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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"

20958 results found.

  1. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  2. GRB 250322A: third epoch of NOT optical observations
  3. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  4. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  5. GRB 250322A: further NOT optical observations
  6. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  7. GRB 250322A: Swift/UVOT Upper Limits
  8. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  9. GRB 250322A: VLT/X-shooter redshift confirmation of the putative host galaxy
  10. GRB 250321B: Swift-XRT observations
  11. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  12. GRB 250322A: Gemini-North redshift of candidate host galaxy
  13. EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
  14. GRB250322A: STEP/T80S optical limits
  15. GRB 250322A: Gemini-South optical observations
  16. GRB 250322A: VLT optical observations
  17. GRB 250322A: VLT near-infrared observations
  18. FRB 250316A: DDOTI Continued Optical Observations
  19. GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  20. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  21. GRB 250322A: MASTER optical observation
  22. EP250321a: Liverpool Telescope optical follow-up
  23. EP250321a: Mondy AZT-33IK Optical Observations
  24. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  25. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  26. EP250321a: KAIT optical observations
  27. EP250321A: COLIBRÍ Continuing Optical Observations
  28. GRB 250321B: Swift ToO observations
  29. EP250321a: WFST optical observations
  30. EP250321a: Xinglong 216 decaying optical observations
  31. EP250321a: SVOM/VT optical observation
  32. EP 250321A: Optical counterpart detection by LCO.
  33. EP250321a: Kinder optical follow-up observations
  34. GRB 250321A: Swift/UVOT Upper Limits
  35. EP250321a: LCO optical counterpart detection
  36. EP250321A: COLIBRÍ Optical Observations
  37. EP250321a: VLT/X-shooter redshift z = 4.368
  38. EP250321a: REM optical/NIR afterglow detection
  39. Fermi GRB 250320B: Global MASTER-Net observations report
  40. EP250321a: Global MASTER-Net observations report
  41. Swift GRB 250321A: Global MASTER-Net observations report
  42. Fermi GRB 250321A: Global MASTER-Net observations report
  43. GRB 250321A: GOTO optical upper limits
  44. GRB 250314A: Keck/NIRC2 J-band upper limit
  45. EP250226a/GRB 250226A: KAIT optical observations
  46. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  47. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  48. Fermi GRB 250319B: Global MASTER-Net observations report
  49. FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations
  50. LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn
  51. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  52. GRB 250314A: ATCA radio upper limits
  53. EP250302a: VLA observations
  54. GRB 250317B: OHP/T193 continued follow-up
  55. GRB 250317B: Leavitt Observatory optical upper limit
  56. GRB 250309B/AT2025dws: further ATCA observations
  57. GRB 250317B: Mondy AZT-33IK Optical Observations
  58. GRB 250317B: NOT optical observations suggest an optical plateau phase
  59. GRB 250317B: GTC/OSIRIS+ spectroscopic redshift z=3.44
  60. GRB 250317B: OHP/T193 optical observations
  61. Fermi trigger No 763933627: Global MASTER-Net observations report
  62. GRB250312A: Swift/UVOT Upper Limits
  63. GRB 250317B: REM optical/NIR observations
  64. GRB 250317B: Swift-XRT observations
  65. GRB 250314A: REM optical/NIR upper limits
  66. GRB 250316A: AbAO AS-32 Optical Upper Limit
  67. EP 250317B: Fading optical counterpart detection by LCO
  68. GRB 250316A: Swift-XRT afterglow detection
  69. GRB 250317B: LCO detection of the fading optical afterglow
  70. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  71. GRB 250316A: Swift-XRT observations
  72. Fermi trigger No 763862734: Global MASTER-Net observations report
  73. Fermi GRB 250316A: Global MASTER-Net observations report
  74. GRB 250316A: Swift ToO observations
  75. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  76. GRB 250314A: EP-FXT afterglow detection
  77. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  78. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection
  79. GRB 250314A: Swift XRT Detection
  80. GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3
  81. GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
  82. GRB 250314A: NOT near-infrared candidate counterpart
  83. GRB 250313A: Swift-XRT observations
  84. Fermi trigger No 763581136: Global MASTER-Net observations report
  85. GRB 250313A: Swift ToO observations
  86. EP trigger ID 01709061302: Lick/Kast spectroscopy with the 3 m Shane telescope
  87. Fermi GRB 250313A: Global MASTER-Net observations report
  88. GRB 250309B: PRIME near-infrared upper limits in 2nd epoch
  89. EP250304a: SVOM/VT optical observation
  90. ATCA detection of the radio counterpart of GRB 250309B-AT2025dws
  91. EP250302a: Chandra X-ray Detection
  92. Fermi trigger No 763509110: Global MASTER-Net observations report
  93. Fermi GRB 250312B: Global MASTER-Net observations report
  94. Swift GRB 250312A: Global MASTER-Net observations report
  95. GRB 250309B/AT2025dws: Daochen/RC-10 optical counterpart observation
  96. GRB 250311A/EP250311a: Optical upper limits with Kinder observations
  97. GRB 250311A: Swift-XRT observations
  98. GRB 250309B: 1.3m DFOT Optical observations
  99. EP250311a: Global MASTER-Net observations report
  100. GRB 250309B: PRIME near-infrared detection

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