  58. GRB 250322A: third epoch of NOT optical observations
  59. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  60. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  61. GRB 250322A: further NOT optical observations
  62. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  63. GRB 250322A: Swift/UVOT Upper Limits
  64. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  65. GRB 250322A: VLT/X-shooter redshift confirmation of the putative host galaxy
  66. GRB 250321B: Swift-XRT observations
  67. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  68. GRB 250322A: Gemini-North redshift of candidate host galaxy
  69. EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
  70. GRB250322A: STEP/T80S optical limits
  71. GRB 250322A: Gemini-South optical observations
  72. GRB 250322A: VLT optical observations
  73. GRB 250322A: VLT near-infrared observations
  74. FRB 250316A: DDOTI Continued Optical Observations
  75. GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  76. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  77. GRB 250322A: MASTER optical observation
  78. EP250321a: Liverpool Telescope optical follow-up
  79. EP250321a: Mondy AZT-33IK Optical Observations
  80. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  81. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  82. EP250321a: KAIT optical observations
  83. EP250321A: COLIBRÍ Continuing Optical Observations
  84. GRB 250321B: Swift ToO observations
  85. EP250321a: WFST optical observations
  86. EP250321a: Xinglong 216 decaying optical observations
  87. EP250321a: SVOM/VT optical observation
  88. EP 250321A: Optical counterpart detection by LCO.
  89. EP250321a: Kinder optical follow-up observations
  90. GRB 250321A: Swift/UVOT Upper Limits
  91. EP250321a: LCO optical counterpart detection
  92. EP250321A: COLIBRÍ Optical Observations
  93. EP250321a: VLT/X-shooter redshift z = 4.368
  94. EP250321a: REM optical/NIR afterglow detection
  95. Fermi GRB 250320B: Global MASTER-Net observations report
  96. EP250321a: Global MASTER-Net observations report
  97. Swift GRB 250321A: Global MASTER-Net observations report
  98. Fermi GRB 250321A: Global MASTER-Net observations report
  99. GRB 250321A: GOTO optical upper limits
  100. GRB 250314A: Keck/NIRC2 J-band upper limit

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